Abstract
India produces huge quantities of agricultural residues and stubbles and mainly disposed by burning on site causing air pollution. The organic matter present in the residues and stubble may be utilized by anaerobic digestion as a source of renewable energy subsequently reducing emission of greenhouse gases caused by burning. In the present study, solid state anaerobic digestion (SSAD) of pearl millet straw was investigated at mesophilic and thermophilic temperature with four different total solid (TS) content (15, 20, 25 and 30%). Results showed that 20 and 25% TS generated maximum methane (124.1 ± 7 and 162.4 ± 9L/kg VS) at mesophilic and thermophilic temperature respectively. However, increasing TS content beyond 25% did not show significant increment on methane yield. Analytical analysis showed correlation between the reduction of volatile solids and methane yield as well as VFA (volatile fatty acid) accumulation at high TS content. Also, VlseKriterijuska Optimizacija Komoromisno Resenje (VIKOR) and Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) methods as MultiCriteria Decision Making modelling (MCDM) applied to select best possible alternative for SSAD of pearl millet. MCDM analysis showed that VIKOR method endorsed the experimental results.
Highlights
Lignocellulosic residues and stubble are promising alternatives to provide fuel and energy security by utilizing them as a source of biomethane production[1,2]
The results showed a linear relationship between the specific methanogenic activity and solid concentration
pearl millet straw (PMS) had high total solid (TS) (93.42%) and VS (92.24% of TS) content and considerable amount of cellulose (36.42%) and hemicellulose (25.31%) with moderate lignin content (15.63%) while VS in inoculum was 65.78% VS (% TS) (Table 2) which shows its suitability for solid state anaerobic digestion (SSAD) for biogas production
Summary
Lignocellulosic residues and stubble are promising alternatives to provide fuel and energy security by utilizing them as a source of biomethane production[1,2]. Effect of ammonia – N accumulation in SSAD process of food waste, fruit and vegetable waste, yard waste and paper waste was performed by Zeshan et al.[10] using the pilot scale thermophilic reactor for the same and results showed that the net energy gain was around 50 to 75% higher in the thermophilic temperature condition to that of mesophilic one. Thermophilic SSAD increases the methane and biogas productivity, it requires heat energy input for the uninterrupted process and net energy gain may be less as compared to mesophilic condition. Thermophilic condition in SSAD enhances the hydrolysis of the substrate by stimulating hydrolytic microorganisms in the reactor This acceleration of hydrolysis in the SSAD reactor may cause a rapid increase and accumulation of VFAs in the reactor[12] that may hamper or inhibit the methanogenesis process of the bioreactor. TS and carbon to nitrogen ratio of substrate(s) will have a noteworthy role in the digestion process[13]
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