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.

Start-up performances of dry anaerobic mesophilic and thermophilic digestions of organic solid wastes

Two dry anaerobic digestions of organic solid wastes were conducted for 6 weeks in a lab-scale batch experiment for investigating the start-up performances under mesophilic and thermophilic conditions. The enzymatic activities, i.e., β-glucosidase, N-α-benzoyl-Largininamide （BAA）-hydrolysing protease, urease and phosphatase activities were analysed. The BAA-hydrolysing protease activity during the first 2-3 weeks was low with low pH, but was enhanced later with the pH increase. β-Glucosidase activity showed the lowest values in weeks 1-2, and recovered with the increase of BAA-hydrolysing protease activity. Acetic acid dominated most of the total VFAs in thermophilic digestion, while propionate and butyrate dominated in mesophilic digestion. Thermophilic digestion was confirmed more feasible for achieving better performance against misbalance, especially during the start-up period in a dry anaerobic digestion process.

Influence of temperature fluctuation on thermophilic anaerobic digestion of municipal organic solid waste

A laboratory-scale experiment was carried out to assess the influence of temperature fluctuation on thermophilic anaerobic digestion of municipal organic solid waste (MOSW). Heating failure was simulated by decreasing temperature suddenly from 55 °C to 20 °C suddenly; 2 h time is needed for temperature decrease and recovery. Under the conditions of 8.0 g/(L·d) and 15 d respectively for MOSW load and retention time, following results were noted: (1) biogas production almost stopped and VFA (volatile fatty acid) accumulated rapidly, accompanied by pH decrease; (2) with low temperature (20 °C) duration of 1, 5, 12 and 24 h, it took 3, 11, 56 and 72 h for the thermophilic anaerobic digestion system to reproduce methane after temperature fluctuation; (3) the longer the low temperature interval lasted, the more the methanogenic bacteria would decay; hydrolysis, acidification and methanogenesis were all influenced by temperature fluctuation; (4) the thermophilic microorganisms were highly resilient to temperature fluctuation.

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.

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.

Enhancement of thermophilic anaerobic digestion of thickened waste activated sludge by combined microwave and alkaline pretreatment

Pretreatment of thickened waste activated sludge （TWAS） by combined microwave and alkaline pretreatment （MAP） was studied to improve thermophilic anaerobic digestion efficiency. Uniform design was applied to determine the combination of target temperature （110-210°C）, microwave holding time （1-51 min）, and NaOH dose （0-2.5 g NaOH/g suspended solids （SS）） in terms of their effect on volatile suspended solids （VSS） solubilization. Maximum solubilization ratio （85.1%） of VSS was observed at 210°C with 0.2 g-NaOH/g-SS and 35 min holding time. The effects of 12 different pretreatment methods were investigated in 28 thermophilic batch reactors by monitoring cumulative methane production （CMP）. Improvements in methane production in the TWAS were directly related to the microwave and alkaline pretreatment of the sludge. The highest CMP was a 27% improvement over the control. In spite of the increase in soluble chemical oxygen demand concentration and the decrease in dewaterability of digested sludge, a semi-continuous thermophilic reactor fed with pretreated TWAS without neutralization （at 170~C with 1 min holding time and 0.05 g NaOH/g SS） was stable and functioned well, with volatile solid （VS） and total chemical oxygen demand （TCOD） reductions of 28% and 18%, respectively, which were higher than those of the control system. Additionally, methane yields （L@STP/g-CODaded, at standard temperature and pressure （STP） conditions of 0°C and 101.325 kPa） and （L@STP/g VSadad） increased by 17% and 13%, respectively, comoared to the control reactor.

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.

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.

High-solids anaerobic mono-digestion of riverbank grass under thermophilic conditions

The purpose of this study was to investigate the potential of high-solids anaerobic mono-digestion of riverbank grass under thermophilic conditions, focusing on the effects of the strength and the amount of inoculum. Ensiled grass was inoculated with three different inocula; inoculum from liquid anaerobic digester（LI）, inoculum from dry anaerobic digester（DI）, and mixture of LI and DI（MI）, at feedstock-to-inoculum ratio（FIR） of 1, 2 and 4. The ensiling process of riverbank grass reduced moisture content（p 〉 0.05）, while the hemicellulose content was significantly increased from 30.88% to 35.15%（p 〈 0.05）, on dry matter basis. The highest methane production was at an FIR of 2 with MI（167 L/kg VSadded）,which was significantly higher（p 〈 0.05） than with DI, but not significant compared to LI（p 〉 0.05）. At an FIR of 4, digesters inoculated with LI and DI failed to produce methane,whereas 135 LCH4/kg VSaddedwas obtained with MI. The kinetic studies showed that at an FIR of 1 with LI and MI, the inoculum had less of effects on the hydrolysis rate constant（0.269 day-1and 0.245 day-1） and methane production（135 versus 149 L/kg VSadded）; rather,it affected the lag phase. In a thermophilic HS-AD of riverbank grass, the mixture of inoculum with low and high total solids content（TS） helps increase the TS of inoculum and digestion process. An FIR of 2 was deducted to be the limit for a better startup time and higher volumetric productivity of methane.

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.

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.

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.

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.

沼渣水热炭与沼渣热解炭强化餐厨垃圾厌氧消化对比研究

餐厨垃圾厌氧消化产生大量沼渣,亟需得到妥善处理。采用水热与热解将沼渣分别制备为水热炭与热解炭,并对比研究了其对餐厨垃圾厌氧消化的影响。结果表明:与对照组(23.8 mL/g)相比,水热炭组(投加量1、5、10 g/L)甲烷产量分别为24.0、38.9、34.9 mL/g,分别提高了0.8%、63.4%、46.6%;热解炭组(投加量1、5、10 g/L)甲烷产量分别为29.7、35.7、31.1 mL/g,分别提高了24.8%、50.0%、30.7%。投加水热炭和热解炭促进了有机物溶出,且水解产酸菌包括Fastidiosipila、 W5053、 Propioniciclava、 Actinomyces (放线菌属)、Norank_f__ST-12K33的总相对丰度由73.0%分别提升至84.6%和82.0%。投加水热炭和热解炭后,Methanosaeta(鬃毛甲烷菌属)相对丰度分别高达60.3%和50.6%,Methanobacterium (甲烷杆菌属)相对丰度仅为26.5%和36.9%。沼渣生物炭可以强化餐厨垃圾厌氧消化,随着投加量的增加,甲烷产量先上升后下降,最优投加量为5 g/L,且水热炭效果优于热解炭。

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。