Study On The Efficiency Of Anoxic-oxic Composite MBR For Ship Domestic Sewage Treatment And Biological Nitrogen And Phosphorus Removal

Along with the shipping industry development, the ship domestic sewage treatment technology has been improved constantly. In order to promote reducing the discharge capacity of ships, the International Maritime Organization (IMO) legislates constantly and the legal system has become generally binding. In the 64th Maritime Environment Protection Committee (MEPC) meeting, the clear and strict emission standards of ship sewage treatment equipments in total nitrogen (TN) and total phosphorus (TP) were put forward first time.Although the membrane bioreactor (MBR), which takes up small space on board, has the excellent ability to degrade pollutants and effluent quality in stable, while, its single dissolved oxygen environment is not conducive to the removal of nitrogen and phosphorus. The improvement of old MBR on ships by adding an anoxic process achieves an alternating operating environment of anoxic and oxic. It has a practical significance to improve the efficiency of nitrogen and phosphorus removal and reduce the investment of new equipments.In the present paper, an Anoxic-Oxic Composite Membrane Bioreactor (A/O-CMBR)was used to treat the ship domestic sewage. The removal efficiency and mechanism of pollutants were investigated. The main study contents are summarized as follows:1. Microbes for microbial egradation of organic pollutants started faster in Anoxic-Oxic Membrane Bioreactor (A/O-MBR) without dosing semi-soft fillers as the microbial carrier.The average removal rate of CODCr in the early period was 92.73%. The removal efficiency of organic pollution was 96.67% when fillers were put in A/O-CMBR.2. The start of the nitrifying bacteria which was responsible for the oxidation of NH3-N in oxic pool was completed within two weeks in the start-up period of A/O-MBR. While the denitrifying bacterias which were responsible for the reduction of NO2--N and NO3--N in the system was mature after five days later. Adding the filler to oxic pool made the average removal rate of TN increase by 9.08%, the average removal rates of NH3-N and TN were 92.35% and 84.11% in A/O-CMBR.3. When the A/O-CMBR operated stably in long-term, the average removal rate of TN was 49.79% in anoxic pool, while there was also an average removal rate 26.79% in the oxic pool because of the simultaneous nitrification and denitrification process. Meanwhile the average concentration of NO2--N in the oxic pool always stayed at lower levels of 1.09mg/L.A/O-CMBR has a good ability to cope with NH3-N impact load and a poor ability to cope with TN impact load when it was in long-term stable operation.4. The efficiency of phosphorus removal was enhanced by dosing fillers,the TP removal rate reached 58.34%.5. The characteristics of membrane surface, structures and elements of pollutants were studied by X-ray spectroscopy (EDS) and scanning electron microscopy (SEM). The results verified previous studies of this subject that proteins and polysaccharides were the main pollutants on the membrane surface. The ability of nitrogen and phosphorus removal can reduce the content of protein and polysaccharide on the membrane surface and significantly improve the anti-fouling ability of membrane.