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

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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
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