Abstract
Abstract In the present study simultaneous alkaline treatment of pearl millet straw (PMS) in solid state anaerobic digestion (SSAD) at 52 °C was attempted to enhance methanogenesis. Alkalis (Ca(OH)2, NaOH and KOH) were added simultaneously as 1, 2, 3 and 4% w/w basis (% alkali/100 g of straw) for enhanced contact time with PMS. Results revealed that mild simultaneous alkali treatment of PMS showed positive impact (140 L/kg of methane at 2% KOH) on SSAD as compared to untreated PMS (85 L/kg VS of methane). In spite of the fact that higher dose of alkali showed enhanced lignin disruption, a decrease in methane yield was observed compared to lower dosing. Based on experimental data, net energy analysis was carried out to see if the input energy and environmental heat loss could be subsided for full scale SSAD plant. The results from lab scale experiments were used for net energy analysis by extrapolating the results obtained in the experiments. The analysis showed that a gross cumulative gain of 82–165 GJ of energy observed for simultaneous alkaline treatment over six months. Also, the results showed that net energy production rate (NEPR) and energy efficiency ratio (EER) of untreated PMS were 61.2% and 2.6 respectively; while, for treated PMS with 2% KOH, it reached to 81.1% and 5.4 respectively.
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