Microbial electro-hydrolysis of sewage sludge for acidogenic production of biohydrogen and volatile fatty acids along with struvite

Synergy of multi-biological unit operations was studied to maximize the resource recovery in line with biorefinery using sewage sludge (SS) as primary feedstock. Microbial electro-hydrolysis systems (MES) were used as a pretreatment system to enhance the SS solubilization against the non-electrochemical control operation (AnT) under alkaline conditions. Comparatively, applied potential MES system (polarized) resulted in high SS solubilization (27.5%) than the corresponding MES-closed circuit (21.5%) and MES-open circuit (14.8%). In contrast, low SS solubilization was found in non-electrochemical system (AnT; 8.8%). Morphological changes in the SS refractory structure before and after pretreatment were examined by field emission scanning electron microscopy (FE-SEM). Energy-dispersive X-ray spectroscopy (EDX) spectrums showed significant changes in elemental composition due the course of pretreatment. Consequent utilization of obtained hydrolysate in the acidogenic fermentative reactors (AFR) resulted in good volatile fatty acids (VFA: 4.65 g/L) and Bio-H-2 (21%) production. The distribution analysis of VFA revealed acetic acid as a major fraction followed by iso-valeric acid, butyric acid and propionic acid, which accounted the high acidification degree (57%) in AFR-3 system. Rich nutrient content of SS hydrolysate resulted in good struvite precipitation (phosphate fertilizer), which was confirmed with structural morphology and crystalline nature.