High-solid Anaerobic Co-digestion of Food Waste and Rice Straw for Biogas Production

Anaerobic co-digestion of food waste（FW） and rice straw（RS） in continuously stirred tank reactor（CSTR） at high organic loading rate（OLR） was investigated. Co-digestion studies of FW and RS with six different mixing ratios were conducted at an initial volatile solid（VS） concentration of more than 3 g VS · L-1. The biogas production, methane contents, degradation efficiency of VS, chemical oxygen demand（COD） and volatile fatty acids（VFAs） were determined to evaluate the stability and performance of the system. The results showed that the co-digestion process had higher system stability and higher volumetric biogas production than mono-digestions. Increase in FW content in the feedstock could increase the methane yield and shorten retention time. The efficiency of co-digestion systems mainly relied on the mixing ratios of FW and RS to some extent. The highest methane yield was 60.55 m L· g V· S-1 · d-1 at a mass ratio（FW/RS） of 3 ： 1, which was 178% and 70% higher than that of mono-digestions of FW and RS, respectively. Consequently, the anaerobic co-digestion of FW and RS could have superior stability and better performance than monodigestions in higher organic loading system.

Coupling System for Food Wastes Anaerobic Digestion and Polyhydroxyalkanoates Production with Ralstonia eutropha

A new technology was developed to couple the anaerobic digestion of food wastes with production of polyhydroxyalkanoates (PHAs). Acetic, propionic, butyric and lactic acids were produced during food wastes anaerobic digestion and their concentrations reached 5.5, 1.8, 27.4 and 32.7 g/L, respectively under appropriate digestion conditions. The fermentative acids were transferred through a dialysis membrane to an air-lift reactor for PHA synthesis by Ralstonia eutropha. Dry cell concentration and PHA content reached 22.7 g/L and 72.6%, respectively. The obtained PHA was a copolymer of b-hydroxybutyrate (HB) and b-hydroxyvalerate (HV) with 2.8% (mole ratio) of HV units in polymer.

Biohythane production from two-stage anaerobic digestion of food waste:A review

The biotransformation of food waste(FW)to bioenergy has attracted considerable research attention as a means to address the energy crisis and waste disposal problems.To this end,a promising technique is two-stage anaerobic digestion(TSAD),in which the FW is transformed to biohythane,a gaseous mixture of biomethane and biohydrogen.This review summarises the main characteristics of FW and describes the basic principle of TSAD.Moreover,the factors influencing the TSAD performance are identified,and an overview of the research status;economic aspects;and strategies such as pre-treatment,co-digestion,and regulation of microbial consortia to increase the biohythane yield from TSAD is provided.Additionally,the challenges and future considerations associated with the treatment of FW by TSAD are highlighted.This paper can provide valuable reference for the improvement and widespread implementation of TSAD-based FW treatment.

Inhibition mechanisms of ammonia and sulfate in high-solids anaerobic digesters for food waste treatment: Microbial community and element distributions responses

The horizontal flow anaerobic digester indicated that high ammonia (2923 mg/L) and SO42-(3653 mg/L)would influence the performance of methane production with food waste as substrates.Therefore,bottle anaerobic digestion reactors were carried out to investigate the effect of ammonia/sulfate concentrations on the methane production.Experimental results manifested that the anaerobic digesters with an ammonia concentration of 3500 mg/L or sulfate of 1600 mg/L showed the best performance of methane production,with an average methane yield of 0.32 and 0.33 L (g VS)^(-1)d^(-1),respectively.Specifically,a higher ammonia (6500 mg/L) or sulfate (1600-3500 mg/L) level hindered the bioconversion of C from liquid to gas phase (2.68%or 1.73%CH_(4)-Gas,respectively),while insignificantly for the hydrolyzation of C and N from solid to liquid phase.Similar to sulfate,high ammonia nitrogen seriously inhibited the methanation process,leading to a significant carbon accumulation in the anaerobic reactor,especially for propionic acid.The predominant archaea Methanosarcina at genus level indicated that aceticlastic methanogenesis was the major methanogenic pathway.Meanwhile,high ammonia level suppressed the activity of Methanosarcina,while modest sulfate improved H_(2)-consuming methanogens activity.A large fraction of unclassified bacteria within the Firmicutes (43.78%-63.17%) and Bacteroidetes (24.20%-33.30%) phylum played an important role in substrates hydrolysis.

Anaerobic digestion of food wastes for biogas production

Five types of food wastes were investigated as feedstock for a potential centralized anaerobic digester system in the area of Sacramento,California to produce biogas energy.The wastes were from a soup processing plant,a cafeteria,a commercial kitchen,a fish farm,and grease trap collection service.Digestibilities of the food wastes,individually and in mixtures,were conducted at mesophilic(35℃)and thermophilic(50℃)temperatures and at two food to microorganism ratios(F/M)of 0.5 and 1.0,for 28 days.A continuously fed mesophilic single-stage anaerobic digester was evaluated using a mixture of the five food wastes at organic loading rates of 0.5 to 1.0 g VS/L/d.In the batch digestion tests,fish and grease trap wastes required longer time to complete the digestion and had higher biogas yields than the other wastes.The continuously-fed digester required the addition of sodium hydroxide to maintain pH at proper levels in the digester.Alkalinity of about 2,500 mg CaCO3/L and pH above 7 was maintained by adding 0.2 g NaOH/g VS.The results of this study indicated that it was necessary to use the chemicals,such as NaOH,to control the pH of the single-stage anaerobic digester treating the food waste.For commercial applications,the cost of chemicals and proper management of additional salts in the digester effluent need to be carefully considered.

Wood waste biochar promoted anaerobic digestion of food waste:focusing on the characteristics of biochar and microbial community analysis

Anaerobic digestion(AD)has been considered as a promising technique for food waste(FW)recycling.However,the accumulation of volatile fatty acids(VFAs)restricts the stability of anaerobic reactors.The present study investigated the use of biochar produced at different conditions(750℃-30 min,750℃-60 min,750℃-120 min,550℃-60 min,650℃-60 min,850℃-60 min,950℃-60 min)for enhancing the AD of FW.Batch experiments showed that all the biochar increased the methane production rates and biochar obtained at 750℃-60 min resulted in the highest enhance-ment by 21.5%.It was further showed surface oxygen-containing functional groups and graphitization degree of biochar were the critical factors for improving methane production.Microbial analysis showed that biochar addi-tion formed different microbial communities,and Methanosaeta,Romboutsia,and norank_f_Anaerolineaceae were enriched,which might be correlated with direct interspecies electron transfer(DIET).This research showed biochar could enhance the AD of FW and also revealed the main characteristics of biochar relating with the enhancement of AD.

A comparative study on the alternating mesophilic and thermophilic two-stage anaerobic digestion of food waste

An alternating mesophilic and thermophilic two stage anaerobic digestion （AD） process was conducted. The temperature of the acidogenic （A） and methanogenic （M） reactors was controlled as follows： System 1 （S1） mesophilic A-mesophilic M; （S2） mesophilic A-thermophilic M; and （S3） thermophilic A-mesophilic M. Initially, the AD reactor was acclimatized and inoculated with digester sludge. Food waste was added with the soluble chemical oxygen demand （SCOD） concentrations of 41.4-47.0 g/L and volatile fatty acids of 2.0-3.2 g/L. Based on the results, the highest total chemical oxygen demand removal （86.6%） was recorded in S2 while S3 exhibited the highest SCOD removal （96.6%）. Comparing S1 with S2, total solids removal increased by 0.5%;S3 on the other hand decreased by 0.1% as compared to S1. However, volatile solids （VS） removal in S1, S2, and S3 was 78.5%, 81.7%, and 79.2%, respectively. S2 also exhibited the highest CH4 content, yield, and production rate of 70.7%, 0.44 L CH4/g VSadded, and 1.23 L CH4/（L.day）, respectively. Bacterial community structure revealed that the richness, diversity, evenness, and dominance of S2 were high except for the archaeal community. The terminal restriction fragments dendrogram also revealed that the microbial community of the acidogenic and methanogenic reactors in S2 was distinct. Therefore, S2 was the best among the systems for the operation of two-stage AD of food waste in terms of CH4 production, nutrient removal, and microbial community structure.

Comparative investigations on pilot-scale anaerobic digestion of food waste at 30℃and 35℃

Parallel pilot-scale anaerobic digestion systems were conducted to evaluate the influence of system temperatures(30℃and 35℃)on digestion performance,greenhouse gas control and economic efficiency.Biogas productions(6.64-12.96 m3/d)and methane yields(0.46-0.61 m3/kg VS)of 35℃digestion system were significantly higher than those of 30℃digestion system with the organic loading rate(OLR)of 2.0-4.5 kg VS/m3·d.Two regression equations of methane yields with increasing OLRs were fitted at 30℃and 35℃to predict the methane production of practical food waste(FW)digestion plants.By analyzing process stability,the optimal operating OLRs of 35℃digestion system(4.0 kg VS/m3·d)was found to be higher than that of 30℃digestion system(3.0 kg VS/m3·d),indicating that the 35℃digestion system had better processing capacity.The greenhouse gas emission under corresponding optimal operating OLR of 35℃digestion system was also calculated to be better than that of 30℃digestion system.Even the system temperature of 30℃was found to be more suitable for the digestion where OLR was less than 3.0 kg VS/m3·d,a higher operational temperature of 35℃was still a better choice for conventional high-solid digestion.

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.

Biogas Production from Co-Digestion of Grass with Food Waste

Management of grasslands in Ghana has become so poor that most rural communities result in bushfires that cause a lot of environmental challenges. Grass could be used for biogas generation. This study investigated the effect of grass and food waste co-digestion on the biogas yield and clarified how the addition of grass enhances the AD performance. Grass (GR) mixed with the co-substrate food waste (FW) was then evaluated under anaerobic conditions for the production of biogas (methane). Five laboratory-scale reactors, R1 (100% FW, 0% GR), R2 (75% FW, 25% GR), R3 (50% FW, 50% GR), R4 (25% FW, 75% GR) and R5 (0% FW, 100% GR) were set up with different proportions of grass and food waste which had 8% total solid concentration. Digestion was carried out for twenty (20) days at room temperature, 35&#176C ± 2&#176C. The biogas yield in the R1, R2, R3, R4, R5 was 805, 840, 485, 243 and 418 mL respectively. Food waste only produced 805 mL and grass only produced 418 mL of biogas. Food waste only produced 50% more biogas than grass. However, co-digestion at 75% FW, 25% resulted in 6% more biogas than food waste only.

Effects of mixture ratio on anaerobic co-digestion with fruit and vegetable waste and food waste of China

The biochemical methane potentials for typical fruit and vegetable waste （FVW） and food waste （FW） from a northern China city were investigated, which were 0.30, 0.56 m3 CH4/kgVS （volatile solids） with biodegradabilities of 59.3% and 83.6%, respectively. Individual anaerobic digestion testes of FVW and FW were conducted at the organic loading rate （OLR） of 3 kg VS/（m3-day） using a lab-scale continuous stirred-tank reactor at 35°C. FVW could be digested stably with the biogas production rate of 2.17 ma/（m3-day） and methane production yield of 0.42 m3 CH4/kg VS. However, anaerobic digestion process for FW was failed due to acids accumulation. The effects of FVW： FW ratio on co-digestion stability and performance were further investigated at the same OLR. At FVW and FW mixing ratios of 2：1 and 1：1, the performance and operation of the digester were maintained stable, with no accumulation of volatile fatty acids （VFA） and ammonia. Changing the feed to a higher FW content in a ratio of FVW to FW 1：2, resulted in an increase in VFAs concentration to 1100-1200 rag/L, and the methanogenesis was slightly inhibited. At the optimum mixture ratio 1：1 for co-digestion of FVW with FW, the methane production yield was 0.49 m3 CH4/kg VS, and the volatile solids and soluble chemical oxygen demand （sCOD） removal efficiencies were 74.9% and 96.1%, respectively.

Fate of antibiotics and antibiotic resistance genes in a full-scale restaurant food waste treatment plant:Implications of the roles beyond heavy metals and mobile genetic elements

Is our food safe and free of the crisis of antibiotics and antibiotic resistance (AR)?And will the derived food waste (FW) impose AR risk to the environment after biological treatment? This study used restaurant FW leachates flowing through a 200 tons-waste/day biological treatment plant as a window to investigate the fate of antibiotics and antibiotic-resistance genes (ARGs) during the acceptance and treatment of FW.Sulfonamides (sulfamethazine,sulfamethoxazole) and quinolones (ciprofloxacin,enrofloxacin,ofloxacin) were detected during FW treatment,while tetracyclines,macrolides and chloramphenicols were not observable.ARGs encoding resistance to sulfonamides,tetracyclines and macrolides emerged in FW leachates.Material flow analysis illustrated that the total amount of antibiotics (except sulfamethazine) and ARGs were constant during FW treatment processes.Both the concentration and total amount of most antibiotics and ARGs fluctuated during treatment,physical processes (screening,centrifugation,solid-liquid and oil-water separation) did not decrease antibiotic or ARGs concentrations or total levels permanently;the affiliated wastewater treatment plant appeared to remove sulfonamides and most ARGs concentrations and total amount.Heavy metals Ni,Co and Cu were important for disseminating antibiotics concentrations and MGEs for distributing ARGs concentrations.Humic substances (fulvic acids,hydrophilic fractions),C-associated and N-associated contents were essential for the distribution of the total amounts of antibiotics and ARGs.Overall,this study implied that human food might not be free of antibiotics and ARGs,and FW was an underestimated AR pool with various determinants.Nonetheless,derived hazards of FW could be mitigated through biological treatment with well-planned daily operations.

餐厨垃圾水力制浆耦合厌氧消化的效果分析

根据餐厨垃圾高含水的特点,从水力模拟、浆化物料特性、设备运行关键指标及项目运行效果等方面对餐厨垃圾水力浆化预处理技术进行综合评价。计算流体力学(CFD)的水力模拟结果表明,浆化过程中流体质点螺旋式汇聚至转叶,形成三股内旋状涡流,在流体内部产生明显的流速差和正负压分区现象,水力作用下可快速实现餐厨垃圾的浆化。浆料和杂质特征分析表明,浆化产物颗粒细小,有机质损失率低,杂质去除率高,可与后端不同资源化技术(如厌氧消化、好氧堆肥等)高度融合。以水力浆化与厌氧消化技术相结合的餐厨垃圾资源化项目为例,餐厨垃圾经水力浆化预处理后,有机质损失率约为8.5%;不可生物降解杂质分选率约94%;粗油脂提取率约91%,吨餐厨垃圾平均产油率为3.76%,产气率为85.57 m^(3)(以标态计)。该处理方式较机械式预处理具有更高的资源化利用率,可大幅提升项目的经济效益。

餐厨垃圾厌氧消化快速启动特性的研究

为明确餐厨垃圾快速启动过程的厌氧消化特性,通过半连续搅拌反应器系统,监测了有机负荷(Organic Loading Rate,OLR)为1.5、2.0、2.5和3.0 gVS·L^(-1)d^(-1)运行过程中沼气产量和甲烷含量、沼液pH值、挥发性脂肪酸(VFA)、碱度和氨氮等参数的变化情况。研究结果表明:OLR从1.5 gVS·L^(-1)d^(-1)提高至3.0 gVS·L^(-1)d^(-1)时,容积产气率提高到2.12±0.05 L·L^(-1)d^(-1),比甲烷产量稳定在273.2±7.8 mLCH_(4)·g^(-1)VS,系统产气性能良好且稳定;挥发性脂肪酸浓度维持较低水平(650 mg·L^(-1)左右),主要成分是乙酸。氨氮含量随着OLR的提升不断增加,最高达到4171 mg·L^(-1),游离氨增加至300~350 mg·L^(-1),对产气性能产生轻微抑制作用;微生物群落分析表明厌氧消化过程主要细菌菌群是Firmicutes、Bacteroidota和Synergistota,优势产甲烷菌群主要以Methanosarcina、Methanobacterium和Methanosaeta为主。厌氧消化启动阶段在有机负荷达到3.0 gVS·L^(-1)d^(-1)时可以稳定运行,反应器成功启动。

不同浓度餐厨垃圾高温厌氧消化研究

为探索餐厨垃圾高温厌氧消化的可行性,研究不同浓度餐厨垃圾高温厌氧消化过程中厌氧罐内参数的变化。通过餐厨垃圾连续厌氧发酵的进料负荷变化试验,试验结果表明,低浓度的餐厨垃圾浆料较高浓度的餐厨垃圾浆料厌氧发酵过程更加稳定,餐厨垃圾沥水浆料在7.5 kg·m^(-3)d^(-1)的COD负荷和6 kg·m^(-3)d^(-1)的TS负荷下可以长时间稳定运行,系统的容积产气率可达4 m^3·m^(-3)d^(-1)并可长期稳定运行。相较餐厨垃圾中温厌氧发酵,高温厌氧发酵能显著提升厌氧罐的进料负荷,从而有效降低厌氧罐体的大小,降低工程投资和运行费用。

餐厨垃圾厌氧处理技术研究进展

餐厨垃圾是城市生活垃圾中有机固体废弃物的主要来源,厌氧消化技术是目前餐厨垃圾资源化的主流处理工艺,文章分析了我国餐厨垃圾的处理技术现状,其中厌氧消化技术作为目前的主流处理工艺,从厌氧反应器类型、厌氧消化工艺等方面着重分析了目前国内外餐厨垃圾厌氧处理技术的发展现状,为提高我国餐厨垃圾资源化水平提供参考。

厨余垃圾厌氧消化反应器起泡的驱动因子

为探析厨余垃圾厌氧消化(AD)反应器起泡的驱动因子,在半连续式厌氧消化反应器中引入超负荷、氨抑制和长链脂肪酸抑制三种扰动诱导反应器起泡,探索了起泡进程中反应器状态参数,消化液流变特性、表面特性、起泡潜能参数及胞外聚合物(EPS)浓度等的响应.结果表明,随着扰动程度的加剧,三个反应器中都诱导出了150~300mm高的泡沫.起泡初期三个反应器内的挥发性脂肪酸(VFAs)、表面活性度(SA)、起泡潜能、表面张力和粘度分别在1948~5978mg/L,8.28~30.15,312.5~350mL,37.89~41.04mN/m和120~183.6mPa·s,可见其起泡阈值并不相同,甚至部分参数的变化趋势与泡沫的发展趋势也不一致.相比之下,EPS相关参数在不同反应器中均与泡沫高度存在明确的相关性,其中溶解型EPS总浓度及其蛋白质浓度、紧密结合型EPS的多糖浓度及总EPS的多糖浓度在三个反应器中都与泡沫高度呈极显著正相关(P<0.01,R^(2):0.64~0.81);紧密结合型EPS和总EPS浓度也与三个反应器的起泡高度呈显著(P<0.05)或极显著(P<0.01)相关(R^(2):0.61~0.81).各类参数的交互分析表明,超负荷和长链脂肪酸抑制反应器中是酸积累刺激了微生物分泌EPS,而氨抑制反应器中游离氨才是EPS浓度上升的主因.但尽管不同反应器中引起EPS积累的内因不同,EPS增加却无一例外会显著增加消化液粘度,甚至改变其表面张力,最终阻碍气体从液相中排除,引起泡沫.后期研究EPS抑制技术也许有望原位、高效的解决反应器起泡问题.

湿热除油强化餐厨垃圾水解酸化产沼气潜力研究

以餐厨垃圾为原料,研究不同湿热预处理除油条件(温度和处理时间),并将其作为厌氧消化底物进行产沼气潜力测试。研究表明,餐厨垃圾的最佳预处理条件为95℃,处理时间90 min,可浮油含量可提升至4.22%;随着温度的升高,浮油去除率逐步提升至2.21%。餐厨垃圾经95℃湿热预处理后,厌氧消化沼气产率达413 mL/g VS。厌氧消化系统中pH值的稳定性较好,保持在6.5~7.5之间,挥发性脂肪酸转化率可达74.31%,处理效果优于其他两个预处理组;挥发性固体(VS)去除率与出料总固体(TS)受温度影响较大,95℃时VS去除率可达56.2%,与未处理组相比提高8.1%。

基于LCA的2种餐厨垃圾处理工艺环境影响分析

文章采用生命周期评价(life cycle assessment,LCA)法,选择我国比较典型的餐厨垃圾处理方式厌氧消化工艺和厌氧消化-好氧堆肥组合处理工艺作为研究对象,并基于实际工程案例,评估并对比这2种工艺的环境影响。结果表明,厌氧消化工艺和厌氧消化-好氧堆肥组合工艺处理餐厨垃圾时的总环境影响潜值分别为4.88×10^(-12)、8.20×10^(-12),厌氧消化工艺的环境效益更好。敏感性分析表明,合理规划餐厨垃圾收运距离和降低能耗可有效降低处理工艺的环境影响。在排除生物CO_(2)的影响后,2种处理工艺的全球变暖环境影响指标均明显降低,其中厌氧消化-好氧堆肥组合工艺降幅更大。研究结果可为餐厨垃圾处理工艺的选择和优化提供参考。