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

• Published in: Environmental research Vol. 183; p. 109175
• Main Authors: Ahmad, Jawairia Imtiaz, Liu, Gang, van der Wielen, Paul W.J.J., Medema, Gertjan, Peter van der Hoek, Jan
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier Inc 01.04.2020
• Subjects: Bacterial community; Biofilm; Cold recovery; Drinking water distribution system; Drinking water quality; Microbial ecology; Opportunistic pathogens; Opportunistic pathogens; Drinking water distribution system; Microbial ecology; Cold recovery; Biofilm; Bacterial community; Drinking water quality
• ISSN: 0013-9351; 1096-0953
• DOI: 10.1016/j.envres.2020.109175

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. •The potential impacts of cold recovery in DWDS on microbial water quality were evaluated.•Cold recovery did not influence the quantity and community of planktonic bacteria.•No impacts were observed for opportunistic pathogens after introducing cold recovery.•Higher biomass and less diversity were found for 38-weeks’ old biofilm after cold recovery.