Membrane Bioreactor for Wastewater Treatment

Membrane Characterization (UF/MF)

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Pore size

Molecullar weigh cut-off using dextran or polyethylene glycol (PEG) rejection. The pore size is determine as the molecular weigh of particle that can be rejected 90% by membrane. The filtration is conducted by filtering the serries of differend dextran MW solution. The rejection profile than defined by the linearization of the rejection-MW curve. Normaly the concentration of the dextran is less than 2% w/w.

Procedure of PEG rejection test (A. D. Sabde et al. [1997]):

Reagents:

5% w/v BaCl2 in 1 N HCl (100 ml)
100 ml of 2% KI (w/v) + 1.27 g I2 --> This mixture than dilluted 10 times.

Procedure:

Add 1 ml reagen 1 to 4 ml sample ---> (I)
Add 1 ml reagen II to solution I ---> (II)
Allow the color development for 15 minutes at room temperature
Read the absorbtion using spectrophotometer at 535 nm againt reagent blank

Note: To get the concentration value, the calibration curve is required.

Pore size distribution

Bubble

Porosity

Surface structure

Lab Scale MBR

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Planning the lab scale MBR

Figure 1. Labscale MBR

Specification:

No	Spare part (unit)	Specification, Price	Notes
1	Bioreactor tank (1)	50x25x30cm (39.93€)
2	Feed tank (1)	-	It can be any used tank in volume of 30-40 liters
3	Level control tank (1)	-	It can be any used tank in volume of 3-4 liters
4	Feed pump (1)	Circulation pump to level control tank (19.80€)
5	Air pump (1)	Maximum flow rate 550 l/h (59.29€)
6	Air diffuser (5 unit)	Bubble size 100-500 µm (1€/Pieces)
7	Air flow meter (1)	-
8	Submerged membrane module (depend on requirement)		Prepared by us
9	Vacuum pump (1)		The purchasing is in progress
10	Centrifugal pump (1)		The purchasing is in progress
11	Pressure gauge (3)		The purchasing is in progress
12	Valve (5)	(1€/Pieces)
13	Pipe line (depend on requirement)	1€ / m
14	Cross flow membrane module		Prepared by us

Price was taken by direct survey to: De Servis Leuven bvba, Diestsstraat 133 - 3000 Leuven

Instrumentation and analysis

Parameters	Price
*MLSS	-
*COD	-
*Turbidity	-
pH	58.99€
Temperature	20.6€
Dissolved oxygen (DO)	Water proof (947.43€), Not water proof (712.69€)
Oxidation-reduction potential (ORP)	136€
pH controller	373.89€
Temperature controller	160€
Flux	-

Remarks:

These is basic instrumentation to operate the activated sludge system or membrane bioreactor. The more instrumentation analysis are required for more detail observation.
The other parametersthat could be required to be tested are, NO^-₂-N, NO^-₃–N, total phospor (TP) and total nitrogen (TN).
The detail can be found and standard method for wastewates analysis.

The operating parameters is determined according to the pilot plant parameters from MBR companies.

Mith and Fact in MBR

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Myth 1: Membrane pore size determines removal efficiency in submerged MBR applications.

Fact 1: Third party independent research (Gunder, et al. The Membrane Coupled Activated Sludge Process) confirms similar performance for microfiltration versus ultrafiltration membranes submerged in mixed liquor.

UF Hollow Fiber (H) vs. MF Flat Plate (P)
Coliform Data

University of Hawaii, Comparison Data

Myth 2: All membranes perform about the same in terms of flux and or permeability.

Fact 2: Membrane performance is a function of multiple parameters not just type or geometry. Some important parameters are given below, but there are several other factors to consider as well.

Myth 3: All MBR Systems are underloaded and do not operate at or near design capacity.

Fact 3: Many Enviroquip MBR Systems run at or above rated capacity during winter and spring seasons. Some plants, like Hyrum, Utah WWTP, are more than 60% utilized throughout the year.

Hyrum, UT WWTP Flow and Utilization Data

Myth 4: Specifying average daily flow (ADF) and peak daily flow (PDF) is sufficient to characterize required capacity.

Fact 4: Establishing peak instantaneous flow (PIF) and durations is as important as ADF & PDF requirements. For example, at the McFarland Creek WWTP, instantaneous flux is much higher than average flux for most of the day between May 12 and May 19.

Myth 5: All membranes should have about the same service life.

Fact 5: Not all membranes have the same service life. Membrane life is not only a function of design and composition it is also determined by operating conditions. Some of the keys to long service life include; low TMP operation, reduced chemical exposure and equal air scouring.

Extensive Kubota membrane life data has been collected in the U.K. indicating membrane life on the order of 12.5 years. Other technologies may only last 3 to 4 years in some cases.

Myth 6: Silt Density Index (SDI) values can increase over time degrading permeate quality.

Fact 6: Recent SDI results from a 0.5 MGD installation averaged less than 2.0. The plant is now in its 9th year of operation.

Source: http://www.Enviroquip.com

Research Project (In Europe)

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AMEDEUS "Accelerate Membrane Development for Urban Sewage Purification"
Specific Targeted Research Project (Priority "Global Change and Ecosystems")
Duration: 01/10/2005 - 30/09/2008
Co-ordination: B. Lesjean, Berlin Centre of Competence for Water
(boris.lesjean(at)kompetenz-wasser.de)

EUROMBRA "Membrane bioreactor technology (MBR) with an EU perspective for advanced municipal wastewater treatment strategies for the 21st century"
Specific Targeted Research Project (Priority "Global Change and Ecosystems")
Duration: 01/10/2005 - 30/09/2008
Co-ordination: T. Leiknes, Norwegian University of Science and Technology
(torove.leiknes(at)ntnu.no)

MBR-TRAIN "Process optimisation and fouling control in membrane bioreactors for wastewater and drinking water treatment"

Marie Curie Host Fellowship for Early Stage Research Training
(Structuring the European Research Area; "Marie Curie Actions")
Duration: 01/01/2006 - 31/12/2009
Co-ordination: RWTH Aachen University, Department of Chemical Engineering
Contact: R. Hochstrat
(hochstrat(at)ivt.rwth-aachen.de)

PURATREAT "New Energy Efficient approach to the operation of Membrane Bioreactors for Decentralised Wastewater Treatment"

Specific Targeted Research or Innovation Project (International Cooperation Action)
Duration: 01/01/2006 - 31/12/2008
Co-ordination: G. Schories, Technologie-Transfer-Zentrum Bremerhaven
(gschories(at)ttz-Bremerhaven.de)

Manufacturer

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The design of the reactor (including membrane, baffle and aerator locations) and the mode of operation of the membrane also appear as key parameters in the optimisation of the system. Several immersed MBR designs are currently proposed by the leading membrane suppliers such as GE-Zenon (Canada), X-Flow (The Netherlands), Siemens-Australia (Australia), Mitsubishi and Kubota (Japan). Kubota has the largest installation base of membrane bioreactors worldwide. In each case, the process proposed is very specific. Not only the membrane material and configuration used are different, but the operating conditions, cleaning protocols and reactor designs also change from a company to another. For example, the flat sheet membrane provided by Kubota does not require backwash operation, while hollow fibre membrane type from Zenon and Memcor (USFilter) have been especially designed to hydraulically backwash the membrane on a given frequency (around every 20 min).

Membrane and plant supplier links:

Flat Sheet
- Enviroquip (A division of EWT) - http://www.Enviroquip.com http://www.impactmovie.com/enviroquip/
- A3 Water Solutions - http://www.a3-gmbh.com
- Brightwater Engineering - http://www.brightwater.uk.com
- Colloide Engineering Systems - http://www.colloide.com
- Huber Technology - http://www.huber-technology.com
- Inge AG - http://www.inge.ag
- Kubota - http://www.kubota-mbr.com
- Microdyn-Nadir – http://www.nadir-filtration.de
- Novasep Orelis - http://www.orelis.com
- Toray Industries - http://www.toray.com
- Weise Water Systems - http://www.weise-water-systems.de
Hollow Fibre
- Asahi-Kasei - http://www.asahi-kasei.co.jp
- GE - Zenon Environmental - http://www.zenon.com
- Koch Membrane Systems - http://www.kochmembrane.com
- Mitsubishi Rayon Engineering - http://www.mrc.co.jp/mre/english/
- Motimo Membrane Technologies - http://www.motimo.com
- Polymem
- Siemens Water Technologies (Memcor) - http://www.water.siemens.com/Memcor
- Ultraflo - http://www.ultra-flo.com.sg
Multitube
- Berghof Membrane Technology - http://www.berghof-gruppe.de
- Norit X-Flow - http://www.norit.com
System Integrators
- Grupo Akvotek, S.A. de C.V. - http://www.akvotek.com

Research Group

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Aachener Verfahrenstechnik - RWTH Aachen http://www.avt.rwth-aachen.de

Anjou Recherche http://www.veoliawater.com/r-and-d/centers/anjou-recherche

BCC Research http://www.bccresearch.com/report/index.php?rcode=mst

Cranfield University http://www.cranfield.ac.uk/sas/water/research/researchareas/membranes.jsp

EMI Twente http://www.membrane.nl

INSA Toulouse http://www.insa-toulouse.fr

KompetenzZentrum Wasser Berlin http://www.kompetenz-wasser.de

NTNU http://www.ntnu.no

TU Berlin http://www.verfahrenstechnik.tu-berlin.de

TU Delft http://www.tudelft.nl

UNSW - UNESCO Centre for Membrane Science & Technology http://www.membrane.unsw.edu.au

VITO http://www.vito.be

Wetsus http://www.wetsus.nl

Industrial membrane module

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1) Mitsubishi Rayon

We provide two types of submerged hollow-fiber membranes for wastewater treatment. We offer products that best meet your purposes and applications.

	Designed for small and medium-scale wastewater treatment (tens to thousands of m³ per day)

	Widely adopted in domestic and industrial wastewater treatment (Installed at a total of over 2,000 plants as of September 2007)

	Multi-unit configuration in accordance with the depth

	Uses polyethylene hollow-fiber membranes

	High cost-effectiveness

	Permanently hydrophilic membrane surface

	Thermally recyclable


Magnified image of the surface of the polyethylene hollow-fiber membrane		STERAPORESUN^TM membrane element		STERAPORESUN^TM membrane unit

Model number		SUR234L	SUR334LB
Membrane surface area		1.5m²	3m²
Pore size		0.4m
Membrane outer diameter		0.54mm
Element size (mm)		1,035×446×13	1,035×524×13
Dry weight		0.6kg	0.64kg
Materials	Hollow-fiber membrane	Polyethylene
	Collecting water pipes	ABS resin
	Potting material	Polyurethane resin

Model number	SUN21034AAD7 (SUN10534AD7)	SUN21034LAN (SUN10534LN)	SUN21034LAP (SUN10534LP)	SUNAAD7 (SUNAD7)
Compatible element	SUR334LA *(SUR234L)			-
Pore size	0.4m			-
Size (DWH, mm)	725×1,538×1,442 (678×1,538×1,442)	614×1,538×1,092 (536×1,538×1,092)	614×1,538×1,442 (536×1,538×1,442)j	711×1,538×350 (673×1,538×350)
Weight**	184kg(175kg)	142kg(140kg)	157kg(155kg)	42kg(35kg)
Membrane surface area	210m²(105m²)			-
Material of water collecting pipes	ABS resin			-
Frame material	SUS304
Normal operating temperature	0~40°C
Standard treatment volume***	52m³ per day (26m³per day)			-
Standard water flow rate	66~99Nm³per hour (57~84Nm³ per hour)
Notes	With rubber slit air diffuser	Without air diffuser For upper layer	With hollowed polyvinyl chloride pipe type air diffuser	Rubber slit type Air diffuser unit

*	The standard model uses the SUR334LB.
**	Dry weight
***	Assuming the treatment of domestic wastewater in an operation that complies with that described in our operating manual

	Designed for large-scale wastewater treatment, such as in public sewerage systems (hundreds to hundreds of thousands of m³ per day)

	Applicable to domestic and industrial wastewater treatment

	Uses PVDF hollow-fiber membranes (SADF membranes)

	High permeability

	High chemical resistance

	Excellent strength


Magnified image of the surface of the SADF membrane made of PVDF		STERAPORESADF^TM membrane element		STERAPORESADF^TM membrane unit

Model number		SADF2590R
Membrane surface area		25m²
Pore size		0.4μm
Membrane outer diameter		2.8mm
Element size (mm)		2,000 × 1,250 × 30
Dry weight		16kg
Materials	Hollow-fiber membrane	PVDF
	Water collecting block	ABS resin
	Potting material	Polyurethane resin
	Strut	SUS 304

Model number	SAA50090APE06
Compatible element	SADF2590R
Number of elements	20
Membrane surface area	500m²
Standard treatment volume*	400m³
Unit size (mm)	1,553 × 1,443 × 3,124
Dry weight	800kg
Frame material	SUS 304
Normal operating temperature	0 ~ 40°C
Notes	With air diffuser

* Assuming the treatment of domestic wastewater in an operation that complies with that described in our operating manual

2) Kubota

Permeate without SS

The membrane separation system removes not only SS but substances difficult to biodegrade such as detergent, by taking advantage of its longer SRT (Sludge Retention Time). Nutrients such as nitrogen and phosphorus can also be cleared. This enables the treated water to be re-used.

Simple Maintenance

Volume control of return sludge or microscopic observation of the microorganism is not necessary. All that is required control of trans-membrane pressure and basic water analysis, both of which can be easily learned. Telemetry is easily applied.

Energy Conservative Operation

KUBOTA Submerged Membrane Unit system is designed for energy conservation. Aeration plays two roles to save energy; oxygen supply for biological treatement and cleaning of membrane surface with turbulent flow.

Remarkably Small Footprint

KUBOTA Submereged Membrane Unit is installed in an aeration tank. Since it carries out high-concentration activated sludge treatment, no settling tank or sludge concentration tank is required. The size of the aeration tank is also minimized.

3) ..........

Membrane Modification

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The common methods for membrane modification is by improving the hydrophilicity of the membrane. The recently reports are:

Mixing with TiO2 nanoparticle
Addition of polyvinylalcohol (PVA)

Membrane characterization

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The general parameter and method for membrane characterization are follow:

(1) Pore size --> Mollecular weight cut-of by dextran or polyethylene glycol rejection

(2) Poresize distribution --> Bubble point method

(3) Microscopic structure --> Scanning electron microscopy (SEM)

(4) Chemical constituent --> Fourier transform infrared (FT-IR) spectroscopy

(5) Porosity

(6) Hidrophilicity/hydrophobicity --> Contac angle meter

Membrane Preparation

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Membrane foulant and gel layer characterization

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(1) Mean oxidation state (MOS) of organic carbon
This parameter is used to estimate the component of gel layer in membrane.
MOS = 4(TOC-COD)/TOC
COD in mol O2/Liter --> Is analyzed using available standard method.
TOC in Mol C/Liter -> Is analyzed using TOC analyzer
To distinguish the composition of gel layer and EPS can be done by comparing the MOS of them.
The interpretation of MOS value is based on estimation protocol proposed by Stumm and Morgan [1981]

(2) PCR analysis

(3) DCGE Analysis

(4) FISH

(5) Particle size distribution analysis

(6) Fourier Transform Infrared (FT-IR) spectroscopy
This method is used in order to obtain the in organic foulant information in the gel layer. The extracted EPS can also e analyzed using this method.

Sample preparation:

Example of FT-IR Spectra

How to analyze the FT-IR Spectra?
Figure a showed spectra for cake layer.
- Peak at 3421cm−1 is attributed to stretching of O-H bond in hydroxyl functional groups
- Peak at 2932cm−1,which is due to stretching of C-H bonds
- Peak at 1653cm−1 is unique to the protein secondary structure amida 1
- Peak at 1558cm−1 is unique to the protein secondary structure amida 2
- Peaks at 1378 cm−1 may be due to presence of methyl bond.
- Peaks at 1247 cm−1 may be due to presence of C=O (ester) bond.
- a broad peak at 1045cm−1 exhibits the character of polysaccharides or polysaccharides-like
substances which indicates that polysaccharideswere presented in the gel layer.
- Another broad peak appears at 600 cm−1 in the finger print region of the spectrum

The similar reference can be used to analyze the spectra b for EPS.

(7) Gel Filtration Chromatography Analysis

Eluent: Pure water
Standard: Different molecular weigh of polyethylene glicol

(8) Particle size distribution (PSD) analysis

(9) Scanning electron microscopy (SEM)

(10) Energy-difussive X-ray Measurement

Fouling Amelioration - (6) Hybrid MBR (Mixed Liquor & Membrane)

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Fouling Amelioration - (5) Hybrid modification (Membrane & Hydrodynamic)

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Fouling Amelioration - (4) Hybrid MBR (Mixed Liquor & Hydrodynamic)

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The approach of fouling limitation technique not always solely deal with individual characteristic of the factors that determine the fouling (membrane, hydrodynamic, and mixed liquor properties). In many cases the fouling limitation method are dealing with more that one of those factors. The techniques that exploiting the mixed liquor properties as well as hydrodynamic are further discussed in this section.

1) Flexible suspended carrier

Addition of flexible suspended carrier was reported by Q. Yang et al., (2006). This method was proposed to reduce polarization layer and cake resistance which are the main contributor of the filtration resistance in MBR. The role of the suspended carrier are to improve the characteristic of activated sludge by adsorbing the small biological flocs and colloidal matter. On the other hand the movement of suspended carrier scours the membrane surface and reduce the cake layer.

) Vibrating membrane + Coagulant [G. Genkin et al. ,2006]

Fouling Amelioration - (3) Mixed Liquor Properties

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Fouling Amelioration - (2) Membrane properties

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Fouling amelioration - (1) Hydrodynamic

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Exploiting the hydrodynamic is one of the mayor approach in order to achieve the higher operation permeability of the membrane. In most of the submerged membrane, air bubble scouring is always used to promote the hydraulic turbulence in the vicinity of the membrane. The bubble especially coarse bubble promote the scouring efect to the fouling layer at the membrane surface. How ever, concerning the energy for aeration and to prevent the damage of the over scouring that can break the floc of the sludge, the air scouring is only can be applied up to certain extent.

The role of bubbles is to provide direct shear, induce secondary flow of liquid and to move the membrane (in case of hollow fiber) [9 in CBB1]. This approach has several disadvantages [CBB1]:

The shear forces experienced by the membranes are relatively weak so that only modes fluxes can be used.
Increasing the bubble flow reaches a "plateau" in term of flux improvement and this make "turn up" to higher throughput difficult.
It is difficult to achieve effective bubble distribution and a significant portion of the aeration energy will have little impact.

In these reasons, applying the new method in exploiting the hydrodynamic to improve the operational flux is necessary.

Many new methods had been applied in order improve the filtration performance of the membrane; novel membrane module, ultrasonic, addition of porous and suspended membrane carrier, external configuration, and advance aeration system.

Vibrating membrane

The method of moving the membrane as attempt to control the concentration polarization and fouling in membrane filtration has been proposed over last two decades; vibratory shear enhanced process (VSEP) for pressure driven membrane process, vibrating membrane in pervaporation, and rotating submerged membrane by Huber Co.

The application of the vibration submerged microfiltration hollow fiber membrane system was reported by Genkin et al., [2006]. The strategy to vibrate the membrane is by connecting the membrane cassette to rotated wheel with amplitudo of 4 cm as shown in Figure 1. By this method, it is possible to vibrate the membrane cassette up to 10 Hz. For further improvement of shear rate at the vicinnity of membrane, vanes was inserted next to the cassette. The system is tested using 5 g/l yiest solution using 4.1011 m-1. The system was evaluated in term of normalized critical flux improvement using 2-10 LMH flux step.

Figure 1. Design of Vibrating membrane

Critical flux of up to 80 LMH are atainable in the vibrating frequency of 10Hz. The obtained flux is significantly higher than what can be achieved with either bubbling or crossflow (Typically 30-40 LMH). Further modification in addition of Vanes provide an approximately double enhancement of critical flux and enable achievement of critical flux of 100LMH at 8.3Hz and 130LMH at 10Hz. such high values of critical flux have not been achieved using traditional static membrane techniques and suggest that non-fouling operation is a possibility. The intellegent manipulation of hydrodynamic condition can produce dramatic improvement in critical flux.

Figure 2. The Oscillation MBR

The another method in order to improve the hydrodynamic properties of the mixed liquor in the vicinity of the membrane is by membrane oscillation; cross oscillation and vertical oscillation [Figure 2]. When testing the membrane system by oscillation frequency of 0.5 Hz resulting laminar velocity of 0.2 m/s, TMP 3.41 Psi, in 1.8-2 g/l MLSS concentration, S. C. Low and his co-worket (2005) found that these approach can maintain the more than 76% of initial flux or even higher for vertical oscillation of 90% during the 5 hours of filtration test.

Local aerator

The smart design of module gives the possibility to localize the aeration. It creats the higher turbulence with less air and energy. Special aeration device was designed by F. I. Hay et al. (2008) to appropriately clean the membrane surface with effective utilization of air [Figure 3]. The air hole 1 mm from the thin pipe was attached on the surface of the module. Air introduced from the top end of the pipes hence effectively cleaned the membrane surface. This specific arrangement of the aeration device enabled efficient utilization of the applied air solely for cleaning purpose by minimizing escape of air bubbles to the sourounding media. With intermittent aeration (Intensity 2.5 l/min, duration 1 min on per 30 min) using this device with periodic chemical cleaning allowed stable operation with no increase in TMP for 2 months of operation.

Figure 3. Local aerator for intensive fouling prevention F. I. Hay et al. (2008).

Fouling Autopsy - Foulant Analysis

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Fluorescent in situ hybridization (FISH)

FISH (Fluorescent in situ hybridization) is a cytogenetic technique that can be used to detect and localize the presence or absence of specific DNA sequences on chromosomes. It uses fluorescent probes that bind to only those parts of the chromosome with which they show a high degree of sequence similarity. Fluorescence microscopy can be used to find out where the fluorescent probe bound to the chromosome. FISH is often used for finding specific features in DNA. These features can be used in genetic counseling, medicine, and species identification. In foulant analysis this method is used to detect Gram negative bacteria with phylogenetic probes monitoring of a-, b- and c-Proteobacteria, of the main ammonia-oxidizing bacteria
(AOB) and nitrite-oxidizing bacteria of the Nitrobacter and Nitrospira genera.

FISH is independent from the culturability of the bacteria and it is increasingly applied as it allows the evaluation of the presence and distribution of specific micro-organisms in activated sludge flocs. Despite the recent increase of FISH applications to activated sludge, the literature is mainly concerned with the investigation of strains with specific characteristics or with the biomass selected in the most common applications (CASP and domestic wastewater treatment).

The membrane in MBR

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The summary of commercial membrane that use in MBR application is summarized as follow:

Table 1: Flatsheet membrane

Table 2: Industrial HF module

The Fouling Amelioration

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The General Method

Numerous method have been developed and reported in order to limit the membrane fouling. Some of the outstanding results are already patented or even applied in industrial MBR. The aproaches for fouling limitation is very broad from selecting the suitable biological parameters to applying the pulsation of electrical current to membrane surface. It is very difficult to make the general thought that may covel all approach that has been proposed and tested.

The methods for addressing the fouling in MBR is presented in Figure 1 and Table 1. Figure 1 shows the overall scheme in addresing the fouling. In this scheme all approach for fouling limitation is being tried to be covered. This scheme is developed in the basis understanding that the fouling is result of interaction between the mixed liquor and membrane to form the fouling layer. From this definition there are three different components that participated in fouling; mixed liquor, membrane and foulant layer it self. In order to limit the membrane fouling, these component mush be exploited to certain extent.

The general strategy and method of fouling limitation is identified by the approach to exploit these factors and devided in five cluster: membrane properties (1), hydrodynamic (2), mixed liquor properties (3), and the combination among them (4 and 5). The summary of the methods that has been reported is shown in Table 1. The further discussion is given in the next sub-section of each cluster.

Figure 1: The schematic diagram of fouling limitation.

Table 1: Summary of fouling limitation methods.

MBR: An Introduction

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Definition

Membrane bioreactor (MBR) is the combination of a membrane process like microfiltration or ultrafiltration with a suspended growth bioreactor, and is now widely used for municipal and industrial wastewater treatment with plant sizes up to 80,000 population equivalent (i.e. 48 MLD).

Overview

When used with domestic wastewater, MBR processes could produce effluent of high quality enough to be discharged to coastal, surface or brackish waterways or to be reclaimed for urban irrigation. Other advantages of MBRs over conventional processes include small footprint, easy retrofit and upgrade of old wastewater treatment plants. Two MBR configurations exist: internal, where the membranes are immersed in and integral to the biological reactor; and external/sidestream, where membranes are a separate unit process requiring an intermediate pumping step.

Recent technical innovation and significant membrane cost reduction have pushed MBRs to become an established process option to treat wastewaters. As a result, the MBR process has now become an attractive option for the treatment and reuse of industrial and municipal wastewaters, as evidenced by their constantly rising numbers and capacity. The current MBR market has been estimated to value around US$216 million in 2006 and to rise to US$363 million by 2010.

MBR history and basic operating parameters

The MBR process was introduced by the late 1960s, as soon as commercial scale ultrafiltration (UF) and microfiltration (MF) membranes were available. The original process was introduced by Dorr-Olivier Inc. and combined the use of an activated sludge bioreactor with a crossflow membrane filtration loop. The flat sheet membranes used in this process were polymeric and featured pore sizes ranging from 0.003 to 0.01 μm. Although the idea of replacing the settling tank of the conventional activated sludge process was attractive, it was difficult to justify the use of such a process because of the high cost of membranes, low economic value of the product (tertiary effluent) and the potential rapid loss of performance due to membrane fouling. As a result, the focus was on the attainment of high fluxes, and it was therefore necessary to pump the mixed liquor suspended solids (MLSS) at high crossflow velocity at significant energy penalty (of the order 10 kWh/m3 product) to reduce fouling. Due to the poor economics of the first generation MBRs, they only found applications in niche areas with special needs like isolated trailer parks or ski resorts for example.

The breakthrough for the MBR came in 1989 with the idea of Yamamoto and co-workers to submerge the membranes in the bioreactor. Until then, MBRs were designed with the separation device located external to the reactor (sidestream MBR) and relied on high transmembrane pressure (TMP) to maintain filtration. With the membrane directly immersed into the bioreactor, submerged MBR systems are usually preferred to sidestream configuration, especially for domestic wastewater treatment. The submerged configuration relies on coarse bubble aeration to produce mixing and limit fouling. The energy demand of the submerged system can be up to 2 orders of magnitude lower than that of the sidestream systems and submerged systems operate at a lower flux, demanding more membrane area. In submerged configurations, aeration is considered as one of the major parameter on process performances both hydraulic and biological. Aeration maintains solids in suspension, scours the membrane surface and provides oxygen to the biomass, leading to a better biodegradability and cell synthesis.

The other key steps in the recent MBR development were the acceptance of modest fluxes (25% or less of those in the first generation), and the idea to use two-phase bubbly flow to control fouling. The lower operating cost obtained with the submerged configuration along with the steady decrease in the membrane cost encouraged an exponential increase in MBR plant installations from the mid 90s. Since then, further improvements in the MBR design and operation have been introduced and incorporated into larger plants. While early MBRs were operated at solid retention times (SRT) as high as 100 days with mixed liquor suspended solids up to 30 g/L, the recent trend is to apply lower solid retention times (around 10-20 days), resulting in more manageable mixed liquor suspended solids (MLSS) levels (10-15 g/L). Thanks to these new operating conditions, the oxygen transfer and the pumping cost in the MBR have tended to decrease and overall maintenance has been simplified. There is now a range of MBR systems commercially available, most of which use submerged membranes although some external modules are available; these external systems also use two-phase flow for fouling control. Typical hydraulic retention times (HRT) range between 3 and 10 hours. In terms of membrane configurations, mainly hollow fibre and flat sheet membranes are applied for MBR applications.

The Road Map of MBR

2008-10-07T13:32:00.000-07:00

This first post is the guideline for the reader to follow the overall content of the blog. Like in a book, this can be considered as list of content. Each of content from this road map is linked to suitable discussion in this blog.

The content of the blog can be expand depend on the need and current popular issue on the MBR. The reader can make any suggestion of the other important issues that may be important to be put to the blog. Another information regarding the MBR online is also provided in the gadget at the bottom of the webpage.

Introduction

Definition
Overview
History and fundamental improvement

MBR Fundamental

Process Operation

The Membrane in MBR

Characteristic
Preparation
Modification
Hollow Fiber VS Flat Sheet which one is the best

Important Parameters in MBR

Biological Parameters
Membrane filtration
Fouling

How to Design the MBR

Labscale
Pilot plan
Industrial scale

Fouling in MBR: An Introduction

Foulant
The Method for Fouling Autopsy
Fouling Mitigation in MBR

MBR Market and the Future Prospect

Research Group in MBR

MBR Manufacturer

The Research Project in MBR

MBR: Hot topics

Miscellaneus