Investigation into biofilms in a local drinking water distribution system

Abstract

Biofilm growth within a water distribution system could lead to operational problems such as pipe corrosion, water quality deterioration and other undesirable impacts in water distribution systems. With the high ambient temperatures experienced in Singapore, the operating environment in water distribution systems is expected to be more conducive to biofilm development. We have recently conducted a survey on biofilms potentially present in a local water distribution system.The survey results indicated that residual chlorine (±standard deviation) decreased from 1.49±0.61 mg/l (water plant outlets) to 0.82±0.21 mg/l (block pipes) or 0.18±0.06 mg/l (unit pipes), respectively. Consumed chlorine, instead of residual chlorine, was found to be correlated with biofilm bacterial population. Assimilable organic carbon (AOC) level was 160±66 μg acetate C/l, and AOC:PO4-P:NO3-N was about 8:13:1. Carbon source seemed to be the limiting nutrient for bacterial growth. The concentration of iron increased from <0.04 mg/l (water plant outlets) to 0.22±0.10 mg/l (all sites). All samples showed negative results in a coliform test. The average heterotrophic plate count (HPC) for the suspended bacteria was 20 colony-forming units (c.f.u.)/ml (2 days, 35 °C) or 290 c.f.u./ml (8 days, 35 °C). The average HPC for the biofilm bacteria was 6500 c.f.u./cm2 (2 days, 35 °C) or 29000 c.f.u./cm2 (8 days, 35 °C). High HPC values in samples B2a, B2b and B3a (representing biofilm samples at site 2 from block/unit pipes and biofilm samples at site 3 from block pipes, respectively) illustrated that the relevant sample sites had a higher probaboility of biofilm growth.

Analysis of the contribution of sedimentation to bacterial mass transport in a parallel plate flow chamber

“…Biofilms can be found nearly everywhere, such as in groundwater, pipelines in waterworks, wastewater treatment plants, on the surfaces of heat exchanger plates and biomedical devices, and on ship hulls [1][2][3][4][5]. Flow displacement systems are widely used to study bacterial adhesion to surfaces [6][7][8][9][10] as they allow control of hydrodynamic conditions, including shear rates and mass transport.…”

Chloraminated drinking water does not generate bacterial resistance to antibiotics in Pseudomonas aeruginosa biofilms

“…Over 95% of the bacteria in drinking water distribution systems (DWDS) are found in biofilms (Hu et al. 2005).…”

“…Biofilms in DWDS can lead to problems of taste, turbidity and odour (Momba et al. 1999), pipe corrosion (Hu et al. 2005), and can also be a reservoir for human pathogens (Momba et al.…”

Effects of phosphorus on biofilm disinfections in model drinking water distribution systems

“…Research has shown that biofilm bacteria grown on different surfaces increase resistance to different chlorine-based agents (LeChevallier et al 1988). doi: 10.2166/wh.2009.303 In a survey conducted by Hu et al (2005), a high biofilm growth potential in a drinking water distribution system was found even with the presence of residual chlorine.…”