Modeling of nitrogen removal from ground water by MBBR

The rise in Nitrate concentration in ground waters of many parts of the world including Tehran's aquifer is becoming very alarming. The source of Nitrate, apart from natural chemistry of soil is mainly contributed to leakage of sewage, industrial effluents and nitrogen based fertilizers. Due to this situation, denitrification of ground water is now gaining ground as public demand for high quality potable water is becoming an important issue. Nitrification and denitrification in Moving Bed Biofilm Reactors (MBBR) have emerged as a new technology for biological removal of harmful nitrogen compounds as nitrates and nitrites. The main advantage of MBBR reactors is due to their capacity for high removal rates and low operational problems such as clogging and settling. In this study biological denitrification method by moving bed biofilm reactor is investigated. Two packed type reactors in series with 3 liter volume each were designed in experimental set up and used in this research. Nitrification reactor worked under aerobic conditions and denitrification reactor was operated under anaerobic conditions. Methanol was used as carbon source in the reactors throughout the study. Liquid residence time was 8 hr in these reactors and 50% of reactor volume was occupied with KMT packing. The concentration of ammonium in these experiments were between 50-400 mg NH4-N/L at feed and the removal efficiencies of NO3-N was about 70% at steady state conditions. Having studied the rate of conversions under different conditions, behavior of nitrate and conversion of the ammonium to nitrate (nitrification) and nitrate to N2 was modeled in these reactors. It was concluded that, first the ammonium present in feed diffuses to the biofilm layer on the packings and by diffusing into autotrophic microorganisms layers consisting of nitrosomonas and nitrobacter, ammonia is used to produce nitrate. At second stage heterotrophic denitrifier bacteria convert nitrate to nitrogen. The behavior of ammonium take-up and nitrogen production was explained by a mathematical model. The model defined under the findings of this research can be used as a powerful tool for designing MBBR reactors for nitrogen removal from ground waters.