Determination of Sustainable Critical Flux through a Long-Term Membrane Resistance Model.

A long-term membrane resistance model (LMR) was established to determine the sustainable critical flux, which developed and simulated polymer film fouling successfully in a lab-scale membrane bioreactor (MBR) in this study. The total polymer film fouling resistance in the model was decomposed into the individual components of pore fouling resistance, sludge cake accumulation and cake layer compression resistance. The model effectively simulated the fouling phenomenon in the MBR at different fluxes. Considering the influence of temperature, the model was calibrated by temperature coefficient τ, and a good result was achieved to simulate the polymer film fouling at 25 and 15 °C. The relationship between flux and operation time was simulated and discussed through the model. The results indicated that there was an exponential correlation between flux and operation time, and the exponential curve could be divided into two parts. By fitting the two parts to two straight lines, respectively, the intersection of the two straight lines was regarded as the sustainable critical flux value. The sustainable critical flux obtained in this study was just 67% of the critical flux. The model in this study was proven to be in good agreement with the measurements under different fluxes and different temperatures. In addition, the sustainable critical flux was first proposed and calculated in this study, and it was shown that the model could be used to predict the sustainable operation time and sustainable critical flux, which provide more practical information for designing MBRs. This study is applicable to polymer films used in a wide variety of applications, and it is helpful for maintaining the long-term stable operation of polymer film modules and improving the efficiency of polymer film modules.

Optimization of MBR hydrodynamics for cake layer fouling control through CFD simulation and RSM design.

Membrane fouling is an important issue for membrane bioreactor (MBR) operation. This paper aims at the investigation and the controlling of reversible membrane fouling due to cake layer formation and foulants deposition by optimizing MBR hydrodynamics through the combination of computational fluid dynamics (CFD) and design of experiment (DOE). The model was validated by comparing simulations with measurements of liquid velocity and dissolved oxygen (DO) concentration in a lab-scale submerged MBR. The results demonstrated that the sludge concentration is the most influencing for responses including shear stress, particle deposition propensity (PDP), sludge viscosity and strain rate. A medium sludge concentration of 8820mgL-1 is optimal for the reduction of reversible fouling in this submerged MBR. The bubble diameter is more decisive than air flowrate for membrane shear stress due to its role in sludge viscosity. The optimal bubble diameter was at around 4.8mm for both of shear stress and PDP.

Influence of carbon sources on nutrient removal in A2/O-MBRs: Availability assessment of internal carbon source.

Both internal carbon source and some external carbon sources were used to improve the nutrient removal in Anaerobic-Anoxic-Oxic-Membrane Bioreactor (A2/O-MBRs), and their technical and cost analysis was investigated. The experimental results showed that the nutrient removals were improved by all the carbon source additions. The total nitrogen and phosphorus removal efficiency were higher in the experiments with external carbon source additions than that with internal carbon source addition. It was found that pathways of nitrogen and phosphorus transform were different dependent on different carbon source additions by the mass balance analysis. With external carbon source addition, the simultaneous nitrification and denitrification occurred in aerobic zone, and the P-uptake in aerobic phase was evident. Therefore, with addition of C-MHP (internal carbon source produced from sludge pretreatment by microwave-H2O2 process), the denitrification and phosphorus-uptake in anoxic zone was notable. Cost analysis showed that the unit nitrogen removal costs were 57.13CNY/kg N of C-acetate addition and 54.48CNY/kgN of C-MHP addition, respectively. The results indicated that the C-MHP has a good technical and economic feasibility to substitute external carbon sources partially for nutrient removal.

CFD simulation and optimization of membrane scouring and nitrogen removal for an airlift external circulation membrane bioreactor.

Cost-effective membrane fouling control and nitrogen removal performance are of great concern in airlift external circulation membrane bioreactors (AEC-MBRs). Computational fluid dynamics (CFD) model incorporating sub-models of bio-kinetics, oxygen transfer and sludge rheology was developed for the cost-effective optimization of a lab-scale AEC-MBR. The model was calibrated and validated by extensive measurements of water velocities and water quality parameters in the AEC-MBR. The validated results demonstrated that the optimized height of gas-liquid dispersion was at around 300mm. The shear stress on membrane surface was equalized and had an average value of 1.2Pa under an air flowrate of 1.0m(3)h(-1). The model further revealed that the high nitrogen removal efficiency (>90%) was achieved due to the high recirculation ratio driven by airlift force without destroying the oxygen deprivation and enrichment in the anoxic and oxic zone, respectively.

Modifying glass fiber surface with grafting acrylamide by UV-grafting copolymerization for preparation of glass fiber reinforced PVDF composite membrane.

Experimental design and response surface methodology (RSM) were used to optimize the modification of conditions for glass surface grafting with acrylamide (AM) monomer for preparation of a glass fiber reinforced poly(vinylidene fluoride) (PVDF) composite membrane (GFRP-CM). The factors considered for experimental design were the UV (ultraviolet)-irradiation time, the concentrations of the initiator and solvent, and the kinds and concentrations of the silane coupling agent. The optimum operating conditions determined were UV-irradiation time of 25 min, an initiator concentration of 0-0.25 wt.%, solvent of N-Dimethylacetamide (DMAC), and silane coupling agent KH570 with a concentration of 7 wt.%. The obtained optimal parameters were located in the valid region and the experimental confirmation tests conducted showed good accordance between predicted and experimental values. Under these optimal conditions, the water absorption of the grafted modified glass fiber was improved from 13.6% to 23%; the tensile strength was enhanced and the peeling strength of the glass fiber reinforced PVDF composite membrane was improved by 23.7% and 32.6% with an AM concentration at 1 wt.% and 2 wt.%. The surface composition and microstructure of AM grafted glass fiber were studied via several techniques including Field Emission Scanning Electron Microscopy (FESEM), Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR) and energy dispersive X-ray spectroscopy (EDX). The analysis of the EDX and FTIR-ATR results confirmed that the AM was grafted to the glass fiber successfully by detecting and proving the existence of nitrogen atoms in the GFRP-CM.

Preparation and characterization of PVDF-glass fiber composite membrane reinforced by interfacial UV-grafting copolymerization.

A novel inorganic-organic composite membrane, namely poly(vinylidene fluoride) PVDF-glass fiber (PGF) composite membrane, was prepared and reinforced by interfacial ultraviolet (UV)-grafting copolymerization to improve the interfacial bonding strength between the membrane layer and the glass fiber. The interfacial polymerization between inorganic-organic interfaces is a chemical cross-linking reaction that depends on the functionalized glass fiber with silane coupling (KH570) as the initiator and the polymer solution with acrylamide monomer (AM) as the grafting block. The Fourier transform infrared spectrometer-attenuated total reflectance (FTIR-ATR) spectra and the energy dispersive X-ray (EDX) pictures of the interface between the glass fiber and polymer matrix confirmed that the AM was grafted to the surface of the glass fiber fabric and that the grafting polymer was successfully embedded in the membrane matrix. The formation mechanisms, permeation, and anti-fouling performance of the PGF composite membrane were measured with different amounts of AM in the doping solutions. The results showed that the grafting composite membrane improved the interfacial bonding strength and permeability, and the peeling strength was improved by 32.6% for PGF composite membranes with an AM concentration at 2wt.%.

[Energy Consumption Comparison and Energy Saving Approaches for Different Wastewater Treatment Processes in a Large-scale Reclaimed Water Plant].

Energy consumption is the main performance indicator of reclaimed water plant (RWP) operation. Methods of specific energy consumption analysis, unit energy consumption analysis and redundancy analysis were applied to investigate the composition and spatio-temporal distribution of energy consumption in Qinghe RWP with inverted A2/O, A2/O and A2/O-MBR processes. And the A2/ O-MBR process was mainly analyzed to identify the main nodes and causes for high energy consumption, approaches for energy saving were explored, and the energy consumption before and after upgrading for energy saving was compared. The results showed that aeration was the key factor affecting energy consumption in both conventional and A2/O-MBR processes, accounting for 42.97% and 50.65% of total energy consumption, respectively. A pulsating aeration allowed an increasing membrane flux and remarkably reduced the energy consumption of the A2/O-MBR process while still meeting the effluent standard, e.g., the membrane flux was increased by 20%, and the energy consumptions per kiloton wastewater and kilogram COD(removed) were decreased by 42.39% to 0.53 kW-h-kg-3 and by 54.74% to 1.29 kW x h x kg(-1), respectively. The decrease of backflow ratio in the A2/O-MBR process within a certain range would not deteriorate the effluent quality due to its insignificant correlation with the effluent quality, and therefore may be considered as one of the ways for further energy saving.

Internal carbon source from sludge pretreated by microwave-H2O2 for nutrient removal in A2/O-membrane bioreactors.

To improve the nutrient removal, the feasibility was studied for the organics released from sludge pretreated by microwave-H2O2 process (MHP) to be used as internal carbon source in two A2/O-membrane bioreactors (MBRs). The experiments were conducted for the nutrient removal and the membrane fouling. The results showed that the removal efficiencies of TN and TP were improved by 11% and 28.34%, respectively, as C/N ratio was adjusted to 8 by adding the internal carbon source, and the ratio of soluble chemical oxygen demand (sCOD) consumed easily for denitrification was about 46% of the total sCOD in the internal carbon source. The addition of the internal carbon sources did not lead to severe membrane fouling in the experimental A2/O-MBR. It is implied that the organics released from sludge pretreated by MHP could be used as the internal carbon source to enhance the nutrient removal in A2/O-MBRs.

Study of a membrane bioreactor with glass fiber flat grille modules and the modules' optimization based on the local critical flux theory.

A novel flat grille membrane module using inorganic glass fibers as filter media is proposed for use in a membrane bioreactor for wastewater treatment. A model which integrates the concepts of back transport velocity, spatial local critical flux and temporal variation of the local flux has been developed. The membrane module was optimized based on experimental results and calculations using the model. The optimized parameters include the volume ratio of membrane solution for the surface modification of glass fibers, the fiber inner diameter and fiber length. The optimal values were 1:2 and 5mm respectively but the length had little effect on the performance of the module. The critical time was then calculated with the model and an equation developed. The result was in very good agreement with the observed one. Finally, the performance of the glass fiber MBR was monitored. The effluent quality and stability of the system were comparable to that of conventional MBRs. This MBR will be a promising technique for wastewater treatment given its low cost, high strength and good effluent quality.

[Dynamic membrane bioreactor with glass fiber tube covered with organic membrane].

A novel grille form complex membrane module composed of glass fiber covered with organic membrane and the dynamic membrane bioreactor (DMBR) with this complex membrane were studied. The results showed that the flux of the dynamic membrane of glass fiber tube without covering with organic membrane solution was only 4 L/(m2 x h) at a trans-membrane pressure (TMP) of 0.02 MPa. After the modification of covering with the organic membrane solution, the complex dynamic membrane flux could reach to a level of 16 L/(m2 x h) at a TMP of 0.01 MPa in operation, and after a hydraulic and chemical cleaning, the membrane flux was up to 17.1 L/(m2 x h) at a lower TMP of 0.003 MPa. When the glass fiber tube was coated with a membrane solution with a concentration of 1:4 (membrane materials/solution in volume ratio), the flux of the complex membrane worked steadily at 14.29 L/(m2 x h) more than 51 days, and according to calculation by TMP rising, the flux could maintain for almost 275 d. The average removal rates of COD and NH4+ -N were 81.96% and 83.66% respectively by the DMBR, and that were 21.01% and 3.61% only by the complex dynamic membrane. Moreover, the cost of complex membrane was approximately 40-60 yuan/m2, which was lower than the traditional organic membrane.

Inorganic nitrogen removal of toilet wastewater with an airlift external circulation membrane bioreactor.

Removal of inorganic nitrogen (inorganic-N) from toilet wastewater, using a pilot-scale airlift external circulation membrane bioreactor (AEC-MBR) was studied. The results showed that the use of AEC-MBR with limited addition of alkaline reagents and volumetric loading rates of inorganic-N of 0.19-0.40 kg inorganic-N/(m3 x d) helped achieve the desired nitrification and denitrification. Furthermore, the effects of pH and dissolved oxygen (DO) on inorganic-N removal were examined. Under the condition of MLSS at 1.56-2.35 g/L, BOD5/ammonia nitrogen (NH4+ -N) at 1.0, pH at 7.0-7.5, and DO at 1.0-2.0 mg/L, the removal efficiencies of NH4+ -N and inorganic-N were 91.5% and 70.0%, respectively, in the AEC-MBR. The cost of addition of alkaline reagent was approximately 0.5-1.5 RMB yuan/m3, and the energy consumption was approximately 0.72 kWh/m3 at the flux of 8 L/(m2 x h).

Performances of biological aerated filter employing hollow fiber membrane segments of surface-improved poly (sulfone) as biofilm carriers.

Using the surface of poly (sulfone) hollow fiber membrane segments as grafted layer, the hydrophilic acrylamide chain was grafted on by UV-photoinduced grafting polymerization. The gained improvement of surface wettability for the modified membrane was tested by measuring the contact-angle as well as FTIR spectra. Then correlation between the hydrophilic ability of support material and the biofilm adherence ability was demonstrated by comparing the pollutant removal rates from urban wastewater via two identical lab-scale up-flow biological aerated filters, one employed the surface wettability modified poly (sulfone) hollow fiber membrane segment as biofilm carrier and the other employed unmodified membrane segment as biofilm carrier. The experimental results showed that under the conditions of influent flux 5 L/h, hydraulic retention time 9 h and gas to liquid ratio (G/L) 10:1, the removal rates of chemical oxygen demand (COD) and ammonium nitrogen (NH4(+)-N) for the modified packing filter and the unmodified packing filter was averaged at 83.64% and 96.25%, respectively, with the former filter being 5%-20% more than the latter. The effluent concentration of COD, NH4(+)-N and turbidity for the modified packing filter was 25.25 mg/L, 2 mg/L and 8 NTU, respectively. Moreover, the ammonium nitrogen removal performance of the filter packing the modified PSF was compared with the other bioreactor packing of an efficient floating medium. The biomass test indicated that the modified membrane matrixes provided better specific adhesion (3310-5653 mg TSS/L support), which gave a mean of 1000 mg TSS/L more than the unmodified membrane did. In addition, the phenomenon of simultaneous denitrification on the inner surface of the support and nitrification on the outer surface was found in this work.

[Study of a new type of tubular self-forming dynamic membrane bioreactor and its application for treatment of landfill leachate].

A new type of fiberglass tubular self-forming dynamic membrane bioreactor (DMBR) and its application for treatment of landfill leachate on laboratory scale were studied. The results showed that the system worked with a average membrane flux 3.75 L/m2 x h) maintained by gravity filtration at a trans-membrane pressure (TMP) of 2 900 Pa for near 80 days. After the modification of membrane module, a higher membrane flux was achieved at a TMP of 1 450 Pa and the membrane flux could be maintained steadily at 6 L/(m2 x h) for a long time. At the same time, the formation and filtration performance of dynamic membrane (DM) was tested. The effluent turbidity was blow 1.0 NTU and the average removal of COD, BOD5 and NH4(+) -N in this system exceeded 71%, 96% and 98% respectively. Moreover, COD removal from the supernatant on an average of 19.34% was made only by the dynamic membrane.

Reuse rate of treated wastewater in water reuse system.

A water quality model for water reuse was made by mathematics induction. The relationship among the reuse rate of treated wastewater (R), pollutant concentration of reused water (Cs), pollutant concentration of influent (C0), removal efficiency of pollutant in wastewater (E), and the standard of reuse water were discussed in this study. According to the experiment result of a toilet wastewater treatment and reuse with membrane bioreactors, R would be set at less than 40%, on which all the concemed parameters could meet with the reuse water standards. To raise R of reuse water in the toilet, an important way was to improve color removal of the wastewater.

[Reducing sludge production by predation and its factors analysis in conventional activated sludge process].

Reducing excess sludge production induced by Oligochaete is carried out in a pilot scale of conventional activated sludge (CAS) reactor for 345 days. Worms occurred for nearly whole operating period except for the first 20 days, and continuously maintained at high density (over 30 total worms/mgVSS in aeration tank) for 172 days. Three types of worm were found, Aeolosoma hemprichicii and Nais elinguis alternatively dominated, but Pristina aequiseta occasionally presented. High worm density greatly contributes to both reducing sludge production and improving the sludge settling characteristics, and Nais elinguis had more potential for sludge reduction than Aeolosoma. Worm growth had impacts on effluent quality, and Nais elinguis growth affected effluent quality much more than Aeolosoma. Worm growth does not disturb the nitrification process, but PO4(3-) -P release into effluent occurres as Nais elinguis dominated. Analysis of factors affecting worm growth show that only SRT has no any impact on neither Aeolosoma nor Nais, however, both temperature and HRT can affect their growth very much.

[The influence of mechanical-cleaning membrane module on membrane flux].

An enhanced mechanical-cleaning membrane module M1 and a mechanical-cleaning membrane module M2 were designed in this research. An orthogonal array design was adopted to investigate effects of operational parameters including aeration intensity, membrane flux, MLSS, ratio of suction time and non-suction time on membrane filtration of two membrane module of M1 and M2. The results showed that M1 could weaken the negative influence of disadvantage parameters including high MLSS, high membrane flux, and low aeration intensity on membrane flux. M1 and M2 module both maintained a high flux of 40 L/(h x m2) under the conditions of MLSS 6 g/L, aeration 0.5 m3/h, ratio of suction time and non-suction time of 12/1, which was selected by the study of orthogonal array. Resistance distribution showed that the mechanism of mechanical-cleaning help to remove the sludge cake pollution on membrane surface.

Minimization of excess sludge production for biological wastewater treatment.

Excess sludge treatment and disposal currently represents a rising challenge for wastewater treatment plants (WWTPs) due to economic, environmental and regulation factors. There is therefore considerable impetus to explore and develop strategies and technologies for reducing excess sludge production in biological wastewater treatment processes. This paper reviews current strategies for reducing sludge production based on these mechanisms: lysis-cryptic growth, uncoupling metabolism, maintenance metabolism, and predation on bacteria. The strategies for sludge reduction should be evaluated and chosen for practical application using costs analysis and assessment of environmental impact. High costs still limit technologies of sludge ozonation-cryptic growth and membrane bioreactor from spreading application in full-scale WWTPs. Bioacclimation and harmful to environment are major bottlenecks for chemical uncoupler in practical application. Sludge reduction induced by oligochaetes may present a cost-effective way for WWTPs if unstable worm growth is solved. Employing any strategy for reducing sludge production may have an impact on microbial community in biological wastewater treatment processes. This impact may influence the sludge characteristics and the quality of effluent.

A pilot scale anoxic/oxic membrane bioreactor (A/O MBR) for woolen mill dyeing wastewater treatment.

A pilot-scale (10 m3/d) anoxic/oxic membrane bioreactor (A/O MBR) was tested for dyeing wastewater treatment of woolen mill without wasting sludge in 125 days operation. Results showed that the effluent quality was excellent, i.e. effluent COD less than 25 mg/L, BOD5 under 5 mg/L, turbidity lower than 0.65 NTU, and colour less than 30 DT, and met with the reuse water standard of China. The removal rates of COD, BOD5, colour, and turbidity were 92.4%, 98.4%, 74% and 98.9%, respectively. Constant-flux operation mode was carried out in this study, and backwash was effective for reducing membrane fouling and maintaining constant flux. Membrane fouling had heavy impact on energy consumption. More attention should be paid on pipe selection and design for the sidestream MBR system, too.

Sewage treatment by a low energy membrane bioreactor.

A new membrane bioreactor (MBR) was developed for treatment of municipal wastewater. The MBR was mainly made up of an activated sludge reactor and a transverse flow membrane module, with an innovative configuration being in application between them. As a result, the transverse flow membrane module and low recirculation flow rate created advantages, such as lower energy consumption and more resistance to membrane fouling. The total energy consumption in the whole system was tested as 1.97+/-0.74 kWh/m(3) (permeate) while using periodical backwash with treated water and backflush with mixed liquor daily, being in the same level as a submerged membrane bioreactor, reported to be 2.4 kWh/m(3) (permeate). Energy consumption analysis in the system shows that the membrane module was more energy consuming than the other four parts listed as pump, aeration, pipe system and return sludge velocity lose, which consumed 37.66-52.20% of the total energy. The effluent from this system could be considered as qualified for greywater reuse in China, showing its potential application in the future.

Comparison performances of membrane bioreactor and conventional activated sludge prcesses on sludge reduction induced by Oligochaete.

Pilot-scale experiments were carried out to compare sludge reduction induced by Oligochaete in a submerged membrane bioreactor (MBR) and a conventional activated sludge (CAS) reactor for 345 d. Worm growth in the CAS reactor was much better than in the MBR. The average worm density of the aeration tank in the CAS reactor was 71 total worms/mg of volatile suspended solids (VSS), much higher than that in the MBR (10 total worms/mg of VSS). Worms did not naturally produce in the MBR, and the dominant worm type in the MBR depended on sludge inoculation from the CAS reactor. Only two types of worms were found in the MBR, Aeolosoma hemprichicii and Nais elinguis. Worm presence and disappearance in the MBR alternated. Worms in the CAS reactor occurred nearly throughout the operating period and were continuously maintained at over 30 total worms/mg of VSS in the aeration tank for 172 d. Three types of worm were found in the CAS reactor, A. hemprichicii, Pristina aequiseta, and N. elinguis, but P. aequiseta was present only occasionally. The alternating dominance of worm types in both reactors changed between Aeolosoma and Nais, and the time of Aeolosoma dominance was longer than that of Nais dominance. Worm growth in the MBR contributed to neither sludge reduction nor improvement of sludge settling characteristics because of low density. But worm presence and bloom in the CAS reactor greatly decreased sludge yield and improved sludge settling characteristics at high density. Both the average sludge yield (0.17 kg of suspended solids (SS)/kg of chemical oxygen demand removed (CODremoved)) and sludge volume index (60 mL/g) in the CAS reactor were much lower than those in the MBR (0.40 kg of SS/kg of CODremoved and 133 mL/g). Nais had more potential for sludge reduction than Aeolosoma. Worm growth had little impact on effluent quality in the MBR but affected effluent quality very much in the CAS reactor.