MEMBRANE SEPARATION PROCESSES
Membranes allow certain molecules or ions to pass through by diffusion and sometimes by specialised ‘facilitated diffusion’. The rate of passage depends on the pressure, concentration and temperature of the molecules or solutes on either side of the membrane, as well as the permeability of the membrane to each solute. This depends on solute size, solubility properties, or chemistry.
Membrane configurations include spiralwrap, tubular, flatsheets and capillary, and are used to separate particles ranging from approximately 10 µm and smaller. The different membrane separation processes are as follows:
Veolia Water Technologies is a specialist in membrane separation, with the full range of ultrafiltration, nanofiltration, microfiltration and reverse osmosis membranes.
Microfiltration (MF) provides a physical barrier to a wide range of microorganisms, pathogens and suspended particles larger than 0.1 µm. It is a critical step in a wide range of treatment applications, including potable water treatment and industrial and municipal wastewater treatment, where it acts as both filter and disinfectant. Microfiltration typically requires less than 2 bar pressure for the membrane separation process.
Ultrafiltration (UF) is used to remove particulates and macromolecules from water in potable water and wastewater treatment. It is used either as a replacement for existing secondary and tertiary filtration, or alongside these processes as an integrated treatment process in water containing high suspended solids. Ultrafiltration membranes have a pore size between 100 and 2 nm and require 1 to 10 bar pressure to operate.
Nanofiltration (NF) is used in water treatment applications with low total dissolved solids. It is used for water softening and the removal of organic by-products that may result from earlier disinfection treatment. By retaining scale-forming hydrated divalent ions while passing smaller hydrated monovalent ions, nanofiltration is an effective water softening solution. Nanofiltration is achieved with membranes with pore sizes from 2 to 1 nm requiring 3 to 20 bar pressure.
Reverse osmosis (RO), which uses membranes with pores of less than 1 nm, is used to separate salts, ions and small organic molecules from feed water. Reverse osmosis is used in treating potable, ultrapure and process water, and is a key process in brackish and seawater desalination. Because of the low porosity of these membranes, RO requires high pressures (typically up to 80 bar) to function.
Speak to Veolia Water Technologies about your membrane separation requirements today! Contact our technical team here.
WE HAVE EXTENSIVE EXPERIENCE IN THE FOLLOWING MEMBRANE APPLICATIONS:
- Desalination of seawater and industrial process streams
- Production of potable water from brackish supply
- Recycling of water and separation of effluent streams
- Recovery of valuable minerals from effluent and process streams
- Removal of sulphate from injection water in off-shore oil production
- Concentration of inorganic and organic constituents in waste streams for recovery or disposal
- Removal of COD / BOD from effluent streams
Membrane processes such as seawater desalination are finding a strong market in the South African municipal sector, while zero liquid discharge installations are saving industrial clients money by recycling their process water and limiting their production and dumping of waste and waste by-products!
MEMBRATEK TUBULAR MEMBRANE RANGE:
Membratek is our specialised membrane manufacturing division, which provides integrated membrane solutions for a global market. The unit offers the full spectrum of membrane filtration products and services.
Membratek also offers a tubular reverse osmosis and ultrafiltration membranes. Tubular modules offer exceptional flexibility, as the internal tube connections are optimised to suit the application. Connections may be parallel, in series or in a parallel/series combination. For applications that demand a particularly robust system, the following types are specified:
Find out more about our range of membranes! Send us your requirements here.
Veolia Technologies and Membranes
Biosep™ Membrane Bioreactor
Veolia South Africa uses the innovative, patented BIOSEP process, developed by its parent company Veolia. Biosep™ is a high performance solution that combines aerobic biological treatment using activated sludge and membrane filtration for the treatment of municipal and industrial effluent. The filtration step can use immersed membranes or external, pressurised membrane filtration. The process ensures a high reduction of carbon, nitrogen and phosphorus pollution, as well as exceptional bacterial removal. Biosep™ combines an aeration tank and a membrane system where the membranes are grouped into modules. After treatment, such as screening, raw water enters the aeration tank where carbon, nitrogen and phosphorus are removed.
Membrane filtration then separates the purified water from the activated sludge. Submerged membranes typically deployed in capillary configuration and positioned vertically, with filtrate being drawn through the membranes under slight vacuum. Pressurised membranes, on the other hand, operate on a cross-flow principle. The treated water is pumped out and excess sludge is directly removed from the tank for dewatering.
Benefits over conventional activated sludge:
- Exceptional treated water quality
- Highly compact system
- No final clarification
- High COD removal
- Reduced reagent levels in phosphorus elimination
- Thickener may also be removed
- Reduced sludge production
The BIOSEP immersed membrane bioreactor is compact in design and environmentally safe, offers reliable biological treatment and delivers high quality, treated effluent. The process is especially suited to applications such as municipal water treatment, food and beverage production, pharmaceutical manufacturing, paper and pulp, and chemical plants, where effluent with organic pollutants needs to be treated. It has the potential to help Veolia in Southern Africa to gain increased market share in the biological treatment of domestic sewage and industrial effluents and will aid the company in upgrading wastewater for re-use, thus bringing long term benefits to the environment.
Read more about Biosep™ here!
Approved by leading international membrane manufacturers, the Hydrex™ 4000 range offers specifically formulated chemicals that keep membranes free of scale and bacterial growth, and aid in extending membrane life. Suitable for any membrane process, these chemicals play an important role during each stage of a plant's life cycle, from pre-treatment to preservation.