Quantification of biodegradable natural organic matter (NOM) fractions and its impact on bacterial regrowth in a South African Water Treatment Plant

Abstract

Natural organic matter (NOM) contributes to bacterial regrowth during potable water treatment and supply. Most conventional water treatment plants insufficiently remove the biodegradable dissolved organic (BDOC) NOM fraction. The presence of labile BDOC in water creates conducive conditions for bacterial regrowth. To reduce NOM and the bacterial regrowth potential (BRP) in water, the study aimed at establishing which of the NOM polarity fractions are biodegradable and if the BRP (enumerated according to the heterotrophic plate count [HPC]) method) can be correlated to biodegradability. Specific ultraviolet absorbance (SUVA) was used to characterise source and treated water NOM fractions (i.e. hydrophilic [Hpi], transphilic [Tpi] and hydrophobic [Hpo]) obtained through the modified polarity rapid assessment method (m-PRAM). The source and treated water SUVA values of the Hpi and Hpo were on average, 3.88 L/mg.m and 2.04 L/mg.m, respectively. The Hpi and Tpi fractions on the source and treated were the most biodegradable fractions, with mean BDOC values ranging between 29.22%, and 35.75 %. The high BDOC of the Tpi and Hpi NOM substantially contributed to BRP by up to 121.4 × 103-197.4 × 103 CFU/mL, respectively. The strong correlation (R2 > 0.96) between BRP and BDOC allows for the effective management of water treatment and supply processes, particularly for microbial control.