Effects of cold recovery technology on the microbial drinking water quality in unchlorinated distribution systems

Effects of cold recovery technology on the microbial drinking water quality in unchlorinated distribution systems

Ahmad, J.I. (TU Delft Sanitary Engineering; National University of Science and Technology (NUST))
Liu, G. (TU Delft Sanitary Engineering; Chinese Academy of Sciences)
van der Wielen, Paul (KWR Water Research Institute; Wageningen University & Research)
Medema, G.J. (TU Delft Sanitary Engineering; KWR Water Research Institute; Michigan State University)
van der Hoek, J.P. (TU Delft Sanitary Engineering; Waternet)

2020

Drinking water distribution systems (DWDSs) are used to supply hygienically safe and biologically stable water for human consumption. The potential of thermal energy recovery from drinking water has been explored recently to provide cooling for buildings. Yet, the effects of increased water temperature induced by this “cold recovery” on the water quality in DWDSs are not known. The objective of this study was to investigate the impact of cold recovery from DWDSs on the microbiological quality of drinking water. For this purpose, three pilot distribution systems were operated in parallel for 38 weeks. System 1 has an operational heat exchanger, mimicking the cold recovery system by maintaining the water temperature at 25 °C; system 2 operated with a non-operational heat exchanger and system 3 run without heat exchanger. The results showed no significant effects on drinking water quality: cell numbers and ATP concentrations remained around 3.5×105 cells/ml and 4 ng ATP/l, comparable observed operational taxonomic units (OTUs) (~470–490) and similar Shannon indices (7.7–8.9). In the system with cold recovery, a higher relative abundance of Pseudomonas spp. and Chryseobacterium spp. was observed in the drinking water microbial community, but only when the cold recovery induced temperature difference (ΔT) was higher than 9 °C. In the 38 weeks’ old biofilm, higher ATP concentration (475 vs. 89 pg/cm2), lower diversity (observed OTUs: 88 vs. ≥200) and a different bacterial community composition (e.g. higher relative abundance of Novosphingobium spp.) were detected, which did not influence water quality. No impacts were observed for the selected opportunisitic pathogens after introducing cold recovery. It is concluded that cold recovery does not affect bacterial water quality. Further investigation for a longer period is commended to understand the dynamic responses of biofilm to the increased temperature caused by cold recovery.

Bacterial community
Biofilm
Cold recovery
Drinking water distribution system
Drinking water quality
Microbial ecology
Opportunistic pathogens

http://resolver.tudelft.nl/uuid:4c4b8f32-0a6a-43ea-b4a0-6119a89f8485

https://doi.org/10.1016/j.envres.2020.109175

0013-9351

Environmental Research, 183

Institutional Repository

journal article

© 2020 J.I. Ahmad, G. Liu, Paul van der Wielen, G.J. Medema, J.P. van der Hoek