As the effluent standards of total nitrogen to surface and ground stream are strengthening, the removal of ammonia nitrogen to fulfill the discharge limits by nitrification and denitrification is needed. In this work, biological treatment of high-strength nitrogen wastewater was studied by a combined anaerobic/aerobic system using a hybrid type upflow sludge bed filter (UBF) and membrane bioreactor (MBR).
Stable effluent quality could be achieved due to the good performance of anaerobic and aerobic reactor. The possible maximum concentration of influent that could be applied in this system was 14,500 mg COD/L and 1,000 mg $NH_4^+$ -N/L. At the internal recycle ratio of Q (influent flow rate), organic and total nitrogen removal rates were 99% and 46%, respectively. Decrease of organic removal efficiency and ammonification, dissimilatory nitrate reduction to ammonia, happened when alkalinity concentration decreased from 4,000 mg/L to 3,000 mg/L (as $CaCO_3$). Higher internal recycle ratio of 3Q enhanced total nitrogen removal efficiency up to the 66.5%.
But this combined process showed severe membrane fouling than unit MBR. Transmembrane pressure (TMP) of the combined process was about 9 times higher than that of the unit process. The reason of this phenomenon was mainly resulted from biological fouling factors such as hydrophobicity and extracellular polymeric substances (EPS), Changes of particle size distribution and surface charge of sludge also affected membrane fouling.
