Removal of C- and N-DBP Precursors in Biologically Active Filters
- Meric Selbes, Jess Brown, James Amburgey, and Tanju Karanfil
Biologically active filter (BAF) is a drinking water treatment process which includes sequential use of ozonation and filtration. Application of ozone is expected to breakdown NOM into bioassimilable organic carbon, which assists the growth of microorganisms attached to the granular media. BAFs have been shown to biodegrade a range of organics (both hydrophilic and hydrophobic) including amines, aliphatic aldehydes, phenols, pharmaceuticals, pesticides, algae metabolites, algal toxins, and taste and odor substances; however, our knowledge about BAFs is still limited especially for disinfection by-product (DBP) precursors. Furthermore, chemical amendments have been shown to enhance the hydraulic performance of BAFs. The main objective of this study was to: (i) investigate the removal of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and carbonaceous- and nitrogenous-DBP precursors in selected BAFs, (ii) monitor conventional and phosphate amended BAFs performance monthly for the removal of DBP precursors for a one year duration, and (iii) evaluate four enhancement techniques in pilot-scale BAFs at two locations which were amended by the injection of nutrients, peroxide, and ethanol to the feed solution, and using anthracite as the filter media.
Objective (i): BAFs successfully reduced DOC and DON by approximately 5 to 50%. The removal of the preceding two parameters corresponded to some decreases in trihalomethanes (5-40%), haloacetic acids (5-60%), haloacetonitriles (0-10%), halonitromethanes (10-50%) and N-nitrosodimethylamine (30-40%) precursors. These results indicate that BAFs can provide removal of DOC in addition to conventional treatment (coagulation/flocculation/sedimentation). The simultaneous removal of DON highlights the potential importance of BAFs for utilities to comply with possible future N-DBP regulations. It was also observed that there was a significant increase in the bromine incorporation factors for trihalomethaness and haloacetic acids.
Objective (ii): The monitored BAFs 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 water quality parameters and DBP’s precursors. 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.
Objective (iii): There was no significant difference in DBP formation potentials among amended biofilter columns. Ethanol, Peroxide and Phosphate supplements did not make a major positive or negative impact on the efficiency on the BAFs for reducing DBP precursors. Anthracite packed column also performed comparable to other columns for DBP precursors despite lower DOC removal.
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