Pretreatment of Surface Waters and Wastewater by a Hemodiafilter for Online Bacterial Counting

Abstract

The online monitoring of bacterial content during drinking water and wastewater treatment processes is an important strategy for enhancing the quality of treated waters. Although real-time bacteriological counting techniques enable online monitoring of bacterial counts, the autofluorescence of background organic constituents in the waters (e.g., humic acids) interferes with such analysis. In this study, the efficacy of a new pretreatment technique involving a hemodiafiltration membrane (termed hemodiafilter) for continuously removing interfering substances is evaluated. Pretreatment of river water, dam water, and a membrane bioreactor's (MBR) effluent using the hemodiafilter demonstrates the effective removal of background interfering substances, thereby improving online bacterial analysis. Online analysis of the MBR effluent stopped after 48 min because the fluorescence intensity of the interfering substances in the pretreated sample reached the maximum measurement level of the counter. Adding an anion exchange resin treatment to the dialysate, dialysis fluid extracting the fine substances from the sample stream, decreases the background fluorescence intensity in the sample and dialysate streams, allowing online analysis for >6 h. The implementation of resin regeneration in the pretreatment system is recommended. This study indicates that the hemodiafilter and anion exchange resin are vital for minimizing substances interfering with online bacterial counting during water treatment.