Estimation of solids and biodegraded metabolites in the raw and processed slurry of the two-phase Nisargruna biogas plant

Abstract

The use of the Nisargruna biogas plant is an efficient approach for solid waste management (SWM) with the simultaneous production of digestate and bioenergy. Monitoring of total solids and biodegraded metabolites of carbohydrates, proteins, and fats at different stages of digestion can provide comprehensive information about the efficiency of biogas plants. The current study was carried out to characterize the generation of solids and degraded biomolecules in the raw, predigested, and digestate (completely digested) slurry during the different stages of the two-phase Nisargruna biogas plant. It was conducted based on standard gravimetric techniques and biochemical assays. Our results indicated a significant reduction in total solids (40%–45%), carbohydrates (60%–65%), proteins (40%–45%), lipids (15%–20%), sugars, and free amino acids (65%–70%) in the predigested slurry, as compared to the raw slurry. In addition, only formic acid (2–2.5μl/ml) was detected in the raw slurry, whereas a significant amount of acetic acid (25–30 μl/ml) and small quantity of butyric acid (1 μl/ml) was detected in the predigested slurry. Furthermore, the digestate slurry showed the absence of volatile fatty acids indicating that they were efficiently utilized for methane formation in the main digester. The specific gravity and oxygen consumption rate in the predigester was estimated to be 1.0190 and 11.22 mg/l/minute, respectively. Lastly, the recyclable water obtained after dewatering the digestate slurry showed the absence of coliforms and a biological oxygen demand of 100 ppm, suggesting its suitability for disposal in the sewerage system. Based on the above chemical analysis of raw and processed slurry, the Nisargruna biogas plant thus proves to be highly efficient for SWM.