Treatment of Wastewater with High Nitrogen Loading by Moving Bed Biofilm Reactor

Abstract

Wastewater of municipal toilets contains higher nitrogen to carbon ratio than other types of wastewater. The removal of nitrogen from municipal toilet wastewater has become a major concern due to problems caused by discharge of insufficiently treated wastewater, such as eutrophication and toxicity. Moving Bed Biofilm Reactor (MBBR) has been developed in order to facilitate nitrogen removal. Treatment of nitrogen is commonly achieved in separate aerobic and anoxic tanks in typical MBBR systems. However the treatment process using a single MBBR tank as an advantageous method because of the low cost and low complexity, has not been thoroughly studied. This research is focused on the performance of MBBR in nitrogen removal based on simultaneous nitrification and de-nitrification in single aerobic MBBR with continuous operation. A moving-bed biofilm reactor system with an anoxic–aerobic arrangement was set up and the wastewater extracted from the wastewater treatment plant at temple of Tooth Relic, Kandy, was kept in the prepared laboratory set up for the accumulation of microorganisms. The operation was carried out in 3 steps. In the first step, the DO concentration in the reactor was maintained at 5 mg/l and the synthetic wastewater was introduced initially to the reactor at low nitrogen concentration. Then, the nitrogen concentration was increased varying the BOD/N. In the second step BOD/N ratio was maintained at 4.2, which is the BOD/N value of public toilet wastewater and the DO concentration was varied. Volatile Suspended Solids (VSS) of the reactor was kept at around 2200 mg/l. In the third step the DO concentration was maintained at 1.5 mg/l since it was the optimum DO concentration for highest de-nitrification in the 2nd step. Then the VSS of the reactor was maintained at 2200 mg/l and the BOD/N ratio was varied. Under the operating conditions, 67% of BOD and COD removal and 60% of TN removal could be achieved from the prepared laboratory set up. Further it was observed that the removal of nitrogen increased when the BOD/N ratio was increased.