Removal of C- and N-DBP Precursors in Biologically Active Filters
- Meric Selbes, James Amburgey, Tanju Karanfil, Erik Rosenfeldt
In addition to retaining particulate matter, a biologically active filter (BAF) also supports the growth of biomass that consumes organic matter. Application of ozone prior to BAF is expected to break down NOM into bioassimilable organic carbon, further assisting the growth of microorganisms. BAFs have been shown to remove organics such as pharmaceuticals, pesticides, algal toxins, as well as taste and odor substances. However, our knowledge about BAFs is still limited, particularly for disinfection by-product (DBP) precursors. The main objective of this study was to: (i) investigate the removal of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), (ii) carbonaceous- and nitrogenous-DBP precursors, and (iii) evaluate the seasonal performance of BAFs to assess the effect of phosphate-enhancement on filter performance. In this study, two full- and two pilot-scale BAFs were examined and the findings for each objective are summarized as follows.
Objective (i): BAFs simultaneously reduced DOC and DON by 5 to 50%. The removal of DON specifically highlights the potential importance of BAFs for utilities in complying with possible future N-DBP regulations. However, there was no distinct change in the levels of bromide and sulfate.
Objective (ii): The removal of the DOC and DON corresponded to some decreases in trihalomethanes (5-40%), haloacetic acids (5-60%), haloacetonitriles (0-10%), halonitromethanes (10-50%) and N-nitrosodimethylamine (30-40%) precursors. It was also observed that there was a significant increase in the bromine incorporation factors for trihalomethanes and haloacetic acids.
Objective (iii): The monitored BAF reduced DOC and DON by 3–36% with higher reductions observed at warmer temperatures. Consequently, higher reductions in DBP precursors were observed during summer months. Phosphate-amendment had some effect on the BAF performance. Phosphate-amendment enhanced the microbial activity during phosphorous-limiting months, which resulted in ~5% greater reduction in trihalomethanes and haloacetic acids precursors than conventional BAFs effluent.
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