Field evaluation of phosphorus limitation in drinking water biofilters

Hydraulic performance issues in drinking-water biofilters have sometimes been associated with phosphorus limitation and increased production of extracellular polymeric substances in previous bench-scale studies. However, field studies utilizing phosphorus supplementation to improve biofilter hydraulic performance have produced mixed results. Here, we determined the ratio of activities for phosphatase to glycosidase (PHO:GLY), which are enzymes involved in acquiring orthophosphate and biodegradable organic carbon from complex organic substrates, to assess phosphorus limitation in 21 pilot- and full-scale biofilters. Supplementation of the pilot-scale biofilter influents with 37 mu g/L orthophosphate-P reduced the PHO:GLY from 1.8-40.3 (mean 14.8) to 0.3-15.9 (mean 5.3), demonstrating that increased orthophosphate availability decreases PHO:GLY. In the absence of phosphorus supplementation, the PHO:GLY of the pilot- and full-scale biofilters ranged from 0.3 to 40.3 (mean 10.1), and no hydraulic performance issues were noted. Thus, severe phosphorus limitation appears uncommon in the field, suggesting that phosphorus supplementation is unlikely to improve hydraulic performance in typical drinking water biofilters.