Operating Requirements

At the time of writing this document the plant has not been operating for a sufficiently long period to be able to provide detailed operating costs for the process. However, it is hoped to provide details at the Conference in March.

3.1 Nutrient Dosing

The provision for nutrient dosing into the feed from the DAF plant has been provided but this has not been utilised to date. It would be possible to add chemicals providing a combination of N P and K to enhance the biological activity in the activated sludge plant and the MBR.

3.2 MBR Cleaning

The MBR control logic allows for backflushing of the hollow fibre membranes on a periodic basis generally set at one hour intervals. Hypochlorite can be introduced into the backflush water to provide a chemically enhanced backwash and this is generally undertaken on a weekly basis.

The trans-membrane pressure (TMP) of the system is typically expected to increase from 0.4 to 1.2 bar g over a period of two months following which dilute backflushing with acid and / or caustic solutions will be required.

3.3 RO Dosing and Cleaning

An anti-scalant is continually dosed at 2.5 mgl"1 concentration in the feed to the RO plant in order to minimise scaling on the concentrate side of the membrane and also to minimise biological fouling.

In addition to the anti-scalant, every week for 30 minutes a non-oxidising biocide is dosed at 400 mgl'1 concentration. This shock dose prevents the formation of biofilms on the RO membrane surface and has the effect of increasing the period required between cleaning-in-place (CIP).

CIP chemicals will be required on a monthly basis and the facility exists to use either high or low pH proprietary solutions for periodic recirculation through and soaking of the RO membranes. A solution is made up manually in the CIP tank and heated up to 40 °C. A small centrifugal pump is then used to force the CIP liquid through the plant. Effective CIP procedures will reduce the net driving pressure required down close to initial requirements thus prolonging the membrane life.

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