CO2 synergistic reduction in a photoanode-driven photoelectrocatalytic (PEC) cell was conducted with a Pt-modified TiO2 nanotube (Pt-TNT) photoanode and a Pt-modified reduced graphene oxide (Pt-RGO) electrocathode to reduce energy consumption and increase CO2 PEC reduction efficiency. The carbon atom conversion rate of CO2 reduction under PEC conditions was 2.3 times higher than that of the total rate under photocatalytic and electrocatalytic conditions. Synergistic CO2 reduction in the PEC cell was mainly due to the use of the photoanode, which played a dual role during CO2 reduction: (1) anode photovoltage compensated and conferred more negative cathode potential for CO2 reduction and (2) anode water decomposition provided protons and electrons for cathode CO2 reduction. System current density, product generation rate of CO2 reduction, and carbon atom conversion rate increased first and then decreased with increasing deposition amount of Pt on TNT. The optimal photocatalytic activity of the Pt-TNT anode was obtained with a Pt loading amount of 5%, which resulted in the highest system current density of 4 mA/cm2 and carbon atom conversion rate of 1250 nmol/(h cm2) under the catalysis of the Pt-RGO cathode.Keywords: Carbon dioxide; Photoanode-driven photoelectrochemical cell; Pt-modified reduced graphene oxide; Pt-modified TiO2 nanotube; Synergistic photoelectrocatalysis;

The catalytic effects of eight industrial wastes rich in Na, Fe, Ca and Al on Jincheng anthracite coal combustion were compared. The thermogravimetric experiments showed that Na-rich brine sludge (BS) and salt sludge (SS) exhibited better catalytic effects on coal combustion than Fe-rich iron mud (IM) and steel residue (SR). However, IM and SR exhibited better catalytic effects than Ca-rich white lime mud (WLM) and calcium carbide residue (CCR). Among the eight industrial wastes, Al-rich alumina residue (AR) and aluminium slag (AS) demonstrated the worst catalytic effects. BS, which contains more Na (mainly in the form of NaCl, which was equivalent to Na2O with a content of 13.14%) than SS (mainly in the form of NaCl and Na3Mg(CO3)2Cl, which were equivalent to Na2O with a content of 7.64%) does, reduced the ignition temperature of Jincheng coal from 582 °C to 561 °C because of the promoted transfer of oxygen to the carbon surface through the cyclic oxidation and reduction reactions between Na2O and Na2O2. IM, which contains more Fe (mainly in the form of γ-Fe2O3, which was equivalent to Fe2O3 with a content of 92.22%) than SR (mainly in the form of Fe2SiO4 and α-Fe, which were equivalent to Fe2O3 with a content of 8.29%) does, reduced the ignition temperature of Jincheng coal to 569 °C as a consequence of the enhanced transfer of oxygen to the carbon surface through the cyclic oxidation and reduction reactions between FeO and Fe2O3.

•Biomass yield of Spirulina mutant increased by 310% after γ-ray irradiation.•The mutant was domesticated under elevated CO2 and obtained hereditary stability.•Biomass yield increased by 500% after domestication under 15 vol.% CO2.•Cell ultrastructures were analysed to elucidate the improved growth rate.Spirulina sp. was mutated by γ-rays from 60Co nuclear irradiation to improve growth and CO2 fixation rate under 15 vol.% CO2 (in flue gas from a power plant). Mutants with enhanced growth phenotype were obtained, with the best strain exhibiting 310% increment in biomass yield on day 4. The mutant was then domesticated with elevated CO2 concentration, and the biomass yield increased by 500% after domestication under 15 vol.% CO2, with stable inheritance. Ultrastructure of Spirulina sp. shows that the fractal dimension of Spirulina cells decreased by 23% after mutation. Pore size in the cell wall of Spirulina mutant increased by 33% after 15 vol.% CO2 domestication. This characteristic facilitated the direct penetration of CO2 into cells, thus improving CO2 biofixation rate.

•In vivo lipids and astaxanthin evolution in H. pluvialis were showed by Raman imaging.•Astaxanthin accumulation rate under 15% CO2 was 5.8 times higher than that under air.•Lipids intensity under 15% CO2 was 27% higher than that under air.•Accumulation rate of lipids was higher than that of astaxanthin during encystment.In vivo spatiotemporal dynamics of lipids and astaxanthin evolution in Haematococcus pluvialis mutant induced with 15% CO2 and high light intensity were monitored with high spatial resolution in a non-destructive and label-free manner using single-cell Raman imaging. Astaxanthin intensity increased by 3.5 times within 12 h under 15% CO2, and the accumulation rate was 5.8 times higher than that under air. Lipids intensity under 15% CO2 was 27% higher than that under air. The lipids initially concentrated in chloroplast under 15% CO2 due to an increase of directly photosynthetic fatty acid, which was different from the whole-cell dispersed lipids under air. Astaxanthin produced in chloroplast first accumulated around nucleus and then spread in cytoplasmic lipids under both air and 15% CO2. The calculation results of kinetic models for lipids and astaxanthin evolutions showed that accumulation rate of lipids was much higher than that of astaxanthin in cells.

•Wet microalgae lipids were heterogeneously catalyzed into fatty acid methyl esters.•Energy consumption in traditional dewatering and drying processes were avoided.•Sulfonation improved conversion efficiency of graphene oxide catalysts by 15.7%.•The higher heating value of obtained biodiesel reached 36.62 MJ/kg.•Hydroxyl groups on catalyst surface played key role in transesterification reactions.Four solid acid catalysts including graphene oxide (GO), sulfonated graphene oxide (SGO), sulfonated graphene (SG), and sulfonated active carbon (SAC) were used to convert lipids in wet microalgae into biodiesel. The physiochemical properties of the catalysts were characterized with scanning electron microscope, X-ray diffraction, and thermogravimetric analysis. SGO provided the highest conversion efficiency (84.6% of sulfuric acid) of lipids to fatty acid methyl esters (FAME). Whereas SAC converted few lipids into FAME. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and elemental analysis revealed that much higher hydrophilic hydroxyl content in SGO catalyst resulted in a considerable higher conversion efficiency of lipids to FAME than that (48.6%) catalyzed by SG, although SO3H groups (0.44 mmol/g) in SGO were less than those (1.69 mmol/g) in SG. Given its higher SO3H group content than GO (0.38 mmol/g), SGO had higher conversion efficiency than GO (73.1%), when they had similar hydrophilic hydroxyl contents.

•Graphene enhanced methane yield (+25%) and production rate (+20%) in AD of ethanol.•Microbial structures of electro-active bacteria and archaea were revealed after AD.•Direct interspecies electron transfer (DIET) via graphene was established in AD.•DIET sustained much higher electron transfer flux than hydrogen transfer.Interspecies electron transfer between bacteria and archaea plays a vital role in enhancing energy efficiency of anaerobic digestion (AD). Conductive carbon materials (i.e. graphene nanomaterial and activated charcoal) were assessed to enhance AD of ethanol (a key intermediate product after acidogenesis of algae). The addition of graphene (1.0 g/L) resulted in the highest biomethane yield (695.0 ± 9.1 mL/g) and production rate (95.7 ± 7.6 mL/g/d), corresponding to an enhancement of 25.0% in biomethane yield and 19.5% in production rate. The ethanol degradation constant was accordingly improved by 29.1% in the presence of graphene. Microbial analyses revealed that electrogenic bacteria of Geobacter and Pseudomonas along with archaea Methanobacterium and Methanospirillum might participate in direct interspecies electron transfer (DIET). Theoretical calculations provided evidence that graphene-based DIET can sustained a much higher electron transfer flux than conventional hydrogen transfer.Download high-res image (123KB)Download full-size image

•SAPO 34 was modified with amine groups to improve CO2/H2 selectivity of MMM.•IL was loaded on modified SAPO 34 to enhance cohesion between SAPO 34 and polymer.•MMM surface became smooth after SAPO 34 was modified with NH2 groups and IL.•Both CO2 permeability and selectivity of MMM increased after the modification.•CO2/H2 selectivity of MMM with IL/SAPO 34-NH2 reached up to 22.1 at 20 °C.Mixed matrix membranes with ionic liquids and molecular sieve particles had high CO2 permeabilities, but CO2 separation from small gas molecules such as H2 was dissatisfied because of bad interfacial interaction between ionic liquid and molecular sieve particles. To solve that, amine groups were introduced to modify surface of molecular sieve particles before loading with ionic liquid. SAPO 34 was adopted as the original filler, and four mixed matrix membranes with different fillers were prepared on the outer surface of ceramic hollow fibers. Both surface voids and hard agglomerations disappeared, and the surface became smooth after SAPO 34 was modified by amine groups and ionic liquid [P66614][2-Op]. Mixed matrix membranes with composites of amine-modified SAPO 34 and ionic liquid exhibited excellent CO2 permeability (408.9 Barrers) and CO2/H2 selectivity (22.1).

•MEA and two ILs with different CO2 capacities were blended with CO2-philic polymer.•FFV of membrane increased after blending ILs while decreased after blending MEA.•Both CO2 permeability and selectivity increased after blending MEA and two ILs.•CO2 absorbent with larger CO2 capacity had a larger increase of CO2 permeability.•Membrane blended with MEA has the highest CO2/H2 and CO2/CH4 selectivity.To research effects of CO2 absorption capacity and type of CO2 absorbent on the CO2 separation and free-volume properties of facilitated transport membranes, two types of CO2 absorbents, namely monoethanolamine (MEA) and ionic liquids (ILs:[P66614][Triz] and [P66614][2-Op]), were adopted. The CO2 absorption capacities of MEA, [P66614][Triz] and [P66614][2-Op] were about 0.561 mol CO2 per mol, 0.95 mol CO2 per mol and 1.60 mol CO2 per mol, respectively. All mean free-volume hole radiuses of membranes decreased after blending CO2 absorbents. After polymer membrane blended with two ILs, number of free-volume hole increased, resulting in modest increase of the fractional free volume. Both CO2 permeability and selectivity increased after blending MEA and ILs. The increasing range of CO2 permeability corresponded with CO2 absorption capacity of CO2 absorbents, and membrane blending with [P66614][2-Op] showed the highest CO2 permeability of 672.1 Barrers at 25 °C. Pebax/PEGDME membrane blending with MEA obtained the highest CO2/H2 and CO2/CH4 selectivity at 17.8 and 20.5, respectively.

•Amino group was introduced to improve surface polarity of PDMS membrane.•The water contact angle of PDMS membrane decreased after the modification.•The concentration of N atom on surface of PDMS membrane reached up to ∼6%.•The density of PDMS membrane decreased while the swelling degree increased.•CO2 permeability increased while selectivity decreased after the modification.This study aimed to improve surface polarity of polydimethylsiloxane (PDMS) membranes and provide surface active sites which were easy to react with other chemicals. 3-Aminopropyltriethoxysilane (APTES) containing an amino group was introduced into a PDMS membrane by crosslinking to prepare polyacrylonitrile hollow fiber-supported PDMS membranes with an amino-functionalized surface. Fourier transform infrared and X-ray photoelectron spectroscopic analyses proved the existence of APTES and its amino group in the PDMS membrane. The concentration of N atoms on the PDMS membrane surface reached ∼6% when the mass ratio of APTES/PDMS oligomer in the PDMS coating solution was increased to 4/3. The water contact angle decreased from ∼114° to ∼87.5°, indicating the improved surface polarization of the PDMS membrane. The density and swelling degree of the PDMS membrane decreased and increased, respectively, with increasing APTES content in PDMS. This phenomenon increased CO2 permeability and decreased CO2/H2 selectivity, CO2/CH4 selectivity, and CO2/N2 selectivity. When the mass ratio of APTES/PDMS oligomer was increased from 0 to 4/3, the CO2 permeation rate of the hollow fiber-supported PDMS membranes initially decreased from ∼2370 GPU to ∼860 GPU and then increased to ∼2000 GPU due to the change in coating solution viscosity.

•Hydrothermal pretreatment (HTP) was used to facilitate food waste solubilization.•Soluble carbohydrates initially rose and then fell when HTP temperature increased.•Solubilization of proteins was dramatically promoted with increasing HTP temperature.•Effect of HTP retention time on solubilization and fermentation was moderate.•Two-stage H2 and CH4 co-production effected an energy conversion efficiency of 78.6%.The growing amount of food waste (FW) in China poses great pressure on the environment. Complex solid organics limit the hydrolysis of FW, hence impairing anaerobic digestion. This study employed hydrothermal pretreatment (HTP) to facilitate the solubilization of FW. When HTP temperature increased from 100 to 200 °C, soluble carbohydrate content first increased to a peak at 140 °C and then decreased, whereas total carbohydrate content was negatively correlated with increasing temperature due to the enhanced degradation and Maillard reactions. Protein solubilization was dramatically promoted after HTP, whereas protein degradation was negligibly enhanced. The hydrogen and methane yields from hydrothermally pretreated FW under the optimum condition (140 °C, 20 min) through two-stage fermentation were 43.0 and 511.6 mL/g volatile solids, respectively, resulting in an energy conversion efficiency (ECE) of 78.6%. The ECE of pretreated FW was higher than that of untreated FW by 31.7%.

•Cassava residue (CR)/Swine manure (SM) were mixed for microwave acid pretreatment.•Mono-fermentation of CR exhibited the highest hydrogen yield of 145.6 mL/g VS.•Mixed CR/SM resulted in the lowest hydrogen yield (107.8 mL/g VS) due to sugar loss.•Pretreatment of mixed CR/SM led to decrease of total sugar yield by 7.2–10.5%.•Reactions between carbonyl (CO) and amino group (NH2) resulted in sugar loss.Co-fermentation of carbon-rich and nitrogen-rich feedstocks with suitable carbon to nitrogen (C/N) ratios is commonly considered as a viable way to enhance biological hydrogen production. In this study, cassava residue (C/N ratio = 29.1) and swine manure (C/N ratio = 8.6) were mixed and subject to microwave-assisted acid hydrothermal pretreatment. The resulting hydrolysates were used for subsequent dark hydrogen fermentation. However, the mixture with a C/N ratio of 15.1 resulted in the lowest hydrogen yield potential of 107.8 mL/g volatile solid (VS). Comparatively, the mono-fermentation of cassava residue exhibited the highest hydrogen yield potential of 145.6 mL/g VS and a peak hydrogen production rate of 8.2 mL/g VS/h. The modified Gompertz model was employed for kinetic analysis, and suggested that the lag-phase time and peak time of hydrogen fermentation exhibited a significantly positive linear correlation with increased C/N ratios. Reducing sugars analysis indicated that pretreatment of mixed cassava residue and swine manure led to a decrease of total sugar yield by 7.2–10.5% due to the Maillard reactions between hydrolyzed sugars and amino acids. A reaction mechanism based on glucose and arginine was proposed to elucidate the Maillard interactions between carbonyl group (CO) and amino group (NH2), which was responsible for the overall sugar loss. The findings of this study suggested that pretreatment for mixed carbohydrate-rich and protein-rich feedstocks needs to be optimised to avoid unexpected fermentable sugars loss.

The biomass yield of Chlorella PY-ZU1 drastically increased when cultivated under high CO2 condition compared with that cultivated under air condition. However, less attention has been given to the microalgae photosynthetic mechanisms response to different CO2 concentrations. The genetic reasons for the higher growth rate, CO2 fixation rate, and photosynthetic efficiency of microalgal cells under higher CO2 concentration have not been clearly defined yet.In this study, the Illumina sequencing and de novo transcriptome assembly of Chlorella PY-ZU1 cells cultivated under 15% CO2 were performed and compared with those of cells grown under air. It was found that carbonic anhydrase (CAs, enzyme for interconversion of bicarbonate to CO2) dramatically decreased to near 0 in 15% CO2-grown cells, which indicated that CO2 molecules directly permeated into cells under high CO2 stress without CO2-concentrating mechanism. Extrapolating from the growth conditions and quantitative Real-Time PCR of CCM-related genes, the Km (CO2) (the minimum intracellular CO2 concentration that rubisco required) of Chlorella PY-ZU1 might be in the range of 80–192 μM. More adenosine triphosphates was saved for carbon fixation-related pathways. The transcript abundance of rubisco (the most important enzyme of CO2 fixation reaction) was 16.3 times higher in 15% CO2-grown cells than that under air. Besides, the transcript abundances of most key genes involved in carbon fixation pathways were also enhanced in 15% CO2-grown cells.Carbon fixation and nitrogen metabolism are the two most important metabolisms in the photosynthetic cells. These genes related to the two most metabolisms with significantly differential expressions were beneficial for microalgal growth (2.85 g L−1) under 15% CO2 concentration. Considering the micro and macro growth phenomena of Chlorella PY-ZU1 under different concentrations of CO2 (0.04–60%), CO2 transport pathways responses to different CO2 (0.04–60%) concentrations was reconstructed.

•An integrated process from cyanobacterium cultivation to utilization was conducted.•High CO2 and NaCl stress boosted carbohydrate accumulation in Arthrospira platensis.•Total carbohydrates in A. platensis occupied 53.4 wt% of dried biomass.•A. platensis cells were sectionally fractured into small debris after pretreatment.•Three-stage fermentation simultaneously promoted H2 yields and overall energy output.An integrated process involving cyanobacterium cultivation and three-stage fermentation was investigated to efficiently produce gaseous biofuels. The content and concentration of total carbohydrates in Arthrospira platensis biomass were remarkably enhanced through nutrient adjustments. Relative nitrogen starvation with continuous 15% (v/v) CO2 bubbling led to the accumulation of large-molecular-weight glycogen as an intracellular energy reserve, whereas 0.5 mol/L NaCl addition at 3rd day resulted in the synthesis of small-molecular-weight carbohydrates (e.g., trehalose) as osmoprotectants. The total carbohydrates in A. platensis cultivated under 15% (v/v) CO2 and 0.5 mol/L NaCl stress occupied 53.4 wt% of the dried biomass. The harvested wet A. platensis biomass was pretreated with dilute acid and steam heating to give the maximum reducing sugar yield of 0.460 g/g volatile solids (VS). Scanning electron microscopy and transmission electron microscopy analyses revealed that the A. platensis cells were fractured section by section and thoroughly disrupted into small debris and fragments after pretreatment. A three-stage process combining dark hydrogen, photo hydrogen, and dark methane fermentation was employed for hydrogen and methane co-production using the pretreated A. platensis biomass. The hydrogen yield was 96 mL/gVS after first-stage dark fermentation, whereas the concentration of soluble metabolic products (SMPs) reached 9.692 g/L. Through the combined dark and photo hydrogen fermentation, the hydrogen yield significantly increased to 429 mL/gVS, corresponding to an SMP removal efficiency of 95.96%. The overall energy yield was boosted to 10.51 kJ/gVS after third-stage dark methane fermentation.

This study involved comprehensively investigating pollutant emissions and control methods of NO, SO2, polycyclic aromatic hydrocarbons (PAHs) and dioxins (PCDD/Fs) in the combustion of biomass pellets prepared with hazardous waste of coal tar residue (CTR) as a binder. The NO emissions from moso bamboo pellets and SO2 emissions from wheat straw pellets corresponded to the highest emissions among the three biomass pellets. In contrast, NO and SO2 emissions from the sawdust pellet corresponded to the lowest emissions among three biomass pellets. When the biomass pellets were prepared with 30 wt% CTR binder, the pollutant emissions of NO, SO2, PAHs and PCDD/Fs were significantly lower than those in the direct combustion of only CTR. The SO2 emissions of wheat straw pellets with 30 wt% CTR binder gradually increased when the furnace temperature increased from 800 °C to 1300 °C. Conversely, the NO emission gradually decreased because more volatiles derived from biomass pellets locally generated stronger reducing atmospheres at a higher temperature to restrict the NO production. The SO2 emission of wheat straw pellets with 30 wt% CTR binder decreased by 55.6%–71.0% when limestone was added with a molar ratio of Ca/S at 2, while emission factors of PAHs and total I-TEQ of PCDD/Fs decreased by 13.3% and 59.9%, respectively, at 1200 °C.

•Dewatering of an Indonesian lignite with microwave irradiation was optimized.•Microwave absorbers increased dewatering rate and decreased energy consumption.•Increased diameter-to-height first increased and then decreased dewatering rate.•Energy consumption of moisture removal was analyzed based on the Page model.Dewatering of an Indonesian lignite with microwave irradiation was optimized to increase dewatering rate and decrease energy consumption. The energy consumption of the microwave dewatering process was affected by different factors, including addition of microwave absorber, diameter-to-height ratio of lignite pile, particle size and initial moisture content of lignite. The experiment results indicated that adding absorber carbon materials (activated carbon and graphite) and metal oxides (Fe3O4, MnO2, etc.) could increase the dewatering rate and decrease the energy consumption. With increased diameter-to-height ratio of lignite pile, dewatering rate initially increased and then decreased. An optimum value exists for diameter-to-height ratio, which presents maximum dewatering rate but with minimum energy consumption. The enhancement of heat accumulation caused by larger particle size increased the dewatering rate of lignite and decreased energy consumption. The energy consumption decreased with increased lignite weight and initial moisture content. However, the energy consumption initially decreased and then increased with enhanced microwave power. Electric power consumption can be well predicted on the basis of the microwave dewatering kinetics of lignite, which can be well described by the Page model under different conditions.

•Pore fractal and combustion characteristics of 18 typical Chinese cokes were investigated.•Pore fractal dimensions of cokes increased from 2.30 to 2.84 for activation energies of coals pyrolysis decreasing.•Pore fractal dimensions of cokes increased with average pore diameters decreasing and specific pore volumes increasing.•Ignition temperatures and activation energies of cokes decreased with pore fractal dimensions of cokes increasing.The pore fractal structures and combustion dynamics of cokes derived from the pyrolysis of 18 typical Chinese power coals were investigated to use the said cokes for boiler combustion and power generation after pyrolysis gas extraction. When the total contents of volatile matter and moisture in raw (air-dried) coals increased from 15.22% to 39.49%, the pore fractal dimensions of the pyrolyzed cokes gradually increased from 2.30 to 2.84 because of the decrease in the activation energies of coal pyrolysis. The average pore diameters of the coke particles gradually decreased, and the peaks of the differential specific surface area formed at a pore diameter of 3.7 nm gradually increased. Accordingly, the ignition temperatures of cokes gradually decreased from 617 °C to 486 °C. Their activation energies also gradually decreased, which resulted in an increase in fixed carbon burnout efficiencies from 84% to 91%. This indicated that cokes derived from lignite pyrolysis had larger pore fractal dimensions and therefore had lower ignition temperatures and higher burnout efficiencies than those from lean coal and anthracite pyrolysis.

To improve the permeation performance of a ceramic hollow fiber-supported poly (amide-b-ethylene oxide) (Pebax)/polyethylene glycol dimethylether (PEGDME) composite membrane during CO2 separation from biohydrogen, a room temperature ionic liquid (RTIL), namely, [P66614][2-Op], with a high CO2 capacity, was adopted to blend in the selective layer. An RTIL-blended selective layer without defects was prepared on the surface of the ceramic hollow fibre. The physicochemical properties and CO2/H2 separation performance of the Pebax/PEGDME/RTIL composite membrane were then compared with those of the Pebax/PEGDME composite membrane. Intermolecular hydrogen bonds were produced after blending RTIL with the Pebax/PEGDME selective layer, and the surface roughness of the composite membrane increased. The CO2 permeation rate increased by ∼35% and reached up to ∼75 GPU at 50 °C, and the CO2/H2 selectivity was maintained at a high value of ∼15 at 30 °C. Blending RTIL with the selective layer inhibited the positive effect of CO2-induced plasticisation on H2 permeability. However, this process improved CO2/H2 selectivity in mixed gases relative to the ideal selectivity by enhancing competitive sorption among gas molecules.

•Palm oil is used as feedstock for jet biofuel production.•Catalysts used to catalyze palm oil into jet biofuel are characterized.•Ni/HY of different Si/Al ratios and Ni contents are used to produce jet biofuel.•Zeolite SAPO-34 exhibits low arene (11%) and high alkane selectivity (65%).The aim of this study is to develop zeolite catalysts to produce jet biofuel from palm oil. Different Ni-loaded zeolites were tested as catalysts in the conversion of palm oil into jet biofuels with high alkane and low arene content. Five zeolite catalyst, were tested: Ni/SAPO-34, Ni/MCM-41, Ni/HY, Ni/SAPO-11 and Ni/Hbeta. Characterization was performed by X-ray diffraction, NH3-temperature-programmed desorption. The Ni/SAPO-34 catalyst exhibited the highest alkane selectivity (65%) and lowest arene selectivity (11%). The jet biofuel yield under catalysis increased from 21.1 to 42.0% when the reaction temperature was increased from 370 to 390 °C. The alkane content of the jet biofuel increased from 71 to 80% and the arene content decreased from 29 to 20%, when the weight ratio of Si/Al in the Ni/HY catalyst was reduced from 11 to 5, but the levels were almost unchanged as the nickel content was increased from 5 to 20%.

Back-propagation (BP) neural network models were developed to accurately predict the ignition temperature and activation energy of 16 typical Chinese coals and 48 of their blends. Pearson correlation analysis showed that ignition temperature and activation energy were most relevant to the moisture, volatile matter, fixed carbon, calorific value and oxygen of coals. Accordingly, three-layer BP neural network models with five input factors were developed to predict the ignition characteristics of power coal blends. The BP neural network for ignition temperature gave a relative mean error of 1.22%, which was considerably lower than 3.7% obtained by the quadratic polynomial regression. The BP neural network for activation energy gave a relative mean error of 3.89%, which was considerably lower than 10.3% obtained by the quadratic polynomial regression. The accuracy of the BP neural network was significantly higher than that of traditional polynomial regression.

Back-propagation (BP) neural network models were developed to accurately predict the maximum burning rate and fixed carbon burnout efficiency of 16 typical Chinese coals and 48 of their blends. Early stopping method was used to prevent the BP neural network from over-fitting. The generalisation performance and prediction accuracy of the neural network thus became significantly improved. Pearson correlation analysis results showed that the maximum burning rate was most relevant to coal calorific value as well as carbon and ash content. Fixed carbon burnout efficiency was most relevant to coal volatile matter, fixed carbon and calorific value. Accordingly, three-layer BP neural network models with three input factors were developed to predict the combustion characteristics of power coal blends. The BP neural network used to predict the maximum burning rate gave a relative mean error of 1.97%, which was considerably lower than that given by the quadratic polynomial regression (7.06%). Moreover, the BP neural network used to predict the fixed carbon burnout efficiency gave a relative mean error of 0.91%, which was significantly lower than that given by the quadratic polynomial regression (4.03%).

•The catalytic effects of four industrial wastes on coal combustion were compared.•The composite promoters of industrial wastes exhibited better catalytic effects.•A cascade chain catalytic mechanism of Na–Fe–Ca composite promoters was proposed.The catalytic effects of brine sludge (rich in NaCl), iron mud (rich in Fe2CO3), steel slag (rich in Fe2SiO4 and α-Fe) and calcium carbide residue (rich in Ca(OH)2) on coal combustion were compared with those of pure NaCl and ZnCl2. Thermobalance experiments showed that the catalytic effects of NaCl and brine sludge on coal combustion were better than those of the others. NaCl and brine sludge reduced the ignition temperature of Jincheng anthracite coal from 582 °C to 560 °C and 561 °C. This result was achieved because Na2O2 more easily obtained electrons from carbon as a result of the lower ionisation energy of the alkali metal Na. This attribute promoted the transport of the oxygen atom from the metal oxide to carbon. A novel cascade chain catalytic mechanism of Na–Fe–Ca composite promoters on coal combustion was proposed. In this mechanism, the oxygen atom was transported based on the order of metal catalytic activity from Na to Fe to Ca to carbon. Conversely, the electrons were transported in the reversed order. The Na–Fe–Ca composite promoters of industrial wastes exhibited better catalytic effects on coal combustion than the individual components, reducing the ignition temperature of Jincheng anthracite coal from 582 °C to 550 °C and augmenting burnout efficiency from 91.8% to 95.4%.

With the upgrading of fermentative biogas to produce gaseous transport fuel, ionic liquid (IL) [P66614][2-Op], which adsorbed CO2 through multiple-site cooperative interactions, was loaded onto molecular sieve MCM-41 to adsorb CO2 in a biohythane atmosphere (CH4 + H2 + CO2). [P66614][2-Op] loaded onto MCM-41 exhibited a higher CO2 adsorption rate than pure IL during the initial stage because of its larger reaction surface area. However, the CO2 adsorption rate of [P66614][2-Op] loaded onto MCM-41 became lower than that of pure IL as the reaction continued because CO2 was inaccessible to the IL blocked within the inner pores of MCM-41. The CO2 adsorption rate of IL loaded onto the molecular sieve (MCM-41–50% IL) was (51.5 mg of CO2 g–1 of IL min–1) 2.1 times higher than that of pure IL during the initial 1 min in a pure CO2 atmosphere and was (24.6 mg of CO2 g–1 of IL min–1) 2.2 times higher than that of pure IL during the initial 2 min in a biohythane atmosphere.

Cu foam combined with Pt-modified reduced graphene oxide (Pt–RGO) was investigated as an efficient cathode for CO2 reduction in a photoelectrocatalytic (PEC) cell with a TiO2 nanotube (TNT) photoanode. The synergistic catalytic mechanisms between photocatalysis and electrocatalysis in such a photoanode driven 2-electrode PEC cell were experimentally verified and theoretically analyzed. The dual functional Cu foam, as a cathode electrode and a Pt-RGO catalyst matrix, markedly increased the carbon atom conversion rate because of its well-defined porosity, large specific surface area, and in particular its affinity for CO2 reduction to hydrocarbons. Combination of the Cu foam matrix and Pt–RGO catalysts resulted in synergistic CO2 reduction in the (Pt–RGO/Cu foam)‖TNT PEC cell. The carbon atom conversion rate markedly increased to 4340 nmol (h−1 cm−2) by optimizing CO2 reduction conditions in the PEC cell, including voltage applied through the cell, Pt loading amount on RGO, and Pt–RGO loading amount on Cu foam.

•CO2 reduction conditions using a Pt-RGO||Pt-TNT cell were optimized.•Carbon atom conversion rate in the PEC cell was increased to 1500 nmol/(cm2 h).•Liquid product selectivity of CO2 reduction in the PEC cell reached 99%.This study aimed to determine the optimum conditions required to increase the carbon atom conversion rate in a Pt-RGO||Pt-TNT photoelectrochemical cell. The effects of Pt-RGO reduction time on CO2 conversion, voltage applied through the cell, catholyte pH, and pore size of nickel foam as a catalyst support were investigated. The conversion rate of C atoms initially increased and then decreased with increasing Pt-RGO reduction time, increasing electrolyte pH, and decreasing nickel foam pore size. Although carbon atom conversion showed sustainable growth as the applied voltage increased, the current efficiency of CO2 reduction products decreased because of enhanced proton interference when the voltage applied through the cell exceeds 2 V. A maximum carbon atom conversion rate of 1500 nmol/(cm2 h) was obtained by Pt-RGO reduction for 24 h when a 2 V voltage was applied through the cell, the catholyte pH was 8.8, and nickel foam with an average pore size of 160 μm was used as a support. Under optimum conditions, the liquid product selectivity of CO2 reduction reached 99%. The results of the study indicate that RGO-based catalysts have potential use as blueprints for CO2 reduction.

•Activated carbon effectively removed fermentative inhibitors to improve H2 yield.•Removal efficiencies of vanillin and 5-HMF in hydrolysate was over 40%.•H2 yield from water hyacinth increased with AC detoxification and HPB domestication.•Sequential methane yield significantly increased the energy conversion efficiency.To improve fermentative hydrogen production from water hyacinth pretreated with microwave-assisted dilute H2SO4 and cellulase, activated carbon (AC) was used to effectively remove fermentative inhibitors in hydrolysates. The removal efficiencies of vanillin, 5-hydroxymethyl furfural and furfural in artificial hydrolysates of water hyacinth were 84.8%, 45.4%, and 39.5%, respectively. The glucose content in the hydrolysates decreased by 13.8% with AC treatment. The hydrolysates of water hyacinth were used to domesticate hydrogen producing bacteria (HPB) and improve their adaptability. The hydrogen yield from the hydrolyzed water hyacinth with AC detoxification and HPB domestication increased from 104.0 to 134.9 mL/g total volatile solids (TVS). The sequential methane yield (107.7 mL/g TVS) significantly increased the energy conversion efficiency from 8.5% to 30.9%.

To upgrade the mixed gas of fermentative hydrogen and methane for the preparation of biohythane as a gaseous fuel for vehicles, a composite membrane of poly(amide-b-ethylene oxide) (Pebax® MH 1657) and polyethylene glycol dimethylether (PEGDME) coated on a porous ceramic hollow fiber was originally proposed for CO2 separation. The Pebax/PEGDME selective layer with high CO2 selectivity was closely adhered and evenly distributed to the porous ceramic hollow fiber as a highly permeable support. The ideal CO2/H2 selectivity of the composite membrane increased from 12 ± 0.7 to 26 ± 1.7 when the temperature decreased from 50 °C to 10 °C. Competitive sorption between different gas molecules was found in the composite membrane. The fast diffusion of small molecular gas (H2) through the nanopores in the selective layer improved the diffusion of relatively large molecular gases (CO2 and CH4) in the gas mixture. On the contrary, the slow diffusion of large molecular gas (CH4) worsened the diffusion of relatively small molecular gases (CO2 and H2).

To overcome the opposing trends in biomass yield and lipid accumulation, Chlorella PY-ZU1 cultures were continuously aerated with 15% CO2 to simultaneously enhance biomass yield (2.78 g L−1) and lipid content (47.04%). Microalgal cells consumed almost all the nitrate in the culture after 1 day to synthesize 24 mg L−1 of chlorophyll, which supported a peak growth rate of 0.675 g L−1 per day. Meanwhile, increased expression of key enzymes related to lipid synthesis (e.g., acetyl coenzyme A) enhanced lipid productivity to 192.10 mg L−1 per day. During the growth process, the carbon content of the dried biomass increased from 47.00% to 56.02% while the nitrogen content decreased from 6.36% to 1.99%. The unsaturated fatty acids decreased and saturated fatty acids increased, thus improving the anti-oxidation stability of microalgal biodiesel.

Philippine lignite with high inherent moisture and oxygen was upgraded by improving the slurryability through microwave irradiation. The physicochemical properties of the upgraded lignite were characterized through Fourier transform infrared spectroscopy, N2 adsorption porosimetry, scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction. The solid concentration of coal water slurry (CWS) that was prepared using the upgraded lignite increased from 51% to 53.4%, and the apparent CWS viscosity decreased from 862 mPa s to 687 mPa s at a shear rate of 100 s−1. These results can be attributed to several reasons. (1) The inherent moisture and hydrophilicity of the upgraded lignite was reduced after microwave irradiation. (2) Hydroxyl and carboxyl, which had the strongest hydrophilicity among the oxygen functional groups, decreased, whereas the carbonyl and ether, which only slightly affected the hydrophilicity, increased. (3) The specific surface area of the upgraded lignite initially decreased because of particle expansion, which was then augmented with increasing microwave time. (4) The aluminosilicate crystalline phase was generated through the mineral interactions in the upgraded lignite, and the soluble alkali ions, such as Ca2+, Mg2+, and Na+, increased on the particle surfaces. It is promising to continuously upgrade Philippine lignite in a tunnel-type microwave irradiation system to improve its slurribility for industrial-scale application.

Nitzschia ZJU1, which originated from the diatom Nitzschia sp. (ash free dry weight of biomass was 0.12 g L−1 and its lipid content was 13.34 %) after 60Co-γ ray irradiation and domestication at high-salinity, was re-mutated by 137Cs-γ irradiation to increase lipid productivity. The lipid yields of the new mutants Nitzschia ZJU2 and Nitzschia ZJU3, which were selected by Nile Red fluorescence, were increased from 209.9 mg L−1 (for the original Nitzschia ZJU1) to 245.5 mg L−1 and 311.6 mg L−1, respectively. The lipid content of the two strains increased to 64.42 and 62.61 % of ash free dry weight, respectively, when the cells were cultured with nitrogen and silicon deprivation. It was found that 3,063 reads of genetic expression including Acetyl-CoA carboxylase and other important genes in lipid synthesis pathway were up-regulated and 4,598 reads of genetic expression were down-regulated in mutant Nitzschia ZJU2, when the cells were cultured in optimized growth medium without nitrogen and silicon. The gene expression levels of ATP-binding cassette transporters, arginine and proline metabolism, and proteasome in metabolic pathways were up-regulated to different degrees in mutant Nitzschia ZJU2 under the same cultivation condition.

This study is aimed to examine the utilization of wastewater produced from the microwave irradiation upgrading process of Indonesian lignite. Physicochemical properties including total organic carbon (TOC), chemical oxygen demand (COD), organic functional groups, inorganic anions, inorganic cations, surface tension, pH, and electrical conductivity (EC) of the removed water were analysed. Results showed that TOC and COD increased with increased microwave time. Organic matters in removed water mainly consists of aromatic, aliphatic, and oxygen functional groups. During the microwave process, inorganic anions (SO42−, F− and Cl−) and cations (Na+, K+, Ca2+, etc.) gradually leached out from lignite. Concentrations of the dominant SO42− and Na+ ions initially increased and then decreased due to the competitive effect of leaching rate of ions and removal rate of water. Thus, EC initially increased and then decreased with total ion concentration, whereas surface tension and pH monotonously decreased. Moreover, pH must be improved and COD must be reduced before discharge or reuse of the removed water.

The photoelectrocatalytic (PEC) reduction of CO2 into high-value chemicals is beneficial in alleviating global warming and advancing a low-carbon economy. In this work, Pt-modified reduced graphene oxide (Pt-RGO) and Pt-modified TiO2 nanotubes (Pt-TNT) were combined as cathode and photoanode catalysts, respectively, to form a PEC reactor for converting CO2 into valuable chemicals. XRD, XPS, TEM, AFM, and SEM were employed to characterize the microstructures of the Pt-RGO and Pt-TNT catalysts. Reduction products, such as C2H5OH and CH3COOH, were obtained from CO2 under band gap illumination and biased voltage. A combined liquid product generation rate (CH3OH, C2H5OH, HCOOH, and CH3COOH) of approximately 600 nmol/(h·cm2) was observed. Carbon atom conversion rate reached 1,130 nmol/(h·cm2), which were much higher than those achieved using Pt-modified carbon nanotubes and platinum carbon as cathode catalysts.

In order to eliminate the inhibition effect of the toxic nitric oxide (NO) in flue gas on microalgal growth and CO2 fixation, NO was converted by a wet UV/H2O2 method to produce nitrate (NO3−), which then be used as a nitrogen source for microalgae to improve its growth. The growth ability and biomass compositions of the microalgae cultivated with the produced NO3− from NO gas were similar to those of the microalgae cultivated with equivalent moles of commercial NaNO3. The NO3− concentration produced from NO increased with UV lamp power, H2O2, and NO concentrations, resulting in an improved microalgal growth. The concentration of NO3− from 500 ppm NO wet-oxidized by 6% (v/v) H2O2 and 55 W UV light was up to 8.8 mM. When the produced nitrate was used as supplementary nitrogen source, the maximum growth productivity of Chlorella PY-ZU1 at 15% (v/v) CO2 reached 1.18 g L−1 per day (0.97 times higher than that cultivated with the standard medium). The peak fixation efficiency of 15% (v/v) CO2 was 69.6% (1.13 times higher than that cultivated with the standard medium).

Swine manure, a typical livestock waste, has great potential for biohydrogen production. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) analyses were employed to study the physicochemical characteristics of swine manure. SEM and TEM reveal that swine manure has a significantly damaged lignocellulosic matrix with cracks and debris on the surface. XRD and FTIR demonstrated that the cellulose crystallinity index of swine manure was higher than that of raw lignocellulosic biomass. A three-stage fermentation process comprising dark hydrogen, photo-hydrogen, and dark methane was performed using swine manure. Through the combined dark and photo-hydrogen production, the hydrogen yield was dramatically increased from 71.8 (dark fermentation only) to 247.7 mL of H2/g of total volatile solids (TVS). The subsequent methane yield was 87.2 mL of CH4/g of TVS using the residue of photofermentation, which increased the heat value conversion efficiency to 29.76%.

•Microwave heating with dilute acid efficiently degraded algae biomass from Taihu Lake.•Domesticated hydrogenogens with acids improved hydrogen yield from algae biomass.•Energy conversion efficiency increased to 47% by cogenerating hydrogen and methane.In order to efficiently utilize the biomass waste of algae bloom in Taihu Lake, China and improve energy conversion efficiency, a three-stage process comprising dark hydrogen fermentation with acid-domesticated hydrogenogens, photohydrogen fermentation, and methanogenesis was undertaken. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses showed that algal cells pretreated by microwave heating with diluted acid were degraded into smaller fragments (<5 μm) than those pretreated by steam heating with diluted acid. The microwave pretreatment of algae resulted in higher saccharification efficiency. The domesticated hydrogenogens in presence of acids improved the dark hydrogen production from microwave-pretreated algae biomass and led to a total combined dark and photofermentation hydrogen yield of 283.4 mL/g-total volatile solid (TVS). The energy conversion efficiency of steam-pretreated algae biomass remarkably increased to 47.0% by cogenerating 256.7 mL/g-TVS hydrogen and 253.5 mL/g-TVS methane in the three-stage process: dark-fermentation, photofermentation, and methanogenesis.

The transcriptomes of original diatom strain (wild-type, Nitzschia sp.) and a mutant strain (Nitzschia ZJU2), which exhibited rapid growth and high lipid productivity after two rounds of mutagenesis by γ-rays, were sequenced using the Illumina sequencing platform. Genes in the metabolic pathway and those related to cell growth and lipid synthesis were compared between the two strains. Up to 25804 and 35228 transcripts were detected in Nitzschia sp. and Nitzschia ZJU2, respectively. A total of 3939 genes were up-regulated in mutant Nitzschia ZJU2. Nine metabolic pathways involved in cell growth and carbohydrate and protein syntheses obviously changed. Genes involved in lipid synthesis, such as acetyl-CoA carboxylase and diacylgycerol O-acyltransferase, were obviously up-regulated. These phenomena promoted cell growth and lipid synthesis, so as to increase the lipid production of cells. Analysis of single nucleotide polymorphisms revealed the presence of 40795 nonsynonymous mutations in Nitzschia ZJU2, which indicated that nuclear irradiation triggers algal mutation.

The sequential generation of hydrogen and methane from xylose by two-stage anaerobic fermentation was investigated for the first time in this study. The effects of substrate concentration, bacteria domestication and nitrogen source on hydrogen yield were studied in the first stage. The genetic characterization of the 16S rDNA was used to analyze the flora of strains domesticated with xylose and glucose. The maximum hydrogen yield is 190.6 ml H2/g xylose when the xylose feedstock concentration is 1% (w/v), hydrogenogens are domesticated with xylose and yeast extract is used as nitrogen source. The soluble metabolite byproducts (SMB) from the hydrogen-producing stage were reutilized by methanogens to produce methane in the second stage. Over 98 wt % of acetate and butyrate in the SMB are reutilized to give a methane yield of 216.5 ml CH4/g xylose. The sequential generation of hydrogen and methane from xylose markedly increases the energy conversion efficiency to 67.5%.Highlights► Hydrogenogens by xylose domestication were characterized using 16S rDNA analysis. ► Metabolite byproducts from H2 production are reused to produce CH4 by fermentation. ► Cogeneration of H2 and CH4 from xylose increases energy conversion efficiency.

Hydrogen production from Arthrospira (Spirulina) platensis wet biomass through heterofermentation by the [FeFe] hydrogenase of hydrogenogens (hydrogen-producing bacteria) and autofermentation by the [NiFe] hydrogenase of Arthrospira platensis was discussed under dark anaerobic conditions. In heterofermentation, wet cyanobacterial biomass without pretreatment was hardly utilized by hydrogenogens for hydrogen production. But the carbohydrates in cyanobacterial cells released after cell wall disruption were effectively utilized by hydrogenogens for hydrogen production. Wet cyanobacterial biomass was pretreated with boiling and bead milling, ultrasonication, and ultrasonication and enzymatic hydrolysis. Wet cyanobacterial biomass pretreated with ultrasonication and enzymatic hydrolysis achieved the maximum reducing sugar yield of 0.407 g/g-DW (83.0% of the theoretical reducing sugar yield). Different concentrations (10 g/l to 40 g/l) of pretreated wet cyanobacterial biomass were used as substrate to produce fermentative hydrogen by hydrogenogens, which were domesticated with the pretreated wet cyanobacterial biomass as carbon source. The maximum hydrogen yield of 92.0 ml H2/g-DW was obtained at 20 g/l of wet cyanobacterial biomass. The main soluble metabolite products (SMPs) in the residual solutions from heterofermentation were acetate and butyrate. In autofermentation, hydrogen yield decreased from 51.4 ml H2/g-DW to 11.0 ml H2/g-DW with increasing substrate concentration from 1 g/l to 20 g/l. The main SMPs in the residual solutions from autofermentation were acetate and ethanol. The hydrogen production peak rate and hydrogen yield at 20 g/l of wet cyanobacterial biomass in heterofermentation showed 110- and 8.4-fold increases, respectively, relative to those in autofementation.Highlights► Wet cyanobacterium is ultrasonically and enzymatically hydrolyzed for reducing sugar. ► Pretreated biomass is fermented by domesticated hydrogenogens to improve H2 yield. ► Heterofermentation gives much higher H2 yield and peak rate than autofermentation.

Arthrospira platensis wet biomass was subjected to microwave-assisted dilute H2SO4 pretreatment to improve saccharification by hydrolysis with glucoamylase and hydrogen production from dark-fermentation. When the hydrolyzed biomass from A. platensis was inoculated with hydrogenogens (heat-treated anaerobic sludge) to produce hydrogen during dark-fermentation, the maximum hydrogen yield of 96.6 ml H2/g DW was obtained. Because high concentration of NH4+ (31.6–56.5 mM) in the residual solution (also containing acetate and butyrate) obtained from dark-fermentation can significantly inhibit the activities of photosynthetic bacteria in sequential photo-fermentation, a modified zeolite was used to extract NH4+ by ion exchange to reduce the NH4+ content to 2.2–2.7 mM (91.8%–95.8% of NH4+ removal efficiency). The treated residual solution was reused for hydrogen production in sequential photo-fermentation. The maximum hydrogen yield from A. platensis wet biomass was significantly enhanced from 96.6 to 337.0 ml H2/g DW using a combination of dark- and photo-fermentation.Highlights► Arthrospira platensis wet biomass is microwaved with acid to improve enzymatic hydrolysis. ► Hydrolyzed microalgae is fermented by hydrogenogens to enhance dark H2 yield. ► NH4+ removal by zeolite between the dark- and photo-fermentation improved H2 yield. ► H2 yield is markedly enhanced from microalgae by dark- and photo-fermentation.

The gene of a hydrogen-promoting protein (which we term HPP) from Enterobacter cloacae IIT-BT 08 was cloned and over-expressed in E. cloacae CICC10017 for the first time in this study, and the overall hydrogen yield was greatly improved using the recombinant strain. A recombinant plasmid containing the gene in-frame with Glutathione-S-Transferase (GST) gene was transformed into a hydrogen producing strain of E. cloacae CICC10017 to produce a GST-fusion protein. SDS-PAGE and western blot analysis confirm the successful expression of the GST-tagged protein. An in vitro assay of cell lysates indicates hydrogenase activity of the recombinant strain is 534.78 ± 18.51 ml/(g-DW·h), nearly 2-fold higher than the wild strain. The hydrogen yield of the recombinant strain is 2.55 ± 0.1 mol/mol-glucose, also 2-fold higher than the wild strain. The recombinant strain produces more acetate and butyrate during hydrogen fermentation, but less ethanol, due to the higher hydrogenase activity with the over-expression of the hydrogen-promoting protein. Together, the results demonstrate that successful expression of a single structural gene improves the overall yield of hydrogen by directing metabolic fluxes away from formation of products that compete for NADH.

Mixed bacteria were used to improve hydrogen yield from cassava starch in combination of dark and photo fermentation. In dark fermentation, mixed anaerobic bacteria (mainly Clostridium species) were used to produce hydrogen from cassava starch. Substrate concentration, fermentation temperature and pH were optimized as 10.4 g/l, 31 °C and 6.3 by response surface methodology (RSM). The maximum hydrogen yield and production rate in dark fermentation were 351 ml H2/g starch (2.53 mol H2/mol hexose) and 334.8 ml H2/l/h, respectively. In photo fermentation, immobilized mixed photosynthetic bacteria (PSB, mainly Rhodopseudomonaspalustris species) were used to produce hydrogen from soluble metabolite products (SMP, mainly acetate and butyrate) of dark fermentation. The maximum hydrogen yield in photo fermentation was 489 ml H2/g starch (3.54 mol H2/mol hexose). The total hydrogen yield was significantly increased from 402 to 840 ml H2/g starch (from 2.91 to 6.07 mol H2/mol hexose) by mixed bacteria and cell immobilization in combination of dark and photo fermentation.

The energy conversion efficiency in hydrogen and methane cogeneration from Arthrospira maxima biomass by two-phase fermentation is improved with bacteria domestication and enzymatic hydrolysis. The A. maxima biomass (dried weight) can theoretically cogenerate hydrogen and methane yields of 318 ml/g and 262 ml/g, which dramatically increases the theoretical energy conversion efficiency from 16.6% in hydrogen only production to 61.9%. The experimental hydrogen yield is increased from 49.7 ml/g to 64.3 ml/g, when the hydrogenogens community is domesticated with A. maxima biomass as carbon source. The hydrogen yield is further increased to 78.7 ml/g when A. maxima biomass is hydrolyzed with glucoamylase, which gives an energy conversion efficiency of 4.1% in hydrogen only production. The soluble metabolite byproducts from the first hydrogen-producing phase are reutilized by methanogens to produce methane of 109.5–145.5 ml/g in the second phase. The cogeneration of hydrogen and methane from A. maxima biomass markedly increases the experimental energy conversion efficiency to 27.7%.Research highlights► A. maxima biomass is enzymatically hydrolyzed to produce H2 by fermentation. ► Hydrogenogens are domesticated with A. maxima biomass to increase H2 yield. ► Cogenerate H2 and CH4 from A. maxima biomass to improve energy conversion.

Rice straw was pretreated by microwave-assisted alkali to improve saccharification in enzymatic hydrolysis and hydrogen yield in combined dark- and photo-fermentation in this paper. A maximum reducing sugar yield of 69.3 g/100 g TVS was obtained when 50 g/l rice straw was pretreated by microwave heating for 15 min at 140 °C in 0.5% NaOH solution and then enzymatically hydrolyzed for 96 h. When hydrolyzed rice straw was used for hydrogen production by anaerobic bacteria in dark-fermentation, a maximum hydrogen yield of 155 ml/g TVS was obtained. The residual solution (mainly acetate and butyrate) from dark-fermentation was reutilized for hydrogen production by immobilized photosynthetic bacteria in photo-fermentation. By combination of dark- and photo-fermentation, the maximum hydrogen yield was greatly enhanced to 463 ml/g TVS, which is 43.2% of the theoretical hydrogen yield.

The nonlinear back-propagation (BP) neural network models were developed to predict the maximum solid concentration of coal water slurry (CWS) which is a substitute for oil fuel, based on physicochemical properties of 37 typical Chinese coals. The Levenberg–Marquardt algorithm was used to train five BP neural network models with different input factors. The data pretreatment method, learning rate and hidden neuron number were optimized by training models. It is found that the Hardgrove grindability index (HGI), moisture and coalification degree of parent coal are 3 indispensable factors for the prediction of CWS maximum solid concentration. Each BP neural network model gives a more accurate prediction result than the traditional polynomial regression equation. The BP neural network model with 3 input factors of HGI, moisture and oxygen/carbon ratio gives the smallest mean absolute error of 0.40%, which is much lower than that of 1.15% given by the traditional polynomial regression equation.

A novel reaction mechanism of H2 and CH4 cogeneration from water hyacinth (Eichhornia crassipes) was originally proposed to increase the energy conversion efficiency. The glucose and xylose hydrolysates derived from cellulose and hemicellulose are fermented to cogenerate H2 and CH4 by two-step anaerobic fermentation. The total volatile solid of hyacinth leaves can theoretically cogenerate H2 and CH4 yields of 303 ml-H2/g-TVS and 211 ml-CH4/g-TVS, which dramatically increases the theoretical energy conversion efficiency from 19.1% in only H2 production to 63.1%. When hyacinth leaves are pretreated with 3 wt% NaOH and cellulase in experiments, the cogeneration of H2 (51.7 ml-H2/g-TVS) and CH4 (143.4 ml-CH4/g-TVS) markedly increases the energy conversion efficiency from 3.3% in only H2 production to 33.2%. Hyacinth leaves, which have the most cellulose and hemicellulose and the least lignin and ash, give the highest H2 and CH4 yields, while hyacinth roots, which have the most ash and the least cellulose and hemicellulose, give the lowest H2 and CH4 yields.

This article discusses the method of producing hydrogen from water hyacinth. Water hyacinth was pretreated with microwave heating and alkali to enhance the enzymatic hydrolysis and hydrogen production in a two-step process of dark- and photo- fermentation. Water hyacinth with various concentrations of 10–40 g/l was pretreated with four methods: (1) steam heating; (2) steam heating and microwave heating/alkali pretreatment; (3) steam heating and enzymatic hydrolysis; (4) steam heating, microwave heating/alkali pretreatment and enzymatic hydrolysis. Water hyacinth (20 g/l) pretreated with method 4 gave the maximum reducing sugar yield of 30.57 g/100 g TVS, which was 45.6% of the theoretical reducing sugar yield (67.0 g/100 g TVS). The pretreated water hyacinth was used to produce hydrogen by mixed H2-producing bacteria in dark fermentation. The maximum hydrogen yield of 76.7 ml H2/g TVS was obtained at 20 g/l of water hyacinth. The residual solutions from dark fermentation (mainly acetate and butyrate) were used to further produce hydrogen by immobilized Rhodopseudomonas palustris in photo fermentation. The maximum hydrogen yield of 522.6 ml H2/g TVS was obtained at 10 g/l of water hyacinth. Through a combined process of dark- and photo- fermentation, the maximum hydrogen yield from water hyacinth was dramatically enhanced from 76.7 to 596.1 ml H2/g TVS, which was 59.6% of the theoretical hydrogen yield.

In this study, we investigated a two-phase process of combining the dark- and photo-fermentation methods to reutilize the residual solution derived from dark fermentation and increase the hydrogen yield (HY) from glucose. In dark fermentation, an orthogonal experimental design was used to optimize the culture medium for Clostridium butyricum (C. butyricum). The optimal culture medium composition was determined as glucose 20 g/l, NaCl 3 g/l, MgCl2 0.1 g/l, FeCl2 0.1 g/l, K2HPO4 2.5 g/l, l-cysteine 0.5 g/l, vitamin solution 10 ml/l, and trace element solution 10 ml/l. In this method, the maximum HY increased from 1.59 to 1.72 mol H2/mol glucose and hydrogen production rate (HPR) from 86.8 to 100 ml H2/l/h. The metabolite byproducts from dark fermentation, mostly containing acetate and butyrate, were inoculated with Rhodopseudomonas palustris (R. palustris) and reutilized to produce hydrogen in photo-fermentation. In photo-fermentation, the maximum HY was 4.16 mol H2/mol glucose, and the maximum removal ratios of acetate and butyrate were 92.3% and 99.8%, respectively. Combining dark fermentation and photo-fermentation caused a dramatic increase of HY from 1.59 to 5.48 mol H2/mol glucose. The conversion efficiency of heat value in dark fermentation surged from 13.3% to 46.0% in the two-phase system.

The combination of dark and photo fermentation was studied with cassava starch as the substrate to increase the hydrogen yield and alleviate the environmental pollution. The different raw cassava starch concentrations of 10–25 g/l give different hydrogen yields in the dark fermentation inoculated with the mixed hydrogen-producing bacteria derived from the preheated activated sludge. The maximum hydrogen yield (HY) of 240.4 ml H2/g starch is obtained at the starch concentration of 10 g/l and the maximum hydrogen production rate (HPR) of 84.4 ml H2/l/h is obtained at the starch concentration of 25 g/l. When the cassava starch, which is gelatinized by heating or hydrolyzed with α-amylase and glucoamylase, is used as the substrate to produce hydrogen, the maximum HY respectively increases to 258.5 and 276.1 ml H2/g starch, and the maximum HPR respectively increases to 172 and 262.4 ml H2/l/h. Meanwhile, the lag time (λ) for hydrogen production decreases from 11 h to 8 h and 5 h respectively, and the fermentation duration decreases from 75–110 h to 44–68 h. The metabolite byproducts in the dark fermentation, which are mainly acetate and butyrate, are reused as the substrates in the photo fermentation inoculated with the Rhodopseudomonas palustris bacteria. The maximum HY and HPR are respectively 131.9 ml H2/g starch and 16.4 ml H2/l/h in the photo fermentation, and the highest utilization ratios of acetate and butyrate are respectively 89.3% and 98.5%. The maximum HY dramatically increases from 240.4 ml H2/g starch only in the dark fermentation to 402.3 ml H2/g starch in the combined dark and photo fermentation, while the energy conversion efficiency increases from 17.5–18.6% to 26.4–27.1% if only the heat value of cassava starch is considered as the input energy. When the input light energy in the photo fermentation is also taken into account, the whole energy conversion efficiency is 4.46–6.04%.

To recycle industrial wastes and reduce SO2 pollutant emission in coal combustion, the mineralogical compositions, porosity structures, surface morphologies, and desulfurization properties of three calcium and sodium industrial wastes were investigated via X-ray diffraction (XRD), porosimeter, scanning electron microscopy (SEM), and a fixed-bed reactor. (1) White lime mud (WLM) mainly composed of CaCO3 with Na2O and K2O impurities has smaller CaCO3 particles and a higher surface area than limestone. But calcined WLM has larger CaO particles and a lower surface area than limestone calcined at 1200 °C for 300 s. (2) Calcium carbide residue (CCR) mainly composed of Ca(OH)2, has the highest surface area and smaller Ca(OH)2 particles than the CaCO3 particles in WLM. Its surface area monotonously and dramatically decreases at 1200 °C for 300 s, but the sintered CaO particles are still smaller than those in the limestone. (3) When brine sludge (BS), mainly composed of NaCl and CaCO3, is heated at 1200 °C for 300 s, the NaCl/CaO eutectic solvent facilitates the aggregation of some complex composites to form many larger particles. (4) WLM gives the highest desulfurization efficiency of 80.4% at 1000 °C and 65.0% at 1100 °C in coal combustion. Combined CCR and limestone give a synergistic desulfurization efficiency of 45.8% at 1200 °C. BS with a molar ratio of Na/Ca at 1:15 effectively promotes the synergistic desulfurization efficiency of combined CCR and limestone to a peak of 54.9% at 1200 °C.

To improve the coal water slurry (CWS) property made from Chinese Shenhua coal with high inherent moisture and oxygen contents, microwave irradiation and thermal heat were employed to modify the coal physicochemical property. Microwave irradiation reduces the inherent moisture and reforms the oxygenic function groups, while it decreases the total specific surface area. Thermal heat markedly decreases the inherent moisture, volatile, and oxygen contents, while it dramatically increases the total specific surface area. Therefore, microwave irradiation gives a higher CWS concentration and a better rheological behavior than thermal heat, while it remarkably reduces the operation time and energy consumption. The maximum CWS concentration given by microwave irradiation at 420 W for 60 s is 62.14%, which is not only higher than that of 60.41% given by thermal heat at 450 °C for 0.5 h but also higher than the initial 58.23%. Meanwhile, the minimum shear stress given by microwave irradiation is 36.4 Pa at the shear rate of 100 s −1, which is not only lower than that of 42.4 Pa given by thermal heat but also lower than the initial 79.8 Pa. The minimum unit energy consumption of 0.115 kWh/(kg of coal) and electricity cost of 4.6 U.S. $/(ton of coal) for CWS concentration promotion by 1% are obtained at 420 W for 20 s in the microwave oven. The unit energy consumptions for CWS concentration promotion and inherent moisture removal by thermal heat are, respectively, 214 and 22.5 times higher than those by microwave irradiation, while the energy use efficiencies are on the converse.

In order to reutilize the residual solutions derived from hydrogen production and increase the energy conversion efficiency, a novel process of cogenerating hydrogen and methane from glucose using a two-phase anaerobic fermentation process was proposed and investigated. The effects of substrate concentration, weight ratio of inoculation to substrate, pH value and nutrient medium on hydrogen production were studied. The maximum specific hydrogen yield is 2.75 mol H2/mol glucose when the initial glucose concentration is 1%, the weight ratio of inoculation to substrate is 2:1 and the pH value is 6. The residual solutions derived from hydrogen production were reused to produce methane by methanogen in another reactor. The maximum specific methane yield is 2.13 mol CH4/mol glucose when the reutilization rates of ethanol, acetic acid, butyric acid, valeric acid, and caproic acid are all above 90%. The cogeneration process can dramatically increase the energy conversion efficiency from 23% (hydrogen only production) to 82%.

The ultrafine coal water slurry (CWS) with the particle size of 1–10 μm, ash content of 1–2%, solid concentration of 50% is a promising substitute fuel for diesel oil. The effects of pore fractal structures of three ultrafine CWSs on their rheological behaviors and combustion dynamics were studied in this paper. When the pore fractal dimensions of Yanzhou, Huainan and Shenhua ultrafine CWSs increase, their apparent viscosities all increase and the increase extents gradually enlarge with decreasing shear rates, while their ignition temperatures and apparent activation energies all decrease. For example, when the pore fractal dimension of Yanzhou coal increases from 2.31 to 2.43, the CWS apparent viscosity at a low shear rate of 12 s−1 increases from 75 mPa s to 2400 mPa s, and that at a high shear rate of 100 s−1 increases from 80 mPa s to 820 mPa s. Meanwhile, the ignition temperature of Yanzhou CWS decreases from 445 °C to 417 °C at a heating rate of 12.5 °C/min, and the apparent activation energy decreases from 104 kJ/mol to 32 kJ/mol.

Biofuels derived from biomass will play a major role in future renewable energy supplies in transport. Gaseous biofuels have superior energy balances, offer greater greenhouse gas emission reductions and produce lower pollutant emissions than liquid biofuels. Biogas derived through fermentation of wet organic substrates will play a major role in future transport systems. Biogas (which is composed of approximately 60% methane/hydrogen and 40% carbon dioxide) requires an upgrading process to reduce the carbon dioxide content to less than 3% before it is used as compressed gas in transport. This paper reviews recent developments in fermentative biogas production and upgrading as a transport fuel. Third generation gaseous biofuels may be generated using marine-based algae via two-stage fermentation, cogenerating hydrogen and methane. Alternative biological upgrading techniques, such as biological methanation and microalgal biogas upgrading, have the potential to simultaneously upgrade biogas, increase gaseous biofuel yield and reduce carbon dioxide emission.

•Enterobacter aerogenes cells were mutated by nuclear irradiation of 60Co γ-rays.•E. aerogenes mutants were screened with larger colour circles of acid by-products.•Hydrogenase activity of the E. aerogenes ZJU1 mutant improved by 75.3%.•Hydrogen yield (301 mL H2/g glucose) with mutant was higher by 81.8% than the wild.Nuclear irradiation was used for the first time to generate efficient mutants of hydrogen-producing bacteria Enterobacter aerogenes, which were screened with larger colour circles of more fermentative acid by-products. E. aerogenes cells were mutated by nuclear irradiation of 60Co γ-rays. The screened E. aerogenes ZJU1 mutant with larger colour circles enhanced the hydrogenase activity from 89.8 of the wild strain to 157.4 mL H2/(g DW h). The hereditary stability of the E. aerogenes ZJU1 mutant was certified after over ten generations of cultivation. The hydrogen yield of 301 mL H2/g glucose with the mutant was higher by 81.8% than that of 166 mL/g glucose with the wild strain. The peak hydrogen production rate of 27.2 mL/(L·h) with the mutant was higher by 40.9% compared with that of 19.3 mL/(L·h) with the wild strain. The mutant produced more acetate and butyrate but less ethanol compared with the wild strain during hydrogen fermentation.

•Transcriptome sequencing and annotation was performed on Haematococcus pluvialis.•Astaxanthin metabolism of H. pluvialis was enhanced by gamma ray and 15% CO2.•Pyruvate and fatty acid metabolism were enhanced to support astaxanthin biosynthesis.Transcriptome sequencing and annotation was performed on Haematococcus pluvialis mutant red cells induced with high light under 15% CO2 to demonstrate why astaxanthin yield of the mutant was 1.7 times higher than that of a wild strain. It was found that 56% of 1947 differentially expressed genes were upregulated in mutant cells. Most significant differences were found in unigenes related to photosynthesis, carotenoid biosynthesis and fatty acid biosynthesis pathways. The pyruvate kinase increased by 3.5-fold in mutant cells. Thus, more pyruvate, which was beneficial to carotenoids and fatty acid biosynthesis, was generated. Phytoene synthase, zeta-carotene desaturase, lycopene beta-cyclase involved in β-carotene biosynthesis in mutant cells were upregulated by 10.4-, 4.4-, and 5.8-fold, respectively. Beta-carotene 3-hydroxylase catalyzing conversion of β-carotene into astaxanthin was upregulated by 18.4-fold. The fatty acid biosynthesis was promoted because of the upregulation of acetyl-CoA synthetase and acetyl-CoA carboxylase, thus increasing astaxanthin esterification and accumulation in mutant cells.

•Cassava residues were pretreated by ionic liquid N-methylmorpholine-N-oxide (NMMO).•NMMO-pretreated cassava residues generated deep grooves (∼4 μm in width) and pores.•Cellulose I became cellulose II in NMMO-pretreated cassava residues.•H2 yield from NMMO-pretreated cassava residues after enzymolysis was enhanced.•Overall energy conversion increased to 21.4–27.9% in H2/CH4 cogeneration.An ionic liquid of N-methylmorpholine-N-oxide (NMMO) was used to effectively pretreat cassava residues for the efficient enzymatical hydrolysis and cogeneration of fermentative hydrogen and methane. The reducing sugar yield of enzymolysed cassava residues with NMMO pretreatment improved from 36 to 42 g/100 g cassava residues. Scanning electron microscopy images revealed the formation of deep grooves (∼4 μm wide) and numerous pores in the cassava residues pretreated with NMMO. X-ray diffraction patterns showed that the crystallinity coefficient of NMMO-pretreated cassava residues decreased from 40 to 34. Fourier transform infrared spectra indicated that crystal cellulose I was partially transformed to amorphous cellulose II in the NMMO-pretreated cassava residues. This transformation resulted in a reduced crystallinity index from 0.85 to 0.77. Hydrogen yield from the enzymolysed cassava residues pretreated with NMMO increased from 92.3 to 126 mL/g TVS, and the sequential methane yield correspondingly increased from 79.4 to 101.6 mL/g TVS.

•The biomass productivity of Haematococcus pluvialis red cells reached 0.66 g L−1 d−1.•CO2 fixation rate of mutant under 15% CO2 was 24 times higher than that under air.•Transcriptome sequencing and annotation was performed on H. pluvialis red cells.•Carbon metabolism of H. pluvialis was enhanced by gamma ray and 15% CO2.To elucidate the mechanism underlying the enhanced growth rate in the Haematococcus pluvialis mutated with 60Co-γ rays and domesticated with 15% CO2, transcriptome sequencing was conducted to clarify the carbon metabolic pathways of mutant cells. The CO2 fixation rate of mutant cells increased to 2.57 g L−1 d−1 under 15% CO2 due to the enhanced photosynthesis, carbon fixation, glycolysis pathways. The upregulation of PetH, ATPF0A and PetJ related to photosynthetic electron transport, ATP synthase and NADPH generation promoted the photosynthesis. The upregulation of genes related to Calvin cycle and ppdK promoted carbon fixation in both C3 and C4 photosynthetic pathways. The reallocation of carbon was also enhanced under 15% CO2. The 19-, 14- and 3.5-fold upregulation of FBA, TPI and PK genes, respectively, remarkably promoted the glycolysis pathways. This accelerated the conversion of photosynthetic carbon to pyruvate, which was an essential precursor for astaxanthin and lipids biosynthesis.

•A water-circulating column photobioreactor (WCC–PBR) was developed in this study.•Bubble generation time decreased by 60.4% in the WCC–PBR.•Mixing time decreased by 41.5% with the WCC–PBR.•Total energy consumption decreased by 21.1% with the WCC–PBR.A water-circulating column photobioreactor (WCC–PBR) was developed to decrease bubble generation time and mixing time for growing microalgal biomass at low energy consumption. Bubble generation time was decreased by 60.4% and mixing time was decreased by 41.5% owing to an enhanced solution velocity with a water pump. Bubble residence time was decreased by 31.1% and mass transfer coefficient was decreased by 0.4% owing to a reduced distance between air aerator and solution surface. Microalgal growth rate was decreased by 12.7% from 128.9 mg/L day in an air-lifting column photobioreactor (ALC-PBR) to 112.6 mg/L day in a WCC–PBR because of the decrease in residence time of bubbles and an additional shear of cells in a water pump. However, total energy consumption of a WCC–PBR with an air compressor and a water pump was lower by 21.1% than that of an ALC–PBR with only an air compressor.

•Graphene oxide (GO) catalyzed wet microalgae lipids into fatty acids methyl esters.•GO contained 0.997 mmol of SO3H groups per gram and many OH groups.•Hydrophilic GO surfaces adsorbed wet microalgal cells.•GO achieved 95.1% lipids conversion efficiency.In order to produce biodiesel from lipids in wet microalgae with graphene oxide (GO) as solid acid catalyst, the effects on lipids conversion efficiencies of catalyst dosage, transesterification temperature, reaction time, methanol dosage and chloroform dosage were investigated. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and elemental analysis revealed that GO contained 0.997 mmol SO3H groups per gram and high amounts of OH groups. Scanning electron microscopy showed that wet microalgae cells were adsorbed on hydrophilic GO surfaces covered with many OH groups. Lipids extracted by chloroform from microalgal cells were transformed into fatty acids methyl esters (FAMEs) through transesterification catalyzed by the acid centers (SO3H groups) in GO catalysts. The lipids conversion efficiency into FAMEs was 95.1% in microwave-assisted transesterification reactions of 5 wt.% GO catalyst at 90 °C for 40 min.Download high-res image (196KB)Download full-size image

•Genes of HycE and HycG were separately over-expressed in Enterobacter aerogenes.•SDS-PAGE analysis confirms the successful expression of HycE and HycG.•Hydrogenase activity of the recombinants is 124% and 67% higher than the wild strain.•H2 yields are 2.16 mol/mol of E. aerogenes/HycE and 1.97 mol/mol of E. aerogenes/HycG.•The recombinants produce more acetate and butyrate as by-product, but less ethanol.The [NiFe]-hydrogenase 3 of Enterobacter aerogenes contains a large subunit of 60 kDa (HycE) and a small subunit of 30 kDa (HycG). The gene of HycE and the gene of HycG were overexpressed in E. aerogenes separately by using the pGEX-4T-2-cat vector, to obtain two recombinant strains: E. aerogenes/HycE and E. aerogenes/HycG. The hydrogen yields were significantly enhanced by the recombinant strains. The hydrogenase activities of the recombinant strains increased by 124% (E. aerogenes/HycE) and 67% (E. aerogenes/HycG) compared with that of the wild strain. The hydrogen yields of the recombinant strains from initial glucose increased by 86.2% to 2.16 mol H2/mol (E. aerogenes/HycE) and by 69.8% to 1.97 mol H2/mol (E. aerogenes/HycG). The recombinant strains produced more acetate and butyrate than the wild strain, and this finding corresponded to the metabolism of NADH.

•Tilmicosin at low concentrations stimulated the growth of microalgae mutant.•Cells fractal dimension increased when initial tilmicosin concentration increased.•Size of microalgal cells decreased when initial tilmicosin concentration increased.•Cellular MDA content increased; SOD activity first increased and then decreased.•Maximum removal efficiency of tilmicosin by microalgae mutant reached 99.8%.The response mechanisms of microalgal mutant Chlorella PY-ZU1 cells were investigated in their removal of antibiotic tilmicosin from wastewater under 15% CO2. Low concentrations (0.01–2 mg L−1) of tilmicosin in wastewater stimulated the growth of microalgal cells, whereas high concentrations (5–50 mg L−1) of tilmicosin significantly inhibited cell growth. When initial tilmicosin concentration increased from 0 to 50 mg L−1, fractal dimension of microalgal cells monotonically increased from 1.36 to 1.62 and cell size monotonically decreased from 4.86 to 3.75 μm. In parallel, malondialdehyde content, which represented the degree of cellular oxidative damage, monotonically increased from 1.92 × 10−7 to 7.07 × 10−7 nmol cell−1. Superoxide dismutase activity that represented cellular antioxidant capacity first increased from 2.59 × 10−4 to the peak of 6.60 × 10−4 U cell−1, then gradually decreased to 2.39 × 10−4 U cell−1. The maximum tilmicosin removal efficiency of 99.8% by Chlorella PY-ZU1 was obtained at the initial tilmicosin concentration of 50 mg L−1.

•Mixed biomass of C. pyrenoidosa and cassava starch was used for H2 fermentation.•Mixed biomass at C/N molar ratio of 25.3 gave the highest dark H2 yield.•Mixed biomass at C/N molar ratio of 15.6 gave the highest dark H2 production rate.•H2 yield was improved to 664.2 mL/g TVS via combined dark and photo fermentation.•Energy production efficiency was enhanced to 67.2% via cogeneration of H2 and CH4.To enhance energy production efficiency (EPE) from microalgae Chlorella pyrenoidosa (CP), cassava starch (CS) was mixed with CP to optimise the carbon/nitrogen (C/N) ratio and facilitate efficient dark hydrogen fermentation, followed by photo hydrogen fermentation and methanogenesis. Steam heating with dilute acid was a preferred pre-treatment method to hydrolyze mixed biomass. The maximum dark hydrogen yield of 276.2 mL/g total volatile solids (TVS) from the mixed biomass at C/N molar ratio of 25.3 showed 3.7-fold and 1.8-fold increases, respectively, compared with those from only CP and only CS. The maximum dark hydrogen production rate of 31.96 mL/g TVS/h from the mixed biomass at the C/N molar ratio of 15.6 showed 3.4-fold and 3.7-fold increases, respectively, compared with those from only CP and only CS. The dark and photo hydrogen yield of 664.2 mL/g TVS and the methane yield of 126.0 mL/g TVS corresponded to a total EPE of 67.2%.

Cu foam combined with Pt-modified reduced graphene oxide (Pt–RGO) was investigated as an efficient cathode for CO2 reduction in a photoelectrocatalytic (PEC) cell with a TiO2 nanotube (TNT) photoanode. The synergistic catalytic mechanisms between photocatalysis and electrocatalysis in such a photoanode driven 2-electrode PEC cell were experimentally verified and theoretically analyzed. The dual functional Cu foam, as a cathode electrode and a Pt-RGO catalyst matrix, markedly increased the carbon atom conversion rate because of its well-defined porosity, large specific surface area, and in particular its affinity for CO2 reduction to hydrocarbons. Combination of the Cu foam matrix and Pt–RGO catalysts resulted in synergistic CO2 reduction in the (Pt–RGO/Cu foam)‖TNT PEC cell. The carbon atom conversion rate markedly increased to 4340 nmol (h−1 cm−2) by optimizing CO2 reduction conditions in the PEC cell, including voltage applied through the cell, Pt loading amount on RGO, and Pt–RGO loading amount on Cu foam.