Enhancement of biogas production from organic fraction of municipal solid waste using alkali pretreatment

Anaerobic digestion is one of the most prospective and economical techniques to recover energy and simultaneously treat organic fraction of municipal solid waste (OFMSW). However, more often than not, the complex polymeric structure of lignocellulosic fraction and high lipid content of Indian OFMSW prove to be hindrances in realizing the full potential of energy recovery through anaerobic digestion. Pretreatment of OFMSW is an effective method to enhance the efficiency of anaerobic digestion. This paper explores the effect of alkali pretreatment on change in characteristics of OFMSW in India and its subsequent impact on biogas generation. Pretreatment was carried out using 5 M sodium hydroxide (NaOH) solution and varying the initial pH of OFMSW in the range of 8-13 for 24 h. Thereafter, batch anaerobic digestion assays of untreated and pretreated OFMSW were carried out using cow excrement as inoculum. Results indicate that NaOH pretreatment was advantageous in solubilizing the organic matter of OFMSW, thus increasing biogas yield and reduced digestion time. The cumulative biogas generation increased by 19.6-34.8% post-NaOH pretreatment. OFMSW pretreated with NaOH at pH 10 had maximum biogas yield of 407.1 mL/gVS with 68.9% methane content, as compared to 301.9 mL/gVS and 50.3% of untreated OFMSW. A preliminary cost assessment indicated a positive net profit for pretreatment of OFMSW with NaOH at pH ranges of 8-10.