With the aim of upgrading current food waste (FW) management strategy, a novel FW hydrothermal pretreatment and air-drying incineration system is proposed and optimized from an energy and exergy perspective. Parameters considered include the extracted steam quality, the final moisture content of dehydrated FW, and the reactor thermal efficiency. Results show that optimal working condition can be obtained when the temperature and pressure of extracted steam are 159 °C and 0.17 MPa, the final moisture content of dehydrated FW is 10%, and the reactor thermal efficiency is 90%. Under such circumstance, the optimal steam energy and exergy increments reach 194.92 and 324.50 kJ/kg-FW, respectively. The novel system is then applied under the local conditions of Hangzhou, China. Results show that approximately 2.7 or 11.6% (from energy or exergy analysis perspective) of electricity can be additionally generated from 1 ton of MSW if the proposed novel FW system is implemented. Besides, comparisons between energy and exergy analysis are also discussed.

The products of asphalt upgrading in supercritical water (SCW) forms a mixture of cracked oil, water, and fine coke particles; this mixture tends to be emulsified, which introduces direct challenges to emulsified water removal. In this study, the asphalt upgrading in SCW was performed at 390–450 °C and 22.4–27.2 MPa for 40 min. A differential scanning calorimetry analysis between −60 and 50 °C was conducted to evaluate the water content and size distribution in the water-in-oil emulsions. The mechanical centrifugation and chemical demulsification were performed to test the water removal efficiency and stability of the emulsions. The results of properties and emulsification characteristics of the oil products indicate that the transition temperature of asphalt upgrading was between 400 and 410 °C. At temperatures lower than the transition temperature, the oil products were similar to the feed asphalt in terms of high viscosity, carbon residue, and asphaltene content. In the emulsification process, the contact between water and oil products was limited by the semisolid state of the oil products, which decreased the water content and size of the droplets in the emulsions. At temperatures higher than the transition temperature, the viscosities of the oil products were below 1.2 Pa·s, and a large number of water droplets were observed clearly in the fluid emulsions. The emulsified water was partially removed by centrifugation; however, the content of fine water droplets with diameters less than 5 μm was still greater than 14% in the centrifuged emulsions. Furthermore, the addition of chemical demulsifier was more effective on demulsification than centrifugation. When the temperature was higher than 430 °C, the water content of the demulsified emulsion was less than 2.5%. On the basis of comprehensive consideration of maltene yield, oil property, and water removal of water-in-oil emulsions, the temperature of 430–440 °C is the most beneficial condition for asphalt upgrading.

The waste management of e-wastes is a significant challenge, especially for the disposal of waste printed circuit boards (WPCBs). An effective, economic and environmental-kind recycling technology is in great demand. Molten salt oxidation (MSO) is a robust thermal process, has the inherent capability of destroying organic constituents of wastes while retaining the inorganic constituents in the molten salt. In the present study MSO is employed for the disposal of waste printed circuit boards aimed at describing the treating method of WPCBs using MSO, and evaluating the efficiency of this alternative. Molten salt oxidation experiments of WPCBs have been conducted in a lab-scale molten salt reactor using a ternary carbonate salt (Li, Na, K)2CO3. The operation parameters investigated are the temperature of molten salts, the excess air factor and the residence time of the reactants in the salt bath. Results show that the retention efficiency of bromine is higher than 99.9%, irrespective of the operating conditions. The emissions of CO and SO2 decrease with temperature increasing, while the emission of NOx first decreases and later increases. And when the residence time is lengthened, the emissions of CO, NOx and SO2 decrease. Compared to the temperature and the residence time’s role, the effect of excess air factor on the emissions of CO, NOx and SO2 is relatively small. Over 95% of the copper in WPCBs are recycled. The fibreglass that is the main component of the ash content is dissolved by the molten carbonates and retains in the salt bath. The results of the present study show molten salt oxidation is an environmentally friendly and effective alternative technology for the disposal of WPCBs.

Pyrolysis/gasification-based waste-to-energy (WtE) techniques, comprising partial oxidation of waste and subsequent syngas combustion, show potential benefits over direct incineration. To facilitate their development under the specific conditions of China, pyrolysis and gasification of typical municipal solid waste (MSW) are investigated in a fluidized bed reactor. The effect of the equivalence ratio (ER), reaction temperature, and moisture content on MSW conversion is studied. A rising ER increases the syngas yield but decreases the syngas heating value. The combustible gas yield is strengthened at lower ERs and later drops when the ER exceeds 0.4 as a result of the continuously enhanced oxidation reactions. A higher temperature favors pyrolysis reactions but causes an evident decrease in the syngas heating value during gasification. When the ER is at 0.4 and the temperature is at 650 °C, an optimum operating performance is obtained under the specific input simulated MSW (S-MSW) and test conditions, with an energy conversion efficiency of 68.5%. Under such a circumstance, the further increase of the MSW moisture content is effective for stimulating H2 production; nevertheless, the quality of syngas degrades, and the energy conversion efficiency declines. The appropriate MSW moisture content is found to be lower than 20–25%. Besides, emiessions, such as heavy metals and dioxins, are also compared to conventional incineration to verify the environmental feasibility of gasification.

With the aim of optimizing gasification systems, air gasification using simulated municipal solid waste is experimentally investigated in a fluidized-bed reactor. Process parameters considered include equivalence ratio (ER) and temperature. On the basis of the experimental results, energy and exergy analyses are performed to assess the thermodynamic quality. Results reveal that the energy and exergy contents of the produced gas increase first with rising temperature and then decline when the temperature exceeds 650 °C. With regard to the ER, a similar tendency is observed with a peak value at an ER of 0.4. The energy content of the produced gas is much higher than its exergy content as a result of the remarkable difference between physical energy and exergy contents of sensible heat. The maximum chemical energy efficiency, total energy efficiency, chemical exergy efficiency, and total exergy efficiency of the products at the gasifier exit are attained at an ER of 0.4 and a temperature of 650 °C, with values of 49.73, 64.05, 47.14, and 51.33%, respectively. The total exergy efficiency is suggested as an effective parameter to evaluate the properties of gasification-based thermal systems, because it expresses the availability of the products from the “first-step” gasifier for subsequent conversion.

Heavy metal emission is a great environmental concern for the development of municipal solid waste (MSW) thermal treatment techniques. In this study, both experimental investigations and theoretical simulations are carried out to identify the partitioning of heavy metals between the gaseous phase and solid fractions during pyrolysis, gasification, and incineration of simulated MSW. Two types of incinerators are used. A tubular furnace is applied to evaluate the evaporation of metals from residues, whereas the metal distribution among bottom ash, cyclone fly ash, and filter fly ash is further examined in a fluidized bed. Six target metals (Cd, Pb, Zn, Cu, Cr, and Ni) are studied. Results show that a reductive atmosphere favors the evaporation of Cd and Zn but refrains Cu, Ni, and Cr volatilization, because metals are mainly reduced to their elemental form or sulfide, according to thermodynamic equilibrium calculation. Oxides are the dominant species under oxidizing condition due to the abundance of alkalis. Pb behaved differently, most probably by forming stable metal-matrix compounds such as Pb3Ca2Si3O11 and PbZnSiO4. The cyclone ash is then separated into different sizes. The metal concentrations recorded reveal that most of the vaporized metals are transferred to the cyclone at its working temperature of 350–600 °C by an evaporation and condensation process; however, entrainment is also a determining factor for the transfer of less-volatile metals. Overall, parameters determining the transfer of heavy metals during MSW thermal treatment can be summarized as (i) metal speciation affected by redox atmosphere, temperature, and the presence of alkalis, chloride, sulfur, and other mineral substances; (ii) system characteristics, such as furnace type and cyclone temperature; and (iii) mechanical entrainment of particles caused by gas velocity.

Municipal solid waste (MSW) source-separated collection was started in Hangzhou since 2010. Life cycle assessment (LCA) is conducted to evaluate its effect on the environment. Four MSW management (MSWM) systems are compared, and the functional unit is defined as the annual MSW generation in the city. Scenario 1 is the mixed collection system, where 50.77 % of the MSW is landfilled and 49.23 % incinerated. Scenario 2 represents the current system under source-separated collection. In addition, two future MSWM plans in the city are also modeled. A new incineration plant is planned to be built as the short-term plan (scenario 3); while food waste biological treatment techniques will be introduced according to the city’s long-term plan (scenario 4). Results show that a total 30, 18, 28 and 29 % of global warming, acidification, nutrient enrichment and photochemical ozone formation has been saved after source separation, respectively. Meanwhile, both the short- and long-term MSWM plans provide positive effect to environmental improvements. Sensitivity analysis further reveals that food waste biological technique is essential with the continuous rise of source separation efficiency; and MSW destined for landfill should be controlled efficiently.

Four commonly used sewage sludge treatment techniques in China are compared, each with and without the combination of anaerobic digestion: composting, co-combustion in power plant, thermal drying-incineration, and cement manufacturing. Life cycle assessment (LCA) is used to quantify the environmental burden, while exergetic life cycle assessment (ELCA) is supplemented to measure the resources conversion efficiency. Afterward, abatement exergy is adopted to determine their degree of environmental sustainability, so that all environmental issues associated with resource use and environmental emissions can be solved simultaneously. Results show that anaerobic digestion is an effective pretreatment approach to reduce environmental burden. Thermal drying-incineration is preferable to co-combustion and cement production, since fossil fuel combustion is the dominant cause of emissions. Composting poses a positive effect to mitigate global warming, but it introduces high heavy metals to the soil. Results from ELCA reveal that thermal techniques present higher resources conversion efficiency than a biological system. Adopting anaerobic digestion obviously improves the performance of composting, but it has reduced the total energy recovered in thermal techniques. For process improvements, an efficient sludge predrying is important; and the use of a combined heat and power system can also provide more effective recovery of energy.

Rapid, accurate measurement of the oil and water contents of oil sludge is vital to determine technological solutions for the treatment of that oil sludge. Low-field 1H NMR as a rapid noninvasive method was used in this study. Carr–Purcell–Meiboom–Gill (CPMG) experiments were conducted to construct the transverse relaxation time (T2) distribution curves. The instrument’s ability to quantify oil sludge’s water and oil contents was verified. MnCl2·4H2O was added to the oil sludge to separate the oil and water signals. For calibration curve construction, excellent results were achieved, with correlation coefficients of 0.9996 and 0.987 for regressions between the mass and the relative peak area in the T2 distribution curve for oil and water separately. Good correlation of R2 = 0.998 was achieved between low-field NMR and azeotropic distillation for both water and oil along with standard deviations of 2.67% and 2.61% for the calibration curve method, or standard deviations of 2.81% and 1.88% for water and oil, with more or less similar correlation coefficients, after correction for the amplitude indices of both the water and the oil.

In the process of oil sludge treatment, water and oil contents are of particular interest. In this study, the performance of a rapid, accurate analysis of water and oil in oil sludge through low-field 1H NMR relaxometry, followed by using partial least-squares (PLS) regression models, is reported. In total, 13 oil sludge samples collected from the Hangzhou petroleum refinery are analyzed. Calibration models are developed by PLS regression with full cross-validation on the data obtained using azeotropic distillation by the Dean–Stark method as a reference. The results indicate that calibration is satisfactory (Rcal2 > 0.99) for both water and oil, when using the raw magnetization decay data for PLS regression; the root mean squared errors of cross-validation (RMSECV) are 0.78% and 0.82% for water and oil, respectively. This shows that low-field 1H NMR relaxometry is a rapid, reliable, nondestructive, and solvent free alternative for determining the water and oil contents of oil sludge.

Reverse flow reactors are regarded as an appropriate tool for removing gaseous pollutants from industrial effluents. This paper presents the results of an experimental study on a particular reverse flow reactor with periodic variations in inlet concentration; these experimental results are compared with those obtained by numerical simulation studies. Catalytic oxidation of methane is chosen as model reaction. When the inlet concentration is low (i.e., close to extinction limits) and periodically varied, the interaction between the feeding cycle period and the flow-reversal cycle period may lead to reactor instability; adjusting the period of flow reversal is one way to maintain thermal stability in such situations. Results of numerical investigations reveal that if the flow-reversal cycle time is an odd multiple of the inlet variation cycle time, a harmonic response will occur, with sharply increased variation of the maximum temperature. Basically, it is the inequality of total methane input during the two half-cycles during flow-reversal operations that cause reactor instability. Adjusting the phase between the two cycle periods may ease the inequality of the inlet concentration values, which procures a second strategy to enhance reactor stability. The temperature maximum is very sensitive to the heat-transfer parameters, when periodic inlet variations are introduced.

An experimental study of methane–benzene binary mixture purification in a bench-scale reverse flow reactor is carried out. Results for catalytic oxidation of the two hydrocarbons with remarkably discrepant chemical properties show that autothermal catalytic combustion of very lean combustible concentration can be achieved with periodic feed reversal. Benzene is well removed, but methane conversion is relatively low and mainly determined by the thermal level of the reactor. If methane is added as auxiliary fuel to maintain autothermal operation when the volatile organic compound (VOC) concentration in the contaminated air is too low, an excess amount is needed. The influences of gas superficial velocity, cycle period, and methane-to-benzene ratio are discussed. A mathematical model is developed and solved using a FORTRAN code, with good correspondence being observed between the two approaches. Results of experimental and numerical study indicate that, during catalytic oxidation of lean VOCs in reverse flow reactor, the mutual inhibition effect between different kinds of hydrocarbon can be neglected.

Oxidation within the system CCl4/CH4/O2/N2 is studied at atmospheric pressure in a tubular flow reactor to investigate the influence of reaction temperature and chlorine content on chlorinated waste combustion and find incineration process optimization methods for pollution control. The reaction temperature varies from 700°C to 1000°C and the CCl4/CH4 (or Cl/H) mole ratio of the inlet mixture varies from 0.21 to 0.84. Products profiles are measured with FT-IR. It is shown that at the same initial CCl4 concentration and reaction temperature adding CH4 favors CCl4 destruction and CO2 formation. But the destruction and removal efficiency (DRE) of CH4 decreases with lower Cl/H and higher concentrations of toxic products of incomplete combustion such as COCl2 and CH3Cl are formed at the same time. The chlorine in the system favors CH4 decomposition, but it also inhibits further oxidation of CO. Higher temperature assists in both CCl4 destruction and CH4 conversion, and the concentration of toxic combustion intermediates is reduced. Increasing the temperature is the most effective way to enhance CCl4 oxidation. The CO2 concentration increases with temperature. A CO concentration peak is observed around 800°C: with a certain Cl/H, the CO concentration first increases with temperature and then declines. The effect of increasing CH4 concentration on CCl4 destruction becomes mild above 900°C. Rather, it enhances the interaction between chlorine and carbonaceous radicals, which leads to higher concentration of toxic products.

In order to eliminate secondary pollution caused by municipal solid waste (MSW) incineration, a MSW gasification and melting process is proposed. The process is expected to reduce the emission of pollutants, especially heavy-metals and dioxins. In this paper, the combustible components of MSW and simulated MSW were gasified in a lab-scale fluidized bed at 400°C–700°C when the excess air ratio (ER) was between 0.2 and 0.8. The experimental results indicated that the MSW could be gasified effectively in a fluidized bed at approximately 600°C–700°C when excess air ratio was 0.2–0.4. The melting characteristics of two typical fly ash samples from MSW incinerators were investigated. The results indicated that fly ash of pure MSW incineration could be melted at approximately 1,300°C and that of MSW and coal co-combustion could be melted at approximately 1,400°C. When temperature was over 1,100°C, more than 99.9% of the dioxins could be decomposed and most of the heavy-metals could be solidified in the slag. Based on the above experiments, two feasible MSW gasification and melting processes were proposed for low calorific value MSW: (1) sieved MSW gasification and melting system, which was based on an idea of multi-recycle; (2) gasification and melting scheme of MSW adding coal as assistant fuel.

•A model that integrates life cycle energy, environment, and economy is developed.•The most important inconsistencies between LCC and LCA are unified.•The methodology improvement of MCDM is supplemented to be more logical.•A two-step sensitivity analysis is added to overcome subjectivity by decision makers.•MSW landfill and incineration are compared for model application.How to choose an energy-efficient, environmentally friendly and economically affordable municipal solid waste (MSW) management system has been a major challenge to be taken up by decision makers. Although life cycle assessment (LCA) has been widely used for the evaluation of energy consumption and environmental burden, the economic factor is not considered yet in LCA procedures. Thus, in the present study life cycle 2E (energy and environment) assessment is extended to a 3E (energy, environment, and economy) model. To evaluate economic performance, life cycle cost (LCC) is adjusted in accordance with LCA. Afterwards, multi-criteria decision making (MCDM) method is improved to integrate 3E factors. Besides, a two-step weight factor analysis is added, not only to test the robustness of the model, but also to adopt different preferences proposed by different stakeholder groups. This novel 3E model is then applied for the comparison of different MSW treatment technologies: (1) landfill; (2) landfill with biogas conversion to electricity; (3) incineration with energy recovery. Results show that incineration scores 0.944/1 and performs best among all scenarios; landfill with biogas to electricity, with final score 0.722/1, ranks second; and landfill without energy recovery (score: 0/1) is the worst choice. Furthermore, the weight factor analysis also shows a highly credibility of the results: when changing each factor’s weight from 0 to 1, less than 30% of the cases exhibit the variation in ranking order; almost no change in ranking order occurs when considering the different perspectives from government, enterprise and residents.

The pharmaceutical residues from chemical synthesis pharmaceutical industry often contain some alkali salts due to the widely use of alkali salts in the manufacturing process, the waste management of such is a significant challenge. Generally, the residues are disposed by landfill and incineration. However landfill is unsustainable and the incineration's efficiency is effected by furnace slag-bonding during combustion, that affects the widely use of incineration. On the other hand, molten salt oxidation is an efficient, flameless thermal process, has the inherent capability of destroying organic constituents of wastes while retaining the inorganic constituents in the molten salt. Therefore, a new access is proposed by disposing the residues using molten salt oxidation. A high salt content pharmaceutical residue that contains 28.82wt% Na has been selected as the sample. Molten salt oxidation experiments have been conducted in a lab-scale molten salt reactor using a ternary salt (Li,Na,K)2CO3. The experimental parameters investigated here are the temperature of molten salt and the excess air factor. The concentrations of the CO, NOx and SOx in the off-gas are monitored on-line. Results show that the concentration of CO decreases with temperature increasing, especially at temperature higher than 600̊C. The SOx in the off-gas has been detected rarely, irrespective of the operating conditions. When the temperature is below 700̊C, the concentrations of NOx in the off-gas are under 200 ppm, but as the temperature reached 700̊C, due to the nitrite in salt bath begins to decompose, the concentration increases dramatically, suggests the operating temperature should below 700̊C in order to suppress the emission of NOx. Compared to the temperature's role, the effect on the residue's oxidation of the excess air factor is relative small. In the drained salt no char has been found and the XRD analysis shows that the main content of the salt is still (Li,Na,K)2CO3. The results of our study show molten salt oxidation is a promising alternative technology for the disposal of high salt content pharmaceutical residues from the chemical synthesis pharmaceutical industry, and it may be also suitable for other high salt content residues from the fine chemical industry, however, more research is needed to verify this possibility.