Monitoring anaerobic digestion: a 2-year brewery case study

Operational data from an anaerobic wastewater treatment plant (expanded granular sludge bed (EGSB) reactor) were analysed before and after a defect with the solids separator. The results presented suggest that a newly available method for the analysis of total volatile fatty acids (VFAs) was ideal as a rapid, onsite, operational indicator of reactor stability. These total VFAs were shown to provide an earlier warning of the separator problem than the other rapid routine methods of monitoring digesters such as alkalinity and suspended solids. Chemical oxygen demand (COD) removal, pH and gas yield were not as useful for monitoring because of their slow response. The results are from a high rate reactor; the loads were 18kg COD/m3/d in the first year and 26 in the second with 4·4 d hydraulic retention time. The results for both years of operation demonstrate a 95% conversion of COD into gas with an additional contribution from solids digestion (specific gas yield of 0·4 l methane (CH4)/g CODrem). This high performance was attributed to the solubility of the COD and the efficient EGSB mixing.