Fecal coliform removal in wastewater treatment plants studied by plate counts and enzymatic methods

Twelve wastewater treatment plants (WWTPs) were sampled in France and Belgium in 1999 and 2000 in order to estimate the fecal coliform (FC) removal efficiency of various types of treatment. Only one of these WWTPs was equipped with a specific step to eliminate microorganisms (UV disinfection preceded by sand filtration). FC abundance was measured in raw and treated sewage by plate counts on selective medium and rapid beta-D-glucuronidase (GLUase)-based assays. Removal of culturable FC was the most efficient in treatments with high retention time (activated sludge process with nitrification and denitrification, lagooning), in biofiltration and in the treatment with a tertiary disinfection step. GLUase activity measurements showed the same removal pattern as plate counts except for UV disinfection, where no reduction of GLUase activity was measured. Specific loads of culturable FC and GLUase activity, i.e. daily amounts of culturable FC or GLUase activity in sewage per inhabitant-equivalent, were calculated in raw and treated wastewater for the different WWTPs.