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Denitrification of drinking water in membrane bioreactor

100%

Burda W., Aniol A., Grajek W., Cyplik P., Malyszka T.

Biotechnologia

1999

issue 2

217-229

The aim of this study was to define denitrification kinetics using bacteria Paracoccus denitrificans cultivated in membrane bioreactor equipped with microfilter module with ceramic cartridge with cut off 0,45 mm. Water used in experiments was loaded with very strong nitrate concentration reaching up to 6,0 g NO3-/L. Methanol was used as carbon source and was added in an amount 30 % higher than the one calculated stoichiometrically. The pH value of water was automatically adjusted to 7,0. As experimental variables the following parameters were tested: i) supplementation of water with some nutrients, including monopotassium phosphate and microelements: molybdenum, copper, ferric and magnesium ions, variable initial cell biomass concentration, ii) different cultivation methods: stationary batch fermentation in glass flasks and continuous fermentation in membrane bioreactor with cell recycling, iii) procedure of water suppl to bioreactor; namely, in a closed system container/membrane bioreactor, and in an open system with continuous water flow through membrane bioreactor. The results obtained in experimental fermentations showed that bacteria Paracoccus denitrificans efficiently removed nitrate ions from water. It was found that fermentation conditions significantly affected bacteria growth and denitrification rate. It was observed that addition of phosphate and microelements into drinking water significantly increased denitrification rate and cell growth. An important factor influencing denitrification rate was the initial cell concentration. However, the effect of that factor lost its significance with the fermentation time. Comparing the effect of fermentation conditions on the denitrification rate, an inhibiting effect of shear forces caused by lobar pump was observed. Upon continuous biodenitrification in membrane bioreactor with open water flow, a maximum volumetric nitrate reduction yield reached 1,7 g NO3- dm^3/ h and specific denitrification rate amounted to 0,0145 g NO3- /h/ g of cell dry matter. After three days of fermentation, cell concentration reached the value of 20-35 g dry matter per liter. On the basis of obtained the results, the mathematical models of cell growth kinetics, denitrification kinetics as well as the model of denitrification rate as a function of cell concentration have been proposed.

Nitrate removal from drinking water in ion exchange - biological denitrification process

100%

Cyplik P., Malyszka T., Grajek W., Burda W., Aniol A.

Biotechnologia

1999

issue 2

203-216

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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2 Biotechnologia

2 1999

2 Aniol A.

2 Burda W.

2 Cyplik P.

2 Grajek W.

2 Malyszka T.

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Denitrification of drinking water in membrane bioreactor

Nitrate removal from drinking water in ion exchange - biological denitrification process