Beverage wastewater treatment by anaerobic digestion in two-stages for organic matter removal and energy production

Abstract

This study evaluated an anaerobic digestion (AD) process in two-stage for both organic matter removal and energy production, treating wastewaters from the beverage industry. The experimental studies were carried out in a continuous mode in an acidogenic reactor (RA) followed by a methanogenic reactor (RM) with a Hydraulic Retention Time (HRT) of 8h and 16 h, respectively, for 107 days. During this period, the geometric mean value of pH in the effluent of the system (RA+RM) was 7.3 and did not show a clear response to organic load rate (OLR) that were in a range of 14.66–50.15 kgCOD/m3·d, while the buffer capacity indicators, intermediate/partial alkalinity (IA/PA) ratio, and FOS/TAC were more effective in monitoring the process stability. IA/PA of 0.34 and a FOS/TAC of 0.18 assured a stable process and prevent an acidic shock for this type of wastewaters. Concerning the energy efficiency (EE) evaluated in the RA, the determining factor was the Low Heating Value (LHV), was directly proportional to the molar fraction of the gas. In particular, the adjusted LHV was 0.51 kJ/mol while the ideal LHV was 242 kJ/mol and the EE was 1.71% and 0.017% respectively. These results evidenced that is necessary to improve the mechanism to monitoring the AD process in each stage to maintain the stability, which will also allow increasing the energy efficiency in the whole system (RA+RM).