MBR – an efficient process
The use of membrane bioreactor (MBR) technology for wastewater treatment began around ten years ago and has grown significantly since then. Today, it's an important sector of the market in its own right. We look at the thinking behind Koch Membrane Systems' Puron technology.
Koch Membrane Systems (KMS) is a leading developer and manufacturer of innovative membrane filtration solutions, and has recently been investing heavily in the development of products for the water and wastewater market place. It is leading the drive to reduce the costs and increase the effectiveness of municipal and industrial water treatment.
The Puron submerged membrane technology has been added in the past 12 months to the already broad range of membrane types and configurations available from KMS. This membrane is in increasing demand for membrane bioreactors.
A membrane bioreactor (MBR) is a hybrid biological wastewater treatment process directly combined with a membrane separation process. The main task of the membrane is to separate water in the treated effluent from the bio-mass by retaining the solids and bacteria.
Membranes have demonstrated that they are able to satisfy this requirement effectively and economically. The membrane enables the hydraulic and solids flow though the plant to be decoupled leading to a smaller plant footprint and a more efficient process. In comparison, conventional wastewater treatment consists of three steps:
- Primary treatment
- Solids / liquid separation
The last part of the process is crucial, as one litre of secondary effluent may contain ten million bacteria. But there is often insufficient removal of bacteria and suspended solids. With MBR technology, the membrane acts as a barrier to bacteria and suspended solids to produce low-turbidity effluent with few bacteria counts.
Applications of MBR technology are now found in municipal WwTW as well as industrial facilities that are interested in an effective recycling technology.
In addition to meeting strict effluent targets, MBR technology occupies a good deal less space than traditional systems and is highly economical on a life-cycle basis compared with conventional options currently available for water recycling.
Taking all of these factors into consideration, it is clear that MBR technology has an extremely important role to play in planning for future water demand.
The economics of MBR technology are based on three main factors:
- Energy consumption
- Membrane lifecycle costs
- Filtration rate
Energy consumption in MBR plants is higher than in conventional plants because the operation requires the use of additional energy, principally the use of air to scour the membranes. It should be noted, however, that not all modules are created equal, and differences in module design affect the energy efficiency of aeration.
The membrane lifecycle cost is governed by the initial membrane cost for new plant, the membrane replacement cost and the membrane life.
Membrane life is affected by the operating conditions of the total process.
In particular, poor performance in the biological step has an adverse impact on membrane life and lifecycle costs. Over the past few years, the price of modules has declined and membrane life has increased while performance in the biological step has improved.
Higher filtration rates lead to a reduction in the required membrane area for an MBR process, thus reducing membrane costs. Furthermore, the peripheral costs related to the membrane modules such as pipes, valves and process control in general reduce in proportion to membrane area.
Koch Membrane Systems’ Puron submerged hollow fibre UF modules optimise both membrane and module design. The patented module is designed to avoid clogging and sludging.
The Puron module features hollow fibre membranes with a pore size of about 0.05 microns. The lower ends of the membrane fibres are fixed in a header while the upper ends are individually sealed and are free to move laterally. All solids and particulates remain on the outside of the fibres while permeate is sucked out of the inside of the fibres by means of a vacuum.
The membrane fibre bundle is where the fibres are arranged in bundles and
submerged vertically into the activated sludge. To maintain the filtration rate of the
membrane modules, air scouring is carried out at regular intervals.
An air nozzle is integrated into the centre of bundles of fibres to apply the air for scouring purposes.
The central arrangement of the air nozzles inside the membrane bundles reduces the energy consumption compared with other MBR designs, since the air is injected at the place where the risk of sludging is highest.
The module design removes even hairs and fibrous compounds from the system, so that a coarser pre-screen can be used, thus improving capital and operating costs.
Another special feature of the Puron membranes is their enormous mechanical strength that is provided by a braid inside the membrane material. The individual fibre bundles are connected in rows. Several of the rows are mounted into a frame made of stainless steel.
The free moving fibres combined with central aeration ensure stable filtration
during plant operation, long membrane life, and low operating costs by reducing the need for energy, cleaning and maintenance.
In addition to their use in the municipal market, MBRs using submerged membrane modules are increasingly applied in industrial wastewater treatment since this technology offers many advantages for industrial companies.
It may help to close water cycles, for example, by reusing the treated wastewater as process water. The costs of wastewater disposal can be reduced considerably while saving fresh water. Examples of industrial applications include:
- Food and beverages
- Pulp and paper production
This technology is also of interest to countries with water shortages where the effluent from MBR plants can be used for irrigation purposes, process water applications, or as part of the treatment process for indirect potable reuse.
The effluent quality often surpasses the applicable regulatory requirements for discharge into the environment and meets the stringent requirements of the European bathing water directive.
In addition to its Puron submerged hollow fibre module, Koch Membrane Systems offers a range of membrane products for municipal and industrial water and
wastewater applications as well as sanitary and non-sanitary industrial processes.
VWI picks Puron for Eire
Veolia Water Ireland (VWI) has placed a major order for Koch Membrane Systems’ Puron submerged membrane modules for the MBR treatment of wastewater from a new housing development at Ashbourne, near Dublin.
VWI’s Joe Higgins says: “Puron is the best available technology for meeting one of the big challenges of the Irish Republic at the present time – the requirement to process wastewater from new housing and meet EC guidelines, without having to depend on a limited infrastructure.”
Puron’s modular character was an additional advantage in this project – half of the modules will be installed immediately and commissioning of the first stage is scheduled for the end of 2006. The remaining half is projected for the future when extra capacity will be required.
The system is designed to process up to 140m3/h domestic wastewater and
the eight Puron modules currently being installed provide a total of 4,000m2 membrane area.