The purpose of a drinking water distribution system is to deliver drinking water to the consumer, preferably with the same quality as when it left the treatment plant. In this context, the maintenance of good microbiological quality is often referred to as biological stability, and the addition of sufficient chlorine residuals is regarded as one way to achieve this. The full-scale drinking water distribution system of Riga (Latvia) was investigated with respect to biological stability in chlorinated drinking water. Flow cytometric (FCM) intact cell concentrations, intracellular adenosine tri-phosphate (ATP), heterotrophic plate counts and residual chlorine measurements were performed to evaluate the drinking water quality and stability at 49 sampling points throughout the distribution network. Cell viability methods were compared and the importance of extracellular ATP measurements was examined as well. FCM intact cell concentrations varied from 5×103 cells mL−1 to 4.66×105 cells mL−1 in the network. While this parameter did not exceed 2.1×104 cells mL−1 in the effluent from any water treatment plant, 50% of all the network samples contained more than 1.06×105 cells mL−1. This indisputably demonstrates biological instability in this particular drinking water distribution system, which was ascribed to a loss of disinfectant residuals and concomitant bacterial growth. The study highlights the potential of using cultivation-independent methods for the assessment of chlorinated water samples. In addition, it underlines the complexity of full-scale drinking water distribution systems, and the resulting challenges to establish the causes of biological instability.

The effect of phosphorus addition on survival of Escherichia coli in an experimental drinking water distribution system was investigated. Higher phosphorus concentrations prolonged the survival of culturable E. coli in water and biofilms. Although phosphorus addition did not affect viable but not culturable (VBNC) E. coli in biofilms, these structures could act as a reservoir of VBNC forms of E. coli in drinking water distribution systems.Pathogens may enter the distribution system either through the source water or at any point within the distribution system (16). In the network enteric microorganisms, such as Escherichia coli, may survive and even exhibit metabolic activity in biofilms on the surfaces of pipes and reservoirs (22,5). This phenomenon compromises the use of E. coli as a reliable indicator for fecal pollution. Due to its very low infection dose the accumulation and subsequent release of pathogenic E. coli from a biofilm to the water phase are increasing the health risk of tap water consumption. The survival and culturability of E. coli in water distribution networks are dependent on many environmental factors, including the disinfectant type and dose (14), the presence of predators (20), the pipe material, the temperature (21), the amount of corrosion products (4), the iron (1), heavy metal, and oxygen concentrations (18), and the water saturation (7). However, the role of nutrients, which in drinking water are normally present at low concentrations, in the survival of E. coli is not fully understood. Phosphorus (P) is an important nutrient and part of biomolecules in bacterial cells (e.g., DNA, polyphosphates, phospholipids, and ATP). In some drinking waters P regulates bacterial growth (12); thus, removal of this nutrient during water treatment (e.g., during chemical coagulation) may lower the bacterial numbers in the water and biofilms (9). P may also influence many mechanisms of E. coli survival, including transport of nutrients into the cell, biofilm formation, and motility. At concentrations below 5 g liter Ϫ1 the mechanisms of nutrient uptake and energy conservation in E. coli change (3). Thus, reducing the P concentration below this level may decrease the potential for E. coli survival in drinking water distribution systems. However, the same effect may be obtained by increasing the levels of P (the growthlimiting nutrient) because this may enhance antagonism reactions by the faster-growing indigenous microbial population (2). The aim of this study was to evaluate the effect of P on survival of E. coli in drinking water distribution networks. Two forms of E. coli, culturable and viable but not culturable (VBNC), were investigated.A model biofilm reactor (Fig. 1), a Propella reactor (Xenard, Mechanique de Precision, Seichamps, France) with a distribution pipe that was 100 mm in diameter and 500 mm long, was used to simulate a drinking water distribution system. The inner surface of the pipe was made of high-density polyethylene. The reactor had a volume of 2.23 liters and a high-density pol...

Effect of microbially available phosphorus (MAP) on biofilm development in drinking water systems was investigated at the pilot-scale experiments over 3 years. Completely mixed biofilm reactors Propella (water detention time 24 h, flow rate 0.25 m s(-1), PVC pipe coupons) were used as water distribution network models. Four experimental runs were carried out with water containing different levels of phosphorus which was limiting nutrient for bacterial growth. Positive correlation between MAP in the inlet water and heterotrophic plate count (correlation coefficient 0.95) in biofilm, as well as for the total bacteria number (correlation coefficient 0.71), was observed. However, our experiments showed that removal of phosphorus down to very low levels (below detection limits of chemical method and MAP < 1 microg L(-1) was not an efficient strategy to eliminate bacterial regrowth and biofilm formation (< 51,00,000 cells/cm2) in drinking water supply systems.

By using industrial aluminium recycling waste, recycled silicate glass from outworn fluorescence lamp recycling plant, calcined kaolinite clay supplemented with alkali activator with different silicate modulus the new type of porous material for biotechnologic processes without the need for additional equipment for pH control was researched. This controlled-release system contains an alkali activated matrix in which NaOH crystals are encased. In this study ability to release NaOH per time in water according to material composition and structure were investigated. Three alkaline activated materials AAM 7.5, 10 and 12.5, with different alkali activator content were characterized.

In the present study the time of adaptation of fixed biomass for biodegradation of natural organic matter was investigated. The experiments were done in columns that are usually used for rapid determination of biodegradable dissolved organic carbon (BDOC). The biomass was adapted to samples with different concentrations of organic substances before measurements by pumping water to be investigated through the columns for several days. The time of adaptation was dependent on the initial concentration of the organic matter in the water sample. The adaptation time increased from 6 to 24 h with increase of concentration of acetate solution from 2 to 10 mg/l, thus adaptation rate decreased simultaneously from 0.28 to 0.11 min(-1). In natural water samples with the initial concentration in the range from 4.61-10.82 mg/l of dissolved organic carbon (DOC) the maximal adaptation time was less than 24 h. During the adaptation period the increase in reproducibility and decrease in the standard deviation was observed. The study showed that adaptation of column to the different concentration of organic matter in water sample is necessary in order to decrease the bias in BDOC measurements when using columns tests.

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Chemical precipitation in combination with biological treatment is a commonly used method for removal of turbidity and dissolved organic carbon (DOC) from drinking water. DOC is largely removed during biological treatment, which includes ozonation and filtration through a biologically active carbon (BAC) filter. Ozone converts humic substances into a biologically labile form that is mineralised by bacteria living in the following BAC filter. This study shows that this approach is often not efficient for removal of DOC from waters with a high amount of humic substances. During chemical treatment, the microbiologically available phosphorus is very efficiently removed, which results in shortages of phosphorus needed for bacteria to mineralise carbon in BAC filters. To enhance removal of DOC by biological treatment, addition of phosphorus prior to the BAC filters should be considered.

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