Biofilm Formation in Water Systems and Membranes: Monitoring and the Influence of Calcium
“Biofilm growth in technical systems such as water distribution systems and reverse osmosis (RO) membranes is still a major problem in water treatment causing problems in operation and maintenance as well as pose a threat to human health.
Biofouling – the unwanted deposition and growth of microbes on surfaces – in non-chlorinated drinking water distribution systems can lead to microbial regrowth providing a niche for potential pathogens. The problem of microbial regrowth can be caused by unwanted quality changes of the drinking water within the distribution system. To control these problems assessment of the regrowth potential of drinking water on a continuous base requires fast and easy-to-use monitoring devices. The biofilm monitor (BFM) is already used for years to assess the biofilm formation rate (BFR) of drinking water and the continuous biofilm monitor (CBM) is a recently optimization of this monitor which determines the Biomass Accumulation Rate (BAR). This study has the aim to improve the monitoring of biofilm formation potential with the further development of the CBM by increasing the sampling frequency with the double CBM (DCBM) and subsequently measurement of the BFR and the BAR in the Continuous Biofouling Monitor. Both modified monitors and the classical BFM were challenged with (i) tap water from the KWR laboratory (this is drinking water produced from anaerobic groundwater) as well as (ii) the filtrate of granular activated carbon (GAC) filters at a surface water treatment plant in Rotterdam. |t could be shown that the sampling frequency with the DCBM could be increased to weekly sampling without significant changes in the biofilm accumulation. The combined measurement of BFR and BAR yielded increased insights in the biofouling properties of both waters. Remarkable, though, and still unexplained was the negative correlation of the BAR/BFR values with the growth potential assessed with the batch methods, AOC and BPP.
Biofouling not only causes problem in water distribution systems but is also responsible for major operational problems in RO membrane treatment applications. In order to overcome these problems extensive pre-treatment and cleaning methods are needed. In this study the possibility of water softening to prevent membrane biofouling is tested. A system with RO membrane modules and the biofilm plate monitor (BPM) – a small-scale model for biofilm formation – are used to assess the effect of hardness removal on biofilm formation and removal. Three chemical cleaning procedures are tested according to a previously developed laboratory method in order to evaluate the effect of hardness removal on cleaning efficiency and simple biofilm detachment tests are used to assess the biofilm cohesion and adhesion forces. Terminal restriction fragment length polymorphism (T-RFLP) is used to investigate differences in microbial communities.
Water softening showed significantly retardation of membrane biofouling and increase cleaning efficiency. A difference in biofilm stability and microbial population could be observed. Additional results demonstrated the specific role of calcium in the biofilm formation process. Further studies are needed to assess the influence Ca concentrations on biofilm formation and to elucidate the relationship with specific bacterial spp. in the biofilm.”
(Citaat: Schulz, F. – Biofilm Formation in Water Systems and Mambranes: Monitoring and the Influence of Calcium)