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

Jawairia Imtiaz Ahmad; Gang Liu; Paul W J J van der Wielen; Gertjan Medema; Jan Peter van der Hoek

doi:10.1016/j.envres.2020.109175

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

Environ Res. 2020 Apr:183:109175. doi: 10.1016/j.envres.2020.109175. Epub 2020 Jan 23.

Authors

Jawairia Imtiaz Ahmad¹, Gang Liu², Paul W J J van der Wielen³, Gertjan Medema⁴, Jan Peter van der Hoek⁵

Affiliations

¹ Sanitary Engineering, Department of Water Management, Faculty of Civil Engineering and Geosciences, Delft University of Technology, P.O. Box 5048, 2600GA, Delft, the Netherlands; Institute of Environmental Sciences and Engineering, School of Civil and Environmental Engineering, National University of Science and Technology, H-12 Sector, Islamabad, Pakistan.
² Sanitary Engineering, Department of Water Management, Faculty of Civil Engineering and Geosciences, Delft University of Technology, P.O. Box 5048, 2600GA, Delft, the Netherlands; Key Laboratory of Drinking Water Science and Technology, Research Centre for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, PR China. Electronic address: g.liu-1@tudelft.nl.
³ KWR Watercycle Research Institute, P.O. Box 1072, 3430 BB, Nieuwegein, the Netherlands; Laboratory of Microbiology, Wageningen University, P.O. Box 8033, 6700, EH, Wageningen, the Netherlands.
⁴ Sanitary Engineering, Department of Water Management, Faculty of Civil Engineering and Geosciences, Delft University of Technology, P.O. Box 5048, 2600GA, Delft, the Netherlands; KWR Watercycle Research Institute, P.O. Box 1072, 3430 BB, Nieuwegein, the Netherlands; Michigan State University, 1405, S Harrison Rd East-Lansing, 48823, USA.
⁵ Sanitary Engineering, Department of Water Management, Faculty of Civil Engineering and Geosciences, Delft University of Technology, P.O. Box 5048, 2600GA, Delft, the Netherlands; Waternet, Korte Ouderkerkerdijk 7, 1096 AC, Amsterdam, the Netherlands.

PMID: 31999996
DOI: 10.1016/j.envres.2020.109175

Abstract

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.

Keywords: Bacterial community; Biofilm; Cold recovery; Drinking water distribution system; Drinking water quality; Microbial ecology; Opportunistic pathogens.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Bacteria
Biofilms
Cold Temperature*
Drinking Water*
Water Microbiology
Water Quality*
Water Supply

Substances

Drinking Water