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

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