Thermal energy recovery from chlorinated drinking water distribution systems: Effect on chlorine and microbial water and biofilm characteristics

Abstract

Thermal energy recovery from drinking water has a high potential in the application of sustainable building and industrial cooling. However, drinking water and biofilm microbial qualities should be concerned because the elevated water temperature after cold recovery may influence the microbial activities in water and biofilm phases in drinking water distribution systems (DWDSs). In this study, the effect of cold recovery on microbial qualities was investigated in a chlorinated DWDS. The chlorine decay was slight (1.1%-15.5%) due to a short contact time (~60 s) and was not affected by the cold recovery (p > 0.05). The concentrations of cellular ATP and intact cell numbers in the bulk water were partially inactivated by the residual chlorine, with the removal rates of 10.1%-16.2% and 22.4%-29.4%, respectively. The chlorine inactivation was probably promoted by heat exchangers but was not further enhanced by higher temperatures. The higher water temperature (25°C) enhanced the growth of biofilm biomass on pipelines. Principle coordination analysis (PCoA) showed that the biofilms on the stainless steel plates of HEs and the plastic pipe inner surfaces had totally different community compositions. Elevated temperatures favored the growth of Pseudomonas spp. and Legionella spp. in the biofilm after cold recovery. The community functional predictions revealed more abundances of five human diseases (e.g. Staphylococcis aureus infection) and beta-lactam resistance pathways in the biofilms at higher temperature. Compared with a previous study with a non-chlorinated DWDS, chlorine dramatically reduced the biofilm biomass growth but raised the relative abundances of the chlorine-resistant genera (i.e. Pseudomonas and Sphingomonas) in bacterial communities.

Implications of Climate Change: How Does Increased Water Temperature Influence Biofilm and Water Quality of Chlorinated Drinking Water Distribution Systems?

“…In addition to the greater potential for biofilm formation at high temperatures, molecular analyses showed that temperature variation significantly modified the structure of biofilm microbial communities from the early stages of biofilm development ( Figures 2 , 3 ). This was in agreement with Stanish et al (2016) that reported that water temperature was determinant for the abundance and composition of bacterial communities in tap water samples, or with Ahmad et al (2020) and Zhou et al (2020) that showed that higher temperatures promoted by cold recovery technologies, in unchlorinated and chlorinated DWDS respectively, produced changes in biofilm communities. In the same way, the results from this study confirm that temperature increase is a driving factor changing the bacterial but also fungal microbial community structure within chlorinated DWDS.…”

Biofilm Formation in Water Distribution Systems

“…In the study by Zhou and coauthors [63], biofilm formation was investigated in models of drinking water networks constructed of stainless steel and adjacent copper. The biofilm formation of chloraminated and chloramine-neutralised water was studied in models constructed with both types of materials.…”

“…This state encompasses the survival of microorganisms following chlorine disinfection and their subsequent or repeated growth despite the physiological and genetic destructive effects of chlorine. The mechanisms of MCR comprise in situ cell aggregation, clumping, and structural modification of the microbial cell surface, EPS production, the formation of resistant spores due to re-proliferation, and good adhesion to surfaces within the biofilm matrix [63,72,74,76].…”

Full-length 16S rRNA gene sequencing reveals the operating mode and chlorination-aggravated SWRO biofouling at a nuclear power plant

“…Pseudomonas is commonly found in the most diverse ecological communities on earth and is essential in biofouling formation. The relative abundance of the chlorine-tolerant genus Pseudomonas is significantly higher in RO systems where chlorine disinfection is used as a biocide (Zhou et al 2020). Wang et al (2021) reported that the relative abundance of the chlorine-tolerant bacterium Pseudomonas showed a significant increase in the relative abundance of the analyzed genes encoding the functions of community sensing, exopolysaccharide biosynthesis, and amino acid biosynthesis after chlorine disinfection.…”