Kinetic modelling and improvement of methane production from the anaerobic co-digestion of swine manure and cassava bagasse

Abstract

Anaerobic co-digestion (AcoD) is a promising biotechnological approach for the management of livestock and agro-industrial wastes with the concomitant production of renewable energy. This study investigated methane production during batch AcoD of swine manure (SM) and different amounts of cassava bagasse (CB), using Na2CO3 to adjust initial pH (8.0) and as buffering agent. The highest methane yield of 41,129 ± 1783.6 mL CH4 L−1 (157,04 ± 6,81 mL CH4 g VSinitial−1) was observed with 90.6 g total solids (TS) L−1, in systems containing 16.87 g TS L−1 from cassava bagasse. At this condition and in comparison, with the control (C1), the reactor R4 presented a superior removal of 83.8% for TS, 101.1% for VS, 42.1% for COD, and 161.6% for CODS. Nevertheless, methane production was inhibited at higher CB additions (22.48–33.72 g TS L−1). Methane production kinetics was well explained by including the first order specific growth rate with metabolism as the limiting step for two different substrates (SM and CB) and the linear buffering capacity behavior from CB. This novel proposed model describes the phenomenon of acid inhibition and inactivation of cell biomass caused by the insufficient buffering capacity. The developed model might apply to other similar systems where acid failure could occur, and can be used for a rational scale-up of batch and continuous processes.