Abstract

Seawater desalination is increasingly used as a means to augment freshwater supplies in regions of the world with high water stress, and reverse osmosis is increasingly the technology of choice because of the lower energy consumption compared to thermal systems. However, seawater reverse osmosis (SWRO) systems suffer from various types of fouling, which can increase energy consumption and the use of chemicals during SWRO operation. In practice, pre-treatment systems are put in place to reduce the particulate and biological fouling potential of SWRO feed water. However, simple, reliable and accurate methods to assess the extent to which biological fouling potential is reduced during pre-treatment are not available for seawater.

A method to measure bacterial growth potential (BGP) was developed using the native bacterial consortium in seawater. New reagents to extract and detect ATP in microbial cells were tested and optimized for seawater. The new lysis and detection reagents overcame the salt interference in seawater and allowed the detection of low concentrations of total ATP, free ATP and microbial ATP in seawater. Incorporating a filtration step increased the sensitivity of the method six fold, enabling ATP detection of ultra-low levels of microbial ATP in seawater (0.06 ng-ATP/L).

The newly developed ATP-based BGP method was applied to monitor and assess the pre-treatment of five full-scale seawater desalination plants around the world, which included dual media filtration, dissolved air flotation and ultrafiltration. A correlation was observed between BGP measured in SWRO feed water and the pressure drop increase in SWRO systems, suggesting the applicability of using the ATP-based BGP method as a biofouling indicator in SWRO. Furthermore, a safe level of Bacterial Growth Potential (<70 µg/L) is tentatively proposed for SWRO feed water in order to ensure a chemical cleaning frequency of once/year or lower. However, to validate these conclusions, more SWRO plants with different pre-treatment systems need to be monitored. In the future, on-line monitoring of ATP and BGP in SWRO feed water may further reduce the consumption of chemicals and energy and improve the overall sustainability of seawater desalination by reverse osmosis.

About Prof Maria Kennedy

Maria Kennedy is Professor of Water Treatment Technology at IHE Delft. She has over 28 years of experience in education, research, consulting and capacity development in water treatment. During the last 28 years, she has been involved in the supervision of over 200 MSc participants and 22 PhD research fellows in the areas of water quality, groundwater treatment, disinfection, advanced oxidation, surface water treatment, desalination and membrane related technology, natural treatment systems, water reuse, water transport and distribution and biological stability. She has over 150 publications in peer reviewed journals, and she has edited several books/book chapters on various aspects of water treatment.

Professor Maria Kennedy has organized numerous international short courses in the field of desalination & membrane related technology e.g. in Jordan, Palestine, Oman, Bahrain, Israel, St. Maarten, Iran, Yemen, South Africa and Korea. She is or has been the director of several (large) capacity development projects in the Middle East region e.g. in Jordan, Palestine, Yemen and Iran. She was also involved in several large EU/Horizon 2020 research projects such as EU MEDINA, EU TECHNEAU, EUROMBRA, H2020 MIDES and EU India H20.