SUSPENDED BACTERIAL, BIOMASS AND ACTIVITY IN FULL-SCALE DRINKING-WATER DISTRIBUTION-SYSTEMS - IMPACT OF WATER-TREATMENT

Bacterial regrowth in drinking water distribution systems is a source of concern since it could result in non-compliance with water quality regulations, taste and odor problems, and may be associated with an in creased risk of gastrointestinal illnesses. Bacterial regrowth is depe ndent on several factors, including the amount of substrate available for growth, such as biodegradable dissolved organic carbon (BDOC), oxi dant residuals and the presence of corrosion. To investigate the impac t of nutrients levels and oxidant residual maintenance, a full-scale i nvestigation of two distribution systems was completed. This study pre sents data obtained from two distribution systems (DS) fed by differen t treatment trains: one DS has low BDOC concentrations and no free oxi dant residual (St. Rose plant, Quebec, Canada), and the other has a hi gh BDOC concentration and moderate concentrations of free oxidant resi dual (Pont Viau plant, Quebec, Canada). Monitoring included heterotrop hic plate counts (HPC), total direct count by epifluorescence after ac ridine orange staining (AODC), direct viable counts (DVC-CTC method) a nd the measurement of bacterial production by H-3-thymidine incorporat ion. Results show that bacterial biomass (AODC and DVC) and bacterial production are lower in the DS fed by the treatment plant with a low B DOC concentration in the plant effluent. This difference is observed i n warm water but not in cold water. The results suggest that HPCs are not a good indicator of bacterial regrowth in DSs. Finally, statistica l analysis demonstrated that the treatment type and cumulative surface to volume ratio are the significant factors affecting regrowth in the distribution systems studied in warm waters. (C) 1998 Elsevier Scienc e Ltd. All rights reserved.