1. Energy consumption and Maintenance

Energy consumption and maintenance are responsible for up to 95% of the running costs of a reverse osmosis plant [1]. Not considered in this are the high building costs of such a plant. Most plants experience severe maintenance problems caused by fouling or breakage of pumps and compressors [1]. As a result most plants run with only 40-80% of their maximum performance and cause increasing water costs due to low productivity [1]. When plants struggle with their productivity production costs for water can rise up to more than 3€/m3 [1]. A water distributor in Aachen, as a comparison, produces its drinking water from surface water with production costs of 0.7€/m3.

2. Desalination

Reverse osmosis guarantees complete purification of water from solvents, making it best suited for seawater desalination. However, water, free from every solvent is not needed for ecological applications. Therefore, important ions and solvents are resolved in the right concentrations after treatment, making reverse osmosis unspecific and the application inefficient. Organisms on the other hand express highly specific transporters, making our Salt Vaults specific for differing ions. In conclusion, resolving of solvents needed for households or agriculture is not needed, making the process significantly more straight-lined.

At the moment it is established to dilute these concentrates with other waste water to lower the salt concentration [2,4]. But there are also problems with chemical burden from agents to enhance flocculation, prevent foaming or to avoid membrane deterioration [7].

When reverse osmotic plants are located inland there is no possibility to pump the concentrate into seawater, making it even more complicated to discharge it [3]. The cost of this process increases the total production costs for inland desalination plants up to 33%, making it an inefficient solution for e.g. industries or municipal sewage treatment plants [8,9]. There are alternative possibilities to discharge the concentrate into the sea but these methods often have low productivity, need high chemical dosages and have high investment costs combined with high energy consumption [3].

References

[1] A. Cipollina, G. Micale, and L. Rizzuti, “A critical assessment of desalination operations in Sicily,” Desalination, vol. 182, 1-3, pp. 1–12, 2005.

[2] G. Mauguin and P. Corsin, “Concentrate and other waste disposals from SWRO plants: Characterization and reduction of their environmental impact,” Desalination, vol. 182, 1-3, pp. 355–364, 2005.

[3] A. Pérez-González, A. M. Urtiaga, R. Ibáñez et al., “State of the art and review on the treatment technologies of water reverse osmosis concentrates,” Water research, vol. 46, no. 2, pp. 267–283, 2012.

[4] D. A. Roberts, E. L. Johnston, and N. A. Knott, “Impacts of desalination plant discharges on the marine environment: A critical review of published studies,” Water research, vol. 44, no. 18, pp. 5117–5128, 2010.

[5] B. Mabrook, “Environmental impact of waste brine disposal of desalination plants, Red Sea, Egypt,” Desalination, vol. 97, 1-3, pp. 453–465, 1994.

[6] R. H. Chesher, “Chapter 6. Biological Impact of a Large-Scale Desalination Plant at Key West, Florida,” in Tropical marine pollution, E. J. F. Wood, Ed., vol. 12, pp. 99–153, Elsevier, Amsterdam, 1975.

[7] G. L. Meerganz von Medeazza, ““Direct” and socially-induced environmental impacts of desalination,” Desalination, vol. 185, 1-3, pp. 57–70, 2005.

[8] M. Ahmed, W. H. Shayya, D. Hoey et al., “Brine disposal from reverse osmosis desalination plants in Oman and the United Arab Emirates,” Desalination, vol. 133, no. 2, pp. 135–147, 2001.

[9] J. M. Arnal, M. Sancho, I. Iborra et al., “Concentration of brines from RO desalination plants by natural evaporation,” Desalination, vol. 182, 1-3, pp. 435–439, 2005.

We conducted measurements of the salt uptake capabilities of different mutants by inoculating a diluted pre-culture in growth medium containing 0.6 M of NaCl. The mutants which showed high ion uptake did not show significant growth. In application, a preculture has to be inoculated separately before desalinization of wastewater, which means another installation for breeding the preculture has to be build. Nevertheless, the yeast is a self- renewing desalination method, which has low maintenance costs. In comparison to the maintenance intensive reverse osmosis, this depicts another advantage.

The relative cell mass over time measured by a growth profiler 960 (EnzyScreen) in 0,6 M NaCl YPDGal.

A specific nutrition-plan is important to check if by-products of industrial processes could be reused or external sugar must be bought from food industry. The cooperation with Sitech has shown that industrial wastewater treatment plants buy cheap sugar from food industry to feed their bacterial mix and do not assume it to be a big cost factor. (Link: NL) Use of a C-source which is by-product of a corresponding industrial process is an optimal solution to confirm the general trend of industries towards a recycling economy.

Most wastewater treatment plants, like the one in Aachen (Link: IHP sewage treatment plant), have traces of heavy metals in their fouling sludge, therefore the sludge is burned after fouling. Industrial plants, like the one at the Chemelot Industrial Site in the Netherlands (Link: sewage treatment plant) burn the sludge directly without fouling, telling us that burning is a well-established method to handle the cells after water treatment. Burning of Salt Vaults leaves behind dry Salt. This salt, like heavy metals, has to be stored permanently after burning. Depending on the purity of the salt, it could be re-used for industrial processes. An example is chloride chemistry, where chloride is needed as a central molecule.