•AC-Ni could reduce the lag phase of food waste anaerobic digestion.•The methane production rate was increased by AC-Ni addition.•The evolution and activity of microbes were promoted with the ...addition of AC-Ni.•AC-Ni could accelerate the degradation of volatile fatty acids.•The environmental risks of AC-Ni could be reduced by anaerobic digestion.
Anaerobic digestion (AD) is frequently restricted with the long lag phase and low methane (CH4) production rate. Laboratory batch experiments were conducted to investigate the impact of different supplements on the performance of food waste AD, including AC-Ni, AC, and Ni. Results showed that the lag phase of AD was reduced with the addition of those supplementations. Compared with the control group without any supplementation, the AC-Ni could shorten the lag phase by 67% and increase the maximum CH4 production rate by 50%, respectively. The speciation analysis indicated that the environmental risks of the AC-Ni was reduced by 30% after digestion. Microbial community structure analysis revealed that the AC-Ni promoted the evolution and activity of the hydrolytic-fermentative bacteria (e.g. Firmicutes and Bacteroidetes) and methanogens (e.g. Methanobacterium, Methanoregula and Methanomassiliicoccus). This study suggested that the AC-Ni waste could be feasible to be applied to enhance the performance of AD.
This study investigated the performance of simulated landfills with different biogas collection practices, including upward biogas collection only (LT) and both upward and downward biogas collection ...(LTB). A simulated landfill was constructed using a stainless steel lysimeter equipped with a compression unit. Upward gas flow was favored in uncompressed MSW when both upward and downward gas flows were allowed (LTB). By reducing void ratio, the preferential flow direction of biogas was changed to downward gas flow along with gravimetric leachate drainage. In LT, porched leachate was formed because high flow resistance by countercurrent gas-liquid flow affected moisture redistribution. It was considered that high pressure buildup in gas-filled pores of LT enhanced uneven moisture distribution and resulted in inhibiting methane production. The cumulative methane volume produced from LTB was 2.5 times as much as that of LT.
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The total plastic waste generation in China has not been reported due to a lack of information on diverted recyclable wastes. This study was conducted with two objectives: to identify the ...characteristics of plastic waste generation, recycling, and compositions in informal and formal waste management sectors in selected Shenzhen (SZ) and Honghuatao Town (HT) study areas in China and to measure the leachability of the heavy metals of waste plastics using the synthetic precipitation leaching procedure (SPLP) and leaching tests with different pHs. The results showed that film plastic waste occupied the largest proportion among plastic components in the mixed MSW. It is estimated that the plastic waste generation rates in SZ and HT were 0.20–0.33 kg/capita/day and 0.08–0.14 kg/capita/day, respectively. The plastic recycling rates of SZ and HT ranged from 6.24 to 11.93% and 16.84–33.31%, respectively. Among the measured heavy metals, Ba, Zn, Cu, Mn contents were high in most plastic samples. In addition, Mn, Pb, Ni, and Zn in plastic wastes occasionally exceeded Chinese national drinking water standards in the different pH leaching tests and SPLP. Therefore, it is suggested that plastic waste should be managed in a controlled manner.
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•Plastic waste generation rates ranged from 0.08 to 0.33 kg/capita/day.•Plastic recycling rate ranged from 6.24 to 33.31%.•Ba, Zn, Cu, Mn contents were high in tested plastic samples.•Mn, Pb, Ni, and Zn in plastic wastes occasionally exceeded Chinese drinking water standard limits.
Main findings of the work: Plastic waste generation and recycling rates in the tested areas and Heavy metal contents and leachability of the plastic waste in MSW.
•H2 production could be enhanced using untreated inoculum.•Significant H2 yield was achieved by selecting a high F/M ratio.•H2 producers could be enriched with a slight addition of ...inoculum.•Two-stage showed a more stable methane production than single-stage process.•Overall energy yield was improved by two-stage process.
This research investigated the possibility to enhance H2 production using untreated inoculum in a two-stage hydrogen-methane process from food waste. Batch experiments were conducted to evaluate the H2 production efficiency at different F/M ratios (ranging from 1:1 to 64:1). The results showed that when a proper F/M ratio was selected, significant H2 production was feasible to be achieved even inoculated with untreated anaerobic sludge. Among the F/M ratios studied, maximum H2 yield (217.98 mL H2 g VS−1 FW) was found in the digester at the F/M of 64:1, which was 93.75 times higher than that of the digester at the F/M of 1:1. Higher hydrogen yield was achieved at the greater F/M ratio, due to the enrichment of the H2 producing bacteria and the reduction of the antagonistic bacteria. The two-stage process allowed more stable methane production and higher overall energy yield compared to the single-stage process.
This investigation explored the combined effects of biochar (BC) and zero-valent iron (ZVI) on food waste anaerobic digestion (AD). The results showed that the AD performance was promoted by ...supplementing with BC or ZVI individually, and could be further improved by simultaneous addition of the two additives. The simultaneous addition of BC and ZVI further reduced the methanogenic lag phase by 13.3% as compared with ZVI added reactor, and raised the cumulative CH4 yield by 19.4% and the maximum CH4 generation rate by 24.5% compared to the BC added reactor. The reason behind these results was that BC and ZVI played different roles for the promotion effects. For example, BC had the greater ability to reduce the methanogenic lag phase as compared with ZVI. While ZVI could greatly enhance the hydrogenotrophic methanogenesis pathway, leading to higher CH4 yield and CH4 generation rate. Accordingly, simultaneous addition strategy could combine the unique advantages of BC and ZVI, and thus developed a complementary promotion effect on CH4 generation. This study suggested that the simultaneous addition of BC and ZVI could be considered as an effective way to improve AD performance.
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•BC and ZVI played different roles for promoting food waste anaerobic digestion.•BC had greater ability for reducing the methanogenic lag phase as compared with ZVI.•ZVI had greater ability for improving the yield and the generation rate of methane.•Simultaneous addition of BC and ZVI greatly improved CH4 production.
•The activation energy of reactions reduced by decreasing sludge particle sizes.•The activation energy of reactions reduced by increasing high heating rate.•The maximum surface area was measured from ...biochar produced at 600°C.•Surface area and pH of biochar were important for Cu(II) adsorption.
In this study, a comprehensive research was conducted for pyrolysis kinetics and biochar characterization with sewage sludge. Pyrolysis kinetics were investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) using sludge samples divided into four particle size ranges. Also, surface properties and Cu(II) adsorption capacities were determined for biochars produced at 300, 500, 600, 700, and 900°C. Similar thermogravimetric analyzer (TGA) profiles were observed with the tested particle size ranges (<2mm). Using a reaction model, estimated kinetic parameters indicated that sludge particle size and heating rate affected activation energy. In biochar characterization study, it was observed that the surface chemical functional groups of biochar was reduced with increasing pyrolysis temperature. The maximum BET surface area was measured from biochar produced at 600°C as 92.3m2/g. Also, the biochar produced at 600°C showed the maximum Cu(II) adsorption capacity (146.7mg/g biochar). Electrostatic adsorption was the main mechanism of Cu(II) adsorption for biochar produced at 600°C, but complexation/precipitation was the main mechanism of Cu(II) adsorption for biochar produced at 300°C and 900°C. These adsorption results indicated that the adsorption mechanism and capacity of biochar could be modified by controlling pyrolysis temperature.
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•Co-disposal of BA with MSW would increase the risk of geotextile clogging in landfills.•Geotextile clogging mainly include CaCO3 precipitation and biofilm formation.•Biomass ...accumulation was the main contributor to the mass increment of geotextile.•The CH4/CO2 ratio generally increased during the clogging process.•CO2 in landfill gas played an important role in the clogging process.
As a main byproduct of municipal solid waste incineration (MSWI), bottom ash (BA) has become a big challenge in operating MSWI plants. The most common method for BA treatment is co-disposal with MSW in landfills, which may cause clogging in the leachate collection system (LCS). This research investigated the characteristics of geotextile clogging in landfills with BA co-disposal. The co-disposal of BA changed the characteristics of leachate, especially increasing the concentration of Ca2+. During the experiment, 0.14 g CaCO3 was precipitated in the MSW geotextile, while it increased to 0.52 g CaCO3 in the BA co-disposed geotextile. Based on mass balance of calcium and thermogravimetric (TG) analysis, the formation of biofilm was the main contributor to the mass increment, accounting for about 82% and 57% mass increment in the MSW and BA co-disposed geotextile, respectively. Moreover, CO2 in landfill gas played an important role in the clogging process, including CaCO3 precipitation and biofilm formation. The results suggested that the co-disposal of BA with MSW can increase the risk of geotextile clogging in landfills.
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•ZVI enhanced the performance of two-stage food waste anaerobic digestion.•ZVI accelerated FW hydrolysis-acidification, H2 and CH4 generations.•ZVI strengthened significantly ...bioenergy recovery efficiency.•Syntrophic bacteria, Pseudomonas and methanogens were enhanced by ZVI addition.
This research investigated the roles of zero-valent iron (ZVI) in a two-stage food waste digestion process. ZVI was added separately to hydrolytic-acidogenic (HA) and methanogenic (MG) stages to understand its impacts on FW hydrolysis-acidification, methanogenesis and bioenergy recovery efficiency. Results showed that ZVI effectively enhanced the overall performance of digestion as compared with the controls without ZVI. Supplementing with ZVI could facilitate the HA process along with faster hydrogen generation. In addition, ZVI shortened the lag phase of MG stage by 42.43–57.23% and raised the maximum methane production rate and yield by 33.99–38.20% and 11–13%, respectively, compared with the controls. Supplementing ZVI to the HA stage could simultaneously raise the bioenergy recovery efficiency of the HA and MG stages by 71.92% and 96.96%, respectively. Further studies demonstrated that iron corrosion contributed little to hydrogen and methane production. The enrichment of syntrophic bacteria, Pseudomonas, and methanogens, and the enhancement of electron transfer among those microbes was supposed to be the main possible mechanism for the enhancement of methanogenesis with ZVI assisted.
Although biochar addition into the anaerobic digestion of food waste (FW) is an efficient means to enhance methane production, the effects of biochar on various FW components remain unclear. ...Laboratory batch experiments were conducted to investigate the impact of sewage sludge-derived biochar (SSB) supplementation on the anaerobic digestion (AD) of major FW components, including carbohydrate-rich, protein-rich, and lipid-rich substrates. The lag phase of AD with the carbohydrate-rich substrate was 48.6% shorter when SSB was added, and the cumulative methane yield was 4.74 times higher compared to AD without biochar. SSB supplementation also increased the rate of methane production from the lipid-rich substrate. However, the effect of SSB addition on AD of the protein-rich substrate was minor. Analysis of the microbial communities revealed that methanogen growth was enhanced during AD of the carbohydrate-rich and lipid-rich substrates, but not the protein-rich substrate, following SSB supplementation. Also, the most dominant methanogenic genus varied with the substrates. SSB addition promoted the growth of hydrolytic and fermentative bacteria, particularly phylum Bacteroidetes.
Implications: Biochar supplementation has been studied to overcome the shortcomings of anaerobic digestion (AD). However, the effects of biochar on different substrates remain unclear. This study compared carbohydrate-rich, protein-rich, and lipid-rich substrates in anaerobic digestion with sewage sludge-derived biochar (SSB). SSB supplementation improved methane generation from all but the protein-rich substrate. The study results imply that the effect of SSB addition on AD varied with the substrate due to the substrates underwent different degradation processes with different microbial communities.
Anaerobic digestion (AD) is a promising technology for food waste management, but frequently restricted with long lag phase as a consequent of acidification. Two laboratory experiments were conducted ...to investigate the effects of iron materials on food waste AD. Experiment 1 compared the effects of iron oxide (IO) and zero valent iron (ZVI) on AD performance. The results showed that both IO and ZVI could enhance methane (CH4) generation, but IO showed better performance regarding the reduction of lag phase. The lag phase of the reactor supplemented with IO was 17.4% and 42.7% shorter than that of the reactor supplemented with ZVI and the control, respectively. Based on these results, experiment 2 was designed to examine the role of IO in alleviation of acid stress at high substrate to inoculum (SI) ratio. The results showed that supplemented IO into reactor could ensure a successful methanogenesis when operating at high SI ratio, while IO-free reactor was failed to generate CH4 although operating for 77 days. Supplementing IO into the reactor after 48 h of digestion could restore the CH4 generation, though its lag phase was 2.6 times of the reactor supplemented with IO at the beginning of the digestion. Microbial community structure analysis revealed that IO could simultaneously enrich Syntrophomonas and methanogens (i.e. Methanobacterium, Methanofollis and Methanosarcina), and might promote electron transfer between those two types of microbes, which were critical for achieving an effective methanogenesis.
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•ZVI and IO could shorten the lag phase of food waste anaerobic digestion.•IO showed higher methane production rate and faster VFAs reduction.•IO could ensure successful methanogenesis under high substrate to inoculum ratio.•Abundance of Syntrophomonas and methanogens were greatly enriched by IO.•IO might promote electron transfer between Syntrophomonas and methanogens.
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