Production of biogas from kitchen waste, Laxman Lama, Sunil ...

L. Lama, SP Lohani, R Lama, and JR Adhikari: Production of biogas from kitchen wasteProduction of biogas from kitchen wasteLaxman Lama 1 *, Sunil Prasad Lohani 2 , Ram Lama 2 , and Jhalak Raj Adhikari 21 Department of Environmental Science and Engineering and 2 Department of Mechanical Engineering, KathmanduUniversity, NepalAbstract- The study was conducted at Kathmandu Universityand this study focuses on production of biogas as an alternativeenergy by using biodegradable kitchen wastes of KathmanduUniversity Premises. The research was conducted on modifiedARTI model compact biogas plant of 1 m 3 digester and 0.75 m 3gasholder in focusing the management of daily producedbiodegradable wastes from households. The main objective of theproject is biogas generation and analysis the feasibility, workingefficiency, health and environmental benefits of modified ARTIcompact biogas plant in urban areas. The maximum methane gaswas recorded as 65% and average maximum carbon dioxide wasrecorded as 58%. The daily temperature inside the digester wasfound in the range of (25-34 0 C) and pH value of the slurry wasfound in between (6.7-5.48). The average gas production wasfound to be 173 L/day. The maximum burning period of the gaswas approximately 62 min/day and average burning period was 26min/day. In the beginning, the proportion of methane is exceededby carbon dioxide and then after gradually methane exceededcarbon dioxide and reached 56 on average. The amount of gasproduced rate during July is low because of rainy season andincreases respectively. Since the daily feeding of 5 kg dry kitchenwaste produce 173 L of gas per day, per kg of kitchen waste canproduce 35 L of gas daily. The system will provide an appropriateand most efficient solution to the problem of kitchen wasteenabling the recovery of energy from waste. 1Index Terms- Biodegradable kichen waste, biogas, ARTImodel compact biogas plant, energy from wasteI. INTRODUCTIONOn a worldwide scale, rapid urbanization and populationgrowth respectively leads to increased solid wastegeneration in urban areas and have magnified the necessityfor adequate solid waste management throughout thecountry. Inadequate management like uncontrolled dumpingbears several adverse environmental and public healthproblem besides destroying the city’s beauty and hinderingcultural and religious activities. It not only leads to anuglification of the living area, but also to a high risk ofpolluting surface and ground water through leachate andfurthermore promotes the breeding of flies, mosquitoes, ratsand other disease vectors. In order to tackle these problemsthe disposal of organic material needs to be avoided. Aimingat sustainable development ent the organic waste as a source ofnutrients and energy has to be reused however, thecomposition of the solid waste varies with cities andcountries depending on the standard of living, lifestyles,social and religious traditions, eating habits and so forth. Inorder to minimize the risk to the environment and humanhealth, economically feasible solutions are sought for thetreatment of solid waste particularly in urban areas. A planto turn solid organic waste (kitchen waste) into energythrough different ent technology has been possible; however,maximum energy recovery, and less discharge is possiblethrough anaerobic digestion that seems viable economic* Corresponding author, Lakshman_la9@hotmail.comoption for the country like Nepal. So, replacing theconventional energy resources from the biogas (modifiedARTI) technology would reduce the effect on globalwarming as well as climate change [1].Modified ARTI is a compact biogas plant which useskitchen waste as feeding material. The slurry of feedingmaterials goes to the anaerobic decomposition to supplybiogas for cooking, replacing Liquid Petroleum Gas (LPG)or Kerosene. It is a floating drum biogas plant. It consists of1000 L capacity digester of simple water storage tank and750 L capacity of gasholder which is placed upside down inthe digester. When gas starts to generate, the gasholder risesto a certain limit. It then falls down to the lower limit afterburning all gases present in the gasholder. Thus, municipalbiodegradable solid waste is in fact not a waste it’s a form ofenergy, which is one of the basic entities for all economicactivities.[1] Biogas does not have any geographicallimitations nor does it require advanced technology forproducing energy, also it is very simple to use and apply.Due to use of too much conventional energy resources dayby day, it is producing more pollution to the environment.To avoid the dependency on conventional energy resources,reduce negative impact on environment and make dailyenergy consumption more cost effective, management ofsuch urban (household) wastes using modified ARTI modelseems to be best way in urban areas.II. MATERIALS AND METHODSDesign and Fabrication of ChopperFig. 1: Drawing of chopperRentech Symposium Compendium, Volume 2, December 201214

L. Lama, SP Lohani, R Lama, and JR Adhikari: Production of biogas from kitchen wasteChopper is used to chop the green cuttings, bio-degradablekitchen waste including fish waste, vegetable and cookedfood to make slurry for the production of biogas. It can alsobe used for the disposal of domestic garbage and convertingit to compost in relatively short time.The components of the chopper comprised of gear,pulleys, bearings, shafts and belt drives etc. The usedpulleys have diameters of 15 inch and 2.5 inch respectivelysince they are easily available in the market and costeffective.We also used the V belt having the total length=π/2(d 1 +d 2 ) +2*x+ (d 1 -d 2 ) 2 /4*x= 85 inchWhere, x=distance between the centers of twopulleys=28 inch, d 1 and d 2 are the diameters of the larger andsmaller pulleys.The velocity ratio of the belt drive is obtained from thefollowing equation:a) Velocity ratio = Diameter of the driver/ Diameter ofthe driven = 15/2.5=6This indicates that the driven pulley rotates six timesthan the driver pulley, which means if we rotate the driverpulley once then driven pulley will rotates six times helpingus to use less effort leading to higher efficiency of thechopper. Similarly, gear ratio is the relationship between thenumbers of teeth on two gears that are meshing together orare connected.b) Gear Ratio = (pitch diameter of Gear A)/(pitchdiameter of Gear B)= 6 inch/2.5 inch= 2.4This gear ratio signifies that the Gear B will have to turnalmost 2.5 times higher than Gear A so that less manualeffort helps to chop the waste in higher rate than normal. Itsaves the time as well as manual energy supply for choppingpurpose.Overall Speed of the Blade:Since the gear ratio and velocity ratio of the gear andpulley are respectively 2.4 and 6, the overall speed of theblade is (2.4+6) = 8.4. This combined ratio signifies that theblades of the chopper rotates eight times than the spinning itby human hand.The modified ARTI model compact biogas plant has twowater storage tank of size 1000L (digester) and 750L(gasholder). The digester was placed on the metal base withinsulator. The inlet pipe is fixed to the bottom of thedigester, which has elbow of 45͑and it is extended to thecentre of the digester and also supported by the metal standto ensure the proper flow of the slurry into the digester.Similarly, the outlet pipe is fixed nearly to the top of thedigester but opposite to the inlet pipe. On the other hand, thegasholder has metal ring surrounding it, this ring isconnected with the two vertical GI pipes to remove the tiltproblem of gasholder as in the case of ARTI model. Here,Gasholder of 750L, which holds the produced gas wasplaced upside down in the digester tank. [2]Fig. 2: Overall biogas plantFig. 3: Sectional view of overall plantIII. MMETHODSFig. 4: Overall processInoculum and Start-up:Rentech Symposium Compendium, Volume 2, December 201215

L. Lama, SP Lohani, R Lama, and JR Adhikari: Production of biogas from kitchen wasteInitially 200-300 kg of cow dung were gradually mixedwith water and made slurry of about 500-600 L withremoval of straw material (Figure 5) [3]. The homogenousmass was then poured into the digester. Following theinstallation and inoculation, the digester was left withoutfeeding for 30 days to develop the culture inside thedigester. After that started to put the kitchen waste into thedigester.Fig. 5: Preparation of cow dung and putting it into the digester tostart- up the processPre-Treatment and Dilution of Feedstock:The objective of pre-treatment is to reduce the size ofsubstrate particles in order to meet the basic requirement offitting into the 4”- inlet-pipe. In addition, increasing thesurface of the feedstock allows better digestion for thebacteria responsible for the hydrolysis. The pieces of bothsubstrates were treated previous to the feeding to attain aparticle size of less than 1cm. In our study, the pre-treatmentof food waste was only needed for the meat, fish and fruitpieces. They were cut up with a kitchen knife. Then putthem into the chopper to make smaller size.Preparation of Feedstock and Feeding Procedure:Organic household waste primarily consists of kitchenwaste, which can be divided into food leftovers and peelingsor pieces of vegetables and fruits. The food leftoversconsisted of rice, lentil, curry, vegetable (beans), potatochips, and pieces of meat with sauce and fish residue.Orange and banana peelings were also merged into the foodremains. Tooth picks and meat bones were frequently amongthe food waste and had to be removed. Fruit and vegetablewaste was also obtained during the waste collection period.Its composition was spoiled fruits (papaya, orange, banana,and pineapple), spoiled vegetables (tomato, eggplant, carrot,potato, cucumber, onion, and broccoli) and vegetablepeelings (cabbage, bean). All wastes were stored in closedbuckets and used within a maximum of 4 days. Daily inaverage 5Kg of dry waste was collected and directly pouredinto the chopper and around 50% of water is also added tomake slurry. Then chop all the kitchen waste by the use ofchopper to make sure that all size of waste are less than1cm.The liquid slurry from the chopper is also directly input tothe digester.Gas Measurements:The daily produced volume of gas was measured by twomethods.1. Height difference method2. Burn methodHeight difference method: This method includes themarking of the minimum and maximum point on thegasholder and then measuring tape was used to measure theexact height of produced gas in the digester. The gear valvewas open to release the gas and then closed to mark theminimum (initial) height. The gas holder rises up to thecertain limit because of daily slurry input and that height isrecorded as final height of the produced gas. The differencebetween the final and initial height gives the exact heightdifference of the produce gas. [4]Burn method: In this method, the gas stove was used toburn the produce gas and daily burning time after theaddition of kitchen waste was also recorded to know the rateof produce gas. [4]Gas Composition:The Dräger X-am 7000 (Gas Analyzer) was used tomeasure the volume percentage of methane (CH 4 ) andcarbon dioxide (CO 2 ) in the biogas. The gas compositionwas measured on a daily basis in the afternoon (beforefeeding) while releasing the gas.Gas (L)250200150100500IV. RESULTS AND DISCUSSIONS1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61DaysFig. 6: Gas production versus daysThe line graph shows how the production of gas changedday by day on daily feeding of average 5 kg of dry kitchenwaste, obtained after the 10 days to 16 days from thefeeding of kitchen waste, measured by height differencemethods. The first day of the feeding of kitchen wasterepresents 31 days in the above graph.Rentech Symposium Compendium, Volume 2, December 2012 16

L. Lama, SP Lohani, R Lama, and JR Adhikari: Production of biogas from kitchen wasteAt the beginning, volume of the gas production was seenlow due to improper digester culture, lower digestertemperature, lack of PH maintain and due to rainy season.Thereafter, gases were consistently above 110 L from 15days daily, rising sharply to a peak of 210L in 25 days. Forthe next however, there was a sudden decreasein gasproduction and reached to 190 L for 26 and 27 days, afterthat gas production rate remained steadily to a value of186L.In conclusion, the amount of biogas increased graduallyalong with increasing amount of feeding materials anddigestion period. The maximum of about 173000 ml/daywas recorded .The gas generation per kg fresh feedingmaterials depends upon the type and digestibility of feedingmaterials as well as digester temperature etc. and fullydeveloped inside culture.% by volumeCH4 and CO2 producion806040CH420CO201 2 3 4 5 6 7 8 9 10 11 12Fig. 8: Methane e versus carbon dioxideOverall, the graph shows that the percentage of methaneexceeded the percentage of carbon dioxide as the timepasses and in fully favorable environment for the bacteria,indicating Methane content also depends upon the digestertemperature and well developed culture.Fig. 7: PH versus daysThe graph shows the variation of PH value of thedigester slurry with days. Here, 31 days in the above linegraph shows the first day for the feeding of kitchen waste,conducted in between July-August, 2012. It is clear to knowthat the daily feeding is about 5 kg dry kitchen wastes inaverage.First of all, it is clearly seen from the graph that at thebeginning, the pH is on higher side (indicating almost 6.7),as reaction inside the digester continues it stars decreasingand it becomes more acidic. The PH of slurry decreaseshighly means reaction is fast, means hydrolysis andacitogenesis reaction is fast as organism utilizes the wastemore speedily than dung. Also the pH reduces as the processgoing on as the bacteria produces fatty acids, is slowreaction compare to other so it is rate limiting step inreaction. Then water added to dilute and thus pH increasesand remains almost constant means dropped to about 5.48)as shown in the Fig 10. It is interesting however, that therange of the PH value was found in between 5.48 to 6.7.In conclusion, PH value entirely depends on the feedingmaterials, the time duration as well as digester temperature.The graph represents the percentage of methane and carbondioxideproduced for twelve days July 22 to August 6, 2012.The most significant feature is that Carbon dioxiderepresents 58% by volume of gas, whereas, methane seemsto be 43%, at the first day of measurement. Thereaftercomposition of CO 2 gradually ly decreases and dropped to avalue of 40% by volume for the last day of experiment. Onthe other hand, the percentage of methane sharply increasesand picked to the value of 62% by volume in last day.Rentech Symposium Compendium, Volume 2, December 2012Fig. 9: Burn time versus daysThe diagram represents the Burn time (minutes)observed in days on daily feeding of 5 kg dry kitchen waste.Here, 35 days in the graph shows fifth day of the feeding ofkitchen waste and so on.In the first day of the burn time measurement, theobserved burn time was 62 min. It was the maximum time ofburning, because, the produced gases are only the outcomesof the homogeneous mass of cow dung and kitchen waste of4/5 days. Then the burn time gradually decreases becausethe produced gases are the outcomes of kitchen waste onlyand because of lower temperature since the research periodis rainy season and then slightly increases because ofincrease in digestion period.3002001000Temp Vs Gas Production1 4 7 1013161922252831Temp(0C)Gas production(L)Fig. 10: Variation of temperature and gas productionThe graph shows the variation of gas production withvarying the digester temperature.Initially, the temperature inside the digester is low .Themeasurement was taken 17 days after the feeding of thekitchen waste, after that production of gradually increasesand picked to 210 L in 29 days. Finally, due to welldevelopedculture and maintained inside temperature gasproduction remained almost constant.17

L. Lama, SP Lohani, R Lama, and JR Adhikari: Production of biogas from kitchen wasteTABLE IDATA SHEET FOR OVERALL MEASUREMENTDate T ( 0 C) P H P (Pa) Slurry in(kg)Slurry Out (kg) Gas (L) CH 4(%)CO 2(%)Burn time (min)July 20July 21July 22July 23July 24July 25July 26July 27July 28July 29July 30July 31Aug-1Aug-2Aug-3Aug-4Aug-5Aug-6Aug-7Aug-8Aug-9Aug-10Aug-11Aug-12Aug-13Aug-14Aug-15Aug-16Aug-17Aug-18Aug-19Aug-20Aug-21Aug-22Aug-23252425272625272827252629292829262830302929292828272830303131326.76.56.426.46.46.265.785.675.675.75.775.85.85.85.85.85.665.635.7565.95.95.95.85.625.525.525.5227327327327327327327327327327327327327327327327327327327327327327327327327327327327327327327327327327327310101010101011111111121212121212126666666111112121313136.2665.85.86.33.43.2332.932.85.65.75.65.75.866.26.356.436.5115.59124.37122.91131.69139153.64160.95168.27175.58197.53208.51199.73203.38201.9219942455155565859616365646458565551464443424240404662323234343637373832333334141414It is interesting to note, however, that the variation oftemperature is because of rainy season and the range ofinside temperature was in between 24 to 33 degree Celsius.V. CONCLUSIONThe Concept of Kitchen Waste Utilization using amodified ARTI Compact Plant for Biogas Production offerseffective Waste Management and Resource Developmentsolutions with positive measures for the economy, improvedair quality and sustained energy security. So, anaerobicdigestion of Kitchen waste using modified ARTI compactbiogas plant is a proven technology for processing sourceseparatedorganic wastes and has experienced significantgrowth recently.In overall, the modified ARTI Compact biogas system(CBS) seems more feasible and economical biogas plant forhouseholds in urban areas, as organic solid waste generatedin rural region are preferably used as animal feed. This planthelps to the management of an organic waste generation inurban areas as well as saves the consumption of LPG gasand money in the long term (by replacing conventionalcooking fuel).In is interesting to note, however, that in our study it wasfound that, the average daily gas production per Kg of drykitchen waste is 35 L. So, by storing the 2-3 days’ gas it willbe equivalent to consumption of 1 days LPG gas.REFERENCES[1] Nijaguna B.T., Biogas Technology, New age international (P) Ltd,Publishers, (2006).[2] H.M. Lungkhimba, A.M. Karki, J. N. Shrestha, “Biogas productionfrom anaerobic digestion of biodegradable household wastes,”Tribhuvan University, Nepal.[3] Karve .A.D., “Compact biogas plant, a low cost digester for biogasfrom waste starch,” (2007). http://www.arti-india.org.[4] ARTI, “ARTI Biogas Plant: A compact digester for producing biogasfrom food waste, how to build the ARTI compact biogas digester,”2008.Rentech Symposium Compendium, Volume 2, December 2012 18