Denitrification of drinking water in membrane bioreactor
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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.
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P. Cyplik, Katedra Biotechnologii i Mikrobiologii Zywnosci, Akademia Rolnicza, ul. Mazowiecka 48, 60-623 Poznan, Poland