Akinola Olugbemide - Sustainable Management of Kitchen Waste through Anaerobic Digestion: Influence of pH and Loading Rates on Biogas Yield

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  Publication Details (including relevant citation   information): Akinola D. Olugbemide*, E. Ohiro2,   Mohammed N. Abdulkadir, A. Oladipo and Damilare I. Ogungbemide   INTRODUCTION A large fraction of municipal solid wastes is   biodegradable, with 20-65% being kitchen waste [1-3]. In Nigeria,   like many other developing countries, large quantities of kitchen   waste are generated in an ever-increasing magnitude with no   commensurate, well-coordinated waste management programmes to   meet up with the challenge. Oguntoyinbo [4] has observed that the   amount of waste that is generated in Nigeria is beyond the   capacity of the environment and the control of the municipal   waste management authority. This menace has been traced to   population explosion, rapid urbanisation and an uneven   distribution of wealth [5,6]. Concerns over air pollution and   diminishing land availability are putting pressures on the   now-widely-used practices of mass burning and land filling [7].   In the past, the performance of a large number of landfills and   incinerators has been quite poor, including landfills that were   built with containment barrier (a clay liner or a synthetic   membrane) [8]. Jain [9] identified some of the adverse   environmental impacts of unscientific handling and indiscriminate   dumping of solid waste. These include the following: a) Ground   water contamination by the leachates generated by the waste   dumps. b) Surface water contamination by the runoff from the   waste dumps. c) Foul odour, pests, rodents and windblown litter   in and around the waste dumps. d) Generation of inflammable gas   (methane) within the waste dumps, resulting in fires at the   landfill with smoke and smog around. e) Release of green house   gases such as carbon dioxide and methane. f) Bird menace above   the waste dumps affecting air traffic. g) Epidemics through stray   animals and other diseases vectors. In large agglomerations of   the developing countries, inadequate waste management is the   cause of serious urban pollution and health hazard [9]. There is   need, therefore, to adopt more environmentally friendly   technologies like anaerobic digestion in tackling the problem of   waste management in Nigeria in order to arrest the difficult   situations experienced at the moment. Anaerobic biological   treatment can be an acceptable solution because it reduces and   stabilises solid wastes volume and produces biogas comprising   mainly of methane and carbon dioxide and trace amounts of other   gases[10]. In addition to biogas, a nutrient-rich digestate is   also produced, which can be used as organic fertilizer [11]. In   the future, it is believed, that anaerobic digestion will be   sought in the perspective of an overall sustainable waste   management [12]. In keeping with this view, a laboratory-scale   study was conducted to evaluate the potential of anaerobic   digestion as a tool for managing kitchen waste, with special   emphasis on the influence of pH and loading rates on the process.   MATERIALS AND METHODS Substrate Collection and Preparation   Kitchen waste used in this experiment was collected from a local   restaurant in Auchi, Edo State, Nigeria. Non-biodegradable   components of the kitchen waste, such as bones, were removed   before the blending was carried out. The substrate was mixed with   some water to enhance blending and homogeneity, the remaining   amount of water was later added. An equal amount of water (1L)   was added to each digester. Experimental Setup Table 1 shows the   experimental design of anaerobic digestion of kitchen waste. Nine   Buchner flasks were used as digesters and labelled based on the   pH values and loading rates. The kitchen waste was charged into   the digesters and stopped with a rubber bung to make it airtight.   Anaerobic digestion of kitchen waste was operated at ambient   temperature of 31+1oC for solid retention time of 24 days. The   influence of pH values and loading rate on biogas yield and   effectiveness of the process was studied. The pH adjustment was   done using NaOH and HCl and monitored with a portable pH meter   (HANNA Instruments, Italy). The volume of biogas was determined   by displacement method. A gas jar filled with saline water was   inverted over a beehive shelf in a trough containing the same   solution. The gas outlet of each flask was fitted with rubber   tubing, which ran through the solution protruding into the   inverted gas collection jars. The volume of evolved gas was   measured daily throughout the experiment [13]. Each digester was   shaken manually once a day to encourage microorganism-substrate   contact. Kinetic Study Kinetics of biodegradation of the best of   each setup was studied using first-order kinetic model proposed   by Jimenez et al.[14]. (1) or (2) Where G (ml) is the volume of   biogas accumulated after a period of time t (days), Gm (ml) is   the maximum accumulated gas at an infinite time, k0 (per day) is   the biogas production rate constant and t (days) is the digestion   time. The value of Gm was considered equivalent to the cumulative   biogas at the expiration of the experiments [15]. RESULTS AND   DISCUSSION Influence of Loading Rates and pH Values on Biogas   Yield Table 1 shows the cumulative biogas yields of the   digesters, which ranged between 0 and 1450 ml. Figure 1, on the   other hand, shows daily biogas yield for the experiments. Biogas   volume for digester A1 reached a daily maximum value of 190 ml on   day 2. The same digester achieved 75% biogas yield in 13 days,   which showed that most of the waste was biodegraded within the   first 2 weeks. Digester A2, on the other hand, achieved 75% yield   in 17 days, with a maximum daily yield of 200 ml. Biogas   production in digester A3 was very poor in comparison to others,   with maximum daily yield of 70 ml. Though digester A3 reached 75%   yield before the others, the yield was very poor and biogas   production was not sustained. Figure 2 shows biogas production   rates for B1 and B2. The digesters displayed comparable trends in   biogas production curves. Both curves peaked on the 8th day,   followed by days of no biogas production until days 20 and 17   when the digestion process resumed. In B3, there was process   failure, leading to no production of biogas. This may be as a   result of rapid acidification that led to accumulation of   volatile fatty acids at this pH value. High concentrations of   volatile fatty acids in the digester would lower the pH, inhibit   methanogenic activity and cause possible failure of the anaerobic   digestion process [16,17]. The daily biogas production curves of   C1, C2 and C3 (figure- 3) showed a departure from the trends   observed in other samples in the sense that peaks were seen   towards the end of the study period. The lag phases in digesters   C1, C2 and C3 were unusually long compared with others. This   inactivity, as suggested by Lalitha et al.[18], maybe due to the   methanogens undergoing a metamorphic growth process by consuming   methane precursors produced from the initial activity. It should   be noted that digesters C1 and C3 had the same biogas yield and   lag phase period, which might suggest that anaerobic digestion   could be carried out at any of the pH values for at the same   loading rate. The fact that B2 (400 g/l) gave the highest yield   showed that the idea of ‘the bigger the better’ does not   necessarily hold in anaerobic digestion of wastes. This is in   agreement with work of Aigbodion et al.[19] on rubber waste, in   which the lowest loading rate gave the highest biogas yield.   Therefore, it is important to determine the optimum loading rate   for any waste to be used in anaerobic digestion. Raposo et   al.[20] observed that if loading is too low, microorganisms will   exhibit a low metabolic activity and very low quantities of gas   will be produced, but on the other hand, if the load is high, the   biogas measurement may be more reliable but lead to an overload   situation in which intermediate volatile fatty acids may build   up, resulting in gas production inhibition. Kinetic Study Results   Figure 4 shows the plot of ln [Gm/(Gm-G)] vs. time for the best   biogas yield of each set of the experiments (A1, B2 and C1).   Biogas production rate constants (k0) ranged between 0.013 and   0.122/day. Digester B2 recorded the highest k0 of 0.122/day,   followed by A1 with 0.082/day, while C1 recorded the least value   of 0.013/day. The k0 for B2 compared favourably with 0.155/day   reported for kitchen waste by Tembhurkar and Mhaisalkar [21] in a   two-phase anaerobic digestion. R2 value fell within the range of   0.8207–0.8890. These results further confirmed better performance   and efficiency of B2 in comparison to other digesters. CONCLUSION   Batch anaerobic digestion of kitchen waste at different pH values   and loading rates was carried out. The results showed that   anaerobic digestion could be used in a sustainable way to manage   wastes that are biodegradable in nature such as kitchen wastes,   thereby mitigating environmental damage caused by improper   disposal of these wastes. The experiments established the fact   that digester B2 was the best of all the setups in terms of   biogas yield and maximum utilisation of waste. Therefore, for   management of kitchen waste, a loading rate of 400 g/l and pH 6.5   should be adopted for maximum yield. Authors believe that, in the   near future, Nigeria and other developing countries in Africa   will adopt anaerobic digestion process as one of the major   programmes for treating solid wastes for sustainable development.   Table 1: Experimental designs and cumulative biogas yield from   kitchen waste Digesters pH Loading rate (g/l) Cumulative biogas   (ml) A1 5.5 200 840 A2 6.5 400 760 A3 7.5 600 220 B1 5.5 200 1420   B2 6.5 400 1450 B3 7.5 600 0 C1 5.5 200 1300 C2 6.5 400 130 C3   7.5 600 1300 Fig. 1: Biogas production rate for digesters A1, A2   and A3. Fig. 2: Biogas production rate for digesters B1, B2 and   B3. Fig. 3: Biogas production rate for digesters C1, C2 and C3.   (A) (B) (C) Fig. 4: Values of ln [(Gm/Gm-G)] vs. time for (a)   digester A1 (b) digester B2 and (c) digester C1. REFERENCE 1.   Tchobanoglous G, Theisen H and Vigil SA. Integrated solid waste   management. McGraw-Hill, Inc., New York, 1993. 2. Isaacson R,   Pfeffer J, Mooij P and Geselbracht J. 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Anaerobic digestion of municipal solid waste and   sludge. Proceedings of the 23rd Intersociety Energy Conversion   Engineering Conference (IECEC), Denver, CO, 31 July-5 August   1988, 4: 407-413. 8. Giust L. A review of waste management   practices and their impact on human health. Waste Management.   2009; 29: 2227-2239. 9. Jain AK. Sustainable development and   waste development. International Society of Environmental   Botanists. 2007; 13(1), Available at   http://www.isebindia.com/05_08/07-01-1.html. Accessed on 4   December, 2012. 10. Stroot PG, McMahon KD, Mackie RI and Raskin   L. Anaerobic codigestion of municipal solid waste and biosolids   under various mixing conditions-I. Digester performance. Water   Research 2001; 35: 1804-1816. 11. Gunaseelan VN. Anaerobic   digestion of biomass for methane production: A review. Biomass   and Bioenergy. 1997; 13: 83-114. 12. Eldelmann W, Joss A and   Engeli H. Two step anaerobic digestion of organic solid wastes.   In Alvarez MJ, Tilehe A and Cecchi J. (eds.) 11 International   symposium on anaerobic digestion of solid wastes. International   Association of Water Quality, Barcelona, Spain, 1999. 13. Wise   DL, Boyd WD, Blanchet MJ, Remedios EC and Jenkins BM. In situ   methane fermentation of combined agricultural residues. Resources   and Conservation. 1981; 6: 275-294. 14. Jimenez AM, Borja R and   Martin A. A comparative kinetic evaluation of the anaerobic   digestion of untreated molasses and molasses previously fermented   with Penicillium decumbens in batch reactors. Biochemical   Engineering Journal. 2004; 18(2): 121-132. 15. Aslanzadeh S,   Taherzadeh MJ and Horvath IS. Pre-treatment of straw fraction of   manure for improved biogas production. BioResource. 2011; 6(4):   5193-5205. 16. Sharma VK, Testa C, Cornacchia G, Lastella G and   Farina R. 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  Abstract: ABSTRACT Nigeria, the most populous   black nation, is confronted with the problem of waste management.   Most of the widely used methods of waste management are proving   ineffective and there is a need for more scientific and   environmentally friendly technologies to meet the challenge   headlong. Anaerobic digestion offers such a viable alternative.   Batch anaerobic digestion of kitchen waste at different pH values   and loading rates was carried out to evaluate the potentials of   the process as a means for waste management. A set of nine   digesters in a batch mode was used and labelled (A1-A3; B1-B3;   and C1-C3). The results showed that digester B2, with loading   rate of 400 g/l run at pH 6.5, gave the highest yield of biogas.   The yield was 72.62% higher than A1 (200 g/l at pH 5.5) and   11.54% higher than C1 and C3. Furthermore, kinetic study showed   that digester B2 had the highest biodegradability, with biogas   production rate constant of 0.122/day. Conclusively, anaerobic   digestion can be an effective option in treating kitchen waste   and generating bioenergy. Keywords: Kitchen waste, Sustainable   management, Anaerobic digestion, pH, Loading rate

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