An Environment Friendly Approach: In-Vessel Composting and Anaerobic Digestion for Methane Gas Generation from Secondary sludge of GESCSL, CETP-Vatva, Ahmedabad, Gujarat, India

Abstract

Any individual or Common Effluent Treatment Plants generates large amounts of sludge, that is ultimately handled by disposing the same to Treatment Storage Disposal Facility (TSDF). There is burning question, how this sludge will be managed? Nowadays large amount of attention has been paid to sludge management, which can be ultimately results in less quantity of sludge disposal and saves large amount of money, which are wasted due to improper handling of sludge. Sludge characterization is most important in implementation of proper sludge management technique. Primary and Secondary sludge of The Green Environment Services Co-Operative Society Ltd.-CETP, Vatva, Ahmedabad, Gujarat, India was analysed first and found Carbon content: 22.64, Nitrogen content: 4.65 and C:N ratio: 4.87 in secondary sludge, which was higher than in primary sludge. Two different sludge management techniques i.e., Composting and anaerobic digestion implemented on secondary sludge. These two different techniques for sludge management pursue two goals; handling of the sludge in a harmless way for the environment and producing more biogas (mainly methane and carbon dioxide). The produced compost can be used as a fertilizer. The produced biogas through Anaerobic Digestion (AD), is a renewable energy source that can be used as a substitute for fossil vehicle fuels (needed to be upgraded to separate the methane content) also for production of heat and electricity. In-Vessel composting method was implemented and secondary sludge was taken in different proportion with Vegetable Waste (VW) as well as with Cow Dung (CD) in different vessels. To check the made compost quality and the best compost among all, Pot study was carried out by using the made compost as a fertilizer in plants. Compost, which is made by using 10 to 30 % of secondary sludge and 70 to 90 % of Cow Dung gave the best results. Usage of secondary sludge more than 30 % does not give good results. Compost which is made by using secondary sludge can be used for non-crop plants which are used for flower gardening and furniture manufacturing rather than crop producing plants, which will be hazardous for human beings because of the migration of toxic substances through food chain. To investigate possible ways to increase the methane production from sludge digestion the digestion of secondary sludge with addition of sewage and vegetable waste (to adjust C:N ratio) was investigated. The procedure adopted for measuring the methane production from the sludge was based on the theoretical calculation, which depends on the Chemical Oxygen Demand (COD) difference of Feed and Outlet of Anaerobic Digester. The methane production is expressed as volume of produced methane per kg COD removed (L CH4 /kg COD). In AD, the observed reduction were 73 % of Total Solids (TS) and 69 % of Volatile Solids (VS) averagely. Also maximum of 96.26 % and minimum of 58.50 % of COD removal has been obtained in AD. Secondary sludge along with continuous feeding of green waste and sewage gave maximum volume of methane gas generation i.e., 217.03 L CH4/g COD on thirteen day after initiation of AD on the basis of COD reduction. During the entire study, average 91.00 L CH4/g COD of cumulative methane gas generation was obtained. After 13 days, Average, 40-50 % of methane gas yield was obtained through Anaerobic Digestion of secondary sludge of GESCSL-CETP, Vatva which was ensure through gas chromatography. Moreover, at site methane generation was ensure by burning of collected gas taken in bladder and continuous flame was observed, which is indication of presence of 40-50 % of methane gas in generated biogas.