9) Think big, spend less: upscaling challenges in desalination technologies

This session focuses on current upscaling challenges in desalination, ranging from laboratory to industrial-scale application. We will discuss theoretical approaches and experimental studies to reduce energy consumption and increase process performance, both for novel and for convential desalination technologies.


Mauro Capocelli, University Campus Bio-Medico di Roma:

Rural and remote areas are disadvantaged because located far away from supply systems and often not connected to the power grid. The demand of reliable and autonomously operating systems for desalination and water reuse is increasing and a large number of small-medium systems are needed (in villages, settlements as well as in urbanized areas where the water source is polluted). There is no doubt that mega-projects of RO desalination are approaching the thermodynamic limit of an ideal solute-solvent separation process. On the other hand, decentralized solutions coupled with renewable sources are very far from the process optimization. In this work, the renewable desalination processes are studied in the particular framework of renewable powered / stand-alone plants focusing on the relation between the scale and the efficiency. Moreover, with tha aim of security and water independence of the territory, a novel process, based on the humidification and dehumidification of air (with very low carbon footprint, reduced environmental impact, low operating and maintenance costs) is presented, together with the preliminary results from the sensitivity analysis.

Bastiaan Blankert, King Abdullah University of Science and Technology:
The family of osmotic membrane processes consists of: reverse osmosis (RO), dialysis (D), pressure retarded osmosis (PRO), forward osmosis (FO) and pressure assisted forward osmosis (PAFO). These processes are fundamentally the same; a suitable system may operate in any of these modes by choosing an appropriate value of the applied pressure. Although these processes greatly differ in their (potential) applications and their technological maturity, they all should serve some economic purpose, which benefits from: energy efficiency, utilization of the membrane area and rejection. There is some trade-off between these objectives and a specific application is defined by their relative importance.
By modeling and optimizing such a system, we can explore which operating settings and membrane types are optimal given a certain application. The corresponding operating mode is inferred from the result. When rejection for only a single component is considered, there are only 4 operating regions: RO, PRO, mixing and isolation; in the latter two a membrane process is not economically feasible. The other processes (D, FO, PAFO) can only find an application in much more specific situations, where multiple components are important.

Huub Rijnaarts, Wageningen University and Research:
In three water technology domains, the importance of a thorough understanding of colloid-polymer mechanisms for technology upscaling is demonstrated. I) Packed bed filtration is a treatment technology to remove colloids such as iron and phosphate particles, and bacteria and viruses from water. Particle retention is controlled by interactions between particles and filter-bed materials, where electrostatic and polymeric repulsions and attractions interfere and depend strongly on the salinity of the water. II) In injection water at oil and gas fields, long-chain charged polymers are added to enhance the product recovery. For their effective use in up scaled application, retention of polymers in Electro-Dialysis desalination units should be avoided, and recovery of viscosity activity is key. III) In biological water treatment systems, polymers a) can capsulate microorganisms into biogranules and can form an osmo-protective firewall against very high salinities, b) can be produced and recovered as flocculants for further use in waste water treatment, and c) can form bio-membranes to enhance particle capture, and after up scaled in-reactor application, enhance organic removal of waste water treating bioreactors.

Gijs Doornbusch, Wetsus & Eindhoven University:
Electrodialysis (ED) is currently used for brackish water desalination and selective removal of ions. For seawater desalination, however, ED is not considered on large scale. In order to investigate the potential of ED for seawater desalination and upscaling, it is needed to optimize stack design and operational parameters to lower energy consumption. In this work, we compared single-stage ED, to a multistage ED in order to investigate design and operational parameters on desalination performance and energy consumption. The multistage ED was comprised of four desalination stages. Using a fixed intermembrane distance, different operational settings in terms of current density and feed flow velocity were tested, to get insight of the salt and water fluxes in a continuous multistage electrodialysis process. In addition, the limiting current density was determined in a four-stage electrodialysis system per stage, and the maximum desalination degree was assessed. We were able to get some distinctive design rules for ED applied for seawater desalination compared to conventional ED applied for brackish water desalination.


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