Biofilm water distribution systems

Keywords biofilms water distribution system water quality secondary contamination... 

This demand will reduce the amount of chlorine available for microbiological control and lead to slime growth, especially in the tower basin and water distribution system, with biofilms and under-deposit corrosion being common effects of this problem. 

Crayton, C., Camper, A. and Warwood, B. (1997) Evaluation of mixed oxidants for the disinfection and removal of biofilms from distribution systems, Proceedings of the American Water Eorks Association Water Quality Technology Conference, 3A6/1-3A6/17. 

Momba, M. N. B., et al. (1998). Evaluation of the impact of disinfection processes on the formation of biofilms in potable surface water distribution systems. Water Science Technol. Wastewater Biological Processes, Proc. 199819th Biennial Conf. Int. Assoc, on Water Quality. Part 7, June 21-26,38, 8-9, 283-289. Elsevier Science Ltd., Exeter, England. 

Sly LI, Hodgkinson MC, Arunpairojana V. 1988. Effect of water velocity on the early development of manganese-depositing biofilm in a drinking water distribution system. FEMS Microbiol Ecol 53 175-186. 

STUDY OF BIOFILM FORMATION ON DIFFERENT PIPE MATERIALS IN A MODEL OF DRINKING WATER DISTRIBUTION SYSTEM AND ITS IMPACT ON MICROBIOLOGICAL WATER QUALITY... 

Abstract. The biofilm formation in drinking water distribution systems depends on many factors and may cause a number of technological and hygienic problems. In this study, the influence of pipe material and flow velocity on the biofilm growth dynamics and its impact on microbiological water quality in a model of drinking water distribution system were assessed. 

Keywords biofilm drinking water distribution system microbiological water quality... 

Biofilm study was carried out in the drinking water supply system DWSS"Yovkovtsy , that supply with water the region of Veliko Tamovo, and in the laboratory model of water distribution system. Some experiments were performed 1) to determine microbiological composition of biofilm samples scraped from mild steel or reinforced concrete s main pipe line and concrete tank of DWSS Yovkovtsy 2) to study biofilm formation process on test pipe from PVC, PE, stainless steel and carbon steel in a laboratory model of drinking water distribution system under flow velocity 0,006 cm/s. 3) to study dynamics of biofilm formation process on polypropylene, the pipe material used during the last years in Bulgaria, in a model water distribution system under flow velocities 0.3 m/s, 0.5 m/s, 0.7 m/s and 1 m/s. 

Because of complex effect of pipe material, water quality and flow velocity on the biofilm in the studied water distribution system, the biofilm formation process was studied in a model system. It was determined the highest bacterial density of the biofilm developed on carbon steel and the lowest ones of the biofilms on plastic pipes (Fig. 2). The results showed strong influence of the pipe material on biofilm density during initial phases of the process compared with mature biofilm. 

FIGURE 1. Bacterial density of biofilms developed on main pipe lines from carbon steel (1,2) or reinforced concrete (3,4) and concrete tank (5,6) in drinking water distribution system Yovkovtsy , domestic installation from galvanized steel (7,8) and test surfaces from stainless (9) or carbon steel (10). 

FIGURE 2. Dynamics of Biofilm formation on different pipe materials in a model water distribution system under low flow velocity. 

TABLE 1. Microbial contamination of drinking water in a model water distribution systems from studied pipe materials in result from biofilm impact. 

Biofilms formed on different materials and under different flow velocities in the model water distribution system made an impact on microbiological quality of drinking water depending on their bacterial density. 

EVALUATION OF BIOFILMS OCCURING IN DRINKING WATER DISTRIBUTION SYSTEM OF BALATONFURED... 

Relatively few studies have included the effect of chlorine dioxide on biofilms. Characklis (1990) mentions that chlorine dioxide has been successfully used to control biofouling in several industrial environments. Walker and Morales (1997) studied the effect of chlorine dioxide on a mixed population of drinking water bacteria in a continuous culture model which was developed to simulate an industrial water system. The addition of Img/L chlorine dioxide for approximately 18 h was sufficient to reduce the viable counts of the planktonic population by 99.9%, whereas 1.5 mg/L chlorine dioxide was required to achieve a similar reduction in the biofilms, suggesting an enhanced resistance of biofilm bacteria to the biocide. There are indications that continuous disinfection of drinking water using chlorine dioxide provides a certain control of biofilm formation. In a French drinking water distribution system, the presence of chlorine dioxide allowed a limited surface colonization, while in regions where chlorine dioxide was below the detection limit, an increase in biofilm formation occurred (Servais et al., 1995). 

Silver and copper ions act synergistically in the killing of Legionella bacteria, which are known to multiply in biofilms in hot water distribution systems. Copper-silver ionization has been used successfully to control Legionella spp. in many US hospital hot water systems after 5 to 11 years of operation however, high pH values and elevated chloride concentrations have negative effects on the biocidal efficacy of copper and silver, respectively, in water systems (Lin et al., 2002). 

Halem, N. B., J. R. West, C. E. Forster, et al. 2001. The Potential for Biofilm Development in Water Distribution Systems. Water Research 35 4063-4071. 

Monochloramine, used as a residual disinfectant for distribution, is usually formed from the reaction of chlorine with ammonia. Careful control of monochloramine formation in water treatment is important to avoid the formation of di- and trichloramines, because these can cause unacceptable tastes and odours. The formation of nitrite as a consequence of microbial activity in biofilms in the distribution system is a possibility when monochloramine is used as a residual disinfectant, particularly if ammonia levels are not sufficiently controlled. 

Physical condition. The physical condition of distribution system pipes influences their tendency to foster biological regrowth. Distribution pipes that have tuber-cules or other surface irregularities commonly harbor microbial encrustations. Certain pipe materials and conditions can lead to a heavy accumulation of bacteria on their walls, a so-called biofilm. By attaching to the surface, microorganisms can be protected from washout and can exploit larger nutrient resources either accumulated at the surface or in the passing water. Moreover, attached bacteria appear to be less affected by disinfectants than those suspended in the disinfected liquid. 

A unique type of corrosion referred to as copper by-product release, cuprosolvency, or blue water occurs in potable water systems constructed of copper tubing, and has been reported worldwide [92-95]. The problem is most often attributed to EPS induced metal concentration cells. The condition is characterized by the release of copper as fine particles in plumbing systems distributing soft water in the neutral or neutral-alkaline pH range. Water may contain between 5 to 300 ppm copper (as Cu +) as finely suspended precipitates. A bacterial biofilm and associated acidic EPS bind copper ions at the metal surface and alter the porosity of the oxide film [96]. Geesey and coworkers [97] characterized binding of an acidic polysaccharide to thin copper films and su ested a cupric ion interaction with carboxyl groups on EPS. These interactions promoted ionization of metallic... 

---