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

A pilot scale(10 m 3/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, BOD 5 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, BOD 5, 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.

Improvement of antifouling characteristics in a bioreactor of polypropylene microporous membrane by the adsorption of Tween 20

Surface modification by physical adsorption of Tween 20 was accomplished on polypropylene microporous membranes （PPMMs）. Attenuated total reflection-Fourier transform infrared spectroscopy （ATR/FT-IR） and field emission scanning electron microscope （FE- SEM） were used to characterize the chemical and morphological changes on the membrane surfaces. Water contact angles and relative pure water fluxes were measured. The data showed that the hydrophilic performance for the modified membranes increased with the increase in the adsorption amount of Tween 20 onto the surface or into the pores of polypropylene microporous membranes. To test the antifouling property of the membranes by the adsorption of Tween 20 in a membrane bioreactor （MBR）, filtration for active sludge was performed using synthetic wastewater. With the help of the data of water fluxes and the FE-SEM photos of the modified PPMMs before or after operating in a MBR for about 12 d, the PPMMs with monolayer adsorption of Tween 20 showed higher remained flux and stronger antifouling ability than unmodified membrane and other modification membranes studied.

Simultaneous nitrogen and phosphor removal in an aerobic submerged membrane bioreactor

Simultaneous nitrification and denitrification （SND） effect and phosphor removal were investigated in a one-staged aerobic submerged membrane bioreactor on pilot-scale with mixed liquor suspended solids （MLSS） 19--20 g/L. The effects of DO concentration, sludge floc size distribution on SND were studied. Test results suggested that SND was successfully performed in the membrane bioreactor （MBR） and about 70% total nitrogen removal efficiency was achieved when DO concentration was set to 0.2-- 0.3 mg/L. The main mechanisms governing SND were the suitable sludge floc size and the low DO concentration which was caused by low oxygen transfer rate with such a high MLSS concentration in the MBR. In the meantime, phosphor removal was also studied with polymer ferric sulfate （PFS） addition and 14 mg/L dosage of PFS was proper for the MBR to remove phosphor. PFS addition also benefited the MBR operation owing to its reduction of extracellular polymer substances （EPS） of mixed liquor.

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/（m^3·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, BODs/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/m^3, and the energy consumption was approximately 0.72 kWh/m^3 at the flux of 8 L/（m^2-h）.

Effect of components in activated sludge liquor on membranefouling in a submerged membrane bioreactor

By a membrane bioreactor with a settle tank in long-term operation and batch experiments, the effects of floes, soluble microorganism products （SMPs） and metal ions in activated sludge liquor on membrane fouling were investigated. The results showed that foulants absorbed each other and formed a fouling layer as a ＂second membrane＂ influencing the permeability of the membrane. The ＂gel layer＂ caused by SMPs and ＂cake layer＂ by floes showed great differences in morphology by analysis of scanning electron microscope and atomic force microscope. The ＂gel layer＂ was more compact and of poor permeability. When the membrane flux was 40 L/（m^2·h）, the rate of membrane fouling caused by supernatant （0.011 MPa/h） was greater than that by sludgc liquor （0.0063 MPa/h）. SMPs played very important roles on membrane fouling. In the bulking sludge, with SMPs increasing, the rate of membrane fouling （0.0132 MPa/h） was faster. While after flocculation of the SMPs, the rate of fouling decreased to 0.0034 M Pa/h. Floes could keep holes in their overlaps. They could alleviate membrane fouling by preventing the SMPs directly attaching on membrane surface.

Diatomite Precoated Nonwoven Membrane Bioreactor for Domestic Wastewater Reclamation

Nonwoven was selected as filtration materials in submerged membrane bioreactor( MBR) for domestic wastewater reclamation. For its hydrophobic membrane surface,diatomite was precoated on nonwoven to improve membrane hydrophilicity. In the precoating stage,diatomite dynamic membrane could be formed on10 μm polyethylene nonwoven surface efficiently and effluent turbidity could be below 5 nephelometric turbidity units( NTU).The MBR system was operated steadily under gravity flow and scanning electron microscope( SEM) analysis showed that nonwoven membrane was only partially fouled at the membrane flux of 5 L/( m2·h). Average removal efficiencies of chemical oxygen demand( COD) and NH +4-N were above 86 % and 50 %,respectively. The effluent turbidity and chromaticity were below 5 NTU and 25°,respectively. Those results could meet the requirements for wastewater reuse.

Fouling Characteristics and Prevention Techniques for Membrane Bioreactor

Membrane fouling is the main problem of membrane bioreactors (MBR), which seriously influ- ences its wastewater treatment effect and running. The characteristics of microbiology and hydrodynamics concerning membrane fouling were investigated and the measure was put forward for optimum operation of MBR. The measure is that 1) the parameters of activated sludge concentration (X) and membrane flux should be lower than the critical values of X and membrane flux respectively, and 2) the activated sludge should be discharged periodically. The experimental results show that the combination backwashing of gas and perme- ated effluent is better than single gas backwashing or single permeated effluent backwashing. This technique can remove the cake layer deposited on the membrane surface, decrease the membrane fouling, and recover the membrane flux effectively. So it is effective for prevention of membrane fouling.

Sludge ozonation and its effect on performance of submerged membrane bio-reactor

To investigate the effects of ozonation on minimizing the excess sludge and enhancing the nitrogen removal in an effluent, batch and continuous experiments in two MBRs with and without sludge ozonation （ namely combined and reference run） were carried out. Through ozonation at a dose of 0. 16 mg O3/mg MLVSS, 53.1% of the treated MLVSS was solubilized, and soluble SCOD/TN ratio of ozonized sludge （OS） was about 8. 6 due to the release of cellular nitrogen-contained materials and SCOD loss by ozone mineralization. In addition, the results of batch nitrification and denitrification tests with OS supernatant indicated that solubilized sludge could act as a reducing power for denitrification and a nitrogen source for nitrification. 40-day operation of-two MBR systems demonstrated that the recirculation of OS into a bioreaetor enabled the combined system have two advantages over the control one. The observed sludge yield （Yobs） was decreased from 0. 13 to 0. 06g MLSS/g COD, while the nitrogen removal was increased from 64. 6% to 72. 3%. And sludge ozonation elevated the inorganic fraction of MLSS, but did not impact sludge activities.

Isolation and characterization of heterotrophic nitrifying bacteria in MBR

The study presented the method for isolating the heterotrophic nitrifiers and the characterization of heterotrophic nitrification. Continuous tests via a membrane bioreactor (MBR) were operated under the controlled conditions to proliferate the nitrifiers. Heterotrophic nitrifying bacteria were isolated from the system in which the efficiency of total nitrogen(TN) removal was up to 80%. Since no autotrophic ammonium and nitrite oxidizers could be detected by fluorescence in situ hybridization(FISH), oxidized-N production was unlikely to be catalyzed by autotrophic nitrifiers during the heterotrophic nitrifiers' isolation in this study. The batch test results indicate that the isolated heterotrophic bacteria were able to nitrify. After 3 weeks incubation, the efficiencies of the COD removal by the three isolated bacterial strains B1, B2, and B3 were 52 6%, 71 7%, and 77 7%, respectively. The efficiencies of the TN removal by B1, B2, and B3 were 35 6%, 61 2% and 68 7%, respectively.

Micro-Polluted Surface Water Treatment by PAC-MBR Process

A kind of hybrid membrane process, which integrated powdered activated carbon (PAC) with membrane bioreactor (MBR), was designed for bench scale experiment for micro-polluted surface water treatment. Molecular weight analysis was used to evaluate the efficiency of each unit process and the integration of them. The result of analysis indicated that organic molecules in the treated water from PAC-MBR process were concentrated on the section of below 1000, while PAC adsorption could enhance the removal efficiency of this section due to the high percent of biodegradation recalcitrant organic matter with low molecular weight. It was demonstrated that PAC adsorption and biological treatment promoted each other in PAC-MBR process, with a removal efficiency of 70% for COD Mn and UV 254, 100% for UV 410 and 92% for ammonia nitrogen in its stable stage.

Engineering application of membrane bioreactor for wastewater treatment in China： Current state and future prospect

China has been the forerunner of large-scale membrane bioreactor （MBR） application. Since the first large-scale MBR （≥ 10 000 m^3·d^-1） was put into operation in 2006, the engineering implementation of MBR in China has attained tremendous development. This paper outlines the commercial application of MBR since 2006 and provides a variety of engineering statistical data, covering the fields of municipal wastewater, industrial wastewater, and polluted surface water treatment. The total treatment capacity of MBRs reached 1× 10^6 m^3·d^-1 in 2010, and has currently exceeded 4.5 × 10^6 m^3·d^-1 with -75% of which pertaining to municipal wastewater treatment. The anaerobic/anoxic/aerobie-MBR and its derivative processes have been the most popular in the large-scale municipal application, with the process features and typical ranges of parameters also presented in this paper. For the treatment of various types of industrial wastewater, the configurations of the MBR-based processes are delineated with representative engineering cases. In view of the significance of the cost issue, statistics of capital and operating costs are also provided, including cost structure and energy composition. With continuous stimulation from the environmental stress, political propulsion, and market demand in China, the total treatment capacity is expected to reach 7.5 × 10^6 m^3·d^-1 by 2015 and a further expansion of the market is foreseeable in the next five years. However, MBR application is facing several challenges, such as the relatively high energy consumption. Judging MBR features and seeking suitable application areas should be of importance for the long-term development of this technology.

Recent advances in membrane bioreactor technology for wastewater treatment in China

Since the introduction of the membrane bioreactor(MBR)in China in the early 1990s,remarkable progress has been achieved on the research and application of this technology.China has now become one of the most active fields in the world in this regard.This review outlines the development of MBR-based processes in China and their performance of treating municipal and industrial wastewaters.Since membrane fouling is a critical operational problem with MBR processes,this paper also proposes updated understanding of fouling mechanisms and strategies of fouling control,which are mainly compiled from publications of Chinese researchers.As for the commercial application of MBR in the country,the latest statistics of large-scale MBR plants(>10000 m^(3)·d^(–1))are provided,and the growth trend of total treatment capacity as well as its driving force is analyzed.

Membrane fouling behavior and microbial community succession in a submerged membrane bioreactor treating harbor oily wastewater

A membrane bioreactor （MBR） was established for treating harbor oily wastewater. It showed good removal performance for chemical oxygen demand （COD）, oil content, suspended solids （SS）, and other pollutants. However, serious membrane fouling occurred. It was recognized that the extracellular polymeric substances （EPS） accumulated on the membrane surface, especially the proteins, were of great importance for the transmembrane pressure （TMP） increment and membrane fouling. The MBR was optimized via improving aeration rate and reducing the ratio of Ar/Ad （At and Ad are the cross-sectional areas of the riser and the downcomer of the MBR）. The increasing rate of TMP was slowed, indicating that the optimization strategy could effectively mitigate membrane fouling. Microbial community evolution was monitored and analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis （PCR-DGGE）, cloning, and sequencing of 16S ribosomal ribonucleic acid （rRNA） fragments. Results revealed that low community shift occurred during the whole operational period. Geobacter sp. and Rhodocyclales sp., which have also been identified by other studies in a petroleum refinery wastewater MBR or an infiltration basin receiving highway runoff, dominated in the MBR system throughout. Comamonas sp. was thought to accommodate the lower aeration rate in this study, while Rhodocyclales sp. preferred the higher aeration rate. In addition, during the operational time under high organic loading rate, a few species were present in abundance, and may have been responsible for the good removal performance at this time.

Enhanced atrazine removal using membrane bioreactor bioaugmented with genetically engineered microorganism

Bioaugmentation with genetically engineered microorganisms(GEMs)in a membrane bioreactor(MBR)for enhanced removal of recalcitrant pollutants was explored.An atrazine-degrading genetically engineered microorganism(GEM)with green fluorescent protein was inoculated into an MBR and the effects of such a bioaugmentation strategy on atrazine removal were investigated.The results show that atrazine removal was improved greatly in the bioaugmented MBR compared with a control system.After a start-up period of 6 days,average 94.7%of atrazine was removed in bioaugmentedMBRwhen atrazine concentration of influent was 14.5 mg/L.The volumetric removal rates increased linearly followed by atrazine loading increase and the maximum was 65.5 mg/(L?d).No negative effects were found on COD removal although carbon oxidation activity of bioaugmented sludge was lower than that of common sludge.After inoculation,adsorption to sludge flocs was favorable for GEM survival.The GEM population size initially decreased shortly and then was kept constant at about 104–105 CFU/mL.Predation of micro-organisms played an important role in the decay of the GEM population.GEM leakage from MBR was less than 102 CFU/mL initially and was then undetectable.In contrast,in a conventionally activated sludge bioreactor(CAS),sludge bulking occurred possibly due to atrazine exposure,resulting in bioaugmentation failure and serious GEM leakage.So MBR was superior to CAS in atrazine bioaugmentation treatment using GEM.

Techno-economic characteristics of wastewater treatment plants retrofitted from the conventional activated sludge process to the membrane bioreactor process

While a growing number of wastewater treatment plants(WWTPs)are being retrofitted from the conventional activated sludge(CAS)process to the membrane bioreactor(MBR)process,the debate on the techno-economy of MBR vs.CAS has continued and calls for a thorough assessment based on techno-economic valuation.In this study,we analyzed the operating data of 20 large-scale WWTPs(capacity≥10000 m^(3)/d)and compared their techno-economy before and after the retrofitting from CAS to MBR.Through cost-benefit analysis,we evaluated the net profit by subtracting the operating cost from the environmental benefit(estimated by the shadow price of pollutant removal and water reclamation).After the retrofitting,the removal rate of pollutants increased(e.g.,from 89.0%to 93.3%on average for NH3-N),the average energy consumption increased from 0.40 to 0.57 kWh/m^(3),but the operating cost did not increase significantly.The average marginal environmental benefit increased remarkably(from 0.47 to 0.66 CNY/g for NH3-N removal),leading to an increase in the average net profit from 19.4 to 24.4 CNY/mJ.We further scored the technical efficiencies via data envelopment analysis based on non-radial directional distance functions.After the retrofitting,the relative cost efficiency increased from 0.70 to 0.73(the theoretical maximum is 1),while the relative energy efficiency did not change significantly.The techno-economy is closely related to the effluent standard adopted,particularly when truncating the extra benefit of pollutant removal beyond the standard in economic modeling.The modeling results suggested that MBR is more profitable than CAS given stricter effluent standards.

Treating both wastewater and excess sludge with an innovative process

The innovative process consists of biological unit for wastewater treatment and ozonation unit for excess sludge treatment. An aerobic membrane bioreactor(MBR) was used to remove organics and nitrogen, and an anaerobic reactor was added to the biological unit for the release of phosphorus contained at aerobic sludge to enhance the removal of phosphorus. For the excess sludge produced in the MBR, which was fed to ozone contact column and reacted with ozone, then the ozonated sludge was returned to the MBR for further biological treatment. Experimental results showed that this process could remove organics, nitrogen and phosphorus efficiently, and the removals for COD, NH 3-N, TN and TP were 93.17%, 97.57%, 82.77% and 79.5%, respectively. Batch test indicated that the specific nitrification rate and specific denitrification rate of the MBR were 1.03 mg NH 3-N/(gMLSS·h) and 0.56 mg NOx-N/(gMLSS·h), and denitrification seems to be the rate-limiting step. Under the test conditions, the sludge concentration in the MBR was kept at 5000—6000 mg/L, and the wasted sludge was ozonated at an ozone dosage of 0.10 kgO 3/kgSS. During the experimental period of two months, no excess sludge was wasted, and a zero withdrawal of excess sludge was implemented. Through economic analysis, it was found that an additional ozonation operating cost for treatment of both wastewater and excess sludge was only 0.045 RMB Yuan(USD 0.0054)/m 3 wastewater.

Shifts in microbial community structure and diversity in a MBR combined with worm reactors treating synthetic wastewater

The chemical oxygen demand（COD） and NH3-N removal, membrane fouling, sludge characteristics and microbial community structure in a membrane bioreactor（MBR） coupled with worm reactors（SSBWR） were evaluated for 210 days. The obtained results were compared to those from a conventional MBR（C-MBR） operated in parallel. The results indicated that the combined MBR（S-MBR） achieved higher COD and NH3-N removal efficiency,slower increase in membrane fouling, better sludge settleability and higher activities of the related enzymes in the activated sludge. Denaturing gradient gel electrophoresis was used to analyze the microbial community structures in the C-MBR and the S-MBR. The microbial community structure in the S-MBR was more diverse than that in the C-MBR. Additionally, the slow-growing microbes such as Saprospiraceae, Actinomyces, Frankia, Clostridium, Comamonas,Pseudomonas, Dechloromonas and Flavobacterium were enriched in the S-MBR, further accounting for the sludge reduction, membrane fouling alleviation and wastewater treatment.

Evaluation of factors influencing soluble microbial product in submerged MBR through hybrid ASM model

In this study,a mathematical model was established to predict the formation of the soluble microbial product(SMP)in a submerged membrane bioreactor.The developed model was calibrated under the reference condition.Simulation results were in good agreement with the measured results under the reference condition.The calibrated model was then used in the scenario studies to evaluate the effect of three chosen operating parameters:hydraulic retention time(HRT),dissolved oxygen concentration,and sludge retention time(SRT).Simulation results revealed that the SMP dominated the soluble organic substances in the supernatant.The scenario studies also revealed that the HRT can be decreased to 1 h without deteriorating the effluent quality;dissolved oxygen concentration in the reactor can be kept at 2–3 mg/L to maintain the effluent quality,reduce the content of SMP,and minimize operating costs;the optimal SRT can be controlled to 10–15 d to achieve complete nitrification process,less membrane fouling potential,and acceptable organic removal efficiency.