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1999 | 2 | 203-216
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Nitrate removal from drinking water in ion exchange - biological denitrification process

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Microbiological denitrification has some disadvantages, including 1) decrease of fermentation activity of bacteria at low temperature, 2) serious risk of water contamination, and 3) production of nitrites. For these reasons, a new method for nitrate removal is required. A promising method seems to be two step process coupling nitrate adsorption on ion exchange resins followed by microbiological denitrification. The aim of this work was to determine usefulness of exchange resins in nitrate ion adsorption, the influence of resin regeneration on the performance of exchange column, the effect of various salt concentrations on biological denitrification, nitrate removal kinetics, as well as mathematical modeling of nitrate exchange in the function of time. Ion exchange experiments were performed using Amberlite IRA 400, Amberlite IRA 410, Wolfatit SKB (Rohm & Haas, USA) and Dowex 2. For denitrification of low salted water, up to 2% NaCl, bacteria Paracoccus denitrificans (ATCC19367) were used, whereas denitrification of higher salted water, with NaCl concentration up to 12% w/v, was performed with a halophilic strain Halobacterium mediterranei (ATCC 33500). Methanol was used as carbon source, with 30% excess compared to stoichiometric amount. To achieve C/P ratio 56/1 potassium monophosphate was added. During fermentation, the pH value of brine was automatically controlled at 6,5-7,0. Initial concentration of nitrate was 7,0 g dm^3. Microbiological denitrification was carried out in batch fermentations. Nitrate concentration in water was determined using spectrophotometric method with salicylate, and nitrate concentration was measured in reaction with sulfanilamide and 1-naphtylenediamine. All used resins showed the ability to adsorb nitrate ions. Adsorption capacity of resins was significantly affected by the number of regeneration courses and decreased with every regeneration course because of strong linkage of ions to the resins. Fermentation was carried out in glass flask. Both microorganisms used in this study demonstrated very good ability to reduce nitrate level. In the case of Paracoccus denitrificans, statistical analysis of experimental data showed that salt concentration significantly affected denitrification efficiency. The denitrification process was inhibited even when 2% solution was used. An important decrease of denitrification rate versus fermentation time was noticed. . Data showed that Halobacterium mediterranei was able to reduce nitrate ions in high chloride concentration. Mathematical analysis proved that the most important factor influencing denitrification rate is chloride concentration. The maximum of denitrification rate appeared in post-regeneration brine with 10% of sodium chloride.

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P. Cyplik, Katedra Biotechnologii i Mikrobiologii Zywnosci, Akademia Rolnicza, ul. Mazowiecka 48, 60-623 Poznan, Poland
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