Studies on biphasic biomethanation of spoiled mango puree

Abstract

In a pilot-scale (175 L) study, spoiled mango puree (8.0-12.0% total solids) was subjected to biphasic biomethanation. For this purpose, an efficient phase separation between puree hydrolysis/acidification and its methanogenesis was achieved by using three acidogenic reactors (ARs) in series, operated aerobically at ambient temperature. The hydrolysate coming out of the AR series contained high percentage of volatile fatty acids (VFAs, 15,000-20,000 mg L^-1), indicating efficient conversion of sugars. Subsequently, this hydrolysate was fed to two methanogenic reactors (MRs), operated anaerobically at 35±1.0°C. About 30% digestate from MRs was further recycled to ARs for enhancing the efficiency of hydrolytic activity. This arrangement permitted the maintenance of optimum <i style="">p</i>H in ARs at 4.5-5.5 range and an efficient anaerobic digestion in MRs as indicated by <i style="">p</i>H of the digestate in 7.2-7.8 range.

The optimized conditions permitted, (i) an increase in feedstock initially from 2.0 to 10.0 L/d, (ii) methanogenic transformation of 15,000-20,000 mg L^-1VFAs, (iii) generation of 100±20 L d^-1 biogas containing 65% methane initially and 550±25 L d^-1 biogas with 78% methane upon stabilization over 180 d, (iv) digestate leaving MRs with 600-1200 mg L^-1VFAs, and (v) around 90% efficiency in terms of VFAs utilized.