Influence of lactic acid on the two-phase anaerobic digestion of kitchen wastes

To evaluate the influence of lactic acid on the methanogenesis, anaerobic digestion of kitchen wastes was firstly conducted in a two-phase anaerobic digestion process, and performance of two digesters fed with lactic acid and glucose was subsequently compared. The results showed that the lactic acid was the main fermentation products of hydrolysis-acidification stage in the two-phase anaerobic digestion process for kitchen wastes. The lactic acid concentration constituted approximately 50% of the chemical oxygen demand （COD） concentration in the hydrolysis-acidification liquid. The maximum organic loading rate was lower in the digester fed with lactic acid than that fed with glucose. Volatile fatty acids （VFAs） and COD removal were deteriorated in the methanogenic reactor fed with lactic acid compared to that fed with glucose. The specific methanogenic activity （SMA） declined to 0.343 g COD/（gVSS-d） when the COD loading were designated as 18.8 g/（L-d） in the digester fed with lactic acid. The propionic acid accumulation occurred due to the high concentration of lactic acid fed. It could be concluded that avoiding the presence of the lactic acid is necessary in the hydrolysis-acidification process for the improvement of the two-phase anaerobic digestion process of kitchen wastes.

Engineering properties for high kitchen waste content municipal solid waste

Engineering properties of municipal solid waste （MSW） depend largely on the waste＇s initial compositionand degree of degradation. MSWs in developing countries usually have a high kitchen waste content（called HKWC MSW）. After comparing and analyzing the laboratory and field test results of physicalcomposition, hydraulic properties, gas generation and gas permeability, and mechanical properties forHKWC MSW and low kitchen waste content MSW （called LKWC MSW）, the following findings wereobtained： （1） HKWC MSW has a higher initial water content （IWC） than LKWC MSW, but the field capacitiesof decomposed HKWC and LKWC MSWs are similar; （2） the hydraulic conductivity and gaspermeability for HKWC MSW are both an order of magnitude smaller than those for LKWC MSW; （3）compared with LKWC MSW, HKWC MSW has a higher landfill gas （LFG） generation rate but a shorterduration and a lower potential capacity; （4） the primary compression feature for decomposed HKWCMSW is similar to that of decomposed LKWC MSW, but the compression induced by degradation ofHKWC MSW is greater than that of LKWC MSW; and （5） the shear strength of HKWC MSW changessignificantly with time and strain. Based on the differences of engineering properties between these twokinds of MSWs, the geo-environmental issues in HKWC MSW landfills were analyzed, including highleachate production, high leachate mounds, low LFG collection efficiency, large settlement and slopestability problem, and corresponding advice for the management and design of HKWC MSW landfills wasrecommended.

Anaerobic digestion of kitchen wastes in a single-phased anaerobic sequencing batch reactor(ASBR) with gas-phased absorb of CO_2

The performance of the single-stage anaerobic digestion of kitchen wastes was investigated in an anaerobic sequencing batch reactor(ASBR) with gas-phased absorb of CO 2. The ASBR was operated at four chemical oxygen demand(COD) loading rates, 2.8, 5.1, 6.2 and 8.4 g/(L·d) respectively. The COD loading rate was increased with the TS concentration and HRT changing. At maximum COD loading rate of 8.4 g/(L·d), the COD, total solid(TS) removal rate and methane gas yield were 69%, 68% and 2.5 L/(L·d) respectively. The operation of the reactor with gas-phased absorb of CO 2 was stable in spite of the low pH(2.6—3.9) and high concentration of TS(142 g/L) of input mixture. The output volatile fatty acid(VFA) concentration was between 2.7—4.7 g/L and had no inhibition on the methanogenic microorganism. The reactor without gas-phased absorb of CO 2 became acidified when the total COD loading rate was increased to 5.1 g/(L·d). Stoichiometry of the methanogenesis for kitchen wastes showed a considerable amount of alkaline will be required to keep pH in the appropriate range for the methanogenic microorganism based on theoretical calculation. Gas-phased absorb of CO 2 effectively reduced the alkaline consumption, hence avoided excessive cation into the reactor.

A Review of Co-processing of Kitchen Waste and Municipal Residual Sludge

In this paper, the methods of kitchen waste disposal in recent years were summed up, and the advantages and disadvantages of the current treatment methods were analyzed. At the same time, it has been found that the co-processing of kitchen waste and residual sludge not only has dealt with both kitchen waste and residual sludge, but also the carbon and nitrogen ratio and moisture content of the mixture are balanced, and increases the processing efficiency significantly. It has a certain processing advantage. At present, most research is about the anaerobic digestion of kitchen waste and residual sludge, and the process is more mature, but the study of VFAs accumulation is still insufficient. Aerobic composting is still in the early stage of development, and there are few studies on it at home and abroad. Meanwhile, prospects for the kitchen waste recycling were made in this article.

Impact on Acidification Characteristics of Anaerobic Digestion of Kitchen Waste by F/M

The effect of F/M on acidification characteristics during anaerobic digestion of kitchen waste was investigated. Under different F/M,p H,alkalinity,ethyl alcohol,volatile fatty acids(VFAs),and biogas production status of acidification effluent in 96 h were observed. The study results showed that the content of propionic acid + acetic acid reached 56%-80% when F/M≤1. 0,which was mainly known as propionic acid type of fermentation and was accompanied by methane. The value of alkalinity was only 3 000-4 000 mg/L,which indicated that the stability was weak in the system. When 1. 0 < F/M≤2. 5,the concentration of butyric acid + acetic acid was in the range of 77%-85%,and acid production rate per unit load was more than 250 mg VFAs/g VS,which was known as butyric acid type of fermentation. The fermentation type was stable and could provide more available VFAs for subsequent methanation processes because the value of alkalinity reached 5 650 mg/L. When F/M≥2. 5,the content of ethanol + acetic acid was 80%-92%,which was known as ethanol type of fermentation. And p H of 96 h was only 5. 0( F/M = 3. 0) and 4. 3(F/M =4.0),and acidification was serious and the stability was weak in the system,which would hinder the subsequent methanation process.Therefore,F/M influenced fermentation type,and it can provide a target product for subsequent methanation process by controlling F/M in a reasonable range.

Synergistic effects of chemical additives and mature compost on reducing H_2S emission during kitchen waste composting

Additives could improve composting performance and reduce gaseous emission,but few studies have explored the synergistic of additives on H_(2)S emission and compost maturity.This research aims to make an investigation about the effects of chemical additives and mature compost on H_(2)S emission and compost maturity of kitchen waste composting.The results showed that additives increased the germination index value and H_(2)S emission reduction over 15 days and the treatment with both chemical additives and mature compost achieved highest germination index value and H_(2)S emission reduction(85%).Except for the treatment with only chemical additives,the total sulfur content increased during the kitchen waste composting.The proportion of effective sulfur was higher with the addition of chemical additives,compared with other groups.The relative abundance of H_(2)S-formation bacterial(Desulfovibrio)was reduced and the relative abundance of bacterial(Pseudomonas and Paracoccus),which could convert sulfur-containing substances and H_(2)S to sulfate was improved with additives.In the composting process with both chemical additives and mature compost,the relative abundance of Desulfovibrio was lowest,while the relative abundance of Pseudomonas and Paracoccus was highest.Taken together,the chemical additives and mature compost achieved H_(2)S emission reduction by regulating the dynamics of microbial community.

Improvement in bioconversion efficiency and reduction of ammonia emission by introduction of fruit fermentation broth in a black soldier fly larvae and kitchen waste conversion system

The black soldier fly(BSF),Hermetia illucens(Diptera:Stratiomyidae),is an insect commonly used for the bioconversion of various organic wastes.Not only can the BSF convert organic waste into macromolecular organic substances,such as insect pro-teins,but it can also lessen the pollution associated with these waste products by reducing ammonia emissions,for example.In this study,we measured the effects of adding fruit fermentation broth(Fer)and commercial lactic acid bacteria fermentation broth(Em)to kitchen waste(KW),as deodorizing auxiliary substances,on the growth performance of black soldier fly larvae(BSFL),the intestinal flora structure of BSFL,the ammonia emis-sion from the KW substrate,and the microbial community structure of the KW substrate.We found that the addition of Fer or Em increased the body weight of BSFL after 6 d of culture,increasing the growth rate by 9.96%and 7.96%,respectively.The addition of Fer not only reduced the pH of the KW substrate but also increased the relative abundance of probiotics,such as Lactobacillus,Lysinibacillus,and Vagococcus,which inhibited the growth of ammonifiers such as Bacillus,Oligella,Paenalcaligenes,Paenibacillus,Pseu-dogracilibacillus,and Pseudomonas,resulting in the reduction of ammonia emission in the KW substrate.Moreover,the addition of Fer or Em significantly increased the rela-tive abundances of Bacteroides,Campylobacter,Dysgonomonas,Enterococcus,and Ig-natzschineria in the gut of BSFL and increased the species diversity and richness in the K W substrate.Our findings provide a novel way to improve the conversion rate of organic waste and reduce the environmental pollution caused by BSF.

Long-tailed object detection of kitchen waste with class-instance balanced detector

Intelligent detection and classification of kitchen waste can promote ecological sustainability by replacing inefficient manual processes.However,the presence of non-degradable waste mixed in kitchen waste often follows a long-tailed distribution,making it challenging to train convolutional neural network-based object detectors,which results in the unsatisfactory detection of tailclass waste.To address this challenge,we propose a class-instance balanced detector(CIB-Det) for intelligent detection and classification of kitchen waste.CIB-Det implements two strategies for the loss function:the class-balanced strategy(CBS)and the instance-balanced strategy(IBS).The CBS focuses more on tail classes,and the IBS concentrates on hard-to-classify instances adaptively during training.Consequently,CIB-Det comprehensively and adaptively addresses the long-tailed issue.Our experiments on a real dataset of kitchen waste images support the effectiveness of CIB-Det for kitchen waste detection.

Preliminary techno-economic analysis of three typical decentralized composting technologies treating rural kitchen waste:a case study in China

This study was designed to evaluate whether the decentralized rural kitchen waste(KW)composting technologies used in China can be widely applied.To this end,we completed a techno-economic analysis of three typical types of KW compositing,namely solar-assisted(SAC),bio-enhanced(BEC),and heat-dewatering composting(HDC).These evaluations revealed that all three technologies produce composting products that meet China’s organic fertilizer standard and that both SAC and BEC are economically self-sustaining and generate net profits(18824.94 and 17791.52 US$/a)and positive net present values(32133.11 and 25035.93 US$).Subsequent sensitivity analysis demonstrated that the KW-handling subsidy plays a critical role in making decentralized composting economically attractive.Based on these analyses,we believe that reducing the coverage area of SAC,reducing the operating cost of BEC and HDC,upgrading composting products,and strengthening secondary pollution control would aid in supporting the technological improvement of these processes.Moreover,providing appropriate subsidies and promulgating specific standards and policies for KW fertilizer are key strategies for decentralized rural KW composting management.

Effects of adding bulking agents on the biodrying of kitchen waste and the odor emissions produced

The effects of adding a bulking agent on the performance and odor emissions（ammonia and eight sulfur-containing odorous compounds） when biodrying kitchen waste were investigated. Three treatments were considered： the addition of either cornstalks（CS） or wood peat（WP） to kitchen waste as a bulking agent before biodrying, and a control treatment（CK）. The water-removal rates for CK, CS, and WP treatments were 0.35, 0.56, and0.43 kg/kg, respectively. Addition of bulking agents to kitchen waste produced less leachate,higher moisture-removal rates, and lower consumption of volatile solids. The CS treatment had the highest biodrying index（4.07）, and those for the WP and CK treatments were 3.67 and 1.97, respectively. Adding cornstalks or wood peat decreased NH3 emissions by 55.8%and 71.7%, respectively. Total sulfur losses were 3.6%–21.6% after 21 days biodrying, and H2 S and Me2 SS were the main（〉 95%） sulfur compounds released. The smallest amounts of sulfur-containing odorous compounds were emitted when cornstalks were added, and adding cornstalks and wood peat decreased total sulfur losses by 50.6%–64.8%.

Use of additive and pretreatment to control odors in municipal kitchen waste during aerobic composting

The effects of adding a bulking agent and chemically pretreating municipal kitchen waste before aerobic composting were studied using a laboratory-scale system. The system used20-L reactors and each test lasted 28 days. The objective was to decrease NH3 and H2S emissions during composting. The bulking agent, dry cornstalks, was mixed with the kitchen waste to give a mixture containing 15%（wet weight） bulking agent. A combined treatment was also conducted, in which kitchen waste mixed with the bulking agent was pretreated with ferric chloride（FeC l3）. Less leachate was produced by the composted kitchen waste mixed with bulking agent than by the kitchen waste alone, when the materials had reached the required maturity. The presence of cornstalks also caused less H2 S to be emitted, but had little impact on the amount of NH3 emitted. The FeC l3 was found to act as an effective chemical flocculant,and its presence significantly decreased the amounts of NH3 and H2S emitted. Kitchen waste mixed with cornstalks and treated with FeC l3 emitted 42% less NH3 and 76% less H2 S during composting than did pure kitchen waste.

Enhanced microalgae cultivation using digested kitchen waste sewage treated with struvite precipitation

This study demonstrated the feasibility of using struvite for nutrient management in algae cultivation on sewage wastewater.The results showed that struvite precipitation treatment dramatically reduced the ammonia in the digested kitchen waste sewage.The untreated sewage was unable to sustain continuous growth of algae,while the algae growth on the treated sewage was comparable with that on an artificial algae culture medium(BG11).The rapid growth on the treated sewage was accompanied by substantial removal of nutrients.The struvite precipitate recovered from the treated sewage was proven to be an alternative source of nitrogen,phosphorus and magnesium.The struvite precipitate was evidenced that it could substitute culture media in algae growth.This study showed that struvite treatment is viable for nutrient management of algae cultivation on sewage wastewaters which do not have suitable nutrient profiles.

A Study on The Management of Municipal Residential Solid Waste in China

As the main organic pollutant in municipal living waste , kitchen waste causes secondary pollution in the course of its being gathered and transported to the landfill by mixing with other refuse and by decomposition. This makes pollution prevention more difficult and raises the cost of landfill engineering. However, the amount of solid waste to be treated can be decreased and such pollution burden lessened by disposing of the solid waste in local municipal areas. The program in Beijing also shows that this works well with our situation in China and can accelerate marketization and public participation.

Biochar from vegetable wastes:agro-environmental characterization

Considering the global issue of vegetable wastes generation and its impact on the environment and resources,this study evalu-ated the conversion of four largely produced vegetable wastes(cauliflower,cabbage,banana peels and corn cob residues)into biochar.Each waste was tested individually and as a combined blend to assess feedstock influences on biochar properties.In addition,various pyrolysis temperatures ranging from 300℃ to 600℃ and two particle size fractions(less than 75μm,75-125μm)were considered.Biochars were characterized for various properties that can influence the biochars’effective-ness as a soil amendment.It was found that pyrolysis temperature was the most dominant factor on biochar properties,but that individual feedstocks produced biochars with different characteristics.The biochars had characteristics that varied as follows:pH 7.2-11.6,ECE 0.15-1.00 mS cm^(−1),CEC 17-cmolc kg^(−1)andζ-potential−0.24 to−43 mV.Based on optimal values of these parameters from the literature,cauliflower and banana peels were determined to be the best feedstocks,though mixed vegetable waste also produced good characteristics.The optimum temperature for pyrolysis was around 400℃,but differed slightly(300-500℃)depending on the distinct feedstock.However,smaller particle size of biochar application was always optimal.Biochar yields were in the range of 20-30%at this temperature range,except for corn cobs which were higher.This study demonstrates that pyrolysis of dried vegetable wastes is a suitable waste valorization approach to produce biochar with good agricultural properties.

Assessment of two faecal sludge treatment plants in urban areas:Case study in Beijing

Every day,human beings produce excreta all over the world,and the sludge that accumulates in waste disposal systems is referred to as the‘faecal sludge(FS)’.FS can cause serious environmental pollution in urban areas if it cannot be disposed of properly.A complete FS management system must include onsite sanitation technologies,FS collection and transport,a treatment plant,and resource recovery or disposal of the treatment end-products.Focusing on the treatment and reuse/disposal step of a FS complete service chain,this research presents two cases of FS treatment in Beijing.In Case 1,FS biogas plant adopts anaerobic digestion(AD)to treat FS,and the digestate can be used as biofertilizer in the surrounding greenhouse.In Case 2,several technologies including solid-liquid separation,dewatering,pyrolysis,AD and co-composting are integrated to find innovative solutions for FS treatment.A comprehensive assessment including the aspects of technology,economy and environment is conducted for further SWOT(Strengths,Weaknesses,Opportunities and Threats)analysis.Then,critical strategies are developed,which include(1)selecting project site for optimized transportation,maximum waste reuse,minimum environmental impact and convenient final effluent disposal;(2)planning technical options at a feasible study stage,considering resource recovery,secondary pollution prevention and fire protection;(3)exploring market channels for by-products sale to increase profitability;(4)guaranteeing engineering quality and service life for the purpose of sustainable operation;(5)minimizing health risks to persons exposed to the untreated FS;and(6)providing necessary training for hygiene protection.The cases in Beijing can provide valuable lessons for urban areas in developing countries and the strategies can provide a reference for stakeholders and decision-makers who intend to develop FS treatment projects.