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Membrane BIOREACTOR (MBR) MEMJET

The so called MEMJET process, developed by ROTREAT jointly with the engineering consultant company EnviCare®. Besides an innovative technology and advanced process control, the MEMJET process is equipped with a highly efficient and cost effective microfiltration membrane.
 
This particular microfiltration membrane is currently in operation in over 470 large scale waste water treatment plants, both in communal or industrial use, with varying throughputs and possesses several years of operational experience. The units are installed in several countries worldwide. 
 
Our experience in operating landfill leachate plants proved to be very useful and was therefore integrated in the process technology of the MEMJET MBR process. Looking at the treatment of leachate it became obvious that the degradation rate for substances like COD or ammonium is significantly higher and also more stable in MBR´s compared to conventional activated sludge process. The disadvantage of many MBR´s built in the 1990´s lay in the external cross-flow filtration and the high specific energy demand (2-10 kWh/m3 waste water). 
Around 50 MBR´s were built in Europe, mainly for the treatment of landfill leachate.
 
The high energy demand and the resulting high operating costs of the external cross flow lead to the development of the so called “submerged filtration systems” with clearly less energy demand.

the MEMJET process is based on this energy efficient submerged membrane filtration.

MBR-Test unit

As a result of variable qualities and pollution of different waste water, it is strongly recommended to test on site.

However, ROTREAT has developed a mobile test unit, placed in a standard ISO-container. This container allows a quick and easy transport to the costumer.
The installation is rather simple, on site only electic power supply and the water- and waste water connection are required.
 
For this reason a test run at the location with the specific waste water of the costumer is highly recommended.
 
All the technical parts are integrated in the container.
 
In the inflow a sedimentation tank and screening are installed. The biology runs selectively anaerobic, anoxic or aerobic, additionally a stirring unit for homogenisation is attached.
 
The plant is equipped with an electric powered crane construcion so that the modules can be easily installed by one person only.
 

The container plant is designed to test variable types of membranes (hollow fibre modules, plates modules and spiral modules, etc.) from different manufacturers with various operation methods and Dead-End or Semi-Cross-Flow.

Chemicals necessary for flocculation and phosphorprecipitation are stored directly in the container and the dosing is fully automatic regulated. Cleaning sequences (backwash, backflush, etc.) are executed automatically as well and completely parameter driven.
 
Accessorily a plant control station with SPS-control unit for operation and fully automatic mode for the membrane filtration plant is intregrated.
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Ansicht von rechts seitlich(hinten)

MEMJET treatment

The filtration area of one technical module is 105 m2. 3 modules are assembled to form a row. The hollow fiber membranes are stretched between 2 permeate collection pipes with a specified over length in order to allow them to swing in the up flowing mixture of air and biomass.

The aeration device below the membranes enhances the turbulence and consequently the scrubbing effect on the membrane surface. 
An intermittent aeration mode and a backwash with clean permeate are possible. 
The trans-membrane pressure of up to 0.6 bar controls the filtration quantity and is provided either by geodetic height difference or by a suction pump.

Membrane

The MEMJET process is equipped with a submerged commercial hollow fiber membrane with a cut-off of 0,4 µm and with an outer diameter of appr. 540 µm.  The membranes are made of polyethylene and they are permanently hydrophilic. The fibers are highly resistant to flexural fatigue. The membranes can be stored dry and do not need to be pre-wetted prior to use.

The individual fibers are assembled to flat “curtains”. The fibers are situated horizontally in the biomass. This type of arrangement guarantees an optimal use of the installed membrane area, since the activated sludge does not block the ends of the fibers as experienced in the vertical set up.
 
Several curtains are mounted in a steel frame, thus forming one module of 105 m² membrane filtration area. The permeate is extracted through to connection pipes.
 
Smaller units are available upon request.

Membrane bioreactor (MBR)

A MBR possesses all typical features of the conventional activated sludge process (anaerobic/anoxic/aerobic treatment of organic compounds and nitrogen) except for the settlement tank. The main difference is that the sludge is 100 % confined to the MBR due to the membrane filtration with a cut-off <0,4 µm – a conventional sedimentation basin becomes unnecessary. Generally spoken there are two different MBR systems, namely external cross flow and submerged systems. Looking at the submerged type the membrane is installed directly in the aerobic nitrification basin (see Sketch). 

An aeration device below the membranes provides an air-stream and thus a coupled hydraulic flow along the membrane surface. The cleaned water is filtrated through the fine pores of the membrane (= permeate) and flows through the hollow fibers to two permeate pipes. The hydraulic flow and extraction of the permeate is achieved through a suction pump or slight hydraulic pressure gradient and is therefore energetically highly efficient (appr. 0,12 kWh/m3). 

 
The main advantages of the MEMJET process are: 
  • Smaller treatment volumes – savings on land
  • No wash-out of biomass due to 100 % withdrawal of biomass on membrane surface
  • Enhanced biological degradation due to highly specific biomass and high sludge age
  • No influence of peak flows on quality of permeate (= clean water)
  • Germ free effluent