Abstract
Conventionally, methane nonproducing organic substrates such as kitchen refuse (KR) are amenable as biogasifiers, similar or even better than that of the naturally biogasifying cow dung (CD) through process modification. Comparative physicochemical and biological analyses revealed that KR had no methanogen and was low on amylase and cellulase positive and total microbial counts. It was observed that the pH level lowered further when the KR alone was biogasified, attributable to the accumulating volatile fatty acids, which indicates the failure of the last and final step of biomethanation. Study of the raw and digested forms of KR, CD, and kitchen refuse fortified with cow dung (KC) revealed that there was a net percentage decrease in dry matter (70.00, 94.33, and 88.88, respectively), total dissolved solids (1, 1.5, and 1.5, respectively), and phosphate contents (12, 19, and 20, respectively), indicating an optimal microbial activity in all the substrates. Although digestion rate in CD was better than that in KR, KC exhibited an enhanced digestion rate over KR attributable to the process being facilitated by increased microbial counts; amylase-, cellulase-, and lipase-positive microbes; and methanogens. Furthermore, the active methanogens in CD inoculum (in KC) facilitated biomethanation by better utilizing the volatile fatty acids that ensured better stability in the pH level throughout. The cumulative biogas production values were 1281, 4448, and 3256.cm(3) in KR, CD, and KC, respectively. Methane production started by the seventh day in CD and KC and reached up to 63.65% and 53%, respectively, by the 21st day in batch operation. Thus, KR is a promising candidate for biogasification, thereby opening a plethora of opportunity to utilize the technology even in urban and periurban locations that are low on cattle resources albeit rich in other organic refuse. There is a necessity to estimate the biomethanation potentials of various other available organic refuse.