Enhancing the volatile fatty acid production from agro-industrial waste streams through sludge pretreatment

Abstract

Acidogenic bioconversion of agro-industrial effluents into potential biopolymer production media was accomplished by sludge modification with subsequent bioprocess assessment. Initially, the food to microbe ratio (0.5, 1.0, and 2.0) was optimized with rice mill effluent. The optimized value was used to study the effect of sludge pretreatment, performed under cyclic acidic and heat shock, to improve the volatile fatty acid (VFA) content of rice mill effluent and brewery effluent for downstream applications. An F/M ratio of 1.0 performed the bioconversion best considering the downstream application. Pretreatment refined the VFA content in the rice mill effluent. Total VFA content and degree of acidification increased from 1897 ± 0.12 in the untreated system to 2437 ± 0.03 mg L⁻¹ and from 75 ± 0.16 to 86 ± 0.13% at their respective peaks. Similarly, for the brewery effluent, the increment was from 1697 ± 0.13 to 2175 ± 0.05 mg L⁻¹ and from 71 ± 0.14 to 85 ± 0.09%. Acetate was in higher amounts among VFAs after pretreatment for both effluents. Chemical oxygen demand was retained in the pretreated system. The pH remained stable in the acidic range for the pretreated system while the pH shifted to an alkaline condition in the untreated system. The sludge acidified rice mill effluent performed better than brewery effluent. Pretreatment enhanced the sludge capacity for acidification, transforming the effluents to suit downstream polymer production.