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Laskowski T.,Poznan University of Technology | Sroka M.,Municipal Water Supply and Sewage Company in Warsaw | Olejnik A.,Municipal Water Supply and Sewage Company in Warsaw | Biernacki W.,Poznan University of Technology | Nawrocki J.,Poznan University of Technology
Desalination and Water Treatment | Year: 2015

Applicability of cast iron filings-based model for a study of nitrate reduction phenomena in water distribution networks is shown in this paper. The experiments were conducted both on 100-m long corroded cast iron pipe and on a laboratory model with cast iron filings. Additionally, the fate of nitrate was monitored at far ends of two real, large distribution systems. Results from all these systems show that nitrate reduction occurs mainly during water stagnation and is an effect of both biotic and abiotic processes. Decreasing concentration of nitrate may be accompanied by ammonia formation, mainly in fresh pipes. However, the changes of nitrogen concentration are not balanced. It is suggested that the lack of stoichiometry is related to denitrification leading to N2 formation. Along with the passing of time, the share of denitrification rises. Chemical disinfection does not prevent the biological denitrification in corroded water supply system. The results prove that the nitrate takes part in corrosion exclusively on fresh, unused surface of cast iron. The decrease in nitrate concentration is mainly connected with biological denitrification, which occurs due to the considerable extent during stagnation of water in the distribution system. The observation of large distribution systems proves that under flow conditions, no nitrate reduction occurs. © 2015 Balaban Desalination Publications. All rights reserved.

Laskowski T.,Adam Mickiewicz University | Swietlik J.,Adam Mickiewicz University | Raczyk-Stanislawiak U.,Adam Mickiewicz University | Piszora P.,Adam Mickiewicz University | And 3 more authors.
Desalination and Water Treatment | Year: 2016

A new model for the investigation of the impact of corrosion on water quality, based on application of cast iron filings, is proposed. The use of filings ensures a large specific surface area which permits observation of changes in water quality in a relatively small amount of material. Two models differing in idea and construction are presented in this paper. The detailed results from the one model where thin layer water flows over the cast iron filings are shown. The rate of water quality changes during stagnant periods could be controlled by different amounts of filings. The results received in the model experiment are compared with those from a real fragment (100 m) of distribution system. Deterioration of water quality observed in model conditions is similar to that in real distribution network. Increase of iron concentration, turbidity, and decrease of oxygen and nitrate concentration were observed in both systems during stagnation periods. No changes of water quality were observed during flow conditions. Elemental and phase composition of corrosion scales collected from both systems was also comparable. © 2015 Balaban Desalination Publications. All rights reserved.

Nawrocki J.,Poznan University of Technology | Raczyk-Stanislawiak U.,Poznan University of Technology | Swietlik J.,Poznan University of Technology | Olejnik A.,Municipal Water Supply and sewage Company in Warsaw | Sroka M.J.,Municipal Water Supply and sewage Company in Warsaw
Water Research | Year: 2010

Corrosion processes in drinking water distribution systems have been investigated for years. This paper proves the existence of a layer of steady water surrounding and partly filling corrosion scale in corroded water pipes. It is expected that steady water may substantially influence the corrosion. The idea of steady water explains why longer retention times would lead to more turbid waters containing more suspended Fe oxides (hydroxides). During stagnation period stagnant water mixes partially with steady water and the compensation of ions' concentration as well as particle diffusion is observed. Steady water is rich in ions and has reductive properties causing quick disappearance of nitrates and unwanted ammonia formation. Ammonia in turn may be responsible for fast oxygen and chlorine decay in the distribution system due to nitrification. Nitrates may also undergo denitrification in steady water, i.e. they would support bacterial existence in the distribution system. Such an environment makes favourable conditions for sulphate reducing bacteria and in fact in all of the steady water samples we have detected sulphides. Moreover, our results have shown that considerable amounts of assimilable organic carbon (AOC) can be formed in the corroded distribution system. © 2009 Elsevier Ltd. All rights reserved.

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