of biogas from kitchen waste

Transcription

1 L. Lama, SP Lohani, R Lama, and JR Adhikari: Production of biogas from kitchen waste Production of biogas from kitchen waste Laxman Lama 1 *, Sunil Prasad Lohani 2, Ram Lama 2, and Jhalak Raj Adhikari 2 1 Department of Environmental Science and Engineering and 2 Department of Mechanical Engineering, Kathmandu University, Nepal Abstract- The study was conducted at Kathmandu University and this study focuses on production of biogas as an alternative energy by using biodegradable kitchen wastes of Kathmandu University Premises. The research was conducted on modified ARTI model compact biogas plant of 1 m digester and.75 m gasholder in focusing the management of daily produced biodegradable wastes from households. The main objective of the project is biogas generation and analysis the feasibility, working efficiency, health and environmental benefits of modified ARTI compact biogas plant in urban areas. The maximum methane gas was recorded as 5% and average maximum carbon dioxide was recorded as 58%. The daily temperature inside the digester was found in the range of (- C) and ph value of the slurry was found in between ( ). The average gas production was found to be 17 L/day. The maximum burning period of the gas was approximately 2 min/day and average burning period was 2 min/day. In the beginning, the proportion of methane is exceeded by carbon dioxide and then after gradually methane exceeded carbon dioxide and reached 5 on average. The amount of gas produced rate during July is low because of rainy season and increases respectively. Since the daily feeding of 5 kg dry kitchen waste produce 17 L of gas per day, per kg of kitchen waste can produce 5 L of gas daily. The system will provide an appropriate and most efficient solution to the problem of kitchen waste enabling the recovery of energy from waste. 1 Index Terms- Biodegradable kichen waste, biogas, ARTI model compact biogas plant, energy from waste I. INTRODUCTION On a worldwide scale, rapid urbanizationn and population growth respectively leads to increased solid waste generation in urban areas and have magnified the necessity for adequate solid waste management throughout the country. Inadequate management like uncontrolled dumping bears several adverse environmental and public health problem besides destroying the city s beauty and hindering cultural and religious activities. It not only leads to an uglification of the living area, but also to a high risk of polluting surface and ground water through leachate and furthermore promotes the breeding of flies, mosquitoes, rats and other disease vectors. In order to tackle these problems the disposal of organic material needs to be avoided. Aiming at sustainable development the organic waste as a source of nutrients and energy has to be reused however, the composition of the solid waste varies with cities and countries depending on the standard of living, lifestyles, social and religious traditions, eating habits and so forth. In order to minimize the risk to the environment and human health, economically feasible solutions are sought for the treatment of solid waste particularly in urban areas. A plan to turn solid organic waste (kitchen waste) into energy through different technology has been possible; however, maximum energy recovery, and less discharge is possible through anaerobic digestion that seems viable economic * Corresponding author, Lakshman_la9@hotmail.com option for the country like Nepal. So, replacing the conventional energy resources from the biogas (modified ARTI) technology would reduce the effect on global warming as well as climate change [1]. Modified ARTI is a compact biogas plant which uses kitchen waste as feeding material. The slurry of feeding materials goes to the anaerobic decomposition to supply biogas for cooking, replacing Liquid Petroleum Gas (LPG) or Kerosene. It is a floating drum biogas plant. It consists of L capacity digester of simple water storage tank and 75 L capacity of gasholder whichh is placed upside down in the digester. When gas starts to generate, the gasholder rises to a certain limit. It then falls down to the lower limit after burning all gases present in the gasholder. Thus, municipal biodegradable solid waste is in fact not a waste it s a form of energy, which is one of the basic entities for all economic activities.[1] Biogas does not have any geographical limitations nor does it require advanced technology for producing energy, also it is very simple to use and apply. Due to use of too much conventional energy resources day by day, it is producing more pollution to the environment. To avoid the dependency on conventional energy resources, reduce negative impact on environment and make daily energy consumption more cost effective, management of such urban (household) wastes using modified ARTI model seems to be best way in urban areas. II. MATERIALS AND METHODS Design and Fabrication of Chopper Fig. 1: Drawing of chopper Rentech Symposium Compendium, Volume 2, December 2

2 Chopper is used to chop the green cuttings, bio-degradable kitchen waste including fish waste, vegetable and cooked food to make slurry for the production of biogas. It can also be used for the disposal of domestic garbage and converting it to compost in relatively short time. The components of the chopper comprised of gear, pulleys, bearings, shafts and belt drives etc. The used pulleys have diameters of 15 inch and 2.5 inch respectively since they are easily available in the market and cost effective. 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 inch Where, x=distance between the centers of two pulleys= inch, d 1 and d 2 are the diameters of the larger and smaller pulleys. The velocity ratio of the belt drive following equation: a) Velocity ratio = Diameter of the driver/ Diameter of the driven = 15/2.5= This indicates that the driven pulley rotates six times than the driver pulley, which means if we rotate the driver pulley once then driven pulley will rotates six times helping us to use less effort leading to higher efficiency of the chopper. Similarly, gear ratio is the relationship between the numbers of teeth on two gears that are meshing together or are connected. b) Gear Ratio = (pitch diameter of Gear A)/(pitch diameter of Gear B) = inch/2.5 inch = 2.4 This gear ratio signifies that the Gear B will have to turn almost 2.5 times higher than Gear A so that less manual effort helps to chop the waste in higher rate than normal. It saves the time as well as manual energy supply for chopping purpose. Overall Speed of the Blade: is obtained from the Since the gear ratio and velocity ratio of the gear and pulley are respectively 2.4 and, the overall speed of the blade is (2.4+) = 8.4. This combined ratio signifies that the blades of the chopper rotates eight times than the spinning it by human hand. The modified ARTI model compact biogas plant has two water storage tank of size L (digester) and 75L (gasholder). The digester was placed on the metal base with insulator. The inlet pipe is fixed to the bottom of the digester, which has elbow of 45 and it is extended to the centre of the digester and also supported by the metal stand to ensure the proper flow of the slurry into the digester. Similarly, the outlet pipe is fixed nearly to the top of the digester but opposite to the inlet pipe. On the other hand, the gasholder has metal ring surrounding it, this ring is connected with the two vertical GI pipes to remove the tilt problem of gasholder as in the case of ARTI model. Here, Gasholder of 75L, which holds the produced gas was placed upside down in the digester tank. [2] Fig. 2: Overall biogas plant Fig. : Sectional view of overall plant III. M METHODS Fig. 4: Overall process Inoculum and Start-up: Rentech Symposium Compendium, Volume 2, December 2 15

3 Initially 2- kg of cow dung were gradually mixed with water and made slurry of about 5- L with removal of straw material (Figure 5) []. The homogenous mass was then poured into the digester. Following the installation and inoculation, the digester was left without feeding for days to develop the culture inside the digester. After that started to put the kitchen waste into the digester. Fig. 5: Preparation of cow dung and putting it into the digester to start- up the process Pre-Treatment and Dilution of Feedstock: The objective of pre-treatment is to reduce the size of substrate particles in order to meet the basic requirement of fitting into the 4 - inlet-pipe. In addition, increasing the surface of the feedstock allows better digestion for the bacteria responsible for the hydrolysis. The pieces of both substrates were treated previous to the feeding to attain a particle size of less than 1cm. In our study, the pre-treatment of food waste was only needed for the meat, fish and fruit pieces. They were cut up with a kitchen knife. Then put them into the chopper to make smaller size. Preparation of Feedstock and Feeding Procedure: Organic household waste primarily consists of kitchen waste, which can be divided into food leftovers and peelings or pieces of vegetables and fruits. The food leftovers consisted of rice, lentil, curry, vegetable (beans), potato chips, and pieces of meat with sauce and fish residue. Orange and banana peelings were also merged into the food remains. Tooth picks and meat bones were frequently among the food waste and had to be removed. Fruit and vegetable waste 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 vegetable peelings (cabbage, bean). All wastes were stored in closed buckets and used within a maximum of 4 days. Daily in average 5Kg of dry waste was collected and directly poured into the chopper and around 5% of water is also added to make slurry. Then chop all the kitchen waste by the use of chopper to make sure that all size of waste are less than1cm. The liquid slurry from the chopper is also directly input to the digester. Gas Measurements: The daily produced volume of gas was measured by two methods. 1. Height difference method 2. Burn method Height difference method: This method includes the marking of the minimum and maximum point on the gasholder and then measuring tape was used to measure the exact height of produced gas in the digester. The gear valve was open to release the gas and then closed to mark the minimum (initial) height. The gas holder rises up to the certain limit because of daily slurry input and that height is recorded as final height of the produced gas. The difference between the final and initial height gives the exact height difference of the produce gas. [4] Burn method: In this method, the gas stove was used to burn the produce gas and daily burning time after the addition of kitchen waste was also recorded to know the rate of produce gas. [4] Gas Composition: The Dräger X-am 7 (Gas Analyzer) was used to measure the volume percentage of methane (CH 4 ) and carbon dioxide (CO 2 ) in the biogas. The gas composition was measured on a daily basis in the afternoon (before feeding) while releasing the gas. Gas (L) IV. RESULTS AND DISCUSSIONS Days Fig. : Gas production versus days The line graph shows how the production of gas changed day by day on daily feeding of average 5 kg of dry kitchen waste, obtained after the days to 1 days from the feeding of kitchen waste, measured by height difference methods. The first day of the feeding of kitchen waste represents 1 days in the above graph. Rentech Symposium Compendium, Volume 2, December 2 1

4 At the beginning, volume of the gas production was seen low due to improper digester culture, lower digester temperature, lack of PH maintain and due to rainy season. Thereafter, gases were consistently above L from 15 days daily, rising sharply to a peak of 2L in days. For the next however, there was a sudden decrease in gas production and reached to 19 L for 2 and days, after that gas production rate remained steadily to a value of 18L. In conclusion, the amount of biogas increased gradually along with increasing amount of feeding materials and digestion period. The maximum of about 17 ml/day was recorded.the gas generation per kg fresh feeding materials depends upon the type and digestibility of feeding materials as well as digester temperature etc. and fully developed inside culture. % by volume CH4 and CO2 producion 8 CH4 2 CO Fig. 8: Methane e versus carbon dioxide Overall, the graph shows that the percentage of methane exceeded the percentage of carbon dioxide as the time passes and in fully favorable environment for the bacteria, indicating Methane content also depends upon the digester temperature and well developed culture. Fig. 7: PH versus days The graph shows the variation of PH value of the digester slurry with days. Here, 1 days in the above line graph shows the first day for the feeding of kitchen waste, conducted in between July-August, 2. It is clear to know that the daily feeding is about 5 kg dry kitchen wastes in average. First of all, it is clearly seen from the graph that at the beginning, the ph is on higher side (indicating almost.7), as reaction inside the digester continues it stars decreasing and it becomes more acidic. The PH of slurry decreases highly means reaction is fast, means hydrolysis and acitogenesis reaction is fast as organism utilizes the waste more speedily than dung. Also the ph reduces as the process going on as the bacteria produces fatty acids, is slow reaction compare to other so it is rate limiting step in reaction. Then water added to dilute and thus ph increases and remains almost constant means dropped to about 5.48) as shown in the Fig. It is interesting however, that the range of the PH value was found in between 5.48 to.7. In conclusion, PH value entirely depends on the feeding materials, the time duration as well as digester temperature. The graph represents the percentage of methane and carbondioxide produced for twelve days July 22 to August, 2. The most significant feature is that Carbon dioxide represents 58% by volume of gas, whereas, methane seems to be 4%, at the first day of measurement. Thereafter composition of CO 2 gradually decreases and dropped to a value of % by volume for the last day of experiment. On the other hand, the percentage of methane sharply increases and picked to the value of 2% by volume in last day. Rentech Symposium Compendium, Volume 2, December 2 Fig. 9: Burn time versus days The diagram represents the Burn time (minutes) observed in days on daily feeding of 5 kg dry kitchen waste. Here, 5 days in the graph shows fifth day of the feeding of kitchen waste and so on. In the first day of the burn time measurement, the observed burn time was 2 min. It was the maximum time of burning, because, the produced gases are only the outcomes of the homogeneous mass of cow dung and kitchen waste of 4/5 days. Then the burn time gradually decreases because the produced gases are the outcomes of kitchen waste only and because of lower temperature since the research period is rainy season and then slightly increases because of increase in digestion period. 2 Temp Vs Gas Production Temp(C) Gas production (L) Fig. : Variation of temperature and gas production The graph shows the variation of gas production with varying the digester temperature. Initially, the temperature inside the digester is low.the measurement was taken 17 days after the feeding of the kitchen waste, after that production of gradually increases and picked to 2 L in days. Finally, due to welldeveloped culture and maintained inside temperature gas production remained almost constant. 17

5 TABLE I DATA SHEET FOR OVERALL MEASUREMENT Date T ( C) P H P (Pa) Slurry in (kg) Slurry Out (kg) Gas (L) CH 4 (%) CO 2 (%) Burn time (min) July 2 July 21 July 22 July 2 July 24 July July 2 July July July July July 1 Aug-1 Aug-2 Aug- Aug-4 Aug-5 Aug- Aug-7 Aug-8 Aug-9 Aug- Aug- Aug- Aug-1 Aug- Aug-15 Aug-1 Aug-17 Aug-18 Aug-19 Aug-2 Aug-21 Aug-22 Aug It is interesting to note, however, that the variation of temperature is because of rainy season and the range of inside temperature was in between 24 to degree Celsius. V. CONCLUSION The Concept of Kitchen Waste Utilization using a modified ARTI Compact Plant for Biogas Production offers effective Waste Management and Resource Development solutions with positive measures for the economy, improved air quality and sustained energy security. So, anaerobic digestion of Kitchen waste using modified ARTI compact biogas plant is a proven technology for processing sourceseparated organic wastes and has experienced significant growth recently. In overall, the modified ARTI Compact biogas system (CBS) seems more feasible and economical biogas plant for households in urban areas, as organic solid waste generated in rural region are preferably used as animal feed. This plant helps to the management of an organic waste generation in urban areas as well as saves the consumption of LPG gas and money in the long term (by replacing conventional cooking fuel). In is interesting to note, however, that in our study it was found that, the average daily gas production per Kg of dry kitchen waste is 5 L. So, by storing the 2- days gas it will be equivalent to consumption of 1 days LPG gas. REFERENCES [1] Nijaguna B.T., Biogas Technology, New age international (P) Ltd, Publishers, (2). [2] H.M. Lungkhimba, A.M. Karki, J. N. Shrestha, Biogas production from anaerobic digestion of biodegradable household wastes, Tribhuvan University, Nepal. [] Karve.A.D., Compact biogas plant, a low cost digester for biogas from waste starch, (27). [4] ARTI, ARTI Biogas Plant: A compact digester for producing biogas from food waste, how to build the ARTI compact biogas digester, 28. Rentech Symposium Compendium, Volume 2, December 2 18