Anaerobic co‐digestion of food waste leachate and piggery wastewater for methane production: statistical optimization of key process parameters

BACKGROUND: Anaerobic co‐digestion of refractory liquid organic wastes is an alternative environmental management strategy with economic benefits arising out of biogas production. Laboratory‐scale experimental investigations were carried out on the anaerobic co‐digestion of two liquid organic wastes, food waste leachate (FWL) and piggery wastewater (PWW). Three important parameters affecting methane yield were chosen for this study, namely, mixing ratio, alkalinity and salinity, which were optimized using response surface methodology. RESULTS: The results were analyzed statistically and the optimum conditions identified as: mixing ratio (FWL: PWW) 33 (in terms of volatile solid, w/w) (2 on v/v), alkalinity 2850 mg CaCO₃ L^?1, and salinity 3.4 g NaCl L^?1. Under the optimum conditions, a cumulative methane yield (CMY) of 310 mL CH₄ g^?1 VS_added and VS reduction (VSR) of 54% were predicted. Mixing ratio and alkalinity showed the greatest individual and interactive effects on CMY and VSR (P < 0.05). A confirmation experiment under optimum conditions showed a CMY and VSR of 323 mL CH₄ g^?1 VS_added and 50%, respectively. This was only 1.04% and 1.1%, respectively, different from the predicted values. CONCLUSION: Anaerobic co‐digestion of FWL and PWW carried out under the optimum condition may be a feasible and efficient treatment option for methane production. Copyright © 2012 Society of Chemical Industry     

Restriction of linoleic acid inhibition of methanization of piggery wastewater and enhancement of its mineralization by adding calcium ions

BACKGROUND: Linoleic acid, which is a major derivative generated from hydrolysis of vegetable oils, is often found at high concentration in food processing and kitchen wastes. This fatty acid could be introduced into an anaerobic system treating piggery wastewater via co‐digestion strategy. In this study, the effect of CaCl₂ on the inhibitory behavior of linoleic acid in the anaerobic digestion of piggery wastewater was investigated. RESULTS: Linoleic acid exerted strong inhibitory effects on methanization of piggery wastewater with IC₅₀ of 376 mg L^?1 and 568 mg L^?1 for ISR (inoculum substrate ratio) 0.38 and 2.0, respectively. Among tested cations (Na⁺, Mg²⁺, Ca²⁺, Al³⁺ and Fe³⁺), only Ca²⁺ effectively reversed linoleic acid inhibition. In addition, it was found that CaCl₂ restricted linoleic acid inhibition only when it was added before or immediately after linoleic acid addition. Without CaCl₂, linoleic acid was stoichiometrically transformed to oleic acid, which persisted for a prolonged period. In the presence of CaCl₂, however, linoleic acid was completely converted to methane without accumulation of oleic acid. It was also found that oleic acid was self‐inhibitory to its oxidation to acetate, and CaCl₂ removed this inhibition. CONCLUSION: From these findings, it was concluded that calcium ion not only mitigated linoleic acid inhibition in the anaerobic digestion of piggery wastewater, but also enhanced its mineralization to methane. Copyright © 2010 Society of Chemical Industry     

Methane production from citrus wastes: process development and cost estimation

BACKGROUND: Because of its extreme toxicity for microorganisms, the limonene content of citrus wastes (CWs) has been a major obstacle to the conversion of CWs to biofuels. The main objective of this study was to develop a new process for the utilization of CWs that can be economically feasible when the supply of CW is low. RESULTS: Steam explosion pre‐treatment was applied to improve the anaerobic digestibility of CWs, resulting in a decrease of initial limonene concentration by 94.3%. A methane potential of 0.537 ± 0.001 m³ kg^?1 VS (volatile solids) was obtained during the following batch digestion of treated CWs, corresponding to an increase of 426% compared with that of the untreated samples. Long‐term effects of the treatment were further investigated by a semi‐continuous co‐digestion process. A methane production of 0.555 ± 0.0159 m³ CH₄ kg^?1 VS day^?1 was achieved when treated CWs (corresponding to 30% of the VS load) were co‐digested with municipal solid waste. CONCLUSION: The process developed can easily be applied to an existing biogas plant. The equipment cost for this process is estimated to be one million USD when utilizing 10 000 tons CWs year^?1. 8.4 L limonene and 107.4 m³ methane can be produced per ton of fresh citrus wastes in this manner. Copyright © 2011 Society of Chemical Industry     

Osmoprotectants enhance methane production from the anaerobic digestion of food wastes containing a high content of salt

BACKGROUND: Treatment and disposal of Korean food waste encounter technical difficulties due to a high‐salt problem. In order to increase methane production from food waste by using osmoprotectants, which are known to overcome osmotic stresses in many plants and other organisms, osmoprotectants including glycine betaine, choline, carnitine and trehalose were added to salt‐containing food wastes for anaerobic digestion. RESULTS: For NaCl‐amended food wastes containing 10 and 35 g L^?1 NaCl, glycine betaine and choline increased methane production by about twofold compared to food waste without any osmoprotectants. For non‐washed food waste containing 11.6 g L^?1 NaCl, glycine betaine increased methane production by about sixfold. Among these osmoprotectants, glycine betaine was the most effective for increasing methane productivity in anaerobic digestion of food waste with salinity. Analysis of glycine betaine in cell extracts using high‐performance liquid chromatography showed that glycine betaine accumulated in the cells of anaerobic sludge. CONCLUSION: Osmoprotectants significantly enhanced methanization of high‐salt food wastes by alleviating the salt‐induced physiological stresses in microorganisms. The application of osmoprotectants provided an effective substitute for other conventional methods to reduce inhibitory effects of high salt, such as dilution and co‐digestion. Copyright © 2008 Society of Chemical Industry     

The nitrogen fertiliser value and other agronomic benefits of industrial biowastes

An estimated 7 million t of industrial biowastes are landspread annually in the UK. Quantitative research into their fertiliser replacement value and agronomic benefit is required to increase their use in agriculture, recycle valuable nutrients, and contribute to the reduction of biodegradable waste sent to landfill. A programme of systematically designed field experiments was established to quantify the agronomic value of a range of industrial biowastes, including examples from the vegetable, meat and dairy processing industries and digested biowastes from industrial aerobic and anaerobic digestion plants. Dewatered anaerobically digested biosolids (DMAD) was included as a reference material. Yield and N offtake responses of perennial ryegrass, at five rates of application of each biowaste type were used to calculate the N equivalency relative to mineral N fertiliser. Liquid thermophilic aerobic digestate (LTAD) of food waste was an effective source of available N, with an N equivalency of 59–76 %. Liquid mesophilic anaerobic co-digestates of livestock slurry and food waste (LcoMAD) had N equivalencies between 68 and 85 %. Vegetable processing waste and brewing waste (yeast) had N equivalency values of 45 and 89 %, respectively. Regarding other nutrient elements, the biowastes were generally a source of P, vegetable wastes were significant sources of K, and DMAD and the dewatered anaerobically digested organic fraction of municipal solid waste (DMADMSW) were effective sources of S. Certain waste types were not effective sources of N for crop growth (e.g. potato processing wastes, kieselguhr) and require further investigation at greater rates of application to determine their agronomic benefit.     

Effect of aerobic pretreatment on anaerobic digestion of olive mill wastewater (OMWW): An ecoefficient treatment

Anaerobic digestion experiments of olive mill wastewater (OMWW) without pretreatment were carried out and signs of inhibition in the biological process were observed after a time equal to 1.5 times the Hydraulic Residence Time (HRT) due to the presence of a high inhibitors concentration in OMWW. Based on these findings, OMWW was subjected to an aerobic pretreatment in order to reduce the concentration of phenolic compounds and decrease Total Chemical Oxygen Demand (TCOD), achieving a reduction of 78% and 90% of the initial polyphenols concentration and 18% and 21% TCOD reduction when the substrate was aerated for 5 and 7 days respectively.Finally, anaerobic digestion experiments using OMWW aerated for 5 and 7 days as substrate were conducted to determine the influence of aeration time on methane yields and TCOD reduction. The results yield 5 days as the aeration time that achieves best results, given that this stabilizes the anaerobic process, can reduce the TCOD by 65% and generates almost 0.39 m³ methane/kg removed TCOD.Anaerobic digestion of OMWW will be economically feasible if the waste is pretreated by aerobic digestion, since the period of return of investment obtained under these conditions does not exceed 6 years.     

缫丝废水综合利用与无害化处理技术的研究

提出了一种新的综合利用和无害化处理缫丝废水的方法.该方法采用气浮技术,通过将小水量高浓度屑物废水单独分离来回收有用悬浮有机物,然后进行厌氧消化,再与大水量低浓度的缫丝废水合并处理,收到了较好的效果.对内江市松林丝绸有限公司及其他企业废水进行了多次试验,结果表明该方法可行和有效.     

Dry anaerobic batch digestion of the organic fraction of municipal solid waste

Anaerobic digestion at high solid concentrations (dry anaerobic digestion) is an attractive method for the stabilization of solid organic wastes. A new concept for dry anaerobic batch digestion (BIOCEL) of the organic fraction of municipal solid waste is presented. The start up of a BIOCEL reactor was studied with several methods of process set up and operation. Dry anaerobic digestion of the pure undiluted organic fraction obtained from a shredding/separation process was not accelerated by partial spatial separation of substrate and methanogenic inoculum (granular sludge) or leachate recycle, or both. With these three methods after 30 days the high organic acids concentration and low pH in the reactor indicated a sour reactor, unable to establish significant methane production. When the organic fraction was digested in combination with compost addition (40% (w/w) of the initial solids) and leachate recycle, the stabilization rate increased significantly. Leachate recycling in combination with partial spatial separation of the substrate/compost mixture and the inoculum showed the shortest lag phase in the methane production and the shortest digestion time. When the digested residue of a completed digestion was applied as the methanogenic inoculum (40% (w/w) of the initial total solids) the digestion time was slightly shorter. It is concluded that dilution with compost had a positive effect on the start up of the dry anaerobic digestion and compensated for a suboptimal amount of initial methanogenic biomass. During the start up of dry anaerobic batch digestion of municipal solid waste the rapid recovery of methane formation from an initial overloading was observed and was found to be the result of a population shift in the methanogenic biomass and the existence of zones in the reactor with more optimal conditions (higher p H, lower organic acids concentration). The observed digestion time was 36 days. Recommendations are given to shorten the period needed, for complete digestion.     

薯干酒精糟液治理途径探讨

针对目前我国酒精糟液治理技术存在的三个主要问题：预处理力度不足、关键处理技术落后以及处理工艺路线不合理，根据污染防治与资源化相结合的原则，提出了适合我国国情薯干酒精糟液的处理技术路线(预处理 高效厌氧生物反应器 好氧生物处理 混凝气浮处理)，该工艺经实践证明不但从技术上可行，而且经济上合理，适合我国目前的经济现状。     

厌氧序批式反应器处理啤酒废水的快速启动研究

以中等浓度啤酒废水为水源,在低温下(14～20℃)研究了厌氧序批式反应器的快速启动过程。试验结果表明:当采用污水厂消化污泥接种,投加粉末活性炭并以间歇搅拌方式运行到第76天时,反应器容积负荷为6.5kg/(m3.d),出水挥发性脂肪酸浓度和CODCr去除效率分别为2.5mmol/L以下和96.1%,污泥停留时间达到了19.4d,同时完成污泥的颗粒化。和未添加活性炭相比污泥颗粒化时间缩短10d,表明厌氧序批式反应器低温下处理啤酒废水的快速启动是可行的。     

A novel combination of methane fermentation and MBR — Kubota Submerged Anaerobic Membrane Bioreactor process

Methane fermentation is considered one of the best placed biological processes to reduce volume of organic waste while keeping small sludge production and recovering energy. One of the disadvantages of early anaerobic digestion technologies was the long hydraulic retention time thus large capacity tanks were required to hold slow growing methanogenic bacteria. New technological attempts such as upflow anaerobic sludge blanket (UASB), fixed or fluidised bed and membrane bioreactor (MBR) appeared as countermeasures.Kubota’s submerged anaerobic membrane biological reactor (KSAMBR) process has been developed in the last decade and successfully applied in a number of full-scale food and beverage industries. It consists of a solubilization tank and a thermophilic digestion tank, the latter incorporating submerged membranes. The biogas generated can be utilized for water heating via boilers. Both permeate and waste anaerobic sludge are further treated in wastewater treatment facilities.One of the main advantages of KSAMBR is that membranes retain the methanogenic bacteria while dissolved methane fermentation inhibitors such as ammonia are filtered out with the permeate. This makes the KSAMBR process very stable. Furthermore, the digester volumes can be scaled down to 1/3 to 1/5 of the conventional digesters provided that biomass is 3 to 5 times as concentrated.Applications include stillage treatment plants for Shouchu (Japanese spirits made from sweet potato, rice or other grains), potato processing sites, sludge liquor and food factory treatment plants.In summary, it is believed that KSAMBR offers the best possible solution combining the benefits of methane fermentation process with the performance of membrane technology. More details will be presented in the proceedings paper and in the presentation.     

Substratspezifische Stoff-Führung bei anaeroben Verfahren zur Methan-Gewinnung

Principles of material flow in anaerobic methane production processes . Rising prices of fossil energy are upgrading the importance of processes for generating fuels from organic wastes and from renewable biomass. Anaerobic digestion is a suitable approach for the production of fuel gas rich in methane from wet or liquid organic feedstock. Depending upon the biochemical characteristics of the digestion process and upon the physical conditions for an optimal mass transport, specific technical solutions have been found for treating typical substrates differing in chemical composition, digestability, and fluid mechanical behaviour; such substrates are waste water, sludges, and organic solids with a high liquid content. A survey is given on the principal systems now used for conducting material to be digested through the whole process and in particular through the bioreactor.     

废水处理过程的抗扰控制研究

厌氧消化废水处理过程中,动态变化的进水组分、组分浓度,组分间耦合等各种不确定因素,使得简单的闭环控制无法获得理想的污水处理效果。为使污水处理出水水质达标,对污水处理过程模型依赖小、对各种变化（扰动）因素鲁棒性强、动态响应好的控制方法可满足工程要求。为此,设计一种能够主动估计并消除扰动的抗扰控制方法,有效估计并补偿污水处理过程中存在的各种不确定因素,以获得期望的污水处理效果。数值仿真结果表明,抗扰控制具有较好的抗干扰能力,能够满足控制要求,是一种可行的污水处理控制方案。     

铜酞菁生产废酸废水综合治理方案探讨

某铜酞菁生产企业将产生的废酸、废水混合后采用生化处理法,其处理成本高、运行效果差。通过调查废酸、废水的来源、水质、水量,提出废酸回收、酞菁蓝漂洗水压滤回用及混合废水的资源化三项方案。方案不但减少了原料消耗、治理了废酸废水,而且回收了高价值铜泥,同时利用废酸吸收生产工艺中的高含氨废气,生产副产品硫酸铵,实现了废物的资源化利用,达到了以废治废的目的,符合循环经济的理念。     

Effect of processing conditions on organics in wastewater from hydrothermal dewatering of low-rank coal

A study was carried out into the effects of processing conditions on the nature and amounts of organics released into wastewater from hydrothermal dewatering (HTD) of low-rank coal. Processing conditions examined included temperature, residence time, water to coal ratio in the slurry, slurry loading, and coal lithotype. High temperature and pressure treatments of low-rank coal slurries were used to simulate the HTD process. It was found that the extent of extraction of organics during HTD processing depended on the coal lithotype and increased with increasing temperature, residence time, and the proportions of steam and water present during processing. For a constant residence time, the concentration of organics in the wastewater increased exponentially with temperature over the temperature range 250-350 °C. A maximum level of approximately 7 g/l (expressed as TOC) of organics was observed following processing at 350 °C. Hot filtration of the coal slurry produced a higher organics loading compared to that found in wastewater obtained at low temperature.     

Application of thermophilic aerobic digestion in protein enrichment of high strength agricultural waste slurry for animal feed supplementation

Thermophilic aerobic digestion (TAD) is a relatively novel waste processing technique with the potential to improve the safety and nutritional value of many agricultural and food industry wastes for use in animal feed supplementation. TAD of model agricultural waste slurry, at soluble chemical oxygen demand (COD) load of approximately 8.0 g L^?1, was implemented to study the effect of the process on crude protein accretion and waste quality. Digestions were carried out under batch conditions at 0.1, 0.25, 0.5 and 1.0 vvm (volume of air per volume of waste slurry per minute) aeration rates and pH 7.0, and at pH 6.0, 7.0, 8.0, 9.0, 9.5 and without pH regulation at 0.5 vvm, all at 55 °C. All reactions were carried out for 156 h using thermophilic populations indigenous to the waste. Digestion at 0.5 and 1.0 vvm led to the greatest degradation of total suspended solids (51.17% and 52.03% respectively) and the highest accretion of crude protein in treated waste (131.28% and 258.94% respectively). Protein content of the digest decreased as digestion pH increased beyond neutral. Slurry soluble protein content decreased with digestion progress, while the ammonium increased early in the process before decreasing progressively. The percentage content of most amino acids in the digest decreased slightly relative to raw waste. The quality of waste protein was comparable with the FAO standard for protein supplement for feed use. Overall, the digested waste was significantly improved relative to the raw waste. With appropriate process optimization TAD has clear potentials for use in the improvement of various wastes for recycling in animal feed. Copyright © 2006 Society of Chemical Industry     

高盐度废水生物处理现状与前景展望

简要介绍了国内外高含盐量废水生物处理的研究进展，主要有两段接触氧化、传统活性污泥法、SBR、膜法SBR、UASB、厌氧滤池、A^2/O工艺等，以及各种工艺的运行条件和处理状况。各种工艺在高含盐量条件下，经过适当的驯化培养，其他条件适宜，取得较好的处理效果。并介绍利用在高盐环境下生存的嗜盐细菌技术处理高含盐量废水的发展前景。     

厌氧消化过程抑制因素的研究进展

厌氧消化是一种高效的废物处理方法。但厌氧消化过程中经常出现诸如甲烷产量低、工序不稳定等问题,使得这项技术不能被广泛应用。废弃物中种类繁多的抑制物质是导致厌氧消化不稳定或失败的主要原因。概述了厌氧消化过程中经常出现的抑制因素的抑制机制和控制因子。     

Evaluation of relationship between biogas production and microbial communities in anaerobic co-digestion

Anaerobic co-digestion (ACD) has been used to treat various organic wastes because nutrient balance in the feed can be improved by mixing different organics. Until now, the correlation between characteristics of feedstocks and biogas production by ACD has been studied mainly in terms of biochemical methane potential. It has been rarely tried to understand the co-digestion process in terms of microbial community development. This study aimed to evaluate the performance of batch anaerobic digestion (AD) reactors fed with activated sludge (AS), swine slurry (SS) and food waste (FW) individually or in a mixture of the three wastes (FW: SS : AS=1 : 3 : 2). The AD reactors fed with the mixture showed better performance than those fed with a single substrate. Microbial communities of the batch AD reactors fed with a single substrate or the mixture were analyzed and the result was related to the performance of the AD reactors.     

剩余污泥消化后预处理高浓度生产废水

将好氧装置的剩余污泥加入污泥消化池,当池内污泥变黑并探测到有可燃气体时,加入生活污水和生产废水对消化污泥进行培养驯化,培养驯化期间应逐步减小生活污水水量,增加高浓度生产废水水量.用经过驯化的消化污泥预处理生产废水,有机物的去除率＞30%,pH也由5～6被提高到7以上.将好氧装置产生的剩余污泥消化后预处理高浓度的生产废水,剩余污泥被再利用,并且也有利于降低整套污水处理装置的运行成本.