典型有机固废厌氧消化微生物研究现状与发展方向

经过人工富集和驯化的兼性和严格厌氧微生物是厌氧消化工艺的核心。不同厌氧消化体系中存在的问题大多可以通过改变微生物群落的代谢活性来得到有效改善。得益于微生物组学检测技术的快速发展,对厌氧消化系统中微生物多样性的认识获得了极大的拓展,同时在微生物类群间、微生物与环境的互作关系研究方面也取得了一系列新的进展。然而,有机固废厌氧消化系统中,各种微生物以及微生物和物质的相互作用构成了更为复杂的代谢网络,所以目前对这些互作关系的解析尚不完善。本文重点关注了厌氧消化过程中的典型菌群互作关系,阐述了典型有机固废厌氧消化系统中存在的问题及微生物在其中发挥的作用,最后,立足于现有组学技术推动的微生物组研究进展,对未来有机固废厌氧消化系统微生物组的研究提出展望。     

A simulation study of a continuous two-phase dry digestion system

In this article a two-phase system for the continuous digestion of wastes with a high solid content is simulated. The studied parameters are: (1) Recirculation from the methanizer to the hydrolyzer, (2) methanizer/hydrolyzer volume ratio, and (3) hydraulic retention time in the hydrolyzer (HRT). Results show that the recirculation ratio is an important operational factor with a large influence on the biodegradation yield, especially at low HRT. Optimum levels of this parameter are established. Some runs of the program have been carried out to test the stability of the system. This has proved to be very stable, especially at low recirculation ratios. The results also show that volume ratio does not appreciably affect the performance of the system, provided it is over a critical value, dictated by the allowable methanizer load.     

Production of biogas from solid organic wastes through anaerobic digestion: a review

Anaerobic digestion treatments have often been used for biological stabilization of solid wastes. These treatment processes generate biogas which can be used as a renewable energy sources. Recently, anaerobic digestion of solid wastes has attracted more interest because of current environmental problems, most especially those concerned with global warming. Thus, laboratory-scale research on this area has increased significantly. In this review paper, the summary of the most recent research activities covering production of biogas from solid wastes according to its origin via various anaerobic technologies was presented.     

A fast kinetic model discrimination applied to the continuous two-phase anaerobic digestion of fruit and vegetable wastes

Summary A simple method to fit the constants of first order, Monod and Chen and Hashimoto models using only one single linear regression, is presented. The method can be applied to continuous operated systems. As an example, the kinetic behaviour of the anaerobic digestion of a mixture of fruit and vegetable wastes is studied. Chen and Hashimoto model yields the best fit.     

Efficiency of the anaerobic digestion of amine wastes

Laboratory-scale anaerobic degradation of monoethanolamine waste (MEAw) with co-substrate organics was conducted at room temperature and organic loading rates from 0.19 to 5.03 kg COD/m³ day for 486 days in a hybrid digester. 90 % feed COD conversion to methane was obtained at the lower loads and only 45 % at the highest MEA waste/COD ratio (MEAwr) of 0.62 due to inhibition of methanogenesis. Inhibition at comparable loads decreased with time, implying that the culture adapted to the challenging feed. Methane yield was negatively correlated to MEAwr applied and inhibition avoided at MEAwr <0.5. Acetate accumulation implies inhibition of acetoclastic methanogenesis that can be caused by ammonia, a product of MEAw degradation. Moderate total ammonia nitrogen and free ammonia nitrogen accumulation, maximum 2.2 g N/l and 90 mg N/l, respectively suggests, however, that other components of MEAw, and/or degradation products of such, also inhibit methanogenesis, disturbing the digester performance.     

A dynamic mathematical model for sequential leach bed anaerobic digestion of organic fraction of municipal solid waste

A mathematical model that describes the operation of a sequential leach bed process for anaerobic digestion of organic fraction of municipal solid waste (MSW) is developed and validated. This model assumes that ultimate mineralisation of the organic component of the waste occurs in three steps, namely solubilisation of particulate matter, fermentation to volatile organic acids (modelled as acetic acid) along with liberation of carbon dioxide and hydrogen, and methanogenesis from acetate and hydrogen. The model incorporates the ionic equilibrium equations arising due to dissolution of carbon dioxide, generation of alkalinity from breakdown of solids and dissociation of acetic acid. Rather than a charge balance, a mass balance on the hydronium and hydroxide ions is used to calculate pH. The flow of liquid through the bed is modelled as occurring through two zones—a permeable zone with high flushing rates and the other more stagnant. Some of the kinetic parameters for the biological processes were obtained from batch MSW digestion experiments. The parameters for flow model were obtained from residence time distribution studies conducted using tritium as a tracer. The model was validated using data from leach bed digestion experiments in which a leachate volume equal to 10% of the fresh waste bed volume was sequenced. The model was then tested, without altering any kinetic or flow parameters, by varying volume of leachate that is sequenced between the beds. Simulations for sequencing/recirculating 5 and 30% of the bed volume are presented and compared with experimental results.     

A multi-criteria ranking of different technologies for the anaerobic digestion for energy recovery of the organic fraction of municipal solid wastes

This paper describes a conceptual framework and methodological tool developed for the evaluation of different anaerobic digestion technologies suitable for treating the organic fraction of municipal solid waste, by introducing the multi-criteria decision support method Electre III and demonstrating its related applicability via a test application. Several anaerobic digestion technologies have been proposed over the last years; when compared to biogas recovery from landfills, their advantage is the stability in biogas production and the stabilization of waste prior to final disposal. Anaerobic digestion technologies also show great adaptability to a broad spectrum of different input material beside the organic fraction of municipal solid waste (e.g. agricultural and animal wastes, sewage sludge) and can also be used in remote and isolated communities, either stand-alone or in conjunction to other renewable energy sources. Main driver for this work was the preliminary screening of such methods for potential application in Hellenic islands in the municipal solid waste management sector. Anaerobic digestion technologies follow different approaches to the anaerobic digestion process and also can include production of compost. In the presented multi-criteria analysis exercise, Electre III is implemented for comparing and ranking 5 selected alternative anaerobic digestion technologies. The results of a performed sensitivity analysis are then discussed. In conclusion, the performed multi-criteria approach was found to be a practical and feasible method for the integrated assessment and ranking of anaerobic digestion technologies by also considering different viewpoints and other uncertainties of the decision-making process.     

Enhanced methane production in a two-phase anaerobic digestion plant, after CO2 capture and addition to organic wastes

Cost-effective technologies are needed to reach the international greenhouse gas (GHG) reduction targets in many fields, including waste and biomass treatment. This work reports the effects of CO₂ capture from a combustion flue gas and its use in a newly-patented, two-phase anaerobic digestion (TPAD) process, to improve energy recovery and to reduce CO₂ emissions. A TPAD process, fed with urban wastewater sludge, was successfully established and maintained for several months at pilot scale. The TPAD process with injection of CO₂ exhibits efficient biomass degradation (58% VSS reduction), increased VFA production during the acidogenic phase (leading to VFA concentration of 8.4 g/L) and high biomethane production (0.350 Sm³/kg_SSV; 0.363 Sm³/m³_react·d). Moreover, CO₂ intake in the acid phase has a positive impact on the overall GHG balance associated to biomethane production, and suggests an improved solution for both emission reduction and biomass conversion into biomethane.     

A half-submerged integrated two-phase anaerobic reactor for agricultural solid waste codigestion

Anaerobic digestion is widely used in bioenergy recovery from waste. In this study, a half-submerged, integrated, two-phase anaerobic reactor consisting of a top roller acting as an acidogenic unit and a recycling bottom reactor acting as a methanogenic unit was developed for the codigestion of wheat straw (WS) and fruit/vegetable waste (FVW). The reactor was operated for 21 batches (nearly 300 d). Anaerobic granular sludge was inoculated into the methanogenic unit. The residence time for the mixed waste was maintained as 10 d when the operation stabilized, and the temperature was kept at 35 °C. The highest organic loading rate was 1.37 kg VS/(m³ d), and the maximum daily biogas production was 328 L/d. Volatile solid removal efficiencies exceeded 85%. WS digestion could be confirmed, and efficiency was affected by both the ratio of WS to FVW and the loading rate. The dominant bacteria were Bacteroides-like species, which are involved in glycan and cellulose decomposition. Methanogenic community structures, pH levels, and volatile fatty acid concentrations in the acidogenic and methanogenic units differed, indicating successful phase separation. This novel reactor can improve the mass transfer and microbial cooperation between acidogenic and methanogenic units and can efficiently and steady codigest solid waste.     

CFD simulation of mixing for high-solids anaerobic digestion

A computational fluid dynamics (CFD) model that simulates mechanical mixing for high-solids anaerobic digestion was developed. Numerical simulations of mixing manure slurry which exhibits non-Newtonian pseudo-plastic fluid behavior were performed for six designs: (i) one helical ribbon impeller; (ii) one anchor impeller; (iii) one curtain-type impeller; (iv) three counterflow (CF-2) impellers; (v) two modified high solidity (MHS 3/39°) impellers; and (vi) two pitched blade turbine impellers. The CFD model was validated against measurements for mixing a Herschel-Bulkley fluid by ribbon and anchor impellers. Based on mixing time with respect to mixing energy level, three impeller types (ribbon, CF-2, and MHS 3/39°) stand out when agitating highly viscous fluids, of these mixing with two MHS 3/39° impellers requires the lowest power input to homogenize the manure slurry. A comparison of digestion material demonstrates that the mixing energy varies with manure type and total solids concentration to obtain a given mixing time. Moreover, an in-depth discussion about the CFD strategy, the influences of flow regime and impeller type on mixing characteristics, and the intrinsic relation between mixing and flow field is included.     

Lactate and ethanol as intermediates in two-phase anaerobic digestion

The thermodynamics of the various anaerobic digestion patterns of hexose to methane are compared. It appears that by directing the hexose-hydrolysis phase towards ethanol and lactic acid production, methanogenesis can be enhanced because the syntrophic bacteria are allocated more potentially available energy. This hypothesis was confirmed in a series of laboratory test runs. They revealed that lactic acid and ethanol as intermediates, in comparison to lower volatile fatty acids, give rise to a considerably higher effluent quality and a slightly larger biogas production.     

Influence of fermentation metabolites on redox potential in anaerobic digestion of proteinaceous solid wastes by Synergistes sp.

The anaerobic digestion of animal fleshing from tannery solid waste was investigated with regard to hydrolytic enzymes, protease and lipase, fermentative enzyme deaminase, soluble protein and amino acids, redox potential (Eh), volatile fatty acids, ammonia and carbon dioxide up to 120 h of retention time. The release of these fermentation metabolites at various retention times greatly influenced the Eh. In the hydrolytic phase, the maximum value of Eh was ?50 mV and it reached the minimum of ?350 mV in 24 h in the fermentative phase. The minimum and maximum values of Eh were ?387 and ?452 mV at 80 h of anaerobic digestion. The release of extracellular metabolites was confirmed by HPLC and GC‐MS. In this study, we have found that the ammonia and pH had a substantial influence on the Eh during the anaerobic digestion of animal fleshing.     

Fractionation of organic substances during anaerobic digestion of farm wastes for biogas generation

Summary Generation rate of biogas and its methane component, as well as changes of major organic fractions during anaerobic digestion of fresh cow dung alone and in combination with each of air-dry rice straw, maize stalks, and cotton stalks at a ratio of 11 (on the basis of 70°C dry weight of either source) have been monitored in laboratory fermenters for 75 days at 35°C. Mixtures of cow dung + maize stalks produced the highest cumulative volumes of both biogas and its methane component; i.e. 17.9 and 8.31/1 fermented material respectively, cow dung alone surpassed all of the tested biomass regarding the yield of methane production in relation to the volatile solids consumed which gave 636 l/kg; the other materials came in the succession: cow dung + maize stalks, cow dung + rice straw and cow dung + cotton stalks. Acetic, propionic, and butyric were the major detectable fatty acids formed during the digestion course. Cow dung excelled the other treatments in amounts of such acids produced. Combination between cow dung and crop residues resulted in reducing the formation of fatty acids and NH ₄ ⁺ and loss of nitrogen, but enhanced the disappearance of volatile solids, fats, hemicellulose and cellulose. The lignin content remained unchanged.

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Fractionnement de substances organiques pendant la digestion anaerobie de déchets de ferme pour la genèse de biogaz

Résumé La vitesse de genèse du biogaz et son contenu en méthane, ainsi que les modifications des principales fractions organiques pendant la digestion anaérobie a été examinée en fermenteurs de laboratoire pendant 75 jours à 35°C pour les bouses bovines fraîches, seules et en mélange 11 (sur la base du poids sec à 70°C) soit avec la paille de riz séchée au soleil, les fânes de maïs ou les tiges de cotonniers. Le mélange de bouses de vache et de fânes de maïs a produit le volume cumulatif le plus élevé tant de biogaz que de son constituant, le méthane, notamment respectivement 17.9 et 8.31/l de matériel fermenté. Les bouses de vache ont surpassé toutes les biomasses testées quant au rendement de la production de méthane par rapport aux solides volatils consommés qui donna 6361/kg; les autres matières viennent dans l'ordre décroissant: bouses de vache plus fânes de maïs, bouses de vache plus paille de riz et bouses de vaches plus tiges de cotonniers. Les acides gras principaux détectés et formés pendant le cours de la digestion étaient l'acide acétique, l'acide propionique et l'acide butyrique. La biométhanisation de bouses de vache a excellé par rapport à celle d'autres substrats quant aux quantités produites de ces acides. Le mélange de bouses de vache et de résidus agricoles a résulté dans la diminution de la formation d'acides gras et d'ammonium et de la perte en azote mais dans l'augmentation de la disparition des solides volatils, des graisses, de l'hémicellulose et de la cellulose. Le contenu en lignine est resté inchangé.

     

Thermophilic anaerobic digestion of solid waste for fuel gas production.

Anaerobic digestion offers a potential means of converting organic solid waste into fuel gas and thereby provide a supplemental and readily utilizable source of energy. We are particularly interested in the use of thermophilic digestion over a mesophilic operation for it can achieve higher rates of digestion, greater conversion of waste organics to gas, faster solid-liquid separation, and minimization of bacterial and viral pathogen accumulation. Our results comparing mesophilic (37 degree C) and thermophilic (65 degree C) anaerobic digestion of domestic solid waste confirm the increased rate and conversion of waste to methane. In addition, utilizing radioactive labeling of glucose and acetic acid, we have measured the volumetric rates of volatile acid production and disappearance under both mesophilic and thermophilic conditions.     

Anaerobic digestion of municipal solid wastes: dry thermophilic performance

The purpose of this study was to analyze the performance of two laboratory-scale reactors (5.0L) treating organic fraction of municipal solid waste (OFMSW): source sorted OFMSW (SS_OFMSW) obtained from a university restaurant and mechanically selected municipal fraction (MS_OFMSW) obtained from a Municipal Treatment Plant placed in Cadiz-Spain. Discontinuous reactors operated at thermophilic (55 degrees C) and dry (20% total solid) conditions. Different decomposition patterns were observed: (1) the SS_OFMSW exhibited the classical waste decomposition pattern with a fast start up phase beginning within 0-5 days and 20-30 and a subsequent stabilization phase. The VS removal was 45% with a cumulative biogas of 120L in approx. 60 days; (2) the MS_OFMSW showed a methanogenic pattern throughout the whole experimental period (60 days) and this gave higher levels of organic biodegradation (56%VSr) and biogas production (82L). Both processes were completed and a high level of cumulative methane production was achieved in less than 60 days, proximally 25-30L.     

Assessing solid digestate from anaerobic digestion as feedstock for ethanol production

Ethanol production using solid digestate (AD fiber) from a completely stirred tank reactor (CSTR) anaerobic digester was assessed comparing to an energy crop of switchgrass, and an agricultural residue of corn stover. A complete random design was fulfilled to optimize the reaction conditions of dilute alkali pretreatment. The most effective dilute alkali pretreatment conditions for raw CSTR AD fiber were 2% sodium hydroxide, 130 °C, and 3 h. Under these pretreatment conditions, the cellulose concentration of the AD fiber was increased from 34% to 48%. Enzymatic hydrolysis of 10% (dry basis) pretreated AD fiber produced 49.8 g/L glucose, while utilizing 62.6% of the raw cellulose in the AD fiber. The ethanol fermentation on the hydrolysate had an 80.3% ethanol yield. The cellulose utilization efficiencies determined that the CSTR AD fiber was a suitable biorefining feedstock compared to switchgrass and corn stover.     

Microbial monitoring by molecular tools of a two-phase anaerobic bioreactor treating fruit and vegetable wastes

Microbial consortia in a two-phase, anaerobic bioreactor using a mixture of fruit and vegetable wastes were established. Bacterial and archaeal communities obtained by a culture-independent approach based on single strand conformation polymorphism analysis of total 16S rDNA showed the adaptation of the microflora to the process parameters. Throughout the 90 d of the study, the species composition of the bacterial community changed significantly. Bacterial 16S rDNA showed at least 7 different major species with a very prominent one corresponding to a Megasphaera elsdenii whereas bacterial 16S rDNA of a methanization bioreactor showed 10 different major species. After two weeks, Prevotella ruminicola became major and its dominance increased continuously until day 50. After an acid shock at pH 5, the 16S rDNA archaeal patterns in the acidogenic reactor showed two major prominent species corresponding to Methanosphaera stadtmanii and Methanobrevibacter wolinii, a hydrogenotrophic bacterium.