Water Treatment Plant Operator

STATISTICAL MODEL DEVELOPMENT TO ANTICIPATE FILTER BREAKTHROUGH AND OPTIMISE CHEMICALS DURING HIGH COLOUR RAW WATER EVENTS  
A model developed and applied in Sydney Water’s Water Treatment Plants
A Mohiuddin, Y Wang
Publication Date (Web): 8 January 2018
DOI: https://doi.org/10.21139/wej.2017.040


Sydney Water operates the Nepean Water Filtration Plant (WFP), which treats raw water from the Nepean Dam situated in south-west of Sydney. In the last few years, the plant has been receiving raw water with higher true colour which, combined with historical lower turbidity of the dam water, has challenged the plant operations team to treat the raw water and maintain the plant’s performance. It is evident from higher true colour raw water that lower floc strength is the key issue, which causes turbidity breakthrough in filters. The filters breakthrough significantly decreases the filters’ run time, and eventually the plant's production rate is reduced by 34%.

Therefore, a process model has been developed to anticipate filter breakthrough during higher true colour of raw water and to optimise chemicals to eliminate filter breakthrough. The process model used the previous few years’ performance data of the dual media gravity filters, and analysed each performance indicator during each filter’s turbidity breakthrough events. The analysis also included the study of a range of process parameters. The process model then correlated all the parameters and differentiated between the optimum and suboptimal condition of the plant under a range of model input scenarios. 

The model developed the following equation to anticipate filter breakthrough:

Filter breakthrough = f (raw water quality, chemicals dose rate, filter design, filter performance indicators)

As an output:
  • The process model can predict any filter turbidity breakthrough and plant performance deterioration due to any sudden rise of raw water true colour. 
  • The process model can provide instantaneous solution of optimum chemicals dose to eliminate the filter breakthrough, and can provide forecast of plant performance improvement at model optimum chemical doses.
  • The model user can select a wide range of data sets from data selection criteria to see all the correlations among parameters.

The developed process model was applied at Nepean WFP during October to December 2016 for raw water turbidity around 2 NTU and true colour at 400 nm around 25 HU. Prior to the application of process model, all the five dual media gravity filters had severe turbidity breakthrough, and as a result the filters’ run times were reduced to 10-25 hours and the plant production rate was reduced to 180 L/s.  Applying the process model, the chemical dose rates were gradually adjusted to stop filter breakthrough. By applying the process model, the filters’ turbidity breakthroughs were fully eliminated, plant production rate was increased by 31% (235 L/s), all the filters’ run times increased by 60-300% (40-48 hours) and significant savings in chemical use was achieved by reducing the dose rates in the range of 20-51%.

The statistical process model is a very quick guide for the plant operators that can indicate any potential plant performance issue relating to raw water quality change, and can continuously suggest the plant operators about the optimum chemical dose for any raw water condition. The developed process model is fully transferrable and can be applied to any WFP.

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