Removal of natural organic matter (NOM) from drinking water supplies by ozone-biofiltration

Removal of natural organic matter (NOM) in biofilters can be affected by ma ny factors including NOM characteristics, use of pre-ozonation, water tempe rature, and biofilter backwashing. Laboratory experiments were performed an d a biofilter simulation model was developed for the purpose of evaluating the effects of each of these factors on NOM removal in biofilters. Four sou rces of NOM were used in this study to represent a broad spectrum of NOM ty pes that may be encountered in water treatment. In batch experiments with r aw NOM, the removal of organic carbon by biodegradation was inversely propo rtional to the UV absorbance (254 nm)-to-TOC ratio and directly proportiona l to the percentage of low molecular weight material (as determined by ultr afiltration). The extent and rate of total organic carbon (TOC) removal typ ically increased as ozone dose increased, but the effects were highly depen dent on NOM characteristics. NOM with a higher percentage of high molecular weight material experienced the greatest enhancement in biodegradability b y ozonation. The performance of laboratory-scale continuous-flow biofilters was not significantly affected by periodic backwashing, because backwashin g was unable to remove large amounts of biomass from the filter media. Mode l simulations confirmed our experimental results and the model was used to further evaluate the effects of temperature and backwashing on biofilter pe rformance. (C) 1999 Published by Elsevier Science Ltd on behalf of the IAWQ , All rights reserved.