Study On Treatment Of High-strength Ammonia Wastewater By Combined Process Of Two-stage Bio-contact Oxidation And MBR

With the development of industry and agriculture, pollution caused by ammonia wastewater has been becoming more and more serious.Most attention is currently paid to membrane bioreactor (MBR) for nitrogen removal because of its high effective separation. However, membrane fouling is the bottleneck which limits its development in the research and practice of conventional MBR. In the experiment, conventional activated sludge process was replaced by two-stage bio-contact oxidation in order to decrease membrane fouling, combined process of two-stage bio-contact oxidation and MBR was formed and treatment of high-strength ammonia wastewater by this combined process was studied.The experiment consisted of two phases.Phase 1 was about nitration of high-strength ammonia wastewater by oxic bio-contact oxidation and MBR (O/O-MBR).The results showed that the process performs well in nitrifying. In phase 2,some improvements were made based on phase 1,which included changing the first oxic bio-contact oxidation zone to anoxic zone which means denitrification was added, feeding no carbon source, and employing a back-flow device to perform the mixed liquor recycle from MBR to the anoxic zone.The results showed that successful nitrogen removal was achieved in combined process of anoxic/oxic bio-contact oxidation and MBR (A/O-MBR).During the O/O-MBR operation period, the CODcr and NH4+-N concentrations of the influent were 305～396mg/L and 82.91～96.80mg/L respectively. The experiment results showed that the average removal efficiencies of CODcr and NH4+-N were 86.7% and 82.5% respectively while the TN removal efficiency on average was only 14.5%.It indicated that the nitrogen removal in O/O-MBR was poor. After improving the process, the influent CODcr and NH4+-N concentrations were 269-767mg/L and 62.94-91.63mg/L respectively. The results showed that CODcr and NH4+-N were eliminated effectively by the process with average efficiencies of 92.5% and 91.2%.When mixed liquor recycle ratio was 3,the TN removal efficiency can;be as high as 89.8%.It was found that soluble microbial products (SMP) would accumulate in MBR. In this paper, the accumulation of SMP and its impacts on the effluent quality were discussed tentatively. The study showed that the changes of SMP in MBR presented a certain pattern, its formation and accumulation had no negative effects on the stability of the system, and the quality of the discharging water was stable.Fouling is still one of the major issues of the MBR research. The adoption of combined process of bio-contact oxidation and MBR alleviated the trend of fouling to a great extent. After entering the second phase of the experiment, membrane fouling almost disappeared due to the adoption of the mixed liquor recycle device.