Enhanced biogas production in dilute acid-thermal pretreatment and cattle dung biochar mediated biomethanation of water hyacinth

Abstract

The effect of dilute acid-thermal pretreatment and cattle dung biochar (BC) addition on anaerobic co-digestion (AcoD) of water hyacinth (WH) with waste activated sludge (WAS) was investigated in this study under mesophilic condition. The dilute acid-thermal pretreatment (2% H2SO4 w/v followed by 121 °C, 60 min) hydrolyzed 38.1% (lignin), 56.8% (cellulose) and 86.7% (hemicellulose) of lignocellulosic fraction and increased the soluble chemical oxygen demand (sCOD) and volatile fatty acids (VFA) concentration by 4.91-folds and 2.20-folds, respectively. The cumulative biogas production in pretreated and biochar amended digesters was 73.4–98.7% higher than the control digester. Methane content in biogas improved by 9.33 – 19.8% in BC supplemented assays over control. The highest methane yield of 235 mL and VS removal (77.4%) were observed for pretreated, and biochar (1% dose) amended digester. The morphological and structural transformations in non-pretreated and dilute acid-thermal pretreated WH biomass were studied by Scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) analysis. SEM results shows the porous and rougher structure with flake-like structures owing to harsh pre-treatment conditions. FTIR analysis revealed significant changes in polymer composition and strong lignification of WH biomass. Thus, the dilute acid-low thermal pretreatment of lignocellulosic feedstock and cattle dung biochar amendments in digester are promising methods for effective biomethanation.