Snehasish Mishra

Fish bioassays for evaluation of raw and bioremediated dairy effluent.

Abstract Short-term static bioassays were conducted for raw and bioremediated dairy effluent with rohu, Labeo rohita to substantiate its usability for fish culture. The 96-h LC 50 of the raw effluent was 25.5% (i.e., 74.5% dilution). After stabilisation, sedimentation and bioremediation with Wolffia for 15 days the effluent showed a decline in toxicity and the 96-h LC 50 was calculated as 73.5% (i.e., 26.5% dilution). Based on this, the dairy effluent could be used in pisciculture as a fertilizer with proper dilution.

Bioprospecting Kitchen Refuse as a Suitable Substrate for Biogasification

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 cm3 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.

Microbial pretreatment of lignocellulosic biomass for enhanced biomethanation and waste management

Biogas obtained from organic remains entails a developed technology and an appreciable methane yield, but its use may not be sustainable. The potential methane yield of various lignocellulose biomass and the operational conditions employed are inherently reviewed. Although of lower methane yields compared to conventional substrates, agricultural biomass is a cheap option. The major challenges encountered during its biogasification are its recalcitrance nature primarily due to the presence of crystalline cellulose and lignin. This necessitates an essential pretreatment step through physical, chemical or biological interventions for enhanced biomethanation potential. Various pretreatment—physical, chemical, and biological—strategies have been developed to overcome the inherent recalcitrance of lignocellulose to anaerobic degradation. Biological pretreatment approach, however, outcompete other pretreatments due to their application in milder conditions, little corrosiveness, and lower byproduct formation. Such pretreatment importantly aids in selectively reducing the lignin content and crystalline nature of the lignocellulosic biomass, which would evidently enhance the hydrolysis and production of monomers for their further anaerobic digestion (AD) for methanation. A variety of applied biological pretreatment strategies comprises microaerobic treatments, ensiling or composting, separation of digestion stages, and pretreatments using various lignocellulolytic fungi alongside. The net energy output through such approaches is substantially more and relatively inexpensive compared to other established chemical and mechanical approaches. The present review highlights the use of biological agents including bacterial, fungal and/or their enzymes which trigger biodegradation of wastes and utilization of lignocellulose for biofuel production. Additionally, the different physical, chemical, and biological pretreatment strategies for biogas yield enhancement are presented.