INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 3, No 1, Copyright by the authors - Licensee IPA- Under Creative Commons license 3.

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1 INTERNATIONAL JOURNAL OF ENVIRONMENTAL SCIENCES Volume 3, No 1, 2012 Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0 Research article ISSN Performance of mixture of vegetable wastes with high carbohydrate content in anaerobic digestion process Dhanalakshmi Sridevi.V 1, Alwar Ramanujam.R 2 1- Department of Chemistry, G K M College of Engineering & Technology, Chennai, India 2- Environment Technology Division, Central Leather Research Institute (CLRI), Council of Scientific and Industrial Research (CSIR), Adyar, Chennai, India vdhsg@yahoo.co.in doi: /ijes ABSTRACT In our present study anaerobic digestion of mixture of vegetable wastes has been conducted in batch reactors of 500 ml capacity. Vegetable wastes having near similar ph and moisture content have been chosen so that total solids content do not vary significantly in the feed composition for the study. Carrot, beans and brinjal having ph 5.4, 5.8 and 5.7 respectively and moisture content 89.8%, 90.29% and 89.4% respectively were chosen for the study. These wastes contain predominantly carbohydrates and less protein and fat. Studies were carried out by preparing the feed consisting of carrot, beans and brinjal in different proportions to obtain organic load in three different ranges namely gvs/ml, gvs/ml and gvs/ml. The reactors were operated at these three different organic loads at various retention times. The performance of the reactors was evaluated by estimating destruction of Total and Volatile Solids and by monitoring daily gas production. Volatile Fatty Acid (VFA) profile was determined for each organic load at the end of each cycle of operation. VFAs particularly acetic acid, propionic acid and valeric acid were present predominantly in all the three organic load ranges. The performance evaluation in terms of specific gas production based on amount of total solids added and volatile solids added has indicated that the mixture of vegetable wastes chosen for the study are amenable to anaerobic digestion. The kinetics of the process has been studied using first order rate equation and reported in the paper. Keywords: Anaerobic digestion, fruit and vegetable wastes, biogas, batch reactor, VFA profile 1. Introduction One of the burning problems faced by the world today is management of all types of wastes and energy crisis. Rapid growth of population and uncontrolled and unmonitored urbanization has created serious problems of energy requirement and solid waste disposal. Vegetable market wastes contribute to a great amount of pollution; hence, there has been a strong need for appropriate vegetable waste management systems. Vegetable wastes that comprise of high fraction of putrecible organic matter cause serious environmental and health risks. India is the second major producer of fruits and vegetables and ranks next to Brazil and China in the world. About 14% of world vegetable production and 10% of fruit production are from India. According to Indian Agricultural Research Data Book 2004, the losses in fruits and vegetables are to the tune of 30%. Estimated production of fruits and vegetables in India is 150 million tons and the total waste generated comes to 50 million tons per annum Received on May 2012 Published on July

2 and become a source of nuisance in municipal landfills causing major environmental pollution problems because of the putrefaction of the organics. Therefore it becomes necessary to develop appropriate waste treatment technology for vegetable wastes to minimize green house gas emission. Anaerobic Digestion is the most environmentally friendly and promising technique which will result in the production of biogas (Bouallagui H et al., 2003, Mata. Alvarez J et al., 1992) and effluent which can be used as soil conditioner (Mata. Alvarez J et al., 1992, Verrier D et al., 1983, Ahring BK et al, 2002) but it required longer treatment time(arvanitoyannis loannis S and Varzakas Theodoros H., ). The process of digestion and production of biogas depends on the composition and the fermentation products of the vegetable wastes. The main objective of this research is to employ anaerobic digestion process as a sustainable technology for digesting the vegetable wastes, produced in large amounts during harvesting, handling, transportation, storage, marketing and processing, and to provide the renewable source of energy as well as to reduce the potential green house gas emission. Vegetable wastes largely contain carbohydrates. Proteins and fats are present relatively in low concentrations. Anaerobic digestion of carbohydrates, fat and proteins are expected to yield 886l ml, 1535l ml and 587l ml of biogas per kgvs d and generate biogas containing 50%, 70% and 84% of methane respectively (Burford, J. L., and Varani, F. T., Trevelyan, 1975). Keeping in view the biogas yield reported for the carbohydrates, fat and proteins, vegetable wastes, which have near similar ph, moisture content and carbohydrates, namely, Carrot, Beans and Brinjal, (Table 1) were chosen as model components to study the performance of mixture of wastes in the anaerobic digestion process. Table 1: Characteristics of the vegetables Sl.No Component Carrot Beans Brinjal 1 ph Moisture Content ** Carbohydrate * Fat* Protein* Except ph all are given in gms, * Amount present in 100gm, ** Moisture content is given in percentage 2. Materials and method 2.1 Experimental procedure Batch studies were carried out in four reactors of 500 ml Capacity (R1, R2, R3 and R4). Experiments were carried out in the mesophilic temperature range (27 o C 31 o C). Each reactor was initially inoculated with 150 ml of sludge, obtained from an active mesophillic digester of vegetable waste treatment plant at Koyembedu, Chennai, and diluted to 300ml working volume. The characteristics of inoculum and the diluted sludge in the reactor are given in the Table 2 182

3 Table 2: The physical and chemical parameter of the inoculum and diluted sludge Parameter Inoculum Diluted sludge R2 R3 R4 Total solids (TS) Volatile solids (VS) ph Except ph all are in percentage. The feedstock selected for the experiment was grinded mixture of three vegetables, namely, Carrot, Beans and Brinjal. Each reactor was charged separately with a quantity of substrate containing g VS/ml (R2), g VS/ml (R3) and g VS/ml (R4) by removing equivalent amount of sludge from the reactor. Reactor R1 was kept as control. Daily biogas production was measured by water displacement method. Six cycles were carried out with different HRT. The quantity and composition of the feedstock added for six cycles for the three different organic loading range for different hydraulic retention time (HRT) is given in the Table 3. At the end of each cycle the contents of the reactors were analyzed for ph, TS, VS and VFA profile. Table 3: The composition and the physical and chemical parameters of the feedstock added for the six cycles Cycle No: HRT (days) R2 organic Load ( gvs/ml) Amount of feed added (g) R3 organic Load ( gvs/ml) R4 organic Load ( gvs/ml) %TS of Feed Mix %VS of Feed Mix ph of Feed Mix I II III IV V VI Analytical methods Analysis of samples for Total solids (TS), Volatile Solids (VS) and ph was carried out in accordance with the procedures prescribed in IS , IS and standard methods of examination of water and waste water (APHA AWWA 1992) as appropriate. The volatile fatty acid levels were determined by Gas Chromatography Capillary column EC1000, ID 0.53, Thickness. 1.2µ - Mayura analytical GC, India - equipped with a flame ionization detector and glass column. The ignition port, detector and oven temperature were maintained at 250 o C. Nitrogen was used as carrier gas. 3. Results and discussion 3.1 Effect of ph, TS and VS on gas production ph, %TS, and %VS, of the feed and drain collected after each cycle and cumulative gas production at the end of each cycle is given Table 4. ph of the drain is ranging from 7.5 to 183

4 8.13 for the three reactors (Figure 1). %TS is ranging from , and (Figure 2) and %VS is ranging from , and (Figure 3) in the drain for the three organic loading. Cumulative biogas produced at the end of each cycle of specified retention time is ranging from ml for gVS/ml organic load, ml for gVS/ml organic load and ml for gVS/ml organic load respectively (Figure 4). Daily biogas production from each reactor for the six cycles as a function of time is shown in Figure 5. The maximum gas production was observed during the first 5 10 days. Table 4: ph, %TS, and %VS, of the feed and drain collected after each cycle CYCLE Days FEED R1 organic loading g VS/ml DRAIN PH %TS %VS PH %TS %VS Cumulative gas produced I II III IV V VI CYCLE Days FEED R2 organic loading g VS/ml DRAIN PH %TS %VS PH %TS %VS Cumulative gas produced I II III IV V VI CYCLE Days FEED R3 organic loading g VS/ml DRAIN PH %TS %VS PH %TS %VS Cumulative gas produced I II III IV V VI

5 Figure 1: Figure showing the ph of feed and drain Figure 2: Figure showing the TS% of feed and drain 185

6 Figure 3: Figure showing the VS% of feed and drain Figure 4: Volume of cumulative biogas production versus days during six cycles 186

7 Figure 5: Volume of daily biogas versus days during six cycles Percentage of TS reduction (Table-5) after each cycle is in the order of , and and VS reduction (Table-05) is , and for the three organic loading. Table 5: Percentage of TS and VS reduction for all the cycles Organic loading Organic loading Organic loading gVS/ml gVS/ml gVS/ml days CYCLE % % % % % % reduction reduction reduction reduction reduction reduction of TS of VS of TS of VS of TS of VS I cy II cy III cy IV cy V cy VFA profile Concentration of various volatile fatty acids present in the drain after each cycle is given in Table-6. VFA profile shows that acetic acid is predominant in all the cycles for the organic load gVS/ml (Figure 6) followed by propionic acid and Valeric and butyric acid. For the organic loading gVS/ml (Figure 7) acetic acid and propionic acid are predominant followed by valeric acid and butyric acid. For the organic loading of gVS/ml (Figure 8) acetic acid and propionic acid seem to be predominant followed by butyric and iso-butyric acid. The predominant presence of acetic acid in all the three organic loading confirm that acid producing bacteria is active and conditions prevailing in the reactor seemed to be favorable for onset of methanogenesis. 187

8 Table 6: Concentration of various acids in mg/ lit Organic loading gmVS /ml Cycle I Cycle II Cycle III Cycle IV Cycle V Cycle VI Acetic acid Propionic acid Iso Butyric acid Butyric acid Iso Valeric acid Valeric acid Organic loading gmVS/ml Name of the acid Cycle i Cycle ii Cycle iii Cycle iv Cycle v Cycle vi Acetic acid Propionic acid Iso Butyric acid Butyric acid Iso Valeric acid Valeric acid Organic loading gmVS/ml Name of the acid Cycle i Cycle ii Cycle iii Cycle iv Cycle v Cycle vi Acetic acid Propionic acid Iso Butyric acid Butyric acid Iso Valeric acid Valeric acid Figure 6: Figure showing VFA profile for the organic loading gVS/ml 188

9 Figure 7: Figure showing VFA profile for the organic loading gVS/ml Figure 8: Figure showing VFA profile for the organic loading gVS/ml 189

10 3.3 Specific gas production Specific gas production based on amount of Total solids added and volatile solids added for each of the organic loading for all the six cycles are given in Table 7. The high specific gas production based on TS and VS added shows that the mixture of wastes is favorable for the anaerobic digestion with the given organic load. And the mixture of vegetable wastes chosen for the study with the carbohydrate content % is amenable to anaerobic digestion. Table 7: Specific gas production for the six cycles Specific gas production Cycle HRT OL gvs/ml OL gVS/ml OL gVS/ml days l / g of TS l / g of VS l / g of TS l / g of VS l / g of TS l / g of VS added added added added added add I II III IV V VI Kinetic Study According to Boshoff (1967) the rate of production of biogas is a function of the concentration of organic matter yet to be digested. Therefore Where dy /dt = K(A-Y) A = Total amount of gas generated during digestion, ml Y = Amount of gas generated in time, t, ml K = Reaction constant, d -1 t = time, d On integrating between the limits t = 0 to t = t, Y = A (1 e Kt ) Substituting K = 1 / t Y = 0.63A The value of K is calculated from the experimental cumulative gas production curve. Value of K is the reciprocal of time required for the generation of 63% of the total volume of gas produced. In the present study variation of measured cumulative gas production with time indicates the kinetics was found to follow first order reaction and the average value of K was found to be 0.5 d Conclusion Maximum gas production was observed during 5-10 days in the anaerobic digestion process. This shows that carbohydrates have been broken down much faster than the proteins and fats present in the waste and produced the gas. VFA profile indicated the predominant presence of acetic acid in the reactor. ph, TS and VS conversion and gas production observed in the reactor has confirmed that VFA profile prevailed is favorable for sustainable methanogenesis 190

11 process. The specific gas production observed in terms of per g of TS added and per g VS added show that the vegetable wastes containing high carbohydrates are amenable to anaerobic digestion process. Anaerobic digestion process was found to follow first order reaction kinetics and the average value of K was 0.5 d -1. Based on these observations further studies are in progress in continuous reactors for various loading ranges. Acknowledgement Authors wish to acknowledge thankfully the support provided by Director, CLRI, Chennai and Management of GKM College of engineering and Technology in carrying out the research work and permission granted to publish the work. 5. References 1. Science Tech Entrepreneur (2007), Fruit and vegetable waste utilization. 2. Bouallagui H., BenCheikh R., Marouani L and Hamdi M., (2003), Mesophilic biogas production from fruit and vegetable waste in tubular digester, Bioresource Technology, 86, pp Mata. Alvarez.J, Cecchi F., llabres P and Pavan P., (1992), Anerobic digestion of the Barcelona central food market organic wastes: plant design and feasibility study, Bioresource Technology, 42, pp Mata. Alvarez J., Cecchi F., llabres P and Pavan P., (1992), Anerobic digestion of the Barcelona central food market organic wastes: plant design and feasibility study, Bioresource Technology, 39, pp Verrier D., Ray.F and Florentz M., (1983), Two stage anaerobic digestion of solid vegetable wastes: bench scale studies In: Proceedings of the 3 rd International symposium of Anaerobic Digestion, Boston, USA, pp Ahring B K., Mladenovska Z., Ianpour R and Westermann P., (2002), State of the art and future perspectives of thermophilic anaerobic digestion, Water Science and technology, 45, pp Arvanitoyannis loannis S and Varzakas Theodoros H., (2008), Critical reviews in Food Science & Nutrition, 48, pp Burford, J. L and Varani, F. T., Energy Potential through Bioconversion of Agricultural wastes, A Report, Colorado Energy Research Institute, and Colorado. 9. Trevelyan W E., (1975), The Methane fermentation, A discussion paper, Tropical science, 17 (4), pp Boshoff W H., (1967), Reaction velocity constants for batch methane fermentation on farms, notably in the tropics, Journal of agricultural science, 68, pp