Identification of correlation relationships and establishment of regression models among multiple microbial indicators in reclaimed waters.

Monitoring and controlling microbial water quality is crucial for ensuring water reuse safety. In particular, existing water reuse guidelines and regulations normally prescribed coliform bacteria as microbial indicators. However, the use of non-unified coliform groups may bring difficulties to compare and optimize the conformity efforts on microbial surveillance. This study has identified the correlation relationships in each pair of four microbial indicators in reclaimed waters, namely the heterotrophic plate counts (HPCs), total coliforms (TC), fecal coliforms (FC) and E. coli (r=0.861-0.987). Ultimately, the built regression model for internal conversion is expressed as: logHPC (MPN/mL)= 0.737×logTC (MPN/L)= 0.830×logFC (MPN/L)= 0.872×logE. coli (MPN/L) with further verification and validation. The developed model can be used to help water reuse regulators and practitioners improve the efficiency in universal microbial risk detection and management. Besides, the resistant microbes in HPCs (e.g. disinfection resistant bacteria and pathogens) after reclaimed water treatment and disinfection also call for future attention.