Nitrogen Removal In Low C/N Ratio Domestic Wastewater

As low C/N domestic wastewater contains less organic contents, we can't get ideal results if we use the traditional nitrogen and phosphorus removal technology to remove nutrient. So how to improve the effect of nitrogen and phosphorus removal of low C/N domestic wastewater has been one of the hottest issues currently. And this paper presented an effective method of biological nitrogen removal that works in low C/N domestic wastewater.We used activated sludge to adsorb the organic matters in the low C/N domestic wastewater, and then the clarification pool was used to separate the activated sludge and the adsorbents from wastewater. Thus the organic matters the activated sludge adsorbed which had been changed were input to denitrification process as carbon source in order to obtain the aim of denitrification.Firstly, we researched the utilization pathway of the system carbon source from raw water. We found that anaerobic activated sludge could absorb COD more than 70%, but nearly no NH₄⁺-N (the highest percentage was only 5% ) could be absorbed. If we used the anaerobic activated sludge to absorb low C/N domestic wastewater, carbon and nitrogen in the raw water would be separated effectively. But the desorption was not very easy. It was very difficult to separate the absorbed organic matters from the activated sludge, no matter to stir or add sodium hypochlorite solution or hydrolyze acidification. At last, the ratio of desorption/absorption was less than 25%.Secondly, we investigated the clarification performance of carbon and nitrogen separation after the activated sludge adsorbing the organic matters. Results showed that the clarification pool could separate the activated sludge and the water to complete carbon and nitrogen separation. 50% of the COD could be adsorpted through carbon and nitrogen separation, while almost no NH₄⁺-N could be adsorpted with average 4.0% removal of NH₄⁺-N.Thirdly, the performance of BAF nitrification was greatly improved after using activated sludge absorbing the organic matters in the influent, the concentration of NH₄⁺-N in the effluent decreased to less than 5 mg/L. When the anaerobic activated sludge adsorbing organics, it carried a part of NH₄⁺-N, causing the NH₄⁺-N of the sedimentation tank effluent to be higher. Then another BAF was added fter the sedimentation tank, then the final effluent NH₄⁺-N reduced to 5mg/L and reached the first-grade A standard.Finally, the factors of denitrification and the effects of denitrification in anoxic bank were studied. Results showed that using the organic matters adsorbed by anaerobic activated sludge from low C/N domestic wastewater as denitrification carbon source could get a better effect of denitrification. The efflent NO3--N concentrations reduced to 1mg/L after 3h's denitrification in the anoxic bank.In a conclusion, using the organic matter adsorpted by anaerobic activated sludge from low C/N domestic wastewater as denitrification carbon source could completely solve the problem that biological nitrogen removal didn't have sufficient carbon source of low C/N sewage, and the final effluent NH₄⁺-N and TN reached the GB 18918-2002 first-grade A standard.Using this method could supply carbon source for denitrification and reduce sludge production and save the cost of sewage treatment. Simultaneously, the organic matters of influent in nitrification process was reduced while the nitrification effect was improve.