Partial Nitrification Of High Ammonium-containing Wastewater With Low C/N In Membrane Bioreactor-Anaerobic Biofilter

The process of partial nitrification and denitrification, as a newly developed biological nitrogen removal process, has economic advantanges compared with complete nitrification and denitrification when used for treating high ammonium-containing wastewater with low C/N. However, it seems to be difficult to achieve long-term partial nitrification since ammonia oxidizing bacteria (AOB) population can be affected by free ammonia and free nitrous acid at low temperature. In this study, our experiments were carried out in AOB seeded membrane bioreactor (MBR) and anaerobic filter (AF) for the treatment of high ammonium-containing artificial wastewater, with activated sludge MBR and AF as the compare system. Furthermore, membrane fouling and change of microbiological community were investigated. The main results were as follows:(1) In the start-up phase, the optimal conditions were as follows:pH7.2～7.8, temperature30℃and dissolved oxygen1～2mg/L. After35days operation, the ammonia oxidizing efficiency of the AOB MBR system reached up to40%, which was20%higher than the activated sludge MBR system. Moreover, nitrite accumulation efficiency stayed more than95%in the AOB MBR system, while it was80～90%in the activated sludge MBR system after25days. The converting efficiency of nitrite nitrogen was as high as90%in the anaerobic filters of two systems after eight days operation, as well as the C/N consumed ratio of6.28～8.97and the biofilm thickness of about1mm.(2) The treatment efficiency of partial nitrification and denitrification and membrane fouling were discussed as the temperature was controlled at30℃. Nitrite accumulation rate of the AOB MBR kept more than95%, and ammonia oxidizing efficiency was20%higher than that of the activated sludge MBR. The denitrification rates of two systems were both close to100%and the evolution of total nitrogen removal efficiency was similar to ammonia oxidizing efficiency in two systems. After membranes were changed at the90th day, membrane in AOB MBR was cleaned twice, while it was three times in activated sludge MBR. According to the observation of scanning eletron microscopy, the hole size of membrane in activated sludge MBR was larger than that in AOB MBR.(3)The variations of stable performance were investigated when the temperature changed with the ambient environment and showed the decreasing tendency. However, nitrite accumulation rate stayed higher than95%and ammonia oxidizing efficiency declined in small degree in AOB MBR. As the temperature decreased below28℃, nitrite accumulation rate of activated sludge MBR exhibited decreasing tendency, which decreased to nearly zero at the320th day and started to increase at the320th day. Ammonia oxidizing efficiency obviously tended to decreasing and then increasing. The decline of temperature had a little effect on the performance of AF of two systems, with the denitrification rate of nearly100%. The removal efficiency of total nitrogen ranged from more than90%to80%in AOB MBR-AF system, while it ranged from90%to65%in activated sludge MBR-AF system.(4) All through the operation period, the ammonia oxidizing activity and nitrite oxidizing activity of AOB kept between0.123-0.17g N/g MLSS/d and less than0.01g N/g MLSS/d respectively, which changed obviously in the activated sludge MBR caused by temperature changing. On the other hand, scanning electron microscope photos displayed that microbial composition in AOB system exhibited stable, with the dominance of AOB in MBR.