Pre-treatment flocculation

Leader

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Challenge

An effective pre-treatment system for reverse osmosis (RO) desalination which alleviates colloidal and organic fouling (the precursors of biofouling) is the key for the success for any RO desalination. Biofouling is caused by the residual organics in inlet raw water and is the major cause of membrane biofouling. Conventional pre-treatment systems cannot reliably remove some pollutants but a small number of studies using micro- and ultra-filtration (MF and UF) membranes have indicated their cost effectiveness in removing colloidal matter. However, the use of MF/UF systems without other processes does lead to organic fouling and unsustainable operation. There is a need to establish an integrated hybrid system incorporating membrane filtration with adsorption and flocculation.

Investigation

Develop and evaluate novel immersed membrane flocculation hybrid systems as pre-treatment processes to both brackish and seawater RO desalination. Construct a semi-pilot scale system and field test at Chowder Bay, Sydney. Test polymeric inorganic and organic flocculants for their effectiveness at removing colloidal matter and a wide range of organic foulants, which should lead to significant chemical and sludge reduction. Evaluate whether any valuable by-products can also be recovered from the chemical sludge.

Outcomes

The effect of flocculation on the performance of MF was investigated using poly ferric silicate, ferric chloride and titanium tetrachloride. All were effective at removing organic however, poly ferric silicate performed better at reducing turbidity and dissolved organic carbon and titanium tetrachloride was more effective at removing low molecular weight compounds and humics. The titanium tetrachloride sludge was incinerated to produce titanium dioxide nanoparticles.

Two hybrid systems were developed and tested, a submerged membrane flocculation system and submerged membrane flocculation- adsorption system. The latter system performed the best in terms of organic compound removal and critical flux. With doses of ferric chloride and powder activated carbon, the system was able to remove 72% of the dissolved organic carbon and reduced fouling incidence by a factor of five.

The organic compound removal by stainless membranes alone was found not to be effective as a pre-treatment system, which was likely due to the large pore sizes of the membrane. The addition of granular activated carbon as a pre-absorbent or into the membrane reactor however, demonstrated an improvement of up to 56% removal of protein-like compounds.

An energy efficient, compact submerged membrane flocculation hybrid pre-treatment system was developed that is able to reduce the organic fouling. The use of chemical usage and subsequent sludge production was reduced through the use of alternative chemicals and effective additional pre-treatment, such as pre-adsorption. Recovery of titanium dioxide from sludge also reduced the final amount of sludge to be discharged. Alternative polymeric inorganic flocculants with or without pre-adsorption reduced the chemical usage and sludge production while achieving superior organic removal.

Future Direction

A series of experiments with in-line flocculation filtration as pre-treatment to RO are planned to test the organic and biofouling reduction, which will be useful for the modification of flocculant dose in the existing desalination plants. Biosorption experiments are planned to determine if this is a viable alternative to adsorption.

Partners

Vigi FR1 partners


 

Total Value: $820,000 (cash and in-kind contributions)

Principal Investigator: Professor Saravanamuth Vigneswaran

Title: Membrane flocculation hybrid system as pre-treatment to brackish water reverse osmosis desalination system: Emphasis on chemical use reduction and recovery

Length: 46 months

Personnel: 15 collaborators contributing 1.75 FTE

Further Information

FR1 UTS Vigneswaran (Flocculation) Summary Poster

Project Summary Poster – flocculation

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