Evaluation of a side-by-side, full-scale conversion to biological filtration

The purpose of this study was to evaluate water quality and operational trends of a side-by-side, full-scale biofiltration conversion. Four filters at a water treatment plant, treating low turbidity and low total organic carbon water, were monitored for one year. One filter was a prechlorinated control, and the other three were biofilters. One was a standard biofilter, one had chlorinated backwash, and the third was supplemented with nutrients. Slightly higher concentrations of adenosine triphosphate (ATP) (175-2,300 ng ATP/cm3) and extracellular polymeric substances (0.00-0.08 mg glucose/g total solids) were found in the biofilters compared with the control. Total trihalomethanes and haloacetic acid were lower in the biofilters relative to the control (60 and 30%, respectively). Conversion to biological filtration resulted in slightly higher (0.019 ntu) and more variable (0.013 ntu) effluent turbidity, but filter run volumes were unaffected. At the conclusion of the study, a decision was made to convert all the filters in the plant to biofilters.