Real-Time Online Monitoring for Assessing Removal of Bacteria by Reverse Osmosis

Rigorous monitoring of microbial water quality is essential to ensure the safety of recycled water after advanced treatment for indirect and direct potable reuse. This study evaluated real-time bacterial monitoring for assessing reverse osmosis (RO) treatment for removal of bacteria. A strategy was employed to monitor bacterial counts online and in real time in the RO feed and permeate water using a real-time continuous bacteriological counter. Over the course of 68 h pilot-scale testing, bacterial counts were monitored in real time over approximate ranges from 1 × 10³ to 4 × 10⁴ and from 4 to 342 counts/mL in the RO feed (ultrafiltration-treated wastewater) and permeate, respectively. The results indicate that the bacteriological counter can track the variations in bacterial counts in the RO feed and permeate. Bacterial concentrations were confirmed by epi-fluorescence microscopy for total bacterial counts. A high correlation (<i>R</i>² = 0.83) was identified between the online bacterial counts and epi-fluorescence counts in the RO feed; a negligible correlation was observed for RO permeate. In this study, we evaluated a real-time bacteriological counter (i.e., counts per milliliter every second) to ensure continuous removal of bacterial contaminants by RO treatment