Åsa Davidsson

Influences of upstream wastewater treatment on the process combination of granular activated carbon (GAC) and ultraviolet (UV) disinfection were studied and the implications of this for wastewater reuse were assessed. GAC is an efficient chemical barrier but contributes little to the removal of indicator bacteria, and generally increases total bacteria concentrations, necessitating disinfection with UV radiation, for example, to ensure the safe reuse of wastewater. The efficiency of UV disinfection is impacted by factors such as particle concentration and UV absorbance of the water and is thus affected by upstream treatment processes. A full-scale wastewater treatment plant with a membrane bioreactor (MBR) followed by GAC filtration was compared to a treatment plant with a conventional activated sludge process and sand filtration, followed by GAC filtration. The removal of indicator bacteria was higher by the GAC filter that was preceded by an MBR. A UV fluence of 400 J/m2 was sufficient to reach irrigation water quality for both process combinations and to meet the criteria for microbial drinking water quality in the MBR + GAC effluent. One sample was selected for chemical analysis, comprising approximately 100 parameters, demonstrating that the MBR + GAC + UV (400 J/m2) effluent met all drinking water criteria except for nitrate levels.