MFUFMBR

Ultrafiltration is a membrane process with the ability to separate molecules in solution based on size. It is a pressure driven process with a typical nominal pore size of 0.01 micron (100,000MWCO), and configurations are either cross flow or dead end filtration. UF removes bacteria and protozoa, including giardia and cryptosporidium. Reduces turbidity to < 0.1 NTU and removes 6 log of viruses. UF is ideal as pretreatment to reverse osmosis, final treatment in the pharmaceutical industry, and potable water applications for a wide range of feed sources in the municipal market. Hollow fiber multibore membrane is the most resilient and reliable membrane manufactured.

UF Pretreatment for RO Systems

Hollow fiber ultrafiltration (UF) is widely accepted today for municipal water treatment applications including production of drinking water from surface water and water reuse applications. UF is also used for industrial water treatment including pretreatment to spiral-wound reverse osmosis (RO) membranes for production of high purity water. Because of the increasing awareness of the need for adequate pretreatment, there has been significant interest in UF as pretreatment for RO for municipal applications in brackish and seawater desalination plants.

Depending on the feed water quality, extensive pretreatment may be needed to provide water that is suitable for RO feed, because the brine spacer in an RO element can be susceptible to solids plugging. UF provides excellent pretreatment to RO because it can consistently deliver filtrate with very low turbidity, regardless of feed water quality. Conventional pretreatment may not reliably produce consistent, high quality water, especially when the feed water changes. In addition, compared to conventional water treatment technologies, UF systems require less space and often have lower operating costs.

UF membranes provide a physical barrier between the feed and product water and they have pore sizes in the range of 0.01 micron. These membranes remove very small contaminants in the feed water, including essentially all suspended solids, colloidal particles, and bacteria and viruses. In general, UF filtrate turbidity is less than 0.1 NTU and has an SDI15 (Silt Density Index) of less than three. This is ideal feed to RO. High quality and consistent feed water can be expected to lead to improved RO system operation, including lower operating pressure for a given flux, less frequent membrane cleaning and less risk of plugging the element with suspended solids.

UF FOR DRINKING WATER

Ultrafiltration is a pressure driven membrane process, which is increasingly applied in advanced drinking water treatment processes, particularly to improve the water quality with respect to organic and microbiological parameters. The combination with coagulation is a promising process combination to remove natural organic matter and maintain a high membrane performance. This hybrid process can also help to reduce subsequent disinfection by-product formation.

Coagulation coupled with ultrafiltration is one of the most promising drinking water production processes. Regarding removal rates and residual aluminium, aluminium sulphate and polyaluminium chloride are better coagulants than sodium aluminate. Iron chloride is a more efficient coagulant than aluminium sulphate. A pH around 6 is recommended during coagulation.
During in-line coagulation, under-dose conditions with acidicpH show the best performance because it is possible to obtain good removal rates of contaminants and improve physical performance. Nevertheless, standard coagulation is superior to in-line coagulation. Dynamic membranes are a promising alternative to current techniques used in drinking water production, because tests show that they perform better than membranes with standard or in line coagulation as a pre-treatment. Metal membranes have a potential for drinking water production, if the production costs can be reduced. Absolute values of pH and coagulant dose depend on the nature of the raw water and on the operational requirements.
Ultrafiltration membranes are a reliable barrier against bacterial, protozoa and viruses. Coupled with coagulation LRVs (log reduction value) of 6.7 can be obtained. This makes them suitable for water disinfection. An improved removal of humic acids can be achieved if fibres with an additive are used for filtration.
Fibers spun under an air gap had both higher flux and higher retention than wet spun fibres. NOM causes membrane fouling. It can be subdivided in particulate (P), colloidal (C) and dissolved organic carbon (D).
The fouling potential of the coagulated fractions can be ordered as follows: (C) > (C+D) > (P+C+D) = (P+C) > (D). Particulates with coagulation pre-treatment help to minimise irreversible fouling. Coagulation cannot minimise the fouling caused by colloids, which is considered the worst type of fouling.

Chemical cleaning is used to restore the membrane permeability. A higher temperature during the cleaning improves the dissolution of organic and inorganic compounds. A two-step cleaning in the sequence base and acid shows the best overall performance. It can enhance a chemical enhanced backwash (CEB) notably, because strongly fouling hydrophobic compounds can as well be removed as inorganic colloids. Removal of organic compounds in cleaning in place (CIP) and cleaning out of place (COP) can be conducted with an oxidant such as NaOCl and inorganic compound removal is best with a citric acid. A direct comparison of the results of the sources used is difficult because different membrane materials, operational modes, experimental setups, and raw waters were used. Recapitulating, the report shows that ultrafiltration is a reliable technique for drinking water production.

Microfiltration is a pressure-driven barrier to suspended solids and bacteria to produce water with very high purity. It is also used as pretreatment for surface water, seawater, and biologically treated municipal effluent before reverse osmosis and other membrane systems.

The MBR process utilises the well proven activated sludge process, but replaces conventional final settlement with an ultrafine membrane which effectively filters the final effluent.

Benefits of MBR

- The membrane is an extremely effective solids separation device.
- High removal efficiency results in a very high effluent quality (2/2/0.5mg/l or better).
- Simplicity of system design.
- Reactor volume is greatly reduced when compared with an activated sludge plant basin due to the fact that it runs at active MLSS values up to 15,000 mg/l, compared with typical values for conventional activated plants of 3000 to 5000 mg/l.
- No requirement for final settlement tanks.
- Offers bacterial removal without the need for complicated ultra violet radiation systems.
- Water re-use applications.