Impacts of Ozone Dose and Empty Bed Contact Time on Total Organic Carbon Removal Through Ozone-Biological Activated Carbon Treatment

摘要

In the face of climate change, pollution, and population growth, water scarcity has become a global threat. Many populations have witnessed their drinking water sources dwindle to an unsustainable level. These severe conditions have sparked interest in potable reuse as an increasingly viable alternative to typical ‘pristine’ drinking water sources. Currently, the California Division of Drinking Water (DDW) provides the most stringent requirements for reuse water quality. The best way to meet these standards is through the use of full advanced treatment (FAT), which consists of reverse osmosis (RO) and an advanced oxidation process (AOP). Alternative treatment trains composed of ozone and biological activated carbon (BAC) have been employed in several locations throughout the world, but these systems have not yet been optimized and are unable to compete with RO-based treatment trains on the basis of total organic carbon (TOC) removal. The purpose of this study was to identify the relationship between ozone dose and empty bed contact time based on TOC removal through ozone-BAC treatment. By evaluating the effects of these two operational parameters on biofilter performance, improved TOC removal may be achieved or more suitable operating conditions identified.A 0.6 liter-per-minute (LPM) pilot-scale ozone-biofiltration reactor was constructed and operated over a 16-month period. During the start-up phase, the biofiltration columns received non-ozonated membrane bioreactor (MBR) filtrate, but the bulk organic matter proved to be too recalcitrant to promote development of the microbial community. Upon ozonation, increases in adenosine triphosphate (ATP) concentration (up to 105-106 pg ATP/g media) were observed within the biofilm, thereby suggesting significant microbial growth on the BAC.When coupled with biofiltration, the results showed that the highest ozone to TOC ratio tested (O3/TOC = 1.12) achieved greater TOC removal than the two lower doses (O3/TOC = 0.35 and 0.62), presumably due to differences in the transformation of bulk organic matter. Biofiltration kinetics also proved to be more rapid than expected. At an O3/TOC ratio of 1.12, the optimum empty bed contact time (EBCT) was 10 minutes, which resulted in a 25% TOC reduction and an effluent TOC concentration of 5.0 mg/L. To further reduce effluent TOC concentrations from ozone-BAC systems, additional treatment in the form of ion exchange or granular activated carbon (GAC) columns could be viable options. A logarithmic relationship between the optimum EBCT and ozone dose appeared to exist but further investigation is warranted to validate the relationship.