Treatment of trace organic compounds by ozone-biological activated carbon for wastewater reuse: The Lake Arrowhead pilot plant

Organic and trace organic performance data for preozonation and biological activated carbon (BAC) filtration of the Lake Arrowhead, California, water reclamation pilot plant secondary effluent were analyzed to determine treatment efficiency of these processes in a potable water reuse project. Five types of organic analysis were performed: dissolved organic carbon (DOC), UV at 254 nm (UV-254), ultimate soluble biochemical oxygen demand (SBODU), base-neutral analysis (BNA), and specific aldehyde analyses. Preozonation favored the breakdown of high-molecular-weight organic matter (> 1000 daltons [Da]), measured as DOC, to biodegradable organic compounds, measured as an increase in SBODU. Also, a shift in mass concentration of BNAs from the higher scan index fraction (< 1000 Da) to the lower scan index fraction was shown by gas chromatography-mass spectrometry profile analysis. After preozonation, organic compounds were sorbed and biodegraded through the BAC filter. Steady state was reached for DOC and UV-254 absorbance after 50 to 100 days. Trace organic compounds started breaking through the column 200 days after BAC startup. Breakthrough was not uniform for BNAs. Apparent differences between the lower and higher molecular weight fractions of BNAs were shown, indicating a greater breakthrough rate for the higher scan index fractions. Finally, lists of tentatively identified BNA compounds were created, highlighting the change in chemical composition of the base-neutral fraction before and after each process.