Solids removal in upflow anaerobic reactors,a review

This desk study deals with the mechanisms and parameters affecting particles separation from wastewater in mainly upflow anaerobic reactors. Despite the fact that the functioning of upflow anaerobic sludge blanket (UASB) systems depends on both physical parameters and biological processes, the physical parameters have been barely reported in the literature. The reason is that the underlying mechanisms are very complex and depend on various interrelated parameters. In addition, the lack of a serious attempt to gather the entire physical theme into one picture has resulted in just a superficial understanding of this field of science. Better understanding of the interaction and role of these parameters is essential for the development of anaerobic treatment technologies. In this study, the various parameters that might affect the solid liquid separation process by filtration through the sludge bed of a UASB have been elaborated. These parameters have been classified into (1) reactor operational conditions (temperature, organic loading rate, hydraulic retention time and upflow velocity), (2) influent characteristics (influent concentration, influent particle size and influent particle charge) and (3) sludge bed characteristics (particle size distribution, extracellular polymeric substances, and charge). The overall output of this study includes (1) a literature review, (2) structuring of this field of science, and (3) highlighting fields where research is needed.     

Anaerobic Processes as the Core Technology for Sustainable Domestic Wastewater Treatment: Consolidated Applications, New Trends, Perspectives, and Challenges

Anaerobic digesters have been responsible for the removal of large fraction of organic matter (mineralization of waste sludge) in conventional aerobic sewage treatment plants since the early years of domestic sewage treatment (DST). Attention on the anaerobic technology for improving the sustainability of sewage treatment has been paid mainly after the energy crisis in the 1970s. The successful use of anaerobic reactors (especially up-flow anaerobic sludge blanket (UASB) reactors) for the treatment of raw domestic sewage in tropical and sub-tropical regions (where ambient temperatures are not restrictive for anaerobic digestion) opened the opportunity to substitute the aerobic processes for the anaerobic technology in removal of the influent organic matter. Despite the success, effluents from anaerobic reactors treating domestic sewage require post-treatment in order to achieve the emission standards prevailing in most countries. Initially, the composition of this effluent rich in reduced compounds has required the adoption of post-treatment (mainly aerobic) systems able to remove the undesirable constituents. Currently, however, a wealth of information obtained on biological and physical-chemical processes related to the recovery or removal of nitrogen, phosphorus and sulfur compounds creates the opportunity for new treatment systems. The design of DST plant with the anaerobic reactor as core unit coupled to the pre- and post-treatment systems in order to promote the recovery of resources and the polishing of effluent quality can improve the sustainability of treatment systems. This paper presents a broader view on the possible applications of anaerobic treatment systems not only for organic matter removal but also for resources recovery aiming at the improvement of the sustainability of DST.     

Winery wastewater treatment: a critical overview of advanced biological processes

Wine production is one of the leading sectors of the food processing industry. The wine industry produces a large amount of wastewater characterized by a high strength in terms of organic pollution and large variability throughout the year. Most of the organic matter is soluble and easily biodegradable. On the other hand, nitrogen and phosphorous are lacking. The aerobic and anaerobic processes are largely applied for winery wastewater treatment because they can quickly react to changes in the organic loading. This review analyzes e applied biological systems, considering both aerobic and anaerobic processes, and different reactor configurations. The performances of different biological processes are evaluated in terms of operational conditions (organic loading rate and hydraulic retention time). Aerobic processes can guarantee chemical oxygen demand removal up to 98% for organic loading rates of some 1-2?kg of chemical oxygen demand m^?3d^?1 but requires good aeration systems to supply the required process oxygen. The management cost of these processes could be high considering the power density in the range 60-70?W m^?3_reactor and that nutrients should be added to support biomass growth. On the other hand, anaerobic processes are able to face high organic loads with low running costs, but COD removal is generally limited to 90%. Combination of the two treatment systems (anaerobic followed by aerobic) could reduce management costs and meet high discharge standards.     

The mass—Energy balance of anaerobic methane production

A theory was developed for the mass and energy balance of microbial processes, with special reference to the anaerobic production of methane. Interrelations of the bioengineering parameters of the process were delineated substrate quality, biodegrability and biological effciency of anaerobic processing of complex organic waste substrates. Application of the method is demonstrated on practical examples.     

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。     

Anaerobic degradation of adsorbable organic halides (AOX) from pulp and paper industry wastewater

Adsorbable organic halides (AOX) are generated in the pulp and paper industry during the bleaching process. These compounds are formed as a result of reaction between residual lignin from wood fibres and chlorine/chlorine compounds used for bleaching. Many of these compounds are recalcitrant and have long half-life periods. Some of them show a tendency to bioaccumulate while some are proven carcinogens and mutagens. Hence, it is necessary to remove or degrade these compounds from wastewater. Physical, chemical and electrochemical methods reported to remove AOX compounds are not economically viable. Different types of aerobic, anaerobic and combined biological treatment processes have been developed for treatment of pulp and paper industry wastewater. Maximum dechlorination is found to occur under anaerobic conditions. However, as these processes are designed specifically for reducing COD and BOD of wastewater, they do not ensure complete removal of AOX. This paper reviews the anaerobic biological treatments developed for pulp and paper industry wastewater and also reviews the specific micro-organisms reported to degrade AOX compounds under anaerobic conditions, their nutritional and biochemical requirements. It is imperative to consider these specific micro-organisms while designing an anaerobic treatment for efficient removal of AOX.     

微生物组学及其在厌氧消化中的研究进展

我国每年产生大量的有机废弃物,如果处置不当将会对生态、气候以及人类健康造成重大影响。厌氧消化是一种可靠的、绿色的、可持续的有机废弃物处理方式,但由于缺乏准确有效的监测手段,厌氧消化微观过程常常被视为“黑盒”。随着微生物组学的发展,学者们在菌群与运行参数关联性分析、代谢途径分析等方面有了更深入的认识。本文从“三阶段、四菌群”的厌氧消化过程出发,介绍了常用微生物组学的类型,包括:16S rRNA基因组、宏基因组、宏转录组和宏蛋白组;详细阐述了物种组成分析、α多样性分析、OTU相似性分析以及多元统计学分析等6种常用的微生物群落生物信息学分析方法;系统回顾了厌氧消化过程的微生物学研究进展,以期能为分析厌氧消化的微生物群落结构和功能、开发新的厌氧消化工艺和技术提供支持。     

Substrate utilization kinetic model for biological treatment process

The applicability of Contois' kinetic equation to aerobic and anaerobic treatments of organic wastes is investigated. A refractory coefficient to account for the nonbiodegradable portion of the organic substrates in the digester is incorporated into the kinetic equation. The kinetic equation is applied to the data for aerobic digestions of organic substrates and for anaerobic treatment of dairy wastes. They all show a very good fit of the kinetic equation to the data. Furthermore, the kinetic parameters and the refractory coefficients are shown to be independent of influent organic substrate concentration. This study confirms previous reports that the effluent quality of biological treatment systems for organic wastes depends on influent organic waste concentration. The effect of temperature on the kinetic parameters and the refractory coefficient for anaerobic treatment of sewage sludge are studied. It shows that the kinetic parameters vary with temperature, while the refractory coefficient remains fairly constant. Equations to predict biodegradable treatment efficiency and volumetric substrate utilization rate are also briefly discussed.     

Food waste valorization via anaerobic processes: a review

The increasing production of food waste worldwide and new international regulations call for the development of new technologies to treat this biowaste. Anaerobic processes are able to treat efficiently organic wastes, producing at the same time different value-added compounds. In addition, due to the lower costs and environmental impacts associated with these processes when compared to other options, they are among the most promising technologies for food waste treatment. This article reviews the state-of-the-art dealing with treatment of food waste by anaerobic processes, with emphasis on the most recent research carried out. The different processes that are assessed are anaerobic digestion for methane production, anaerobic fermentation for hydrogen and/or volatile fatty acids production and 2-stage systems. The primary issues associated with each alternative are presented, paying special attention to accumulation of ammonia and volatile fatty acids in the reactor. In addition, the latest developments to overcome the complications of each system are also described, focusing on how they improve its stability and performance. Moreover, the relevant economic and environmental research has also been reviewed, including several life cycle analyses that compare anaerobic processes with other technologies used for food waste treatment. Different case studies are also presented. Finally, recommendations for future research for the anaerobic processes studied and options for process integration are discussed. Moving towards the idea of a circular economy, a potential biorefinery for food waste valorization is also proposed.     

Biological nutrients removal from the supernatant originating from the anaerobic digestion of the organic fraction of municipal solid waste

Abstract

This study critically evaluates the biological processes and techniques applied to remove nitrogen and phosphorus from the anaerobic supernatant produced from the treatment of the organic fraction of municipal solid waste (OFMSW) and from its co-digestion with other biodegradable organic waste (BOW) streams. The wide application of anaerobic digestion for the treatment of several organic waste streams results in the production of high quantities of anaerobic effluents. Such effluents are characterized by high nutrient content, because organic and particulate nitrogen and phosphorus are hydrolyzed in the anaerobic digestion process. Consequently, adequate post-treatment is required in order to comply with the existing land application and discharge legislation in the European Union countries. This may include physicochemical and biological processes, with the latter being more advantageous due to their lower cost. Nitrogen removal is accomplished through the conventional nitrification/denitrification, nitritation/denitritation and the complete autotrophic nitrogen removal process; the latter is accomplished by nitritation coupled with the anoxic ammonium oxidation process. As anaerobic digestion effluents are characterized by low COD/TKN ratio, conventional denitrification/nitrification is not an attractive option; short-cut nitrogen removal processes are more promising. Both suspended and attached growth processes have been employed to treat the anaerobic supernatant. Specifically, the sequencing batch reactor, the membrane bioreactor, the conventional activated sludge and the moving bed biofilm reactor processes have been investigated. Physicochemical phosphorus removal via struvite precipitation has been extensively examined. Enhanced biological phosphorus removal from the anaerobic supernatant can take place through the sequencing anaerobic/aerobic process. More recently, denitrifying phosphorus removal via nitrite or nitrate has been explored. The removal of phosphorus from the anaerobic supernatant of OFMSW is an interesting research topic that has not yet been explored. At the moment, standardization in the design of facilities that treat anaerobic supernatant produced from the treatment of OFMSW is still under development. To move toward this direction, it is first necessary to assess the performance of alternative treatment options. It study concentrates existing data regarding the characteristics of the anaerobic supernatant produced from the treatment of OFMSW and from their co-digestion with other BOW. This provides data documenting the effect of the anaerobic digestion operating conditions on the supernatant quality and critically evaluates alternative options for the post-treatment of the liquid fraction produced from the anaerobic digestion process.     

A microbiological study of an underground gas storage in the process of gas extraction

The numbers of microorganisms belonging to ecologically significant groups and the rates of terminal microbial processes of sulfate reduction and methanogenesis were determined in the liquid phase of an underground gas storage (UGS) in the period of gas extraction. The total number of microorganisms in water samples from the operation and injection wells reached 2.1 x 10(6) cells/ml. Aerobic organotrophs (including hydrocarbon- and oil-oxidizing ones) and various anaerobic microorganisms (fermenting bacteria, methanogens, acetogens, sulfate-, nitrate-, and iron-reducing bacteria) were constituent parts of the community. The radioisotopic method showed that, in all the UGS units, the terminal stages of organic matter decomposition included sulfate reduction and methanogenesis, with the maximal rate of these processes recorded in the aqueous phase of above-ground technological equipment which the gas enters from the operation wells. A comparative analysis by these parameters of different anaerobic ecotopes, including natural hydrocarbon fields, allows us to assess the rate of these processes in the UGS as high throughout the annual cycle of its operation. The data obtained indicate the existence in the UGS of a bacterial community that is unique in its diversity and metabolic capacities and able to make a certain contribution to the geochemistry of organic and inorganic compounds in the natural and technogenic ecosystem of the UGS and thus influence the industrial gas composition.     

Mass-energy balance for microbial product synthesis-biochemical and cultural aspects

Interrelations between the rates of the product synthesis, cell biomass growth, respiration, and organic substrate consumption have been studied by the mass-energy balance method. This method is based on the utilization of a special unit of substance reducity, namely redoxon. Biochemical parameters have been found which are involved in these interrelations and which describe the processes of high-energy bond gain and energy expenditure during metabolism. In order to find these, the separation of the whole metabolism into several partial metabolisms has been applied. Equations have been obtained describing the dependences of the product yield and process specific productivity on the biochemical parameters and two macroscopic rates (e.g., rates of dilution and substrate consumption). Both aerobic and anaerobic product syntheses have been considered. The estimate of the upper limit of process productivity has been obtained. Mechanisms of the influence of the producer's intracellular characteristics on the rates of physiological processes and the culture productivity are discussed.     

A microbiological study of an underground gas storage in the process of gas extraction

The numbers of microorganisms belonging to ecologically significant groups and the rates of terminal microbial processes of sulfate reduction and methanogenesis were determined in the liquid phase of an underground gas storage (UGS) in the period of gas extraction. The total number of microorganisms in water samples from the operation and injection wells reached 2.1 × 10⁶ cells/ml. Aerobic organotrophs (including hydrocarbon-and oil-oxidizing ones) and various anaerobic microorganisms (fermenting bacteria, methanogens, acetogens, sulfate-, nitrate-, and iron-reducing bacteria) were constituent parts of the community. The radioisotopic method showed that, in all the UGS units, the terminal stages of organic matter decomposition included sulfate reduction and methanogenesis, with the maximal rate of these processes recorded in the aqueous phase of above-ground technological equipment which the gas enters from the operation wells. A comparative analysis by these parameters of different anaerobic ecotopes, including natural hydrocarbon fields, allows us to assess the rate of these processes in the UGS as high throughout the annual cycle of its operation. The data obtained indicate the existence in the UGS of a bacterial community that is unique in its diversity and metabolic capacities and able to make a certain contribution to the geochemistry of organic and inorganic compounds in the natural and technogenic ecosystem of the UGS and thus influence the industrial gas composition.     

Contributions to the ecology of halophytes: D.N. Sen and K.S. Rajpurohit (Editors), Tasks for Vegetation Science. Vol. 2, Junk,The Hague, 1982, 272 pp., US$69.50, Dfl. 165, ISBN 90-6193-942-9, ISBN 90-6193-897-X (series).

Mature tissue and particulate organic decomposition products of the submersed aquatic plant Myriophyllum heterophyllum Michx were analysed by Curie-point pyrolysis low voltage ionisation mass spectrometry. Decomposition was performed under controlled aerobic and anaerobic conditions at 10°C and 25°C for 180 days. Particulate components were analysed at 0, 2, 4, 10, 24, 48, 90 and 180-day intervals.The composition of the native plant material changed markedly during the decomposition period, as was demonstrated qualitatively and quantitatively by factor analysis of the pyrolysis mass spectrometric data.The particulate residues were characterized by increasing amounts of proteins and N-acetyl aminosugars, especially at the longer decomposition intervals.Decreasing weight loss correlated with an increasing presence of these polymers in or on the decomposing plant structural matter. This process took place faster at the higher decomposition temperatures. The anaerobic processes were more sensitive to temperature than the aerobic processes.     

Modelling of the mesophilic anaerobic co-digestion of olive mill wastewater with olive mill solid waste using anaerobic digestion model No. 1 (ADM1)

The anaerobic digestion model No. 1 (ADM1), conceived by the international water association (IWA) task group for mathematical modelling of anaerobic digestion processes is a structured generic model which includes multiples steps describing biochemical and physicochemical processes encountered in the anaerobic degradation of complex organic substrates and a common platform for further model enhancement and validation of dynamic simulations for a variety of anaerobic processes. In this study the ADM1 model was modified and applied to simulate the mesophilic anaerobic co-digestion of olive mill wastewater (OMW) with olive mill solid waste (OMSW). The ADM1 equations were coded and implemented using the simulation software package MATLAB/Simulink. The most sensitive parameters were calibrated and validated using updated experimental data of our previous work. The results indicated that the ADM1 model could simulate with good accuracy: gas flows, methane and carbon-dioxide contents, pH and total volatile fatty acids (TVFA) concentrations of effluents for various feed concentrations digested at different hydraulic retention times (HRTs) and especially at HRTs of 36 and 24 days. Furthermore, effluent alkalinity and ammonium nitrogen were successfully predicted by the model at HRTs of 12 and 24 days for some feed concentrations.     

Fundamental Mechanisms of Phosphate Removal by Anaerobic/Aerobic Activated Sludge in Treating Municipal Wastewater

Acetate is thought to be an important substrate for phosphate removal in anaerobic/aerobic activated sludge (AS) processes. The acetate content in municipal wastewater is low, and the main organic compounds in such wastewater are particulate organic matters (POMs) that are converted to endogenous substrates in AS processes when municipal wastewater is introduced into AS reactors. The question which then arises is which substrate, acetate or POM, is important for phosphate removal in full‐scale AS plants. The rates of phosphate release and substrate uptake were determined using AS harvested from a full‐scale anaerobic/aerobic AS plant and also AS acclimated to peptone under alternate anaerobic and aerobic conditions for 26 months. The rate of phosphate release upon POM addition per AS concentration per unit of time was about 0.84 mg PO₄‐P/(g MLSS·h) irrespective of the wastewater quality. This value was about 0.05 in the case of AS acclimated to peptone for 26 months. When the AS concentration is 2.5 g/L and the mixed liquor retention time is 2 h in the anaerobic zone, about 4.2 mg/L PO₄‐P is released upon POM addition. Hence, phosphate can be removed from municipal wastewater using full‐scale AS plants running under these conditions.     

Monitoring and control of an anaerobic upflow fixed-bed reactor for high-loading-rate operation and rejection of disturbances

A new control strategy has been introduced for operating anaerobic digestion processes efficiently at high load. The control system includes a cascade controller embedded into a rule-based supervisory system based on extremum-seeking control. Three process parameters, considered to be the most realistic variables for monitoring of the bioprocess, were selected (pH, biogas production rate, and the difference between the actual biogas flow and its setpoint). The control system examines these variables and varies the organic load by manipulating the influent flow. Good control performance was achieved during the start-up, during steady-state running operations, and during rejection of disturbances. The main advantages of this control approach can be attributed to its ability to adjust control parameters automatically, both for high-load operation and for rejection of disturbances. Furthermore, the influent flow can be tuned automatically according to variations in organic matter in the feed without the characteristics of the influent being considered.     

A dynamic phosphate budget model for a eutrophic lake

The relations between the external nutrient loading of lakes, recycling through sediments and the resulting productivity are complicated by feed-back mechanisms, seasonal variations and trends. Simulation is a useful tool for the identification of controlling factors and the assessment of the effects of management measures, supplementary to experimental research. The model variables in our dynamic phosphate budget model include inorganic and organic particulate phosphate and dissolved o-phosphate, in both sediments and overlying water. Sediments may be aerobic or anaerobic, depending on topography, temperature and composition. The major processes described are primary production, mineralisation, sedimentation, adsorption and diffusion. Several model parameters have been estimated directly for Lake Brielle (Netherlands). The sediment dilution rate, the extent of anaerobic conditions and the number and character of adsorption sites are important controlling factors.     

Sulfate reduction,methanogenesis, and methane oxidation in the Holocene sediments of the Vyborg Bay,Baltic Sea

Methane content and the rates of microbial processes of the carbon and sulfur cycles were determined for the sediments of the Vyborg Bay, Baltic Sea. Formation of the gas-bearing surface sediments in the Vyborg Bay was found to depend on the activity of the modern microbial processes of the transformation of organic matter, resulting in production of significant amounts of reduced gases (methane and hydrogen sulfide). Rapid consumption of sulfate in the course of sulfate reduction coupled to organic matter decomposition both suppressed anaerobic oxidation of methane and promoted microbial methanogenesis. The gasbearing sediments of this area therefore become a source of methane, and methane concentration in the near-bottom water increases significantly.