[show abstract][hide abstract] ABSTRACT: A continuous stirred tank reactor (CSTR) type of hollow fiber membrane biofilm reactor (HF-MBfR) using composite membranes was investigated for the nitrogen removal in synthetic wastewater. The CSTR-type of HF-MBfR process couples autotrophic biological nitrogen removal reactors with the bubbleless mass transfer of oxygen and hydrogen through hollow fiber membranes. For nitrification, CSTR-type of HF-MBfR was operated over 400 days and for hydrogenotrophic denitrification, CSTR-type of HF-MBfR was operated over 300 days. The maximum steady-state NH4+-N removal rate achieved was 0.25 kg N/m3 day (2.06 g N/m2 day) and the denitrification rate achieved was 0.22 kg N/m3 day (1.72 g N/m2 day). Consequently, in the HF-MBfRs, biofilms were formed stably on surface of membranes, and nitrification and hydrogenotrophic denitrification were performed successfully during long-term operation.
[show abstract][hide abstract] ABSTRACT: Carbon dioxide is one of the global warming gases. Utilization of a sustainable energy is one of the effective technologies for the mitigation of CO 2 accumulation in the atmosphere. If renewable energy can be used for methane synthesis, H 2 is converted to methane by reducing CO 2 . We investigated the conversion of CO 2 to CH 4 using a novel hollow-fiber membrane biofilm reactor. We have converted CO 2 to CH 4 with autotrophic methanogens using CO 2 and H 2 . All the gases were diffused into water through the membrane without bubbles. We have successfully operated the Hf–MBfR for stable methane production from CO 2 and H 2 under continuous operations for 60–70 days at acidic and neutral pH. The methane ratio of the gas produced depended on the pH condition and reached about 60% at neutral pH and 80–90% at acidic pH. The produced methane contents were 751 mL day À1 on average from 20 to 58 days at neutral pH and 135 mL day À1 on average from 36 to 43 days, 247 mL day À1 on average from 44 to 70 days at acidic pH. At neutral pH, during the operating periods, acetic acid was continuously produced to 4000–7000 mg/L so that produced methane was considered to have been pro-duced by hydrogenotrophic methanogens and acetoclastic methanogens. At acidic pH, during the initial operating periods, pH was maintained to 5.9–6.6 so that acetic acid was produced by acetogens. After adjusting to less than pH 5.5, however, it was decreased. At the same time, the methane contents produced were considered to have increased by acetoclastic methanogens.
[show abstract][hide abstract] ABSTRACT: In order to enhance performances of organics removal and nitrification for the treatment of swine wastewater containing high concentration of organic solids and nitrogen than conventional biological nitrogen removal process, a submerged membrane bioreactor (MBR) was followed by an anaerobic upflow bed filter (AUBF) reactor in this research (AUBF–MBR process). The AUBF reactor is a hybrid reactor, which is the combination of an anoxic filter for denitrification and upflow anaerobic sludge blanket (UASB) for acid fermentation. In the AUBF–MBR process, it showed a considerable enhancement of the effluent quality in terms of COD removal and nitrification. The submerged MBR could maintain more than 14,000 mg VSS/L of the biomass concentration. Total nitrogen (T-N) removal efficiency represented 60% when internal recycle ratio was three times of flow-rate (Q), although the nitrification occurred completely. Although the volatile fatty acids produced in AUBF reactor can enhance denitrification rate, but the AUBF–MBR process showed reduction of overall removal efficiency of the nitrogen due to the reduction of carbon source by methane production in the AUBF reactor compared to that of theoretical nitrogen removal efficiency.Long-term operation of the submerged MBR showed that the throughputs of the submerged MBR were respectively 74, 63, and 31 days at 10, 15, and 30 L/m2 h (LMH) of permeate flux. Resistance to filtration by rejected solid is the primary cause of fouling, however the priority of cake resistance (Rc) and fouling resistance (Rf) with respect to filtration phenomenon was different according to the amount of permeate flux. The submerged MBR, here, achieved a steady-state flux of 15 LMH at 0.4 atm. of trans-membrane pressure (TMP) but the flux can be enhanced in the future because shear force by tangential flow will be greater when multi-layer sheets of membrane were used.
[show abstract][hide abstract] ABSTRACT: A hollow-fiber membrane biofilm reactor (HF-MBfR) treating nitrogen in synthetic wastewater was studied in respect to nitrification and denitrification ability using autotrophic microorganism over a period of 260 days. The hybrid HF-MBfR system consists of a nitrification HF-MBfR and denitrification HF-MBfR. Oxygen and hydrogen were supplied through the lumen of fibers as electron acceptor and donor. In Phase I, two HF-MBfR were operated separately during the period of 149 days. And then, the HF-MBfR were operated by hybrid system that is connected continuously. The hybrid HF-MBfR was operated at hydraulic retention time (HRT) of 4 h, 2 h, and the volumetric NH4+-N loading rate increased from 0.42 to 1 28 kgNH4+-N/m3d by increasing NH4+-N concentration of influent from 150 to 200 mgN/L. The average total nitrogen removal efficiency was above 98% during the experiment steps and the maximum volumetric total nitrogen removal rate was 1.20 kgN/m3d in the hybrid HF-MBfR system. In this study, the results suggested that this hybrid HF-MBfR system operated effectively for nitrogen removal in an inorganic environment and can be used stably as a high rate nitrogen removal technology.
[show abstract][hide abstract] ABSTRACT: The objective of this study was to develop an integrated nitrogen treatment system using autotrophic organisms. A treatment system consists of an aerobic hollow-fiber membrane biofilm reactor (HfMBR) and anaerobic HfMBR. In the aerobic HfMBR, a mixture gas of air and O2 was supplied through the fibers for nitrification. Denitrification occurred in the anaerobic HfMBR using H2 as the electron donor. The treatment system was continuously operated during 190 days. NH4-N removal efficiencies ranging from 95% to 97% were achieved at NH4-N concentrations of influent in range from 50 to 100 mgN/L. When gucose was added in influent, the simultaneous nitrification and denitrification were occurred in the aerobic HfMBR and nitrogen removal rates were changed according to the COD/NH4-N ratio of influent. In the anaerobic HfMBR, autotrophic denitrification using H2 was occurred and the removal rates achieved in this study were 23 ~ 58 mgN/m2·d. In this study, the achieved removal efficiency was some low than other study findings, however, the result suggested that this hybrid HfMBR system can be used effectively for nitrogen removal in the oligotrophic water.
Proceedings of the Water Environment Federation. 12/2004;