Rejections and membrane fouling of submerged direct contact hollow-fiber membrane distillation as post-treatment for anaerobic fluidized bed bioreactor treating domestic sewage.

In this study, submerged direct contact membrane distillation (SDCMD) with a hollow-fiber membrane was applied as a post-treatment for an anaerobic fluidized bed bioreactor (AFBR) treating domestic sewage. The rejection efficiency of organic contaminants and nutrients, such as ammonia nitrogen and phosphate in SDCMD were investigated. As the transmembrane temperature difference increased, the permeate flux of SDCMD increased, while the rejection efficiency of ammonia nitrogen decreased. Regardless of the transmembrane temperature applied in this study, rejection efficiencies greater than 90% were achieved for organics and phosphate by SDCMD treatment of the AFBR effluent. A higher solution pH resulted in a lower ammonia nitrogen rejection efficiency, probably because nitrogen dominantly exists in the gaseous form and can easily pass through the hollow-fiber membrane. Long-term operation with the integrated AFBR-SDCMD process over 50 d at a transmembrane temperature of 30 °C and solution pH of 5.5 showed rejection efficiencies of 98.7%, 98.1%, and 90.5% for ammonia nitrogen, phosphate, and dissolved organic carbon (DOC), respectively. During the entire integrated process for treating domestic sewage, both DOC and nutrients present in the bulk solution of the SDCMD reactor were effectively removed to a concentrate. However, the permeate flux produced by the SDCMD membrane decreased over time, mainly because of the progressive biofouling.

Combined Effect of Activated Carbon Particles and Non-Adsorptive Spherical Beads as Fluidized Media on Fouling, Organic Removal and Microbial Communities in Anaerobic Membrane Bioreactor.

The combined effect of acrylonitrile butadiene styrene (ABS) spherical beads and granular activated carbon (GAC) particles as fluidized media on the performance of anaerobic fluidized bed membrane bioreactor (AFMBR) was investigated. GAC particles and ABS beads were fluidized together in a single AFMBR to investigate membrane fouling and organic removal efficiency as well as energy consumption. The density difference between these two similarly sized media caused the stratified bed layer where ABS beads are fluidized above the GAC along the membrane. Membrane relaxation was effective to reduce the fouling and trans-membrane pressure (TMP) below 0.25 bar could be achieved at 6 h of hydraulic retention time (HRT). More than 90% of soluble chemical oxygen demand (SCOD) was removed after 80 d operation. Biogas consisting of 65% of methane was produced by AFMBR, suggesting that combined use of GAC and ABS beads did not have any adverse effect on methane production during the operational period. Scanning Electron Microscope (SEM) examinations showed the adherence of microbes to both media. However, 16S rRNA results revealed that fewer microbes attached to ABS beads than GAC. There were also compositional differences between the ABS and GAC microbial communities. The abundance of the syntrophs and exoelectrogens population on ABS beads was relatively low compared to that of GAC. Our result implied that syntrophic synergy and possible occurrence of direct interspecies electron transfer (DIET) might be facilitated in AFMBR by GAC, while traditional methanogenic pathways were dominant in ABS beads. The electrical energy required was 0.02 kWh/m3, and it was only about 13% of that produced by AFMBR.

Hybrid forward osmosis/membrane distillation integrated with anaerobic fluidized bed bioreactor for advanced wastewater treatment.

Forward osmosis (FO)-membrane distillation (MD) process was integrated with anaerobic fluidized bed bioreactor (AFBR) to advance wastewater treatment. Low removal efficiency of nutrients such as ammonia nitrogen was improved significantly by combining FO-MD process with AFBR. The MD membrane was applied to concentrate the draw solution (DS) which can be diluted by FO filtration. By using 1 M of NaCl as DS, about 80% of ammonia nitrogen was further removed by the FO membrane while the phosphorous was removed almost completely (99%). However, the accumulation of ammonia nitrogen in DS and the reverse salt flux through the FO membrane was unavoidable. Nevertheless, combining MD membrane produced excellent removal efficiency yielding only 4 and 5.6 mg/L of ammonia nitrogen and chemical oxygen demand (COD) in MD permeate, respectively at 15 â„ƒ of transmembrane temperature. Alternatively, there is the possibility that the FO-MD process can be superior to concentrate resources such as nitrogen and phosphorous present in AFBR. The reverse salt flux from DS into AFBR bulk suspension did not show adverse effects on the performances of bioreactor with respect to COD removal efficiency, conductivity and methane production during operational period. Deposit of the fouling layer on FO membrane was also observed, but the fouling on MD membrane was not severe probably because crystallization rate could be retarded by diluting the DS during FO filtration.