Pretreatment is a crucial step for valorization of lignocellulosic biomass into valuable products such as H2, ethanol, acids, and methane. As pretreatment can change several decisive factors concurrently, it is difficult to predict its effectiveness. Furthermore, the effectiveness of pretreatments is usually assessed by enzymatic digestibility or merely according to the yield of the target fermentation products. The present study proposed the concept of “precise pretreatment,” distinguished the major decisive factors of lignocellulosic materials by precise pretreatment, and evaluated the complete profile of all fermentation products and by-products. In brief, hemicellulose and lignin were selectively removed from dewaxed rice straw, and the cellulose was further modified to alter the crystalline allomorphs. The subsequent fermentation performance of the selectively pretreated lignocellulose was assessed using the cellulolytic, ethanologenic, and hydrogenetic Clostridium thermocellum through a holistic characterization of the liquid, solid, and gaseous products and residues.The transformation of crystalline cellulose forms from I to II and from Iα to Iβ improved the production of H2 and ethanol by 65 and 29%, respectively. At the same time, the hydrolysis efficiency was merely improved by 10%, revealing that the crystalline forms not only influenced the accessibility of cellulose but also affected the metabolic preferences and flux of the system. The fermentation efficiency was independent of the specific surface area and degree of polymerization. Furthermore, the pretreatments resulted in 43–45% of the carbon in the liquid hydrolysates unexplainable by forming ethanol and acetate products. A tandem pretreatment with peracetic acid and alkali improved ethanol production by 45.5%, but also increased the production of non-ethanolic low-value by-products by 136%, resulting in a huge burden on wastewater treatment requirements.Cellulose allomorphs significantly affected fermentation metabolic pathway, except for hydrolysis efficiency. Furthermore, with the increasing effectiveness of the pretreatment for ethanol production, more non-ethanolic low-value by-products or contaminants were produced, intensifying environmental burden. Therefore, the effectiveness of the pretreatment should not only be determined on the basis of energy auditing and inhibitors generated, but should also be assessed in terms of the environmental benefits of the whole integrated system from a holistic view.

•Use intact lipid analysis as a routine measure to monitor the active microbes.•Discard the digestate liquid to control the accumulation of potential inhibitors.•Optimize the solid retention time of the dry anaerobic digestion process.•Identify the possible factors affecting the process performance.One-stage dry anaerobic digestion with solid-liquid-separated digestate recirculation was applied to treat synthetic organic solid waste at Digestion Time (DT) of 15, 25, 35 days for several cycles. The highest methane yield of 0.360 ± 0.045 m3/kg-VSadd with lowest accumulation of hydrolytes was achieved under DT of 15 days. The analysis of intact lipid profiles, including phospholipid fatty acid for bacteria and phospholipid ether lipid for archaea, indicated that the inoculum breakdown occurred, mainly during the start of the process. A significant decline of hydrolytic bacteria was observed during the granular breakdown, which was likely related to the lower methane yield in subsequent cycles. In contrast, the amount of methanogens was still stable even after granular breakdown occurred. The accumulated ammonia in the liquid digestate was partially removed by solid-liquid separation before digestate recirculation, which relieved possible inhibition to some extent with minor microorganism loss. Hence the levels of ammonia, which was highly possible to be the inhibitor causing the decline of methane production, were lower in DT15 than in DT25 and DT35. In this case, it could be implied that the microorganism community reconstruction in DT15 may face less challenges comparing to the other two setups.

•A large-scale (5 m × 5 m × 7.5 m) bioreactor experiment was conducted on unprocessed high food waste content (HFWC) MSW.•A large quantity of self-released leachate was collected within two months after waste filling.•A rapid build-up of high leachate level was observed after waste filling.•A linear increase of compression strain with an increase of leachate draining rate was found.A large-scale bioreactor experiment lasting for 2 years was presented in this paper to investigate the biochemical, hydrological and mechanical behaviors of high food waste content (HFWC) MSW. The experimental cell was 5 m in length, 5 m in width and 7.5 m in depth, filled with unprocessed HFWC-MSWs of 91.3 tons. In the experiment, a surcharge loading of 33.4 kPa was applied on waste surface, mature leachate refilling and warm leachate recirculation were performed to improve the degradation process. In this paper, the measurements of leachate quantity, leachate level, leachate biochemistry, gas composition, waste temperature, earth pressure and waste settlement were presented, and the following observations were made: (1) 26.8 m3 leachate collected from the 91.3 tons HFWC-MSW within the first two months, being 96% of the total amount collected in one year. (2) The leachate level was 88% of the waste thickness after waste filling in a close system, and reached to over 100% after a surcharge loading of 33.4 kPa. (3) The self-weight effective stress of waste was observed to be close to zero under the condition of high leachate mound. Leachate drawdown led to a gain of self-weight effective stress. (4) A rapid development of waste settlement took place within the first two months, with compression strains of 0.38–0.47, being over 95% of the strain recorded in one year. The compression strain tended to increase linearly with an increase of leachate draining rate during that two months.

•All pretreatments improved solubilization of the sludge.•Solubilization degree didn’t correspond to anaerobic biodegradability.•Excessive release of biopolymers deteriorated the dewaterability.•FTIR and SERS revealed the key role of tightly-bound EPS.•SERS were effective to probe the minor changes in EPS after pretreatment.The effectiveness and optimization strategy of various pretreatment methods to enhance the anaerobic biodegradability and dewaterability of waste activated sludge are still inconclusive. In order to explore the intrinsic triggers determining the apparent biodegradability and dewaterability, sludges pretreated by freeze-thawing, acid, alkali, sonication, thermal autoclaving, and ultraviolet radiation were fractionized according to the cohesion of extracellular polymeric substances (EPS). The fractionized EPS and cells were characterized for microscopic properties by biochemical and elemental composition, Fourier transform infrared spectroscopy, and surface-enhanced Raman spectroscopy. Multivariate statistical analysis was used to mining the key microscopic factors affecting the apparent biodegradability or dewaterability of sludge. Results show that, solubilization degree significantly determined the dewaterability of the pretreated sludge, but did not affect the biodegradability. The properties of slime and lightly-bound EPS were different from other fractions, and inclined to be altered by various pretreatments. However, only the H content, H/C ratio and some functional groups of tightly-bound EPS have significant correlation with the ultimate methane production yield, while the N/C ratio of lightly-bound EPS was important for the initial methane production rate. Free-thawing improved sludge’s biodegradability and dewaterability through dehydration in micro-zones. Autoclaving and ultraviolet weakened sludge’s biodegradability and dewaterability by accelerating the denaturation of some collagen proteins in tightly-bound EPS, transforming it into a viscous gel-like network with higher water-holding capacity. Sonication acted similarly but at a micro-zone level. Acid and alkali pretreatments improved biodegradability by accelerating the release of cell endocytes including pigments carotene and carotenoids.Download high-res image (133KB)Download full-size image

Rice straw is one of the most abundant agricultural wastes, and has potential as the feedstock for biofuel production. In this study, rice straw was pretreated with 1.5 % (m/m) sulfuric acid at 121 °C for 60 min and then subjected to consolidated bioprocessing (CBP) by Clostridium thermocellum at 55 °C. The composition, morphology, surface area and cellulose crystal structure of rice straw were determined to evaluate effects of the pretreatment on physicochemical characteristics of rice straw, and CBP performance was evaluated by the production of H2 and ethanol. The results showed that 90 % of hemicellulose was removed, the Brunauer–Emmett–Teller surface area was increased by 5.2-fold, amorphous cellulose lost, and lignin amount increased by 53 % after the pretreatment. The maximum H2 productions from unpretreated (Unpre) and pretreated (Pre) rice straw were 33.3 and 35.7 mmol L−1, respectively, the values were 0.6 and 0.8 g L−1 respectively for ethanol. Over the first 4 days, the H2 productions from Unpre and Pre made up 46.2 and 70.6 % of their maximum H2 productions respectively, and the values were about 62.6 and 70.5 % for ethanol. The differences of physicochemical characteristics and metabolic pathways between Unpre and Pre both contributed to the different accelerating effects of the pretreatment on H2 and ethanol production.

Arsenic-containing industrial wastes contain high levels of hazardous arsenic compounds, for which proper pollution control and resource recovery is a high priority and a matter of great urgency. In this study, a process that combines alkaline leaching and acid precipitation was investigated with a view to extracting and recovering arsenic from the sludge-like waste generated during phosphoric acid production, as well as reducing the quantity of the waste to be disposed. The effects of NaOH concentration, liquid-to-solid (L/S) ratio, and extraction time on arsenic leaching were studied. Results indicated that 98.7 % of arsenic could be extracted from the waste when it was leached for 100 min using a NaOH solution of 1.875 mol/L, and a L/S ratio of 8 L/kg. The solid residue accounted for only 5.6 % of the raw waste, suggesting a significant reduction of the quantity requiring safe disposal. Arsenic trioxide was recovered from the alkaline leachate by acid precipitation, at an optimal H2SO4/arsenic ratio of 1.9 mol/mol; after washing with diluted acid, the purity of arsenic trioxide reached 93.4 % and the total recovery ratio of arsenic was 79 %. This relatively simple process was found to be an effective method for arsenic removal and recovery from the sludge-like waste.

Incineration for the disposal of sludge is drawing increased attention, and SO2 and NOx are the main secondary pollutants produced during the incineration process. Process control during incineration is the most reasonable method to reduce the production of secondary gaseous pollutants. In this study, batch combustion tests of sludge were carried out in CO2/O2 and N2/O2 atmospheres to investigate SO2 and NOx emissions. The emissions were characterized by different temperatures, varying oxygen concentrations in the feed gas and two atmospheres. The results showed that the maximum value and appearance time of the peak of SO2 concentration curve were affected by temperature. In CO2/O2 and 80%N2/20%O2 atmospheres, the average SO2 concentration increased from 650 °C to 750 °C, while at 800 °C the transformation rate of sulfur in the sludge was nearly 100%. At the same temperature, the average SO2 concentration in the N2/O2 atmosphere was higher than that in the CO2/O2 atmosphere. The maximum value and peak shape of the NOx concentration curve changed with temperature. Specifically, the average NOx concentration increased from 550 °C to 650 °C and declined from 650 °C to 950 °C. As the oxygen concentration increased, the average SO2 and NOx concentration also increased. The difference in the NOx emission between the 80%N2/20%O2 and 80%CO2/20%O2 atmosphere was significant when the temperature was lower than 750 °C, but not at 750–950 °C. Overall, the results of this study indicate that sludge combustion under a 80%CO2/20%O2 atmosphere might simultaneously reduce SO2 and NOx emissions.Highlights► SO2 and NOx emissions during sludge combustion were investigated under a CO2/O2 atmosphere. ► From 550 to 950 °C, the average NOx concentration firstly increased and then declined. ► As the oxygen concentration increased, the average SO2 and NOx concentration increased. ► Sludge combustion under a CO2/O2 atmosphere could simultaneously reduce SO2 and NOx emissions.

Previous publications on phosphorus (P) in sewage sludge and sludge ash have mostly focused on the total contents, while information on the fraction distribution of P is rarely examined. In this study, P in sewage sludge was, for the first time, fractioned into NH4Cl-P, BD-P, NaOH-P, HCl-P and Res-P via increasing chemical reagents. Its speciation evolution during sludge incineration was also investigated. Results showed that the total P content in sewage sludge had a wide range (0.97–1.74%), and NaOH-P and Res-P were the dominant fractions, which contributed with 67.1–81.2% of sludge P. Sludge incineration process increased the relative proportion of HCl-P from the initial 9.1–11.7% (sewage sludge) to 63.0–78.0% (from ash when sludge was incinerated at 900°C). Furthermore, P in sludge ash was respectively extracted by acid (HCl) and base (NaOH). It was found that the extraction percentage by HCl reached more than 90%, while that by NaOH was less than 30%. The different extraction efficiencies could be explained by the P sequential extraction procedure applied in this study.

To quantify the contribution of syntrophic acetate oxidation to thermophilic anaerobic methanogenesis under the stressed condition induced by acidification, the methanogenic conversion process of 100 mmol/L acetate was monitored simultaneously by using isotopic tracing and selective inhibition techniques, supplemented with the analysis of unculturable microorganisms. Both quantitative methods demonstrated that, in the presence of aceticlastic and hydrogenotrophic methanogens, a large percentage of methane (up to 89%) was initially derived from CO2 reduction, indicating the predominant contribution of the syntrophic acetate oxidation pathway to acetate degradation at high acid concentrations. A temporal decrease of the fraction of hydrogenotrophic methanogenesis from more than 60% to less than 40% reflected the gradual prevalence of the aceticlastic methanogenesis pathway along with the reduction of acetate. This apparent discrimination of acetate methanization pathways highlighted the importance of the syntrophic acetate-oxidizing bacteria to initialize methanogenesis from high organic loadings.

To test the dose effect of ammonium (NH4+) fertilization on soil methane (CH4) oxidation by methanotrophic communities, batch incubations were conducted at a wide scale of NH4+ amendments: 0, 100, 250, 500, and 1,000 mg N kgdry soil−1. Denaturing gradient gel electrophoresis and real-time quantitative PCR analysis were conducted to investigate the correlation between the CH4 oxidation capacity and methanotrophic communities. Immediately after the addition of NH4+, temporal inhibition of CH4 oxidation occurred, and this might have been due to the non-specific salt effect (osmotic stress). After a lag phase, the CH4 oxidation rates of the soils with NH4+ fertilization were promoted to levels higher than those of the controls. More than 100 mg N kgdry soil−1 of NH4+ addition resulted in the reduction of type II/type I MOB ratios and an obvious evolution of type II MOB communities, while less than 100 mg N kgdry soil−1 of NH4+ addition induced nearly no change of methanotrophic community compositions. The NH4+-derived stimulation after the lag phase was attributed to the improvement of N availability for type I MOB. Compared with the controls, 100 mg N kgdry soil−1 of NH4+ addition doubled the CH4 oxidation peak value to more than 20 mg CH4 kgdry soil−1 h−1. Therefore, an appropriate amount of leachate irrigation on the landfill cover layer might efficiently mitigate the CH4 emissions.

To understand the influence patterns and interactions of three important environmental factors, i.e. soil water content, oxygen concentration, and ammonium addition, on methane oxidation, the soils from landfill cover layers were incubated under full factorial parameter settings. In addition to the methane oxidation rate, the quantities and community structures of methanotrophs were analyzed to determine the methane oxidation capacity of the soils. Canonical correspondence analysis was utilized to distinguish the important impact factors. Water content was found to be the most important factor influencing the methane oxidation rate and Type II methanotrophs, and the optimum value was 15% (w/w), which induced methane oxidation rates 10- and 6- times greater than those observed at 5% (w/w) and 20% (w/w), respectively. Ambient oxygen conditions were more suitable for methane oxidation than 3% oxygen. The addition of 100 mg-N·kgdrysoil−1 of ammonium induced different effects on methane oxidation capacity when conducted at low or high water content. With regard to the methanotrophs, Type II was sensitive to the changes of water content, while Type I was influenced by oxygen content. Furthermore, the methanotrophic acidophile, Verrucomicrobia, was detected in soils with a pH of 4.9, which extended their known living environments.

Batch biosorption experiments were conducted to remove Cr(III) from aqueous solutions using activated sludge from a sewage treatment plant. An investigation was conducted on the effects of the initial pH, contact time, temperature, and initial Cr(III) concentration in the biosorption process. The results revealed that the activated sludge exhibited the highest Cr(III) uptake capacity (120 mg·g−1) at 45°C, initial pH of 4, and initial Cr(III) concentration of 100 mg·L−1. The biosorption results obtained at various temperatures showed that the biosorption pattern accurately followed the Langmuir model. The calculated thermodynamic parameters, ΔGo° ( − 0.8–4.58 kJ·mol−1), ΔH° (15.6–44.4 kJ·mol−1), and ΔS° (0.06–0.15 kJ·mol−1·K−1) clearly indicated that the biosorption process was feasible, spontaneous, endothermic, and physical. The pseudo first-order and second-order kinetic models were adopted to describe the experimental data, which revealed that the Cr(III) biosorption process conformed to the second-order rate expression and the biosorption rate constants decreased with increasing Cr (III) concentration. The analysis of the values of biosorption activation energy (Ea = −7 kJ·mol−1) and the intraparticle diffusion model demonstrated that Cr(III) biosorption was film-diffusion-controlled.

This paper describes the feasibility of fresh leachate treatment by an upflow blanket filter (UBF). Through dilution and partial effluent recycling, the organic loading rates increased from 0.51 to 14.56 kg COD/(m3·d), meanwhile the corresponding hydraulic retention time decreased from 9.0 to 3.6 d. The reactor was able to achieve steady-state within 80 d. Based on the distribution of COD fluxes in the process, it was concluded that anabolism was the main pathway of COD removal in the initial phase (1–33 d), accounting for 57%–85% of total COD removed. As the anaerobic consortium of bacteria reached steady-state (after 70–86 d), the majority of COD removed was transformed into methane, because the specific methane yield was close to the theoretical value (0.36 L CH4/(g CODdeg)).

•A reliable process was developed to prepare a nanocomposite from CES.•The optimal process parameters were studied.•The characterizations of MPCON under different pH conditions were studied.•MPCON has a high reflectance (around 56%) in the near-infrared.A nanocomposite composed of metal-phosphates and chromium oxide was prepared from a Cr(III)-containing electroplating sludge (CES) by a facile three-step (extraction–precipitation–calcination) process. Optimal process parameters were determined, and the structure of the metal-phosphate/chromium oxide nanocomposite (MPCON) was investigated by field-emission scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The results show that the optimal extraction pH is 2.0. The MPCON presents a polyhedral morphology with average particle size of around 100 nm. The components of MPCON vary from AlPO4/Cr2O3 to Mg3(PO4)2/AlPO4/Cr2O3 at different solution pH during precipitation. Meanwhile, the optical performance of the nanocomposite as a pigment is discussed. The reflectance of MPCON-6.5 in the near-infrared range is around 56%, making it a strong prospect to be used as a functional pigment in energy-efficient buildings. This study proposes a novel recycling process for the conversion of CES into high-value products, which is beneficial for the treatment of waste.

•We established a comprehensive LCI method for landfill construction and operation.•We reported the consumption of materials and energy in a generic Chinese landfill.•The contribution of C&O to the impacts of total landfilling is not negligible.•Non-toxic and toxic impacts are attributed to diesel and mineral usage, respectively.•Replacing minerals with synthetic materials is effective in mitigating impacts.An inventory of material and energy consumption during the construction and operation (C&O) of a typical sanitary landfill site in China was calculated based on Chinese industrial standards for landfill management and design reports. The environmental impacts of landfill C&O were evaluated through life cycle assessment (LCA). The amounts of materials and energy used during this type of undertaking in China are comparable to those in developed countries, except that the consumption of concrete and asphalt is significantly higher in China. A comparison of the normalized impact potential between landfill C&O and the total landfilling technology implies that the contribution of C&O to overall landfill emissions is not negligible. The non-toxic impacts induced by C&O can be attributed mainly to the consumption of diesel used for daily operation, while the toxic impacts are primarily due to the use of mineral materials. To test the influences of different landfill C&O approaches on environmental impacts, six baseline alternatives were assessed through sensitivity analysis. If geomembranes and geonets were utilized to replace daily and intermediate soil covers and gravel drainage systems, respectively, the environmental burdens of C&O could be mitigated by between 2% and 27%. During the LCA of landfill C&O, the research scope or system boundary has to be declared when referring to material consumption values taken from the literature; for example, the misapplication of data could lead to an underestimation of diesel consumption by 60–80%.

•Successfully operating decentralized on-site treatments for 6 month.•Source-separated collection was successfully applied in rural areas.•The products of the mini-scaled on-site treatment were safe and stable.•The waste treatment had no impact to nearby communities.•The appropriate scale of on-site treatment facility was discussed.The application of on-site waste treatment significantly reduces the need for expensive waste collection and transportation in rural areas; hence, it is considered of fundamental importance in developing countries. In this study, the effects of in-field operation of two types of mini-scale on-site solid waste treatment facilities on de-centralized communities, one using mesophilic two-phase anaerobic digestion combined with composting (TPAD, 50 kg/d) and another using decentralized composting (DC, 0.6–2 t/d), were investigated. Source-separated collection was applied to provide organic waste for combined process, in which the amount of waste showed significant seasonal variation. The highest collection amount was 0.18 kg/capital day and 0.6 kg/household day. Both sites showed good performance after operating for more than 6 months, with peak waste reduction rates of 53.5% in TPAD process and 63.2% in DC process. Additionally, the windrow temperature exceeded 55 °C for >5 days, indicating that the composting products from both facilities were safe. These results were supported by 4 days aerobic static respiration rate tests. The emissions were low enough to avoid any impact on nearby communities (distance <100 m). Partial energy could be recovered by the combined process but with complicated operation. Hence, the choice of process must be considered in case separately.

•An-Flush and An-Fenton test were not able to achieve further stabilization for low-lignin-content MSW.•O2 consumption related indicators were much more sensitive than CH4 production related indicators.•HA and (HA + FA)/HyI were appropriate as termination indicators, but FA and HyI were inappropriate.To understand the applicability of the termination indicators for landfill municipal solid waste (MSW) with low initial lignin content, four different accelerated landfill stabilization techniques were applied to anaerobic landfilled waste, including anaerobic flushing with water, anaerobic flushing with Fenton-treated leachate, and aerobic flushing with Fenton-treated and UV/H2O2-treated leachate. Termination indicators, including total organic carbon (TOC), ammonia-N (NH4+-N), the ratio of UV absorbance at 254 nm to TOC concentration (SUVA254), fluorescence spectra of leachate, methane production, oxygen consumption, lignocellulose content, and humus-like content were evaluated. Results suggest that oxygen consumption related indicators used as a termination indicator for low-lignin-content MSW were more sensitive than methane consumption related indicators. Aeration increased humic acid (HA) and (HA + FA)/HyI content by 2.9 and 1.7 times compared to the anaerobically stabilized low-lignin-content MSW. On the other hand, both the fulvic acid (FA) and hydrophilic (HyI) fractions remained constant regardless of stabilization technique. The target value developed for low-lignin-content MSW was quite different than developed countries mainly due to low residual biodegradable organic carbon content in stabilized low-lignin-content MSW.

•A leachate quantification method was established for MSW landfilling.•Water squeezed out of waste is non-negligible for waste with high moisture content.•Leachate generation performances differ in various geographic regions in China.•Leachate amounts are significantly lower in northwestern China.•Long-term generation contribute more than 60% in southern China.The quantity of leachate is crucial when assessing pollution emanating from municipal landfills. In most cases, existing leachate quantification measures only take into account one source – precipitation, which resulted in serious underestimation in China due to its waste properties: high moisture contents. To overcome this problem, a new estimation method was established considering two sources: (1) precipitation infiltrated throughout waste layers, which was simulated with the HELP model, (2) water squeezed out of the waste itself, which was theoretically calculated using actual data of Chinese waste. The two sources depended on climate conditions and waste characteristics, respectively, which both varied in different regions. In this study, 31 Chinese cities were investigated and classified into three geographic regions according to landfill leachate generation performance: northwestern China (China-NW) with semi-arid and temperate climate and waste moisture content of about 46.0%, northern China (China-N) with semi-humid and temperate climate and waste moisture content of about 58.2%, and southern China (China-S) with humid and sub-tropical/tropical climate and waste moisture content of about 58.2%. In China-NW, accumulated leachate amounts were very low and mainly the result of waste degradation, implying on-site spraying/irrigation or recirculation may be an economic approach to treatment. In China-N, water squeezed out of waste by compaction totaled 22–45% of overall leachate amounts in the first 40 years, so decreasing the initial moisture content of waste arriving at landfills could reduce leachate generation. In China-S, the leachate generated by infiltrated precipitation after HDPE geomembranes in top cover started failing, contributed more than 60% of the overall amounts over 100 years of landfilling. Therefore, the quality and placing of HDPE geomembranes in the top cover should be controlled strictly for the purpose of mitigation leachate generation.Download high-res image (113KB)Download full-size image

•Anaerobic degradation parameters of nut waste were different from other food waste.•Paper should be subdivided into degradable paper and refractory paper.•Garden waste should be divided into grass and leaves, and branches.•Wood should not be subdivided according to CSF.We studied the biochemical and anaerobic degradation characteristics of 29 types of materials to evaluate the effects of a physical composition classification method for degradable solid waste on the computation of anaerobic degradation parameters, including the methane yield potential (L0), anaerobic decay rate (k), and carbon sequestration factor (CSF). Biochemical methane potential tests were conducted to determine the anaerobic degradation parameters of each material. The results indicated that the anaerobic degradation parameters of nut waste were quite different from those of other food waste and nut waste was classified separately. Paper was subdivided into two categories according to its lignin content: degradable paper with lignin content of <0.05 g g VS−1, and refractory paper with lignin content >0.15 g g VS−1. The L0, k, and CSF parameters of leaves, a type of garden waste, were similar to those of grass. This classification method for degradable solid waste may provide a theoretical basis that facilitates the more accurate calculation of anaerobic degradation parameters.

•The leaching behavior of Ca-based compounds commonly in MSWI residues was studied.•pH is the crucial factor for calcium leaching process.•CaCO3 was the most sensitive to leaching temperature and Ca3(PO4)2 was the least.•Ca leaching of MSWIBA and SAPCR attributed to CaCO3 and Ca3(PO4)2 respectively.•Potential clogging ability of MSWI residues leachate in open air was calculated.Leachate collection system (LCS) clogging caused by calcium precipitation would be disadvantageous to landfill stability and operation. Meanwhile, calcium-based compounds are the main constituents in both municipal solid waste incineration bottom ash (MSWIBA) and stabilized air pollution control residues (SAPCR), which would increase the risk of LCS clogging once these calcium-rich residues were disposed in landfills. The leaching behaviors of calcium from the four compounds and municipal solid waste incineration (MSWI) residues were studied, and the influencing factors on leaching were discussed. The results showed that pH was the crucial factor in the calcium leaching process. CaCO3 and CaSiO3 began leaching when the leachate pH decreased to less than 7 and 10, respectively, while Ca3(PO4)2 leached at pH < 12. CaSO4 could hardly dissolve in the experimental conditions. Moreover, the sequence of the leaching rate for the different calcium-based compounds is as follows: CaSiO3 > Ca3(PO4)2 > CaCO3. The calcium leaching from the MSWIBA and SAPCR separately started from pH < 7 and pH < 12, resulting from CaCO3 and Ca3(PO4)2 leaching respectively, which was proven by the X-ray diffraction results. Based on the leaching characteristics of the different calcium compounds and the mineral phase of calcium in the incineration residues, simulated computation of their clogging potential was conducted, providing the theoretical basis for the risk assessment pertaining to LCS clogging in landfills.

•Emissions of VOCs, H2S and NH3 during waste composting were investigated on a pilot scale.•Addition of rice straw reduced emissions of sulfur compounds and VFAs.•Level of rice straw incorporation slightly influenced aromatics and ammonia emissions.•Addition of rice straw influenced VOCs and NH3 emissions by increasing oxygen diffusion.The effects of rice straw addition level on odorous compounds emissions in a pilot-scale organic fraction of municipal solid waste (OFMSW) composting plant were investigated. The cumulative odorous compounds emissions occurred in a descending order of 40.22, 28.71 and 27.83 mg/dry kg of OFMSW for piles with rice straw addition level at ratio of 1:10, 2:10 and 3:10 (mixing ratio of rice straw to OFMSW on a wet basis), respectively. The mixing ratio of rice straw to OFMSW had a statistically significant effect on the reduction of malodorous sulfur compounds emissions, which had no statistically significant effect on the reduction of VFAs, alcohols, aldehydes, ketones, aromatics and ammonia emissions during composting, respectively. The cumulative emissions of malodorous sulfur compounds from piles with the increasing rice straw addition level were 1.17, 1.08 and 0.88 mg/dry kg of OFMSW, respectively. The optimal mixing ratio of rice straw to OFMSW was 1:5. Using this addition level, the cumulative malodorous sulfur compounds emissions based on the organic matter degradation were the lowest during composting of OFMSW.

Bio-drying has been applied to improve the heating value of municipal solid waste (MSW) prior to combustion. In the present study, evolution of heavy metals in MSW during bio-drying and subsequent combustion was studied using one aerobic and two combined hydrolytic–aerobic scenarios. Heavy metals were concentrated during bio-drying and transformed between different metal fractions, namely the exchangeable, carbonate-bound, iron- and manganese-oxides-bound, organic-matter-bound and residual fractions. The amounts of heavy metals per kg of bio-dried MSW transferred into combustion flue gas increased with bio-drying time, primarily due to metals enrichment from organics degradation. Because of their volatility, the partitioning ratios of As and Hg in flue gas remained stable so that bio-drying and heavy metal speciation had little effect on their transfer and partitioning during combustion. In contrast, the partitioning ratios of Pb, Zn and Cu tended to increase after bio-drying, which likely enhanced their release potential during combustion.

The high water content of municipal solid waste (MSW) will reduce the efficiency of mechanical sorting, consequently unfavorable for beneficial utilization. In this study, a combined hydrolytic-aerobic biodrying technology was introduced to remove water from MSW. The total water removals were proved to depend on the ventilation frequency and the temporal span in the hydrolytic stage. The ventilation frequency of 6 times/d was preferable in the hydrolytic stage. The hydrolytic span should not be prolonged more than 4 d. At this optimal scenario, the final water content was 50.5% reduced from the initial water content of 72.0%, presenting a high water removal efficiency up to 78.5%. A positive correlation was observed between the organics losses and the water losses in both hydrolytic and aerobic stages (R = 0.944, p < 0.01). The evolutions of extracellular enzyme activities were shown to be consistent with the organics losses.