Biological stability for vacuum UV advanced oxidation treatment of surface water

Vacuum UV (VUV) involving UV 185 nm has been extensively studied as a viable and robust advanced oxidation process (AOP) for drinking water purification. It is highly efficient for the removal of micro-pollutants including pesticides, herbicides, personal care products and cynobacterial toxins. However, at the applied ultraviolet (UV) dose for micro-pollutant removal, the natural organic matter (NOM) present in surface water is not completely mineralized. The breakdown of NOM from larger molecular weight fractions leads to an increase in the smaller and more biodegradable molecular weight compounds. This may lead to increases in assimilable organic carbon (AOC) and disinfection by-product (DBP) precursors. An increase in AOC will result in reduced biological stability, triggering bacterial regrowth in the distribution system. Hence, it becomes important to study the impact of VUV AOP on biological stability of the treated water. In this research, AOC and biodegradable dissolved organic carbon (BDOC) assessments were used to quantify changes in the bio-stability of water. Laboratory scale experiments were carried out in batch and continuous modes using two different setups. The batch setup involved a custom built collimated beam, containing an ozone generating low-pressure amalgam mercury lamp. This was used to study the kinetics of AOC formation during irradiation with 185 and 254 nm UV. Surface water from various sources across BC were used. The second setup consisted of a flow through reactor, equipped with similar VUV lamp, used to investigate the changes in water quality under different operating conditions. Trihalomethane (THM) formation (uniform formation conditions), chlorine demand measurements and size exclusion chromatography analysis further assessed changes in the treated water quality. The results showed increases in the AOC (100 – 200 % increase) and BDOC (50 – 150 % increase) after VUV treatment (max. 1800 mJ/cm2 fluence, 254 nm UV equivalent). To address the issue of reduced biological stability, biological activated carbon (BAC) treatment was evaluated as a potential treatment, post VUV process. The results for the combined VUV and BAC treatment showed 75% reduction in AOC relative to untreated water, thus significantly improving the water quality.Applied Science, Faculty ofChemical and Biological Engineering, Department ofGraduat