Challenges of point-of-use devices in purifying tap water: The growth of biofilm on filters and the formation of disinfection byproducts

Currently, polypropylene (PP) and granular activated carbon (GAC) are widely used as the filters in point-of-use devices (POUs). However, the effect of biofilms formation in aged filters and subsequent formation/removal of disinfection byproducts (DBPs) during the use of POUs on purifying tap water remains unclear. In this study, the influence of filter replace event and filter usage time on the removal of DBPs by pristine or aged filters, such as trihalomethanes (THMs) and haloacetic acids (HAAs), was investigated. Additionally, the effect of biofilms-attached PP filters and GAC filters on DBPs concentration in treated water was explored. The results showed that POUs effectively removed over 60% of THMs and HAAs from tap water, while the removal efficiency decreased with the operation time. The increase in usage time of PP filters led to elevated levels of DBPs. Moreover, the pristine pre-GAC filters removed 12.31% of THMs and 6.62% of HAAs, respectively, while aged GAC filters enhanced the removal of HAAs. SEM and high-throughput sequencing analysis confirmed the attached growth of biofilms on aged PP and GAC filters. The biofilms growth on PP filters led to the formation of THMs and HAAs, and the formed DBPs increased with increasing influent chlorine concentration, lengthened filters usage time and stagnation time. Nevertheless, the DBPs in effluent of biofilms-attached GAC filters increased with increasing influent chlorine concentration and filter usage time while decreased with stagnation time. These results indicated that growth of biofilms commonly observed in filters of POUs leads to the formation of DBPs and increases the risk of DBPs exposure to users of POU devices.