Effect of Co-Digestion of Leachate and Cotton Gin on The Production of Biogas from Cow Dung

Abstract

Pakistan has been facing major hindrance in the economic development due to the energy crises. Luckily, Pakistan has massive biomass resources available as crop residues, food waste, sugarcane bagasse, wood, industrial waste, dung, feces, and poultry litter etc. which could be used to produce biogas, an alternative renewable fuel. The current research was conducted to study the potential to produce biogas from cow dung with the co-digestion of cotton gin with the objective of increasing the biogas production through the addition of municipal solid waste leachate in different proportion under mesophilic conditions. For this reason, batch digestion was performed in the laboratory of IESE, NUST. In each case six digesters having working volume of 1.2 liters were used. First three digesters were filled with cotton gin and cow dung in leachate and other three with cotton gin and cow dung in water. Same proportions (900ml) of liquid (leachate or water) was added in the digesters. The solid substrates (cotton gin and cow dung) were added in three different combinations (1:2.5, 1:5 and 1:7). To adjust the pH of digesters, Na2CO3 was used to buffer any sharp drop. Results showed that the highest percentage reduction in VS (80.3%) was found in the digesters containing cotton gin and cow dung filled as 1:2.5 in leachate thus producing maximum volume of gas. Combination 1 (1:1.25) cumulatively produced highest amount of biogas which was approximately 1350 ml/g of VS while digester with the same solid content ratios in water produced 1000ml/g of VS. Co-digestion in leachate and water resulted in 12.95 times and 10.83 times higher biogas production then raw (leachate and gin independently) respectively. Average methane content in biogas after attaining stability was 67.8% for combination 1 in leachate while 35.5% for the same combination in water. Percentage reduction in COD was highest in leachate. All three leachate samples showed changes of 61.4% to 71.2% reduction of COD. From the results, it was concluded that leachate addition had a positive effect on biogas production from both type of solid waste but this effect was more considerable in the digester containing highest ratio of cotton gin.