Update on Mt Pleasant WTP Incorporating the MIEX ® DOC Process and How it Compares With a Plant Operating in Enhanced Coagulation Mode

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Courtesy of IXOM Watercare

Natural organic matter (NOM) is a major factor impacting on water treatment processes. NOM is a precursor of disinfectant by-products (DBP), a food source for regrowth of micro-organisms and makes downstream processes such as membrane filtration and activated carbon less efficient. Reducing NOM in conventional treatment plants can be achieved by using enhanced coagulation, whereby additional coagulant is applied at a reduced pH. More recently the MIEX® DOC Process was developed specifically for the removal of NOM in drinking water production. This process has been operating at the Mt Pleasant plant in South Australia since 2001 where it has been applied in two treatment streams in combination with conventional coagulation/filtration and membrane filtration. Plant operation has been closely monitored to ensure that any unforeseen problems are detected at an early stage as this is of particular concern when introducing a new technology such as MIEX®.

The plant has gone through significant changes since early 2004 including replacement of the filter media and nozzles in the Stream 1 coagulation train following a problem with achieving effective filter backwashing. The cause was found to be filter nozzles blocked with sand and normal operation was achieved once nozzles of suitable size were installed. The second upgrade was replacement of the membrane modules of the Microfiltration plant of Stream 2 during December 2004 due to poor membrane cleaning and increasing transmembrane pressure. The cause was attributed to inefficient and infrequent clean in place (CIP) causing increased inorganic fouling. Once the membranes were replaced and a more rigorous CIP strategy put in place, the plant displayed a significant improvement in the resistance values and much lower operating pressures. A new control strategy was established in 2005 which has enabled operators to maintain a stable resin concentration in the contactors despite variable raw water flows.

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