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Optimal Water Quality to Minimise Distribution System Problems

December 1, 2010

Mimicking drinking water distribution systems could lead to a better understanding of water quality at the tap

(Project 1008) Project Leader – Mary Drikas, AWQC

All water utilities aim to provide good quality water at the customer tap. This involves management of raw water sources followed by the use of one or more treatment processes. Treated water is then delivered to customers via pipe networks – from the distribution mains to the tap. Water utilities spend considerable time and money cleaning and flushing distribution systems to minimise water quality deterioration, however, one of the key parameters affecting water quality at the customer tap is the quality of the water entering the distribution system. Until now there has not been a focus on identifying the appropriate water quality to minimise deterioration in the distribution system. As particles and organic matter play a key role in water quality deterioration, the treatment processes should, at a minimum, provide effective removal of these components.

Substantial external funding from a number of industry partners highlights the interest in identifying the impact of incoming water quality on distribution system performance and water quality reaching the customer tap. This project aims to determine how much treatment is necessary to minimise water quality deterioration after passage though the distribution system. This will be achieved by comparing the impact of a range of water qualities from four different treatment schemes on four parallel pilot distribution systems (PDS) , with varying detention times. Water entering the PDSs will be chlorinated to satisfy chlorine demand but with minimal chlorine residual – to maximise biofilm growth.

The proposed treatment processes to supply these test rigs are: Coagulation/sedimentation/high rate filtration as used in a conventional treatment plant to provide removal of particulates and some organics MIEX® for removal of organics followed by coagulation for solids removal, with and without granular activated carbon (GAC) for further removal of biodegradable organics Nanofiltration, with microfiltration as pre-treatment, to provide high purity water A range of water quality parameters and analytical tools, including on-line techniques, will be used to monitor treated water quality and changes within the distribution systems. The key parameters to be monitored will include particle composition, microbial growth, NOM concentration and character, and biofilm growth. This will then enable selection of water quality parameters and analytical tools most suited for monitoring water quality within distribution systems, which can be used to predict water quality deterioration.

Mt Pleasant - 1008 Project Equipment Shed

Inset: Photo courtesy of SA Water of the Project Equipment Shed. Four different pilot scale treatment trains are housed within this area.

Direct comparison of the differences in water quality from the 4 treatments will allow the key factors causing water quality deterioration in the network to be identified. This will help establish guidelines for treated water quality to minimise its deterioration in distribution systems.
The desired outcome from this project will be a set of water quality parameters and analytical tools, best suited for monitoring water quality within distribution systems, which can be used to predict water quality deterioration. Dutch collaborator Jasper Verberk, of Delft University, will use information from this project to validate and build on established modelling tools to enable prediction of water quality at the customer tap based on the water quality leaving the treatment plant.
A successful project partner meeting was held in December 2009, where an update on the project was provided together with details of the trials and tribulations experienced to date. A site visit was also undertaken to show the partners the treatment processes, electrical control systems and distribution test rigs.

Whilst there have been some issues with leaking PDS, the partners remain interested and supportive of the project and are all keen to see the project progress.
Extensive flushing was completed in all four streams and the PDS system was operational in late April but suffered another setback when further distribution system leaks occurred in July. Following repairs the system was fully operational in late July and routine monitoring of treatment streams and distribution systems has been in place since. All online remote and automated systems are now operating, although the processing of the s::can data has not been fully commissioned by the installation company.

Raw water, supplied from the River Murray, has varied significantly with dissolved organic carbon increasing from 5mg/L to greater than 13mg/L in two months. This has proved challenging to treat effectively but is resulting in significant water quality differences between the various treatments. Data collected to date has shown interesting bacterial removal trends. Conventional treatment is providing 1 log bacterial removal while MIEX/coagulation and Microfiltration (with or without nanofiltration) provide between 2.5- 3 log removal. Interestingly GAC filtration reduces the overall log removal to1.5 due to bacterial release as it is now operating in the biological mode. Water quality changes are also apparent between the individual PDS and these differences will be monitored over the next 12 months.