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Household biogas digesters for faecesFigure 1: Hanging toiletsFigure 2: Toilet discharging into thebackwatersIn order to reduce the environmental problems andhealth hazards of inhabitants, caused by the lack ofappropriate sanitation infrastructure and municipalsolid waste management, the local Kerala based NGOBIOTECH assisted the community with the endeavourto improve 150 toilets linking them to biogas digestersas well as setting up 650 digesters for food waste fromkitchens. Main objective, besides reducing environmentaldegradation of the backwaters, was to hereby generatebiogas for cooking, as well as produce organic fertilizerfor the families and their gardens.discussions with the family operating the biogas plantto obtain an idea on how the owners and users operatethe facility and to engage with them on clarifying theobjectives of the study and designing specific proceduresfor data collection. The study tried to limit its influenceon usual practice, nevertheless one has to assume thatthe influence of having a researcher on site regularly mayin fact influence normal practice of the family. The biogasplant was monitored during an 8 week period regardingthe following aspects: Analysis of feedstock in terms of mass andcharacteristics Analysis of effluent in terms of volume andcomposition Measurement of gas production and gascompositionIn collaboration with BIOTECH, Eawag/Sandec conductedan assessment of the currently implemented householdscale biogas plants in 2010 to evaluate the strengthsand weaknesses and establish recommendations forimprovement. The assessment comprised a technicalperformance evaluation, economic feasibility and socialacceptance (Estoppey, 2010). As there is a overall generallack of well documented information on the performanceof household biogas systems using faeces and solidwaste in low and middle income countries, the technicalassessment evaluated two reactors; one fed only withorganic solid waste (called: Food Waste Biogas Plant)and the other fed with food waste but also connected tothe toilet (called: Toilet Linked Biogas Plant). Parameterswhich were monitored during the technical assessmentcomprised: gas production, treatment efficiency andeffluent quality.The users were asked to collect their kitchen wastedaily in buckets, separating the solid food waste fromthe organic waste water (waste water that originatesin the kitchen). This waste was then sorted on five daysper week to better characterise the waste amounts andtype. On the two other remaining days, the families wereasked to write down the estimated quantities of whatthey fed into the biogas plant. Those estimations werenot used in the calculations but rather allowed a crosscheck or unusual quantities of waste. After sampling,the feedstock samples were homogenised with a kitchenblender at the BIOTECH offices for about 30 minutes.Smaller portions of these homogenized samples werethen analysed for Total Solids (TS) and Volatile Solids (VS)at “Cochin University of Science and Technology”.This present paper focuses on the results related tothe toilet linked biogas plant and discusses the resultswith regard to the suitability as a sustainable sanitationoption.MethodsFor estimating toilet waste, the users were asked to noteon a sheet of papers if he/she urinated, defecated ordid both, as well as if he/she used the 4L toilet flush ornot. Once a week, over a period of 24 hours, the familycollected the black water (urine, faeces and flushingUnderstanding the functionality of the biogas plantand assessing key parameters was a challenging task inthe local context. A first period of two weeks entailedSustainable Sanitation Practice5Issue 9/2011

Household biogas digesters for faecesFigure 3: Cross section and top view of a toilet linked biogas plantWhereas the toilet waste is directly flushed into thedigester (using either pour flush or full flush toilets), thefood waste is first cut into small pieces, mixed with waterand then fed into the digester through a separate inlet.The generated biogas is used directly for cooking withoutany gas cleaning step. Merely the condensed water inthe gas pipe is removed regularly. The effluent from thereactor, the digestate, is either used as fertilizer in thegarden, but more often is directly discharged into thebackwaters without any further treatment.water) by connecting the toilet to a 10 litre bucket whichwas emptied regularly into an 80 litre storage tank.This tank then served as sampling point, where afterstrong stirring and mixing 500 ml of liquid was collectedfor analysis. In addition, two samples of black waterwere taken using sterile tubes of 15ml for pathogensmeasurements.To gain information on the economic feasibility and thesocio-cultural aspects of the new sanitation system, ahousehold survey was conducted with 17 owners of atoilet linked biogas plant and 10 owners of a food wastebiogas plant.The total costs of such a biogas system amounts up toaround 600 US . In the past subsidies were granted fromthe Central Government, the Kerala Local Governmentand the Kumbalangi basic unit of administration(Panchayat). The financing system for constructioninvolved the families paying for the cement (100 kg), thebricks (25 normal and 8 cement ones), the excavationof the pit and the cow dung (100 kg) to inoculate thesystem. In total the contribution of a family was around120 US . However, for all biogas systems installed since2010 a new design and new materials were establishedas standard. These are prefabricated portable plantsentirely made of fibreglass reinforced plastic. Althoughthis makes it significantly easier to construct a biogassystems it also makes the system more expensive (about800 US per unit). At the same time the governmentalsubsidies decreased considerably and the costs forinstalling a biogas plant amounts to 600 US per family.This high cost makes the system unaffordable for mostfamilies.Specifications of biogas system and costThe domestic toilet linked biogas plants installed by BIOTECHall have a floating dome design and consist of a digestertank (A), a gasholder drum (B), a food waste inlet (C), a toiletwaste inlet (D), an effluent outlet (E) and a biogas outlet (F).The digester tank with an external diameter of 142 cm ismade of prefabricated reinforced cement concrete (RCC)elements fitted together in an excavated pit. An orthogonalbarrier (a1) of 70 cm height separates the lower part ofthe tank into two compartments in order to increase theretention time of solid particles.The gasholder is made of fibreglass reinforced plastic (FRP).A metallic central rod as axis (a3) serves as a guide frame forthe gasholder and prevents the gasholder from tilting whenthe gasholder is elevated (i.e. full). The water jacket (a2) isa newer development by BIOTECH. It provides water filledguidance groove for the lifting and descending gasholderand avoids contact between digesting material andatmosphere thus also avoiding gas losses. In the stagnantwater of the water jacket a few drops of kerosene are addedto avoid breeding of mosquitoes. In order to increase thegas pressure, a stone of 20 kg is put onto the gasholder (b1).Sustainable Sanitation PracticeResults and DiscussionTechnical performanceThe monitoring of the toilet linked biogas plant (TLBP)showed that the system is working satisfactorilyregarding its technical performance. The systemreceives an average of 3.6 kg waste per day, consistingof faeces and kitchen waste, whereby these are mainly6Issue 9/2011

Household biogas digesters for faecesFigure 4: Treatment efficiency of TLBP plantrice leftovers. Interestingly, the owner of the monitoredfacility also collects kitchen waste from three otherfamilies to increase the gas production. The liquid wasteadded to the reactor amounts to an average of 36.5 litresper day. Half of this liquid waste is flushing water withoutany or very little organic content and the rest is urine andgreywater from the cooking of rice.concentration of E. Coli and total Coliforms with theWHO-guidelines for “safe use of wastewater, excretaand greywater” (WHO, 2006) would only allow forrestricted irrigation. Thus the families should be carefuland only use the effluent on crops that are cookedbefore consumption. In addition, contact with mouthor wounds have to be avoided and hands must bewashed after contact. Furthermore the effluent shouldbe applied directly on the soil as close to the roots aspossible and not be sprayed over the crops. Appropriateuse includes irrigation of banana and coconut trees.The high amount of flushing water in the TLBP leadsto a very low concentration of volatile fatty acids of 82mg/l and a low organic loading rate of 0.58 kgVS/m3.Nevertheless the average hydraulic retention time is 37days which corresponds to the range as recommendedin literature. The treatment efficiency of the plant can beregarded as good showing a high reduction in total solids(TS), volatile solids (VS) and chemical oxygen demand(COD) (Figure 4). Of the generated biogas the methanecontent was always stable at around 60%. The averagedaily biogas production of 690 litres is sufficient to cookthe main dishes of a family. The pH remains stable at 6.9and thus is in the optimal range for anaerobic digestionwhich lies between 6.7 - 7.5. The temperature insidethe digester was stable at around 29 C , which is slightlybelow the optimum of 32-42 C for mesophilic conditions(Deublein and Steinhauser, 2008).A household survey revealed that several familiesdischarge the effluent directly into the backwaters(Figure 5). Given the environmental standards fordischarge of environmental pollutants by the Ministryof Environment & Forests (Government of India) andthe measured values for CODtot and Ntot of the effluent,it is obvious that the environmental standards areexceeded and an additional treatment step would beneeded (e.g. filter bed) to further reduce the organicload of the effluent before safe discharge.Quality of effluentThe effluent from the biogas plant (i.e. the digestate)is very high in water content as most solid parts aredecomposed during digestion. The nutrient content inthe effluent shows nitrogen values of Ntot 871 mgN/l,potassium of Ktot 766 mgK/l and phosphorus of Ptot 61 mgP/l. However, it is difficult to evaluate its qualityas a liquid fertilizer as this depends very much on theplants where the fertilizer is applied.Figure 5: Biogas plant discharging directlyinto the backwatersThe reduction in pathogen content was foundto be very high, but nevertheless comparing theSustainable Sanitation Practice7Issue 9/2011

Household biogas digesters for faecesRegarding the use of biogas which derives from faecesfor cooking, only one family had objections. Theodorous effluent however was of major concern; anissue which was not raised with families only feedingkitchen waste into their digester.Economic feasibilityWith the change in materials used for the biogasreactor and the decrease in governmental subsidies,the investment costs of a biogas reactor for a familyamounts to approximately 600 US . This is a significantincrease compared to a cost per family of 120 US when the initiative could still benefit from subsidiesand cheaper material design. The amount of 600US corresponds to about five monthly salaries of anaverage labourer on Kumbalangi. Costs for operationand maintenance however are comparatively low,the system proves to be very robust and low inmaintenance. About 3 US per year have to be investedto replace broken pieces (stove knob, valve lever ongas holder).The majority of families are pleased with the amountsof biogas they can obtain on a daily basis. All use anadditional cooking fuel when they want to cook fasteror when they need a second stove.User knowledge of operation and maintenanceinstructions were lacking. None of the familiesinterviewed were aware of the recommendedmaximum daily load or on the recommended dilutionof the feedstock. Only half of the users were awarethat they shouldn’t use chemicals to clean the toilets.Despite of these difficulties and challenges, all biogasplants were working well and the gas production wassatisfactory.In terms of financial benefits, the generated biogas cansubstitute traditional cooking fuel, mostly firewoodand liquefied petroleum gas (LPG). The savings fromreplacing firewood and LPG with biogas accountfor about 40 US per year. The 690 l/d of biogas areenough to cook for approximately 3h and 15min perday and thus allows preparation of the main dishes.The families however can not completely rely solely onbiogas as they will still need a second stove for cooking.ConclusionsIn principle biogas sanitation systems for thehousehold level could be an appropriate sanitationtechnology. Main benefit is the production of biogaswhich is easily available for cooking and replaces aconsiderable amount of traditional cooking fuel. Theco-treatment with other organic household wasteis highly recommended in order to increase the gasproduction. The survey showed a high satisfaction ofthe users and little objection to using the biogas fromfaeces as cooking fuel. Furthermore, the low operationand maintenance efforts required makes the systemattractive as also waste handling is simple and doesnot require any direct human contact with the toiletwaste.The payback period of the new design with its currentsubsidy system compared to the old design andsubsidies increased from 3 years to 15 years, takinginto account savings in replacing other fuels. Costs ofprevious kitchen or toilet waste management are notconsidered, as most families used to dispose of theirwaste in the streets and used to defecate into thebackwaters. The environmental benefits as a result ofthe new sanitation system and replacement of the oldunacceptable situation were not quantified.However two major challenges still must beresearched and improved if such a technology was tobe implemented at wide scale in the region.The economic feasibility of the system is thusrather weak. Hence widespread replication andimplementation is only possible if the investmentcosts can be reduced considerably. Mass production,cheaper materials, higher subsidies or other incentivesystems could be options to reduce investment costs.Else, using the current design, biogas plants will onlybe affordable to wealthy families.1. The study showed clearly that the quality of theeffluent is not sufficient for use as fertilizer withoutrestrictions or even for discharge into water bodiesand that a post-treatment step is needed. Basically,the same technologies as for wastewater can beconsidered. In the context of decentralized biogassystems in low and middle-income countries, thiscan for example be an anaerobic baffled reactor witha subsequent planted horizontal or vertical filter(Borda, 2009, Tilley et al, 2008, Morel and Diener,2006).2. Current investment costs for a biogas reactor, ofthe type that is disseminated in the region, arefar too high for an average family on KumbalangiIsland. With the current subsidy system and thecurrent design and construction cost, the paybackrate is 15 years. Additional technical measuresfor effluent treatment would even increase theSocial aspectsA household survey showed that the acceptance ofthe biogas systems is in general very good and mostfamilies that have one would recommend it to others.The improved waste management and the productionof biogas were mentioned as the main advantages.The smell of the effluent (when using toilet waste),not enough biogas, slower cooking with biogas andthe difficult access and design of the toilet facilities(steep and unsafe stairs) were mentioned as maindisadvantages.Sustainable Sanitation Practice8Issue 9/2011

Household biogas digesters for faecescurrent investment cost making the system surelyunaffordable for most families. Reducing costcontribution by the individual family is an urgentrequirement, be this through subsidies or reductionsof construction costs. Possible solutions could be tolower cost though mass production, to lower theunit cost, or else provide solutions constructed withother materials, such as the older brick built versionsor simple plastic drum type reactors.AcknowledgementsWe would like to express our gratitude to BIOTECH forallowing us to analyse the project and providing all thenecessary support, information and documentation.Moreover, the authors wish to thank the Swiss Agencyfor Development and Cooperation (SDC), the SwissNational Centre of Competence in Research (NCCR)North-South, and the Swiss Federal Institute of AquaticScience and Technology (Eawag) for their supporttowards this research work.ReferencesBorda (2009): Decentralised Wastewater Treatment Systems (DEWATS)and Sanitation in Developing Countries. A Practical Guide. BremenOverseas Research and Development Association. Germany. ISBN:978 1 84380 128 3Deublein, D., Steinhauser, A. (2008): Biogas from waste and renewableresources: an introduction. Wiley-VCH. Weinheim, Germany.Estoppey, N. (2010): Evaluation of small-scale biogas systems for thetreatment of faeces and kitchen waste. Case study Kochi, SouthIndia. Sandec Report, Swiss Federal Institute of Aquatic Science andTechnology (Eawag), Dübendorf, Switzerland.Ministry of Environment and Forest (undated): EnvironmentalStandards - General Standards for discharge of environmentalpollutants. Government of India. Delhi.Morel, A., Diener, S. (2006): Greywater Management in Low andMiddle-Income Countries. Review of different treatment systemsfor households or neighbourhoods. Swiss Federal Institute ofAquatic Science and Technology (Eawag). Dübendorf, Switzerland.Tilley, E., Lüthi, C., Morel, A., Zurbrügg, C., Schertenleib, R. (2008):Compendium of Sanitation Systems and Technologies. SwissFederal Institute of Aquatic Science and Technology (Eawag).Dübendorf, Switzerland.Name: Christian ZurbrüggOrganisation: Swiss Federal Institute ofAquatic Science and TechnologyTown, Country: Zurich, SwitzerlandeMail: zurbrugg@eawag.chWorld Health Organization (2006): WHO guidelines for the safe useof wastewater, excreta and greywater. Volume 4: Excreta andgreywater use in agriculture. 2nd edition, Geneva, Switzerland.Name: Yvonne VögeliOrganisation: Swiss Federal Institute ofAquatic Science and TechnologyTown, Country: Zurich, SwitzerlandeMail: yvonne.voegeli@eawag.chName: Nicolas EstoppeyOrganisation: Swiss Federal Institute ofAquatic Science and TechnologyTown, Country: Zurich, SwitzerlandeMail: Nicolas estoppey@bluewin.chSustainable Sanitation Practice9Issue 9/2011

Biogas Systems in Lesotho: an effective way togenerate energy while sanitizing wastewaterIn Maseru, Lesotho, the Non-Governmental Organization TED constructs biogassystems for decentralized wastewater treatment (BiogasDEWATS) since 2003 inhouseholds, schools, orphanages and military camps, improving food securitythrough the re-use of plant nutrients in the treated water by irrigation.Author: Mantopi MdP Lebofa, Elisabeth M. HubaAbstractThis article describes Biogas as a decentralized wastewater treatment system implemented in Lesotho, where in 2002 agroup of technicians, with strong interest in the link between environmental protection and human well-being, startedto implement household biogas digesters for sanitation purposes in peri-urban settlements of the capital Maseru. Thedemand for the technology is created by problems with overflowing or leaking septic tanks and high-priced drinkingwater commonly used for irrigation. No subsidy is provid

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