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

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