Sewage sludge disposal is troublesome because of the presence of microbes, toxins, and heavy metals in it. Co-gasification of sewage sludge with wood is a promising pathway to dispose of sewage sludge and generate usable syngas, simultaneously. By using a sorbent for in situ sorption of CO2, H2 fraction in the generated syngas can be enhanced considerably. An equilibrium model was developed taking wood and sewage sludge as the model compounds and CaO as the sorbent. This evaluation was performed by employing ASPEN PLUS (V 8.8) software. Principle of Gibbs free-energy minimization was adopted to predict the outlet gas composition and gas yield. The impact of reactor temperature (600 to 900 °C) and sludge content (0 to 100 wt % at 700 °C) in the feedstock on syngas yield and constituents were assessed. With 30 wt % sludge, maximum gas yield was observed as 0.526 kg h–1 at 900 °C while minimum CO2 fraction was achieved at 700 °C. At 700 °C, the highest gas yield of 0.251 kg h–1 was recorded at 50 wt % sludge, whereas minimum CO2 concentration was observed at 30 wt % sludge. The model predictions were in good agreement with the experimental findings. The study reflects that CO2-sorption enhanced gasification of sewage sludge with other biomass such as wood is an attractive option to dispose of sewage sludge in an environmental friendly manner and to generate hydrogen-rich fuel gas.

•The PEP process couples ozonation, UV, and cathodic H2O2 generation to produce OH.•Significant synergy for 1,4-dioxane degradation can be obtained in the PEP process.•The PEP process mineralizes 1,4-dioxane much faster than UV/O3 and EP process.•The PEP process works more efficiently with Na2SO4 electrolytes than with NaCl.•The PEP process is more effective at pollutant mineralization with increasing pH.This study investigated the degradation of 1,4-dioxane by the photoelectro-peroxone (PEP) process, which combines conventional ozonation, UV photolysis, and electrochemical hydrogen peroxide (H2O2) generation to effectively produce hydroxyl radicals (OH) for advanced oxidation wastewater treatment. Results show that the combination of ozonation, ultraviolet (UV), and electro-generation of H2O2 could lead to significant synergistic effects that enhanced the pseudo-first order rate constant for 1,4-dioxane degradation to 33 times that of the simple linear addition of the three single processes. In addition, the PEP process could mineralize total organic carbon (TOC) from 1,4-dioxane solutions much faster than the three single processes, as well as their binary combinations (UV/O3 and the electro-peroxone (EP) process). After 45 min of treatment, the UV/O3, EP, and PEP processes removed ∼70%, 37%, and 98% TOC with a specific energy consumption (SEC) of ∼0.38, 0.22, and 0.30 kW h/g TOCremoved, respectively. Increasing ozone (O3) dose, applied current, and solution pH increased generally the rate of TOC removal during the PEP process. When sodium chloride (NaCl) was used as the supporting electrolyte, chlorine (Cl2) and hypochlorous acid/hypochlorite (HClO/ClO−, formed from anodic oxidation of Cl−) would react with H2O2, thus diminishing its synergistic effects with O3 and UV for pollutant degradation. Consequently, TOC removal was much less efficient when the PEP process was conducted in NaCl electrolytes than in sodium sulfate (Na2SO4) electrolytes, especially when using anodes (ruthenium and iridium oxide coated titanium, RuO2-IrO2/Ti) with higher chlorine evolution activity. These results indicate that careful optimizations of the operational parameters are critical to maximize the synergistic effects of the PEP process for pollutant degradation.

•RhB-saturated PAC can be effectively regenerated by electro-peroxone (EP) process.•Desorbed organics can be simultaneously mineralized during the EP regeneration.•PAC retained 76% of its virgin adsorption capacity after five regeneration cycles.•The EP regeneration extends the lifetime of PAC for adsorption applications.Due to the lack of feasible regeneration methods, spent powdered activated carbon (PAC) is conventionally disposed of by incineration or landfill after its adsorption capacity is exhausted in adsorption applications. In this study, an electro-peroxone (EP) process (a combined process of conventional ozonation and in situ cathodic hydrogen peroxide (H2O2) production) was proposed to regenerate PAC saturated with Rhodamine B (RhB) dye. Results show that the adsorption of RhB onto PAC involved primarily irreversible chemisorption. Therefore, the RhB-saturated PAC could not be regenerated upon dilution by water washing. In contrast, by oxidatively converting irreversibly sorbed RhB to more desorbable oxidation by-products (e.g., carboxylic acids), both ozonation and the EP regenerations could restore >90% of the adsorption capacity of the PAC for RhB reloading. However, ozonation regeneration could not effectively mineralize the desorbed pollutants due to the selective oxidation characteristics of ozone (O3). In contrast, due to the substantial generation of hydroxyl radicals (OH) from the reaction of bubbled O3 with electro-produced H2O2, the EP regeneration was capable of completely mineralizing the desorbed pollutants. During the EP regeneration, PAC was oxidized to some extents, thus gradually losing its adsorption capacity. By optimizing the applied current, ozone dose, and regeneration time, ∼76% of the adsorption capacity of the virgin PAC could still be retained after five cycles of RhB adsorption and the EP regeneration. The results of this study indicate that the EP process may provide an environmentally-friendly and sustainable way to regenerate spent PAC for reuse.

•Upgrade of ozonation to E-peroxone greatly accelerates MIB and geosmin abatement.•E-peroxone enhances the extent of MIB and geosmin abatement moderately.•Bromate formation is significantly reduced during the E-peroxone process.•E-peroxone provides an attractive backup of ozonation during algal blooms.In this study methylisoborneol (MIB) and geosmin abatement in a surface water by conventional ozonation and the electro-peroxone (E-peroxone) process was compared. Batch tests with addition of ozone (O3) stock solutions and semi-batch tests with continuous O2/O3 gas sparging (simulating real ozone contactors) were conducted to investigate O3 decomposition, •OH production, MIB and geosmin abatement, and bromate formation during the two processes. Results show that with specific ozone doses typically used in routine drinking water treatment (0.5–1.0 mg O3/mg dissolved organic carbon (DOC)), conventional ozonation could not adequately abate MIB and geosmin in a surface water. While increasing the specific ozone doses (1.0–2.5 mg O3/mg DOC) could enhance MIB and geosmin abatement by conventional ozonation, this approach resulted in significant bromate formation. By installing a carbon-based cathode to electrochemically produce H2O2 from cathodic oxygen reduction, conventional ozonation can be conveniently upgraded to an E-peroxone process. The electro-generated H2O2 considerably enhanced the kinetics and to a lesser extent the yields of hydroxyl radical (•OH) from O3 decomposition. Consequently, during the E-peroxone process, abatement of MIB and geosmin occurred at much higher rates than during conventional ozonation. In addition, for a given specific ozone dose, the MIB and geosmin abatement efficiencies increased moderately in the E-peroxone (by ∼8–9% and ∼10–25% in the batch and semi-batch tests, respectively) with significantly lower bromate formation compared to conventional ozonation. These results suggest that the E-peroxone process may serve as an attractive backup of conventional ozonation processes during accidental spills or seasonal events such as algal blooms when high ozone doses are required to enhance MIB and geosmin abatement.

This study investigated the regeneration of phenol-saturated activated carbon fiber (ACF) by an electro-peroxone (E-peroxone) process. Results show that approximately ∼30% of the sorbed phenol was irreversibly adsorbed on ACF, and could not be effectively desorbed by conventional cathodic regeneration. Therefore, the cathodic regeneration restored only about 68% of the adsorption capacity of ACF for phenol reloading. In comparison, by combining the cathodic regeneration with ozonation, the E-peroxone regeneration process could oxidatively convert irreversibly sorbed phenol to more desorbable transformation products, and thus enhanced the regeneration efficiency up to ∼90%. Due to the irreversible adsorption of phenol and oxidation of ACF by oxidants such as O3 and OH, the adsorption capacity of ACF declined during multiple cycles of phenol adsorption and E-peroxone regeneration, especially when high ozone dose was used in the regeneration. By optimizing the ozone dose, the modifications of ACF properties due to O3 and OH oxidation could be minimized. Consequently, after twelve cycles of the E-peroxone regeneration, the ACF retained still ∼72% of the adsorption capacity of the virgin control. These results suggest that the E-peroxone process may provide a more effective alternative to conventional cathodic regeneration for the regeneration of ACs saturated with irreversibly sorbed organics.

This study investigated the regeneration of p-nitrophenol (PNP) saturated activated carbon fiber (ACF) by a novel electro-peroxone (E-peroxone) approach, which aimed to simultaneously regenerate exhausted ACF and mineralize desorbed pollutants by coupling conventional cathodic regeneration with ozonation. PNP-saturated ACF was attached to a carbon-polytetrafluorethylene cathode, which was then applied a current to drive cathodic desorption of pre-loaded PNP and electrochemical generation of H2O2 from O2 in the sparged ozone generator effluent (O2 and O3 gas mixture). The electro-generated H2O2 then reacts with sparged O3 to yield OH, which can rapidly mineralize the desorbed pollutants (PNP and its derivatives). After 3 h regeneration, the E-peroxone process restored ∼95% of the ACF adsorption capacity, and effectively mineralized the desorbed pollutants. In addition, the E-peroxone regeneration did not considerably modify the structural and chemical properties of ACF. Consequently, the ACF exhibited no evident decline in the adsorption capacity after twelve cycles of PNP adsorption and E-peroxone regeneration. These results indicate that the E-peroxone regeneration can successfully achieve the goal of simultaneous regeneration of saturated ACFs and mineralization of desorbed pollutants, and may thus provide an attractive and viable alternative for the regeneration of organic-saturated ACs.

A series of phosphorus (P) and phosphorus/nickel (P/Ni) modified ZSM-5 zeolites were prepared by impregnation of a conventional ZSM-5 zeolite with P and subsequent Ni. The conventional, P-, and P/Ni-modified ZSM-5 zeolites were then tested as the catalysts for petrochemical production from co-feed catalytic fast pyrolysis (CFP) of pine wood and low-density polyethylene (LDPE) mixtures. Results showed that the yield of valuable petrochemicals (olefins and aromatic hydrocarbons) from co-feed CFP increased from 42.9 C% for conventional ZSM-5 to 52.8–54.1 C% for P- and P/Ni-modified ZSM-5, while the yields of low-value alkanes and undesired char/coke decreased from 17.3 C% and 22.6 C% to 9.6–10.2 C% and 18.9–15.7 C%, respectively. ZSM-5 impregnation with P and P/Ni thus significantly improved the product distribution in co-feed CFP of biomass and LDPE. In addition, modification with P and P/Ni improved considerably the hydrothermal stability of zeolites to resist steam-induced catalyst deactivation that may occur in co-feed CFP. When the conventional ZSM-5 zeolite was pretreated with 100% steam at 550 °C for 3–9 h, it produced 26.7–32.1% lower aromatic yields than untreated ZSM-5 in co-feed CFP. In contrast, steam pretreatment did not considerably affect the activity of P- and P/Ni-ZSM-5 zeolites for aromatic production. They maintained comparable aromatic yields in co-feed CFP when they had been steam pretreated for up to 9 h. These results indicate that ZSM-5 modification with P and P/Ni may provide a viable way to improve the catalyst's activity and life time for petrochemical production from co-feed CFP of biomass and plastics.

The relationship between the chemical contaminants and soil microbial toxicity of waste foundry sand (WFS) was investigated. Five different types of WFS from typical ferrous, aluminum, and steel foundries in China were examined for total metals, leachable metals, and organic contaminants. The soil microbial toxicity of each WFS was evaluated by measuring the dehydrogenase activity (DHA) of a blended soil and WFS mixture and then comparing it to that of unblended soil. The results show that the five WFSs had very different compositions of metal and organic contaminants and thus exhibited very different levels of soil microbial inhibition when blended with soil. For a given WFS blended with soil in the range of 10 wt.%–50 wt.% WFS, the DHA decreased almost linearly with increased blending ratio. Furthermore, for a given blending ratio, the WFSs with higher concentrations of metal and organic contaminants exhibited greater microbial toxicity. Correlation analysis shows that the relationship between ecotoxicity and metal and organic contaminants of WFSs can be described by an empirical logarithmic linear model. This model may be used to control WFS blending ratios in soil-related applications based on chemical analysis results to prevent significant inhibition of soil microbial activity.

•Landfill leachate concentrate is effectively treated by a novel E-peroxone process.•E-peroxone process combines ozonation with electrolysis to drive peroxone reaction.•H2O2 is electro-generated in situ from O2 in sparged gas from an ozone generator.•Hydroxyl radicals are produced from sparged O3 and electro-generated H2O2.•Refractory organic pollutants can be effectively mineralized in E-peroxone process.A novel electrochemically driven process (E-peroxone) was employed to treat landfill leachate concentrates that were generated from reverse osmosis of biologically pretreated leachate. In the E-peroxone system, O3 was produced from O2 using an ozone generator. The O2 and O3 gas mixture from the ozone generator was then sparged into a reactor that had a carbon–polytetrafluorethylene (carbon–PTFE) cathode, which can convert O2 to H2O2 effectively. The in situ generated H2O2 then reacted with the sparged O3 to produce a very powerful oxidant OH, thus achieving synergy of O3 and H2O2 (i.e., peroxone) on organic pollutant degradation. Up to 87% of the total organic carbon (TOC) was removed from the leachate concentrates after 4 h of the E-peroxone process. In comparison, ozonation, conventional peroxone (using externally added H2O2), and electro-Fenton treatment removed only 45%, 65%, and 71% TOC, respectively, under similar reaction conditions in 4 h. The results indicate that the E-peroxone process may provide a convenient and effective alternative to conventional advanced oxidation processes for degrading refractory organic pollutants in wastewater.

A new electrochemically driven process (E-peroxone) was developed to treat methylene blue (MB) wastewater. During the E-peroxone process, ozone generator effluent (O2 and O3 gas mixture) is continuously sparged into a reactor that has a carbon-polytetrafluorethylene (carbon-PTFE) cathode, which can electrochemically convert the sparged O2 to H2O2 effectively. The in situ generated H2O2 then reacts with the sparged O3 to produce hydroxyl radicals (OH), which are a much stronger oxidant than O3. Thus, by utilizing the sparged O2 that has little value in ozonation processes to produce H2O2 in situ, the E-peroxone process can achieve the synergy of O3 and H2O2 (peroxone) on pollutant degradation. The E-peroxone process therefore mineralized MB much more effectively than ozonation. The total organic carbon removal was 93 and 22% after 2 h of the E-peroxone and ozonation treatment, respectively. The E-peroxone process may thus offer a simple and effective method to degrade ozone-refractory organic pollutants in wastewater.Highlights► A new electrochemically driven process (electro-peroxone) was developed. ► H2O2 is electro-generated in situ from O2 in sparged O2 and O3 gas mixture. ► The E-peroxone process can achieve synergy of H2O2 and O3 for organic degradation. ► The E-peroxone process is an effective method for degrading refractory organics.

Catalytic fast pyrolysis (CFP) of Kraft lignins with HZSM-5 zeolite for producing aromatics was investigated using analytical pyrolysis methods. Two Kraft lignins were fast pyrolyzed in the absence and presence of HZSM-5 in a Curie-point pyrolyzer. Without the catalyst, fast pyrolysis of lignin predominantly produced phenols and guaiacols that were derived from the subunits of lignin. However, the presence of HZSM-5 changed the product distribution dramatically. As the SiO2/Al2O3 ratio of HZSM-5 decreased from 200 to 25 and the catalyst-to-lignin ratio increased from 1 to 20, the lignin-derived oxygenates progressively decreased to trace and the aromatics increased substantially. The aromatic yield increased considerably as the pyrolysis temperature increased from 500°C to 650°C, but then decreased with yet further increase of pyrolysis temperature. Under optimal reaction conditions, the aromatic yields were 2.0 wt.% and 5.2 wt.% for the two lignins that had effective hydrogen indexes of 0.08 and 0.35.

Analytical pyrolysis was conducted to evaluate the major hazardous air pollutant (HAP) emissions from pyrolysis of bituminous coal and a furan binder, which are the two most commonly used casting materials for making green sand and furan no-bake molds in Chinese foundries. These two materials were flash pyrolyzed in a Curie-point pyrolyzer at 920 °C and slowly pyrolyzed in a thermogravimetric analyzer (TGA) from ambient temperature to 1000 °C with a heating rate of 30 °C/min. The emissions from Curie-point and TGA pyrolysis were analyzed with gas chromatography–mass spectrometer/flame ionization detector. Thirteen HAP species were identified and quantified in the pyrolysis emissions of the two materials. The prominent HAP emissions were cresols, benzene, toluene, phenol, and naphthalene for the bituminous coal, whereas they were m,p,o-xylenes for the furan binder. Xylenesulfonic acid, the acidic catalyst in furan binder, was found to be the major source of xylene emissions. Thermogravimetry-mass spectrometer monitored the evolution of HAP emissions during TGA pyrolysis. For both of the casting materials, most of the emissions were released in the temperature range of 350–700 °C.

Demonstration-scale metal pouring emission tests and bench-scale Curie-point pyrolysis emission tests were conducted to identify and quantify the hazardous air pollutant (HAP) emissions of five kinds of casting materials, namely, bituminous coal, cellulose, conventional phenolic urethane binder (PUB), naphthalene-depleted PUB, and a collagen-based binder. For a given casting material, the major HAP species generated in Curie-point pyrolysis were essentially the same as those generated in demonstration-scale metal pouring. The 8–10 HAP species identified in the Curie-point pyrolysis tests comprised 65–98% (by weight) of the total HAP emissions quantified in the demonstration-scale pouring emission tests. Furthermore, with these two protocols, we appraised the relative emission changes that would be associated with (a) replacing conventional PUB with collagen-based binder, (b) replacing conventional PUB with naphthalene-depleted PUB, and (c) replacing bituminous coal with cellulose for making sand molds or cores in the casting process. The relative emission changes associated with the use of alternative casting materials exhibited similar trends for most of the major HAP species in the demonstration-scale pouring and Curie-point pyrolysis emission tests. The results indicated that Curie-point pyrolysis emission test could be employed as a convenient and cost-effective screening tool to identify the major HAP species and to compare the relative HAP emission levels for various casting materials.

•ZSM-5 impregnation with boron decreases slightly the zeolite effective pore size.•Boron-modified ZSM-5 inhibits polyaromatic formation in catalytic fast pyrolysis.•Boron-modified ZSM-5 enhances p-xylene production over m- and o-xylenes.•Co-feeding of cellulose with LDPE improves the product distribution in catalytic fast pyrolysis.This study investigated the effects of ZSM-5 impregnation with boron on its catalytic properties in catalytic fast pyrolysis (CFP) of cellulose, low-density polyethylene (LDPE), and their mixtures. A series of boron-modified ZSM-5 zeolites were prepared by impregnating a conventional ZSM-5 with different boron loadings (0.5–3 wt.%). Due to boron deposition, the acidity and pore size of ZSM-5 decreased with increasing the boron loading. When impregnated with 1 wt.% boron, ZSM-5 preserved sufficient catalytic activity for the production of valuable monoaromatic hydrocarbons and decreased the formation of undesired polyaromatic hydrocarbons in CFP of cellulose. In addition, the pore narrowing of ZSM-5 by boron deposition greatly enhanced p-xylene production over m- and o-xylenes in CFP. This result indicates that slightly decreasing the pore size of ZSM-5 can improve aromatic distribution toward more valuable products in CFP. Co-feeding of cellulose with LDPE in CFP further improved the product distribution. As a result of boron modification and co-feeding, the monoaromatic yield increased from 20.0 C% for CFP of cellulose alone with the parent ZSM-5 to 24.6 C% for co-feed CFP of cellulose and LDPE mixture (mixing ratio of 4:1) with the boron-modified ZSM-5, while the polyaromatic yield decreased from 11.3 C% to 6.0 C%. The yield for p-xylene also increased from 2.23 C% to 5.57 C% while the selectivity increased from 47.9% to 75.2%. The results indicate that ZSM-5 modification with boron and co-feeding of plastics have a beneficial effect for improving aromatic product distribution in CFP of biomass.Download high-res image (221KB)Download full-size image

•Competition between cathodic O2 and O3 reduction dictates the E-peroxone mechanisms.•O3 is preferentially reduced at more positive potentials than O2 at carbon cathodes.•Cathodic O2 reduction is inhibited when cathodic O3 reduction is current limited.•Cathodic O2 reduction occurs to enable E-peroxone when cathodic O3 reduction is mass-transfer limited.Previous studies indicate that effective generation of hydrogen peroxide (H2O2) from cathodic oxygen (O2) reduction is critical for the improved water treatment performance (e.g., enhanced pollutant degradation and reduced bromate formation) during the electro-peroxone (E-peroxone) process (a combined process of electrolysis and ozonation). However, undesired reactions (e.g., O3, H2O2, and H2O reductions) may occur in competition with O2 reduction at the cathode. To get a better understanding of how these side reactions would affect the process, this study investigated the cathodic reaction mechanisms during electrolysis with O2/O3 gas mixture sparging using various electrochemical techniques (e.g., linear sweep voltammetry and stepped-current chronopotentiometry). Results show that when a carbon brush cathode was used during electrolysis with O2/O3 sparging, H2O and H2O2 reductions were usually negligible cathodic reactions. However, O3 can be preferentially reduced at much more positive potentials (ca. 0.9 V vs. SCE) than O2 (ca. −0.1 V vs. SCE) at the carbon cathode. Therefore, cathodic O2 reduction was inhibited when the process was operated under current limited conditions for cathodic O3 reduction. The inhibition of O2 reduction prevented the desired E-peroxone process (cathodic O2 reduction to H2O2 and ensuing reaction of H2O2 with O3 to OH) from occurring. In contrast, when cathodic O3 reduction was limited by O3 mass transfer to the cathode, cathodic O2 reduction to H2O2 could occur, thus enabling the E-peroxone process to enhance pollutant degradation and mineralization. Many process and water parameters (applied current, ozone dose, and reactivity of water constituents with O3) can cause fundamental changes in the cathodic reaction mechanisms, thus profoundly influencing water treatment performance during the E-peroxone process. To exploit the benefits of H2O2 in water treatment, reaction conditions should be carefully controlled to promote cathodic O2 reduction during the E-peroxone process.Download high-res image (189KB)Download full-size image