Airlift Membrane Bioreactor Research Articles

Experimental Solid–Liquid Mass Transfer around Free-Moving Particles in an Air-Lift Membrane Bioreactor with Optical Techniques

This article focuses on the study of the mass transfer involved in the application of a bacterial antifouling technique for membrane bioreactors (MBR), via the addition of solid media. These alginate objects can contain a biological system capable of producing an enzyme that degrades the signal molecules responsible for membrane fouling. The objective of this article is to quantify the mass transfer by distinguishing two main types: the transfer from the liquid to the solid media and the transfer from solid media to the liquid phase. For this purpose, a model molecule was chosen, and experiments were specifically developed with an optical device to track the concentration of the dye in the liquid phase, considering three different shapes for the particles (beads, hollow cylinders, and flat sheets). The experiments were first performed in jar tests and then in a lab-scale reactor. The results of this study revealed that the total amount of dye transferred into the sheets was greater than that transferred into the cylinders or the beads, which was attributed to the sheets having a larger exchange area for the same volume. When the dyed media were implemented in the MBR (loading rate of solid media: 0.45% v/v—no biomass), the global transfer coefficient from the sheets to the liquid was found to be greater than for the other shapes, indicating a faster transfer phenomenon. The effect of aeration in the MBR was investigated and an optimal air flowrate for fostering the transfer was found, based on the highest transfer coefficient that was obtained. This study provided key information about mass transfer in MBRs and how it is affected by the particle shapes and the MBR operating conditions.

Treatment of Real Paper-Recycling Wastewater in a Novel Hybrid Airlift Membrane Bioreactor (HAMBR) for Simultaneous Removal of Organic Matter and Nutrients

In this study, a novel integrated Hybrid Airlift Membrane Bioreactor (HAMBR) composed of oxic, anoxic, and anaerobic zones was developed to simultaneously remove organic matter and nitrogen from real paper-recycling wastewater. The removal efficiencies of Chemical Oxygen Demand (COD), ammonium, nitrite, nitrate and Total Nitrogen (TN) for permeate and supernatant were in the range of 88-99%, 54-83%, 70-90%, 65-95% and 61-90%, respectively. In addition, the membrane fouling was evaluated by Trans-Membrane Pressure (TMP) monitoring during the experimental period at a constant flux of 12 L/m2h,and the rate of TMP increase was 1.75 mbar/day. The results showed that the hybrid airlift membrane bioreactor can be applied effectively to the simultaneous removal of organic and nutrient from real wastewater and the performance of the membrane bioreactor was satisfactory in terms of resistance against membrane fouling phenomenon, which is an important parameter during HAMBR operation.

Hydrodynamics Characterization of the Impact of Free-Moving Particles in an Air-Lift Membrane Bioreactor

Membrane fouling is one of the most investigated topics in the field of membrane processes because it is the main weakness that prevents membrane bioreactors (MBRs) from being widely applied. With ...

Performance of airlift MBR for on-site treatment of slaughterhouse wastewater in urban areas of Vietnam

In many cities in Vietnam, wastewater generated in slaughterhouses is normally discharged directly into surface waters without treatment. Management of slaughterhouse wastewater (SHWW) is difficult due to the lack of infrastructure for conveyance to centralized facilities. On-site treatment presents one cost-effective way of managing SHWW compared to mass improvement of infrastructure. This study evaluates the application of an airlift membrane bioreactor (AL-MBR) for on-site treatment of SHWW. The concentrations of chemical oxygen demand (COD), biochemical oxygen demand (BOD), total nitrogen (TN) and NH4+-N in the simulated SHWW were 1,697 ± 317 mg/L, 891 ± 137 mg/L, 246 ± 65 mg/L and 171 ± 4.2 mg/L, respectively. The mixed-liquor volatile suspended solids in the aerobic and anoxic tanks were maintained at 5,000-6,000 mg/L. Air flow rate and cross flow velocity were maintained at 0.2 L/min and 0.8 m/s, respectively, to keep the trans-membrane pressure (TMP) stable at 0.8 bar and the membrane flux at 15-18 L/m2 h bar (LMH/bar). The removal efficiencies of COD and TN were 95 ± 1.9% and 70 ± 3.3%, respectively, at a hydraulic retention time (HRT) of 2.5 days. This study shows that GL-MBR is a promising on-site solution for SHWW treatment.

Hydraulic optimization of membrane bioreactor via baffle modification using computational fluid dynamics

Baffles are a key component of an airlift membrane bioreactor (MBR), which could enhance membrane surface shear for fouling control. In order to obtain an optimal hydraulic condition of the reactor, the effects of baffle location and size were systematically explored in this study. Computational fluid dynamics (CFD) was used to investigate the hydrodynamics in a bench-scale airlift flat sheet MBR with various baffle locations and sizes. Validated simulation results showed that side baffles were more effective in elevating membrane surface shear than front baffles. The maximum average shear stress was achieved by adjusting baffle size when both front and side baffles were installed. With the optimized baffle configuration, the shear stress was 10–30% higher than that without baffles at a same aeration intensity (specific air demand per membrane area in the range of 0–0.45m3m−2h−1). The effectiveness of baffles was particularly prominent at lower aeration intensities.

Performance of An Airlift Membrane Bioreactor Under Different Aeration Rates

The treatment of a synthetic oily wastewater in an airlift submerged membrane bioreactor (AMBR) has been studied. A flat sheet Kubota membrane has been used for this purpose in the reactor with a working volume of 19 L. The volumetric oxygen transfer coefficient, oxygen uptake rate, treatment efficiency and fouling intensity were investigated for various aeration rates (0.2, 0.5, 0.7 and 1 m3/h). Based on the results, a COD removal efficiency of more than 93% - even for the lowest aeration rate – is reported. However, increasing the aeration rate resulted in higher kLa and higher microbial activity. The high aeration intensity resulted in breakage of activated sludge flocs and hence reduction in mean flocs size and release of extracellular polymeric substances (EPS). At an aeration intensity as high as 1m3/h, the maximum irreversible fouling was observed which is due to higher concentration of EPS and colloids that are the major foulants. Although the aeration may scour the membrane surface and avoid the formation of cake layer, it could induce more pore blocking fouling. In the studied range, the 0.7 m3/h is found to be the optimum aeration rate and the alteration of the aeration rate deteriorated the AMBR’s performance.

PERFORMANCE OF AIRLIFT MEMBRANE BIOREACTOR TREATING WASTEWATER FROM INDUSTRIAL PARK IN HO CHI MINH CITY

This study investigated operational performance and fouling behavior of Airlift Membrane Bioreactor (AMBR) system for industrial wastewater treatment. Pilot scale study of AMBR was carried out at central wastewater treatment plant (CWWTP) of Tan Binh industrial park in Ho Chi Minh city, Viet Nam. The influent wastewater of AMBR was taken directly from equalization tank of CWWTP with the concentrations of COD and colour level was 350 ± 48 mg/L and 313 ±30 Pt-Co, respectively. The effluent quality from the AMBR system was relatively compared with the existing full-scale Sequencing Batch Reactor (SBR). The AMBR with external tubular membrane module was maintained at the hydraulic retention time (HRT) of 9.6 h and sludge retention time (SRT) of 30 days, and flux of 30 LMH (L/m2.h). It is observed that the AMBR was in stable operation with the flux for months. The COD and colour of membrane permeate was 15 ± 6 mg/L and 35 ± 5 Pt-Co, respectively. Membrane permeate was free of suspended solids. In addition, membrane fouling was controlled and occurred very slowly during the study period. Only one chemical enhanced backwash was applied in every two months of operation. This reveals the treated water quality of AMBR could meet the Viet Nam national technical regulation for industrial wastewater (level A, QCVN 24:2009/ BTNMT) and water reuse standards. This airlift membrane bioreactor system could be an attractive technology for water reuse purpose for industrial parks in near future.

Analyze and control fouling in an airlift membrane bioreactor: CFD simulation and experimental studies

In this study, experiments and computational fluid dynamics were used to evaluate the fouling of membrane surfaces. Based on the resistance-in-series model, the total filtration resistance (Rt) was divided into cake resistance (Rc), adsorption resistance (Ra), internal-plugging (pore-blockage) resistance (Rpb) and intrinsic-membrane resistance (Rm). The values of each resistance and their relative percentages as a function of the operating parameters were experimentally determined. The effect of inlet air-flow rate and the baffle angle on the resistances were also investigated. It was then shown that the permeate flux and resistances could be related to the wall shear stresses of air and liquid flows at the membrane surface. Average shear stress was found to increase by increasing the air-flow rate. The change in baffle angle from 90° to 85° increased the shear stress of air on the membrane surface. At low air-flow rates there was a lower meandering of air as well as the area of the membrane, which is not subject to high-shear increases. The shear stresses of air and liquid on the membrane surface were determined by computational fluid dynamics and correlations were proposed for estimating each resistance of the membrane from these shear stresses.

Membrane bioreactor for treatment of pharmaceutical wastewater containing acetaminophen

Treatment of pharmaceutical wastewater is a real challenge for wastewater engineers. In this study, a pilot-scale system including an external loop airlift membrane bioreactor (ELAMBR) was applied for treatment of a synthetic pharmaceutical wastewater. The performance of this system was evaluated in removal of acetaminophen as the main pollutant of a pharmaceutical wastewater. A conventional activated sludge (CAS process) laboratory system was used in parallel with this system to compare both systems in regard to their ability for acetaminophen removal. The performance of the ELAMBR system was monitored for approximately one month to investigate the long-term operational stability of the system and possible effects of solids retention time on the efficiency of removal of acetaminophen. The removal efficiency was significantly higher in the ELAMBR system than the CAS process. 100% of the acetaminophen was removed after 2 days in this system. The results also showed that initial concentration of acetaminophen, chemical oxygen demand (COD) and mixed liquid suspended solids (MLSS) are the most effective parameters in removal of a pollutant such as acetaminophen. This study demonstrates the usefulness of ELAMBR system for pharmaceutical wastewater treatment with the advantages such as: (i) simple operation and maintenance, (ii) efficient removal of pharmaceutical pollutant and COD and (iii) low-energy consumption.

AirLift MBR for municipal wastewater treatment: out of the box performance

In recent years, Norit has developed and proven a totally new concept for treating domestic wastewater. The concept applies the side-stream AirLift principle using the robust and reliable side-stream cross-flow concept while incorporating all the advantages of the low energy consuming submerged systems. Based on this ‘outside the box thinking’, a new membrane bioreactor (MBR) concept was developed offering the solution, which is fully beneficial to the potential of ultrafiltration (UF) membranes. The biological box can be designed and operated optimally, while the UF installation can be handled as a separate unit, performing cleanly, safely and efficiently, while producing bacteria and virus-free water for recycling or ecological discharge. Recently, the first full-scale installations have been commissioned successfully, while currently larger installations are under construction and will be commissioned soon. This article presents the development of the AirLift MBR concept from the proof of concept till ...

A long-term application of a pilot airlift membrane bioreactor for domestic wastewater treatment

Current and impending legislation for public health and environmental compliance regarding effluent are becoming very stringent. For unrestricted domestic effluent reuse and environmental friendly disposal, the need for advanced treatment processes has attracted great attention during the last decade. Membrane-based treatment technologies for low quality water have exhibited improved performance as well as a reduction of operating and maintenance expenses. Membrane technology also provides a preferable alternative for wastewater reclamation in small and isolated communities. This study presents a long term study of an airlift membrane bioreactor (MBR) for domestic wastewater treatment using a hollow fibre membrane module of ZW-10 under ambient desert conditions (Kiryat Sde-Boker, Israel). In this system, the crossflow velocity across the membrane surface was induced by a cylindrical draft tube to reduce the membrane fouling. Under optimal operating conditions, the system was stable and efficient without external chemical cleaning during the experimental period. The system produces a high quality permeate, and the removal efficiencies of COD and BOD5 were around 94% and 99%, respectively. Nitrate concentration in the effluent (permeate) was higher (by 40%) than that in the reactor mixed liquor, probably due to extra nitrification carried out by Nitrospira bacteria on the membrane biofilm. The system shows potential and promising applications for localized, decentralized sewage treatment facilities.

Yield stress and rheological characteristics of activated sludge in an airlift membrane bioreactor

The viscosity of activated sludge plays a major role on oxygen transfer and mass transport and consequently influences the hydrodynamic regime and the system performance of a membrane bioreactor (MBR). Yield stress is an important concept in rheology related to the mixing and power requirements in a stirred tank. This study examined the rheological characteristics of activated sludge sampled in a pilot airlift MBR system for domestic wastewater treatment under ambient desert conditions, using a rotational rheometer (AR 2000, TA Instruments, USA) equipped with cone-plate geometry. Both static and dynamic yield stresses were observed at the transition point of 25 s −1 of shear rate for an MLSS concentration range of 2.74–10.2 g/L. The static yield stress is a phenomenon that has not yet been evaluated for activated sludge. The mechanisms of the co-existence of both static and dynamic yield stresses and their engineering significance are discussed. In addition, a mathematical model to describe the rheological properties of the sludge is proposed. The relationships between viscosity, MLSS, temperature and shear rate were obtained statistically. The activation energy for the viscosity of the sludge in the airlift sMBR was found to be 9.217 kJ mol −1, and could be the cause of rapid fluctuation of transmembrane pressure with temperature variations.

Flow Characteristics in an Airlift Membrane Bioreactor

Effect of changing the liquid level in an airlift membrane bioreactor of 0.7 m height, 0.24 m width and 0.18 m depth was studied both experimentally and by simulation. Three-dimensional simulations of the airlift membrane bioreactor were carried out at two different liquid levels above the membrane. The simulations were based on the two-fluid model with the standard k–? model for the turbulence. The results showed that by lowering the liquid level, the quality of mixing and uniformity of the velocity distribution of liquid phase in the riser would be improved while the shear stress on the membrane surface would be reduced. Higher shear stress on the membrane surface at high levels of liquid minimizes the extent to which particles settle on the membrane, thus, fouling will be reduced and flux of liquid through membrane will be enhanced. Moreover, it was shown that by lowering the liquid level, the fraction of air in the downcomers becomes lower.

Character of Extracellular Polymeric Substances and Soluble Microbial Products and Their Effect on Membrane Hydraulics During Airlift Membrane Bioreactor Applications

The effect of extracellular polymeric substances and soluble microbial products developed from wastewater and mature landfill leachate biomass was assessed using a pilot-scale membrane bioreactor operating polymeric and ceramic air-lift sidestream multichannel membranes. The plant was operated under identical conditions of sludge retention time, system hydrodynamics ,and parity of food-to-microorganism ratios. Biomass samples were extracted and fractionated (fixed and bound material, carbohydrate and protein extracts) and chemically and physically analyzed with the feedwaters. Both ceramic and polymeric membranes were tested and the critical flux (J(C)) determined according to the classical flux-step analysis. Although permeability (K) of both materials reduced with increasing flux (J), the ceramic material had a higher resistance to fouling, demonstrating a higher K (by a factor of 1.2 and 3.2 for wastewater and leachate, respectively, at J of 30 L x m(-2) x h(-1)) and lower fouling rate (dP/dt) (by more than an order of magnitude at the same J) than the polymeric membrane. Evidence suggests that deterioration of membrane permeability resulting from leachate biomass arises from the feedwater itself, rather than the products derived from the biomass, and that colloidal and/or soluble total organic carbon is primarily responsible for it.

NORIT AirLift MBR: side-stream system for municipal waste water treatment

The Ootmarsum wastewater treatment plant (WWTP) is owned by the water authority Regge & Dinkel (WRD) and is situated in the municipality of Dinkelland (eastern part of The Netherlands). The WWTP must be modernised, because it discharges the treated wastewater into a water system with considerable ecological vulnerability. In the restructuring plan the urban water chain/cycle was integrated into an ecological water management approach. In cooperation with Grontmij engineering consultants a design study was carried out resulting in the choice for a so-called hybrid system. Such a system combines a conventional system followed by a sand filter with a membrane bioreactor (MBR). With a hybrid MBR, the costs can be reduced relatively to those of a complete MBR plant without making concessions in terms of effluent quality. After an intensive selection procedure NORIT Membrane Technology (NMT) was selected with the novel NORIT AirLift MBR system. The construction work of the 650 m 3/h plant started in mid-2005 and will be completed by late 2006; start-up of the full scale will be early 2007. As preparation for the full scale plant operation an intensive pilot study is currently being performed in order to develop a start-up protocol, to train operators, to check control philosophies, and to optimise the overall processing.