Do municipal wastewater treatment processes produce methane emissions?
Methane emissions from municipal wastewater treatment processes. Environmental Science and Technology 27 (12), 2472e2477.
How is methane produced in the environment?
Fossil fuel production, rice cultivation, biomass burning, and waste management are some of the activities that release methane. In the case of organic waste, it is produced from microbial decomposition of organic matter in the absence of oxygen (Anaerobic decomposition).
What are the activities that release methane?
Fossil fuel production, rice cultivation, biomass burning, and waste management are some of the activities that release methane. In case of organic waste, it is produced from microbial decomposition of organic matter in the absence of oxygen (Anaerobic decomposition).
How is methane used for electric and heat generation?
Digester gas for electric and heat generation with combined heat and power (CHP) Facilities can use recovered methane as fuel to generate electricity and heat in a CHP system using a variety of prime movers, such as reciprocating engines, micro- turbines, and fuel cells.
Which sewage treatment process produces methane as a byproduct?
Anaerobic digestionAnaerobic digestion reduces the volume of the waste, produces methane for use, and provides a by-product that can be used as fertilizer. In addition to animal waste, plant waste from agriculture can be processed by anaerobic digestion.
In which treatment biogas is produced?
During sewage treatment in secondary treatment the biogas is produced in anaerotric sludge digestor have anaerobic bacteria which produce gases like CO2, H2S, CH4.
Does sewage treatment produce methane?
Municipal wastewater treatment plants emit methane. Since methane is a potent greenhouse gas that contributes to climate change, the abatement of the emission is necessary to achieve a more sustainable urban water management.
What are the main steps of treatment of municipal wastewater?
Treatment StepsStep 1: Screening and Pumping. ... Step 2: Grit Removal. ... Step 3: Primary Settling. ... Step 4: Aeration / Activated Sludge. ... Step 5: Secondary Settling. ... Step 6: Filtration. ... Step 7: Disinfection. ... Step 8: Oxygen Uptake.
In which stage of sewage treatment is biogas produced?
The digestion of municipal sewage sludge (MSS) occurs in three basic steps: acidogen, methanogens, and methanogens. During a 30-day digestion period, 80–85% of the biogas is produced in the first 15–18 days.
In which stage of water treatment is biogas produced?
Biogas, when treating municipal waste is released during the fermentation of precipitation in the primary clarifiers and excess activated sludge in the digesters at thermophilic mode of its implementation.
What is thermal hydrolysis process?
Thermal hydrolysis is a process technology applied in wastewater treatment plants with anaerobic digestion. Thermal hydrolysis exposes sewage sludge or other types of wet organic waste to high temperature and pressure. The process is similar to preparing meals using steam.
How is methane gas produced out of wastes?
When MSW is first deposited in a landfill, it undergoes an aerobic (with oxygen) decomposition stage when little methane is generated. Then, typically within less than 1 year, anaerobic conditions are established and methane-producing bacteria begin to decompose the waste and generate methane.
Which treatment method is used in primary wastewater treatment?
There are three basic biological treatment methods: the trickling filter, the activated sludge process, and the oxidation pond. A fourth, less common method is the rotating biological contacter.
What is municipal treatment?
Municipal or domestic waste water treatment is the process of removing contaminants from waste water by using physical, chemical, and biological processes to remove physical, chemical and biological contaminants.
What is secondary treatment of municipal water?
Secondary treatment is the removal of biodegradable organic matter (in solution or suspension) from sewage or similar kinds of wastewater. The aim is to achieve a certain degree of effluent quality in a sewage treatment plant suitable for the intended disposal or reuse option.
Which type of treatment method are used for municipal and industrial wastewater?
Which of the following type of treatment methods are used for municipal and industrial waste waters? Explanation: Slow Rate (SR) systems are the predominant form of land treatment for municipal and industrial waste-water.
How is biogas treated?
In general terms, biogas treatment is accomplished by physico-chemical methods, scrubbing being extensively used for H2S and CO2 removal. However, dilution (venting) has been an extensive disposal method in some small- and medium-size anaerobic plants treating municipal wastewaters.
How biogas is produced?
Biogas is produced when bacteria digest organic matter (biomass) in the absence of oxygen. This process is called anaerobic digestion. It occurs naturally anywhere from the within the digestive system to the depth of effluent ponds and can be reproduced artificially in engineered containers called digesters.
Is biogas produced by aerobic or anaerobic fermentation?
Biogas is produced throughout the anaerobic digestion process. Biogas is a renewable energy source that can be used in a variety of ways.
In which of the following conditions biogas is produced?
Biogas is produced by anaerobic digestion with anaerobic organisms or methanogen inside an anaerobic digester, biodigester or a bioreactor. S), moisture and siloxanes.
What is the effect of methane on wastewater?
Municipal wastewater treatment plants emit methane. Since methane is a potent greenhouse gas that contributes to climate change, the abatement of the emission is necessary to achieve a more sustainable urban water management. This requires thorough knowledge of the amount of methane that is emitted from a plant, ...
What is the methane emissions from the Kralingseveer WWTP?
While the methane emission of the Kortenoord and the Papendrecht WWTP could be mainly attributed to the methane in the influent, the methane emission from the Kralingseveer WWTP was mainly due the anaerobic sludge treatment . This also explains this plant's higher emission in comparison with the Jinan and the Durnham plant, both without anaerobic sludge treatment. 72 ± 23% of the total methane emissions came from the unit processes that are related to the anaerobic digestion facility: the gravitational thickener for the primary sludge, the centrifuge, the buffer tank for the effluent of the digester, the storage tank that contains the dewatered sludge and the methane slip from the gas engines. Therefore, the anaerobic digestion facilities should certainly be taken into account when determining the greenhouse gas footprint of a WWTP.
What are the gases that are released from wastewater treatment plants?
During wastewater treatment, the greenhouse gases carbon dioxide (CO 2 ), methane (CH 4) and nitrous oxide (N 2 O) can be emitted to the atmosphere ( Hofman et al., 2011 ). Carbon dioxide is produced indirectly as a result of fossil fuel combustion to generate the energy required for the operation of the wastewater treatment plant, or it is produced directly during the respiration of organic matter. In the latter case it concerns short-cycle carbon dioxide that does not contribute to increased atmospheric carbon dioxide concentrations. Nitrous oxide is expected to be emitted during biological nitrogen removal from wastewater, through nitrification and subsequent denitrification ( Kampschreur et al., 2009 ). Since nitrous oxide has a global warming potential of 300 CO 2 -equivalents over a 100 year time horizon ( IPCC, 2007 ), even a low emission contributes significantly to a WWTP's greenhouse gas footprint. Not in the least due to its high impact, nitrous oxide emission from wastewater treatment processes recently received a lot of attention. Methane, having a global warming potential of 25 CO 2 -equivalents over a 100 year time horizon, is expected to be formed in the sewer system ( Guisasola et al., 2008) and in those parts of the WWTP where anaerobic conditions prevail. Hitherto, the emission of methane from wastewater treatment received far less attention than the nitrous oxide emission.
Does sludge storage contribute to methane?
From the mass balances, it is evident that sludge storage contributes significantly to the methane emissions. Methane is produced both in the digested sludge buffer tank, as well as in the dewatered sludge storage tank.
Is primary sludge biodegradable?
Primary sludge contains a lot of readily biodegradable matter. Since the gravitary thickener for the primary sludge has a residence time of about one day, since the conditions are anaerobic and since the primary sludge is inoculated with methanogenic bacteria from the sewer, it is perfectly understandable that this is a source of methane, be it less than the other sources ( Table 2 ).
Who funded the research in the Netherlands?
This research was financed by Stichting Toegepast Onderzoek Waterbeheer ( STOWA), the Dutch Foundation for Applied Water Research. The authors are much obliged to Hoogheemraadschap van Schieland en Krimpenerwaard, the Water Board of Schieland and Krimpenerwaard, and to Dmitry Sorokin, who instructed us about the salting-out method. Eveline Volcke is a post-doctoral research fellow of the Research Foundation Flanders (Belgium) (FWO).
Can methane be converted to carbon dioxide?
Dissolved methane which enters an activated sludge tank can either be biologically converted to carbon dioxide and water or it can be stripped. Since methane has a global warming potential of 25 CO 2 -equivalents, conversion of methane to carbon dioxide leads to a smaller greenhouse gas footprint. Therefore, efforts should be made to promote conversion over stripping. In the case of Kralingseveer WWTP, 80% of the dissolved methane entering the plug flow reactor was converted. If this tank would be a CSTR instead of a plug flow, the dissolved methane in the tank would be more diluted. As a result, the driving force for stripping would be smaller, allowing more methane to stay in solution and to be biologically converted. The methane oxidizing capacity of activated sludge could also be applied for the conversion of gaseous methane, provided that the mass transfer of methane from the gas phase to the liquid phase is enhanced, for instance by using the methane containing off-gases in a bubble aeration system instead of surface aeration.
What is the final product of the anaerobic decomposition of organic matter?
Methane is the final product of the anaerobic decomposition of organic matter. The conversion of organic matter to methane (methanogenesis) as a mechanism for energy conservation is exclusively attributed to the archaeal domain. Methane is oxidized by methanotrophic microorganisms using oxygen or alternative terminal electron acceptors. Aerobic methanotrophic bacteria belong to the phyla Proteobacteria and Verrucomicrobia, while anaerobic methane oxidation is also mediated by more recently discovered anaerobic methanotrophs with representatives in both the bacteria and the archaea domains. The anaerobic oxidation of methane is coupled to the reduction of nitrate, nitrite, iron, manganese, sulfate, and organic electron acceptors (e.g., humic substances) as terminal electron acceptors. This review highlights the relevance of methanotrophy in natural and anthropogenically influenced ecosystems, emphasizing the environmental conditions, distribution, function, coexistence , interactions, and the availability of electron acceptors that likely play a key role in regulating their function. A systematic overview of key aspects of ecology, physiology, metabolism, and genomics is crucial to understand the contribution of methanotrophs in the mitigation of methane efflux to the atmosphere. We give significance to the processes under microaerophilic and anaerobic conditions for both aerobic and anaerobic methane oxidizers. In the context of anthropogenically influenced ecosystems, we emphasize the current and potential future applications of methanotrophs from two different angles, namely methane mitigation in wastewater treatment through the application of anaerobic methanotrophs, and the biotechnological applications of aerobic methanotrophs in resource recovery from methane waste streams. Finally, we identify knowledge gaps that may lead to opportunities to harness further the biotechnological benefits of methanotrophs in methane mitigation and for the production of valuable bioproducts enabling a bio-based and circular economy.
What is the solution to remove ammonia from wastewater?
A potential solution for this is a combination of simultaneous ammonia and methane oxidation by anaerobic ammonia-oxidizing (anammox) bacteria and nitrite/nitrate-dependent anaerobic methane oxidizing (N-damo) microorganisms. When applied, these microorganisms will be exposed to oxygen but little is known about the effect of a low concentration of oxygen on a culture containing these microorganisms. In this study, a stable co-culture containing anammox and N-damo microorganisms in a laboratory scale bioreactor was established under oxygen limitation. Membrane inlet mass spectrometry (MIMS) was used to directly measure the in situ simultaneous activity of N-damo, anammox and aerobic ammonia oxidizing microorganisms. In addition, batch tests revealed that the bioreactor also harbored aerobic methanotrophs and anaerobic methanogens. Together with FISH analysis and metagenomics, these results indicate that the combination of N-damo and anammox activity under the continuous supply of limiting oxygen concentrations is feasible and can be implemented for the removal of methane and ammonia from anaerobic digester effluents. Importance Nitrogen in wastewater leads to eutrophication of the receiving water bodies and methane is a potent greenhouse gas; it is therefore important that these are removed from wastewater. A potential solution for the simultaneous removal of nitrogenous compounds and methane is the application of a combination of nitrite/nitrate depended methane oxidation (N-damo) and anammox. In order to do so, it is important to investigate the effect of oxygen on these two anaerobic processes. In this study, we investigate the effect of a continuous oxygen supply on the activity of an anaerobic methane and ammonia oxidizing coculture. The findings presented in this study are important for the potential application of these two microbial processes in wastewater treatment.
What is CH4 in sewers?
Production of methane (CH4), an essential anthropogenic greenhouse gas , from municipal sewer sediment is a problem deserving intensive attention. Based on long-term laboratory batch tests in conjunction with 16s rRNA gene sequencing and metagenomics, this study provides the first detailed assessment of the variable sediment CH4 production in response to different pollution source-associated sewer sediment types and hydrological patterns, while addressing the role of the sediment microbiome. The high CH4-production capability of sanitary sewer sediment is shaped by enriched biologically active substrate and dominated by acetoclastic methanogenesis (genus Methanosaeta). Moreover, it involves syntrophic interactions among fermentation bacteria, hydrogen-producing acetogens and methanogens. Distinct source-associated microbial species, denitrifying bacteria and sulfate-reducing bacteria occur in storm sewer and illicit discharge-associated (IDA) storm sewer sediments. This reveals their insufficient microbial function capabilities to support efficient methanogenesis. Hydrogenotrophic methanogenesis (genus Methanobacterium) prevails in both these sediments. In this context, storm sewer sediment has an extremely low CH4-production capability, while IDA storm sewer sediment still shows significant carbon emission through a possibly unique mechanism. Hydrological connections promote the sewer sediment biodegradability and CH4-production capability. In contrast, hydrological disconnection facilitates the prevalence of acetoclastic methanogenesis, sulfate-reducing enzymes, denitrification enzymes and the sulfur-utilizing chemolithoautotrophic denitrifier, which drastically decreases CH4 production. Turbulent suspension of sediments results in relative stagnation of methanogenesis. This work bridges the knowledge gap and will help to stimulate and guide the resolution of ‘bottom-up’ system-scale carbon budgets and GHG sources, as well as the target CH4 abatement interventions.
What is LCA in wastewater?
This paper presents a critical review of published LCAs related to municipal wastewater management with a focus on developing systematic guidance for researchers and practitioners to conduct LCA studies to inform planning, design, and optimization of wastewater management and infrastructure (wastewater treatment plants, WWTPs; collection and reuse systems; related treatment technologies and policies), and to support the development of new technologies to advance treatment objectives and the sustainability of wastewater management. The paper guides the reader step by step through LCA methodology to make informed decisions on i) the definition of the goal and scope, ii) the selection of the functional unit and system boundaries, iii) the selection of variables to include and their sources to obtain inventories, iv) the identification on the best selection of impact assessment methods, and v) the selection of an effective approach for data interpretation and communication to decision-makers.
What are the effects of wastewater treatment plants?
Despite the benefits of implementing the WWTP, their operations can also cause polluting effects, mainly associated with the emission of greenhouse gases (GHG), among which carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). While contributions to CO2 generation are mainly related to energy consumption within the WWTP boundaries, CH4 and N2O emissions are associated with biological carbon and nitrogen conversion processes, such as methanogenesis, nitrification and denitrification. In this chapter, the role of different processes in GHG production is assessed. Besides, operational strategies to minimize GHG emissions from WWTP are also addressed, including the control of several variables within the plants facilities, such as dissolved oxygen concentration, applied load, temperature, pH, hydraulic and solids retention time. Treatment approaches for GHG streams that are inevitably produced and innovative processes, such as Anammox, Coupled Aerobic-Anoxic Nitrous Decomposition Operation and cocultures of bacteria and microalgae, capable of generating less GHG and allowing better use of wastewater resources, are also described. Finally, the effects of climate change and its associated consequences (e.g., increased rainfall intensity and temperature), on the performance and operation of current wastewater treatment systems are presented.
Is methane a good electron donor?
Using methane as electron donor to biologically reduce these contaminants into nontoxic forms is a promising solution to remediate polluted water, considering that methane is a widely available and inexpensive electron donor. The understanding of methane-based biological reduction processes and the responsible microorganisms has grown in the past decade. This review summarizes the fundamentals of metabolic pathways and microorganisms mediating microbial methane oxidation. Experimental demonstrations of methane as an electron donor to remove oxidized contaminants are summarized, compared, and evaluated. Finally, the review identifies opportunities and unsolved questions that deserve future explorations for broadening understanding of methane oxidation and promoting its practical applications.
Is methane a renewable resource?
Methane is a type of renewable fuel that can generate many types of high value-added chemicals, however, besides heat and power production, there is little methane utilization in most of the wastewater treatment plants (WWTPs) all round the world currently. In this review, the status of methane production performance from WWTPs was firstly investigated. Subsequently, based on the identification and classification of methane oxidizing bacteria (MOB), the key enzymes and metabolic pathway of MOB were presented in depth. Then the production, extraction and purification process of high value-added chemicals, including methanol, ectoine, biofuel, bioplastic, methane protein and extracellular polysaccharides, were introduced in detail, which was conducive to understand the bioconversion process of methane. Finally, the use of methane in wastewater treatment process, including nitrogen removal, emerging contaminants removal as well as resource recovery was extensively explored. These findings could provide guidance in the development of sustainable economy and environment, and facilitate biological methane conversion by using MOB in further attempts.
How is methane emitted from a WWTP?
Methane is emitted from a WWTP after it enters the plantvia stripping from the incoming wastewater, or after it isformed at the plant itself. The influent of a WWTP containsdissolved methane that is formed in the sewer system. Recentstudies indicate that methane formation in sewer systems can
Is primary sludge biodegradable?
Primary sludge contains a lot of readily biodegradable matter.Since the gravitary thickener for the primary sludge hasa residence time of about one day, since the conditions areanaerobic and since the primary sludge is inoculated withmethanogenic bacteria from the sewer, it is perfectlyunderstandable that this is a source of methane, be it less thanthe other sources (Table 2).
How is methane emitted?
Methane is emitted during the handling and treatment of municipal wastewater through the anaerobic decomposition of organic material. Most developed countries rely on centralized aerobic wastewater treatment systems to collect and treat municipal wastewater. These systems produce small amounts of methane emissions, but also large amounts of biosolids that can result in high rates of methane emissions. In developing countries with little or no collection
What is methane produced from?
Methane is emitted during the production and transport of coal, natural gas and oil. Emissions also are produced by the decay of organic matter in municipal solid waste landfills, some livestock manure storage systems, and certain agro-industrial and municipal wastewater treatment systems.
What is aerobic wastewater treatment?
Most developed countries rely on centralized aerobic wastewater treatment systems to collect and treat municipal wastewater. These systems produce small amounts of methane emissions, but also large amounts of biosolids that can result in high rates of methane emissions.
Is methane greater than CO?
While methane persists in the atmosphere for a shorter period of time and is emitted in smaller quantities than CO. 2. , its ability to trap heat in the atmosphere, known as its “global warming potential,” is 21 times greater than that of CO. 2.
Is methane a natural gas?
Unlike other GHGs, methane is the primary component of natural gas and can be converted to usable energy. The reduction of methane therefore serves as a cost-effective method to reduce GHGs and increase energy security, enhance economic growth, improve air quality and improve work safety.
What is methane emitted from?
Methane emission from waste water treatment plants can earn carbon revenue. Methane (CH 4) is emitted from both anthropogenic and natural sources. Fossil fuel production, rice cultivation, biomass burning, and waste management are some of the activities that release methane. In the case of organic waste, it is produced from microbial decomposition ...
What are some activities that release methane?
Fossil fuel production, rice cultivation, biomass burning, and waste management are some of the activities that release methane. In the case of organic waste, it is produced from microbial decomposition of organic matter in the absence of oxygen (Anaerobic decomposition).
How can methane be avoided?
Methane emissions can be avoided, however, by treating the wastewater and the associated sludge under aerobic conditions or by capturing methane released under anaerobic conditions. Projects with technology that can capture methane from ...
Where is wastewater treated?
Wastewater from domestic (municipal sewage) and industrial sources are treated in municipal sewage treatment facilities and private effluent treatment plants (ETPs). If the wastewater contains loads of organic constituents (with high Chemical Oxygen Demand- COD) then it is treated anaerobically.
How does anaerobic bacteria help the environment?
Within this suitable environment, anaerobic bacteria grow rapidly and help in the breakdown of the organic compounds present in the wastewater. This consequently leads to methane generation from the organic content of the wastewater which gets released into the atmosphere. Covered anaerobic digesters (GHG emission reduction project activity in ...
Why should biogas be treated?
Raw biogas should be treated to prevent corrosionof installed equipment or to achieve adequatequality standards for use as a natural gas substitu-te or transport fuel. An overview of available tech-niques for biogas treatment is provided in Table 6.
How do fuel cells work?
Fuel cells make use of direct electrochemical con-version of the fuel with oxygen to generate elec-tricity and heat with near-zero emissions. The fuel(methane in the case of biogas) is converted tohydrogen by the action of a catalyst or high tem-perature steam reforming. The H2is then electro-chemically converted to electricity and heat.Water and CO2are the main by-products. Thepotential electrical efficiency is > 50% while thethermal efficiency is approx. 35%. For utilisationof biogas two fuel cell types are most relevant forthe near future. Phosphoric acid fuel cells (PAFC)are at present applied in a number of 200 kW to2 MW power plants operating on natural gas witha practical electrical efficiency of 41% [46]. ThePAFC operates at approx. 200 ºC which allowsusable heat recovery. Utilisation of biogas in aPAFC requires near-complete removal of sulphi-des and halogenated compounds [46], [50]. InJapan a 200 kWe PAFC is used in a brewery forconversion of biogas from wastewater effluent[51]. Before entering the fuel cell the biogas ispurified in a pre-treatment section composed of adesulphuriser, an ammonia/salt removing unit, abuffer tank and a gas analyser. Impurities are ade-quately removed while at the same time CO2isremoved from the gas. The overall conversion effi-ciency (electricity + heat) is 80% [51]. SolidOxide Fuel Cells (SOFC) operate at temperatures> 900 ºC. The SOFC has a relatively high toleran-ce for impurities, although it also requires near-complete removal of sulphides and halogens. Thehigh operating temperature allows direct methaneconversion and recovery of high temperatureheat. The attainable electrical efficiency on naturalgas is > 40%. In The Netherlands the utilisation ofbiogas from animal manure in an SOFC system iscurrently being explored at farm scale [52]. The utilisation of biogas in fuel cells is an impor-tant strategy to enhance the efficiency of electrici-ty generation. A substantial cost reduction of fuelcells is however required for large-scale applica-tion. The conversion of fermentation gases in fuelcells is being explored in ‘BFCNet’: ‘Network onBiomass Fermentation Towards Usage in FuelCells’ [53]. The objectives of BFCNet includeR&D and demonstration, and the development ofstandards on EU level.
What is agricultural waste?
Agricultural wastes contain remains of the processsuch as cut flowers, bulbs, verge grass, potatoes,chicory, ensilaged weed etc. This type of waste issuitable for re-use after fermentation, as the typeof waste collected is 'cleaner' than ordinary VFY[34].
What is anaerobic digestion?
Anaerobic digestion is an established technology for the treatment of wastes and wastewater. The finalproduct is biogas: a mixture of methane (55-75 vol%) and carbon dioxide (25-45 vol%) that can be usedfor heating, upgrading to natural gas quality or co-generation of electricity and heat. Digestion installa-tions are technologically simple with low energy and space requirements. Anaerobic treatment systemsare divided into 'high-rate' systems involving biomass retention and 'low-rate' systems without biomassretention. High-rate systems are characterised by a relatively short hydraulic retention time but longsludge retention time and can be used to treat many types of wastewater. Low-rate systems are general-ly used to digest slurries and solid wastes and are characterised by a long hydraulic retention time, equalto the sludge retention time. The biogas yield varies with the type and concentration of the feedstockand process conditions. For the organic fraction of municipal solid waste and animal manure biogasyields of 80-200 m3per tonne and 2-45 m3 per m3are reported, respectively. Co-digestion is an impor-tant factor for improving reactor efficiency and economic feasibility. In The Netherlands co-digestion isonly allowed for a limited range of substrates, due to legislation on the use of digested substrate in agri-culture. Maximising the sale of all usable co-products will improve the economic merits of anaerobictreatment. Furthermore, financial incentives for renewable energy production will enhance the compe-titiveness of anaerobic digestion versus aerobic composting. Anaerobic digestion systems currently ope-rational in Europe have a total capacity of 1,500 MW, while the potential deployment in 2010 is esti-mated at 5,300-6,300 MW. Worldwide a capacity up to 20,000 MW could be realised by 2010.Environmental pressures to improve waste management and production of sustainable energy as well asimproving the technology’s economics will contribute to broader application.
Is industrial wastewater heterogeneous?
Industrial wastewater is heterogeneous, both incomposition and volume. Effluents from the Food& Beverage (F&B) industry contain the highestconcentration of organic compounds [41].Anaerobic wastewater treatment is widely appliedin this branch of industry as in the Pulp and Paperindustry, as is shown in Table 3 and Figure 14.
Is anaerobic digestion a technique?
Anaerobic digestion is a proven technique and atpresent applied to a variety of waste (water) streams but world wide application is still limitedand a large potential energy source is being ne-glected. Moreover some potential sources, whichare now treated otherwise, are an excellent sub-strate for anaerobic treatment and could contribu-te to renewable energy production rather thanconsuming energy during treatment.
