Seawater desalination is increasingly being used as a means to augment freshwater supplies in regions with high water stress, and reverse osmosis is increasingly the technology of choice because of the low energy consumption. 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.
This research developed a new method to measure bacterial growth potential (BGP) using the native bacterial consortium in seawater. New reagents to extract and detect ATP in microbial cells were specifically developed for seawater. The new lysis and detection reagents overcame the salt interference in seawater and allow low detection of total ATP, free ATP and microbial ATP in seawater. Incorporating a filtration step further increased the sensitivity of the method six fold, enabling ATP detection of ultra-low levels of microbial ATP in seawater.
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. A good correlation was observed between BGP measured in SWRO feed water and the pressure drop increase in the SWRO systems, suggesting the applicability of using the ATP-based BGP method as a biofouling indicator in SWRO. Furthermore, a safe level of BGP (<70 µg/L) is proposed for SWRO feed water in order to ensure a chemical cleaning frequency of once/year or lower. However, to validate this conclusion, more SWRO plants with different pre-treatment systems need to be monitored.
In the future, on-line monitoring of 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.
1 General introduction, 2 Direct measurement of ATP in seawater and application of ATP to monitor bacterial growth potential in SWRO pre-treatment systems, 3 ATP measurement in seawater reverse osmosis systems: elimination seawater matrix effects using a filtration-based method, 4 Assessing pretreatment and seawater reverse osmosis performance using an ATP-based bacterial growth potential method, 5 Correlating bacterial growth potential measurement to fouling development in full-scale SWRO, 6 Fouling removal in seawater media filtration used as pre-treatment of a full scale SWRO desalination plant, 7 General conclusions and future perspective.
IHE Delft PhD programme leads to a deepening of a field of specialisation. PhD fellows do scientific research, often with conclusions that directly influence their region. At IHE Delft, PhD researchers from around the world participate in problem-focused and solution-oriented research on development issues, resulting in an inspiring research environment. PhD fellows work together with other researchers from many countries dealing with topics related to water and the environment.
PhD research is often carried out in the ‘sandwich’ model. Preparation and final reporting – the first and last portion of the programme – are carried out in Delft, while actual research is done in the fellow’s home country, under co-supervision of a local institute. Regular contacts with the promotor are maintained through visits and long-distance communication. This enables researchers to employ solutions directly to problems in their geographical region.
IHE Delft PhD degrees are awarded jointly with a university. The degrees are highly valued and fully recognised in all parts of the world.