Modelling Steady-State Biofilm in a Drinking Water Distribution System

“In the Netherlands, the distributed drinking water does not rely on residual disinfectants. To control and limit growth of microorganisms, the drinking water is produced with low concentrations of biodegradable compounds. Still, biomass in the water can change during residence in the drinking water distribution system (DWDS), and a biofilm is formed. More than 95% of the biomass in the DWDS is associated with biofilm. Also, it has been observed that the total microbial biomass and the dominant bacterial composition remains stable during distribution to the consumers. This stability is probably due to the fact that under normal operational circumstances in the DWDS the biofilm is in equilibrium with its environment and there is little net exchange of biomass between water and biofilm, i.e. is in a steady state. In case of a disturbance of the steady state there is a risk of biofilm detachment which may result in discolouration and/or detachment of biofilm related to opportunistic pathogens such as Legionella pneumophila or Pseudomonas aeruginosa.
In a risk based approach information is required on (i) the probability of biomass detachment and (ii) the effect of biomass detachment. The probability of biomass detachment is determined by (ia) the amount of biomass that can be maintained on the pipe wall and (ib) the probability of disturbance of the steady state of the biofilm. Research has been done on biofilm formation and detachment, mainly under laboratory conditions in static batch tests, and under dynamic conditions in test rigs. In this paper we focus only on aspect (ia) the amount of biomass that can be maintained in the steady state biofilm.
Our goal is to develop a model that describe the amount of steady state biofilm, under specific DWDS circumstances (pipe material, pipe diameter, hydraulic circumstances, incoming water quality, etc.). This paper describes the conceptual model and a first numerical model, linking physics and biology. These models are based on the literature, and still need validation. Experiments on the influence of temperature, flow velocities, pipe diameter, chlorine levels and AOC levels are needed to further improve our understanding of biofilm maintenance under various circumstances.”

(Citaat: Blokker, E.J., van der Wielen, P.W.J.J. – Modelling Steady-State Biofilm in a Drinking Water Distribution System – 1st International WDSA/CCWI 2018 Joint Conference, Kingston, Ontario, Canada, 23-25 July – Vol 1(2018) -064)