Sydney Water and UNSW measure floc strength to improve plant performance

Researchers at Sydney Water and the University of New South Wales (UNSW) have collaborated on a project to help the utility deal with rising levels of natural organic matter (NOM) in its catchment. 

Growing concentrations of NOM in raw water supplies, particularly after heavy rain, can lead to a reduction in floc strength. 

During flocculation for water treatment, particles come together to form flocs, which are eventually removed from the water. Stronger flocs make the treatment process more efficient, while weaker flocs can reduce the capacity of a plant.

For Sydney Water, failure to successfully address the NOM issue – and the resulting reduced floc strength – could lead to hundreds of millions of dollars in upgrades to its 10 water filtration plants over the next decade. 

The issue is particularly evident at its Nepean Water Filtration Plant, which produces about 40% less water after heavy rain events because of the increase in NOM. 

Sydney Water Principal Scientist – Treatment Dr Heri Bustamante said the best way to address this and increase floc stability is to optimise the coagulation chemicals used during treatment.

However, there is currently no standard technique to determine floc strength in direct filtration, which is used at the Nepean facility.

To solve the problem, Sydney Water scientists and a team from UNSW startup Instrument Works set out to create their own tool, which is currently being validated.

“We needed to develop an instrument that could measure the strength of flocs in a direct water filtration plant,” Bustamante said.

“This is so we could adjust the chemicals to ensure the flocs are as strong as possible, which helps maximise the plant capacity.

“If we can get stronger flocs, the filter will be able to operate for a much longer period of time, which means it will be necessary to backwash less frequently, saving water and additional chemical use.”

The team first developed a model that simulated flocs passing through a filter. Next, they designed a device that mimics the shear in the filters and the effect this has on the flocs.

The result is an instrument that can detect changes in floc size and shape, without the need for expensive particle-sized equipment. It can be used by plant operators to adjust the chemicals in the treatment process based on changing NOM levels.

Although Sydney Water is one of the few utilities in Australia that uses direct filtration, Bustamante said the tool could be used across the industry.

“The whole purpose of the project was to develop something that could be deployed at various Sydney Water plants,” he said.

“But other utilities can also use it, particularly if they want to optimise their processes.” 

Research projects like these will be on show at the Australian Water Association's annual conference, Ozwater'20. To submit a paper, panel or workshop to the event, click here.