Municipal solid waste leachate treatment by three-stage membrane aeration biofilm reactor system.

A combined process of coagulation pretreatment and three-stage membrane aeration biofilm reactor (MABR) system was successfully applied for the first time to treat actual municipal solid waste leachate (MSWL), which was characterized by high concentrations of toxic hard-to-degrade organics and salinity. The results showed that 9.8% - 21.3% of organics could be removed from actual MSWL by coagulation with polymeric aluminum chloride (PAC). Three-stage MABR contributed 95.6% of the chemical oxygen demand (COD) removal, with the influent COD concentration ranging from 6000 to 7000 mg/L. At the same time, the removal efficiencies of total nitrogen (TN) and ammonia (NH4+-N) could reach to 84.3% and 79.9% without the addition of external carbon source, respectively. The nitrifying/denitrifying bacteria were enriched in the biofilm including Thiobacillus, Azoarcus and Methyloversatilis, which supported the MABR with high nitrogen removal efficiency and significantly toxic tolerance. Principal component analysis (PCA) and the Pearson correlation coefficients (r) illustrated that aeration pressure is a crucial operational parameter, exhibiting a strong correlation between the MABR performance and microbial communities. This work demonstrates that MABR is an effective and low-energy option for simultaneous removal of carbon and nitrogen in the treatment of MSWL.

Steel pickling rinse wastewater treatment by two-stage MABR system: Reactor performance, extracellular polymeric substances (EPS) and microbial community.

A bench-scale two-stage membrane-aerated biofilm reactor (MABR) system was applied to treat steel pickling rinse wastewater with high salinity and refractory organic. The effects of salinity and aeration pressure on the treatment efficiency, extracellular polymeric substances (EPS) characteristics and microbial community structure were studied. The optimal removal efficiencies of COD, NH+ 4-N and TN reached to 62.84%, 99.57% and 51.65%, respectively. Shortcut nitrification was achieved at low aeration, and the salinity less than 4% did not remarkable affect system performance. Colorimetric determination, three-dimensional exaction-emission matrix (3D-EEM) and Fourier transform infrared spectrum (FTIR) were employed to characterize the content and composition of proteins (PN) and polysaccharides (PS) in EPS of the biofilm. The results indicated that PN, not PS, response to changes of environmental conditions played a key role. Moreover, EPS might alleviate intracellular and extracellular osmotic pressure imbalance induced by high salinity, which imparted the biofilm in MABR with prominent salt-tolerant. High-throughput sequencing displayed that nitrifiers (Nitrosomonas, Nitrospira), denitrifiers (Dechloromonas, Hyphomicrobium, Denitromonas, Denitratisoma, Candidatus_Competibacter) and aerobic denitrifiers (Pseudomonas, Thauera) were predominant salt-tolerant bacteria.

Advanced treatment of coal chemical reverse osmosis concentrate with three-stage MABR.

The issue of reverse osmosis concentrate (ROC) has attracted significant attention due to its complex and toxic constituents under high salinity conditions. In this work, a three-stage membrane-aerated biofilm reactor (MABR) system was constructed to treat such wastewater without an external carbon source. The effects of operating conditions including aeration pressure, reflux ratio, temperature and hydraulic retention time on the removal performance of the integrated system were evaluated and optimized. Under the optimal operating parameters, the removal efficiencies of COD, NH4 +-N, NO3 --N, and TN reached 69.36%, 80.95%, 54.55%, and 54.36%, respectively. Three-dimensional fluorescence analysis indicated that humic acid was mostly removed from raw water. Moreover, microbial diversity analysis indicated that the microbial community structure of each reactor could be individually modulated to exert different functions and enhance the system performance. The integrated MABR system exhibits great feasibility and potential for the advanced treatment of coal chemical ROC.

Enhanced carbon and nitrogen removal in an integrated anaerobic/anoxic/aerobic-membrane aerated biofilm reactor system.

A pilot-scale anaerobic/anoxic/aerobic-membrane aerated biofilm reactor (A2/O-MABR) system was constructed to enhance carbon and nitrogen removal. The effects of major operating parameters including the nitrate recycling ratio (R), sludge recycling ratio (r), and aerobic tank dissolved oxygen (DO) concentration on the system performance were investigated. The average removal efficiencies of the chemical oxygen demand (COD), ammonium nitrogen (NH4 +-N), and total nitrogen (TN) were 89.0 ± 3.2%, 98.8 ± 1.3%, and 68.5 ± 4.2%, respectively, and their effluent concentrations were averagely 22.6 ± 7.3, 0.32 ± 0.2, and 13.3 ± 1.2 mg L-1. The suspended sludge and biofilm in aerobic tank facilitated the simultaneous nitrification and denitrification (SND) processes. Indeed, unique biofilm layered structure and abundant microbial community in the biofilm on MABR would enhance nitrogen removal. Compared with the A2/O system, the A2/O-MABR system exhibited higher nitrifying bacteria oxygen uptake rate (OUR) of 58.1 and 54.5 mgO2 per gMLSS per h in suspended sludge and biofilm, respectively, and the lower mixed liquor suspended solid (MLSS) concentration of 1800 mg L-1. Moreover, high-throughput sequencing indicated that putative nitrogen removal bacteria such as Thauera and Paracoccus could be effectively enriched in the biofilm. Since the volume proportions of the anaerobic, anoxic, aerobic and settling tank in the existing A2/O system of the WWTP was not changed, the A2/O-MABR system was simple and practical for the upgrading of A2/O system.