Holistic Assessment of Trace Organic Compounds (TOrC) in Wastewater Treatment

A study of trace organic compound (TOrC) reactivity to selected, advanced wastewater treatment processes was conducted as part of a demonstration-scale pilot study. The pilot facilities consisted of a biological nitrogen removal (BNR) activated sludge treatment process, parallel membrane and granular media filtration processes and a biologically active filter preceded by ozone treatment, and three parallel disinfection processes: free chlorine, ozone, and UV irradiation. Twelve trace organic indicator compounds were selected to represent the treatability of a breadth of compounds. Measurements of TOrC concentrations entering and exiting each unit process were made over a period of nine months, under a range of operating conditions to assess the treatability of each compound by each process. Comparisons were made to TOrC treatability through the existing full scale plant, a high purity oxygen activated sludge (HPOAS) secondary treatment plant using chloramination for disinfection. Eight of the twelve studied indicator TOrCs were reduced through the BNR process. Removals through the BNR process were more effective than removals through the HPOAS process, likely owing to longer solids retention time (SRT) and higher mixed liquor suspended solids (MLSS) concentration in the BNR process providing more bio-oxidation capacity than in the HPOAS process. Neither membrane nor granular media filtration was effective in reducing TOrCs, implying TOrCs are not particle associated. Many of the TOrCs were reduced by ozone treatment preceding biologically active filtration. The biologically active filter was not effective at reducing TOrCs, with the exception of NDMA, which was formed during ozonation, but then reduced through the bio-filter. Post-filtration disinfection processes had varying degrees of effectiveness reducing TOrCs, with ozone being most effective, followed by chlorine and UV.