Effect of Disinfection Byproduct Formation Potential by Microbubble-Biofiltration

Lake Ron, a reservoir located on Kinman Island, is prone to eutrophication and seasonal algae blooming due to excessive livestock farming and inadequate water management. The results in elevated dissolved organic carbon (DOC) concentrations in the reservoir, which can be removed partially in conventional water treatment processes. The DOC in raw water will react with chlorine to form disinfection byproducts (DBPs), such as trihalomethanes (THMs), haloacetic acids (HAAs) which are also known as carbonaceous DBPs (C-DBPs). Furthermore, nitrogenous DBPs (N-DBPs) such as haloacetonitriles (HANs), halonitromethanes (HNMs), which may have higher toxicity than C-DBPs, are also produced. Advanced water treatment processes can control the formation of DBPs. However, high energy consumption may be an important issue. Microbubble with the diameter is less than 50 µm, will gradually decrease in size and collapse in water. Oxidative free radicals will be generated after the microbubble eruption. The objectives of this study are to increase the ratio of biodegradable organic carbon (BDOC) in DOC and oxidize the hydrophobic natural organic matter(NOM) by microbubble aeration. At the same time, microbubble aeration is used in combination with biological filtration (biofiltration) to enhance the DOC removal efficiency. Moreover, microbubble aeration can also increase the dissolved oxygen (DO) concentration and enhance the biological activity in the biofilters. The DBP formation potential (DBP FP) test was used to evaluate DBP precursors removal efficiency with different disinfectants. The results showed that it was less effective in the removal of DOC but effective in removing to the precursors of THMs and HANs by both air- and oxygen-microbubble. In the microbubble aeration combined with biofiltration recycling process, it also showed no apparent DOC concentration reduction, the precursors of THMs, HAAs and HANs removal efficiency enhancement. Compared with direct biofiltration recycling process, the ozone-microbubble combined with biofiltration recycling process could indeed increase the removal efficiency of the DOC, but it still showed no noticeably increasing in the removal efficiency of DBP FP. Among original and microbubble ozonation, both of them had the similar ability to remove DOC and DBP FP. Hence, the microbubble treatment can only change the DOC structures slightly. In conclusion, application of the oxidizing potential of microbubbles in drinking water treatment processes requests attention for further research.