Developing RO Cleaning Strategies based on Minimizing Energy and CIP Costs

This paper documents an economic analysis that was performed to determine the most effective cleaning interval for the RO membrane in the OCWD GWR System. This system consists of 15 individual 5 million gallon per day rated RO units. The purpose of the analysis was to determine the optimum interval of operation between CIP cleanings in a year, based on the energy required to operate each individual train. Most individual trains had calculated optimum cleaning intervals falling into two categories – 5 month intervals and 8 month intervals. This assessment was based on the current condition and rate of fouling for each of the trains. The results of the analysis are dependent on several variables that could change over time. As a consequence, the investigation needs to be repeated if a significant change in the fouling rate is observed. Just prior to performing this analysis, OCWD had been performing cleanings with a frequency of <4 months. From this investigation, the optimum cleaning interval is greater than 5 months, and extending cleaning intervals from <4 months into the range of 5-8 months offers a significant savings to O&M costs for the GWRS system as a whole. As a comparison, implementing this model is anticipated to save the District as much as $250,000 over a quarterly cleaning philosophy. Similarly, the District would save up to $118,000 over a four month cleaning interval.

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