(234u) Innovative Water Treatment Process Based on Electrochemical Oxidation for the Regeneration and Reuse of Water in Marine Recirculating Aquaculture Systems: Eloxiras

World aquaculture accounted for 90.4 million tonnes (Mt) of aquatic products in 2012, compared to 92.5 Mt reached by fishing [1, 2]. Considering the 24 Mt of fishing that will not be intended for human consumption, aquaculture is already the highest provider of food to worldwide population. Aquaculture keeps a significant growth rate that has increased by 8.9% in 2012. Asia is the largest aquaculture producer region, accounting over 88% of total production, followed by America (4.78%) and Europe (4.32%). According to FAO [3], world aquaculture production reached a market value of US$144.4 billion. Most of this aquaculture species are farmed in open-circuits, but entailing a lower process efficiency. The production trends are shifting to closed loop circuits to foster the productivity.

The economic feasibility of inland hatchery aquaculture activities requires high biomass culture densities (kg species/m³ of water) obtained by means of the so called Recirculating Aquaculture Systems (RAS), in which water leaving the systems is recirculated after adequate treatment. Conventional treatments systems (mainly based on biofilters) are not able to provide satisfactory removal of highly concerned pollutants in RAS (ammonia, nitrite, organic matter, bacteria and viruses, etc.). This implies fast accumulation of toxic metabolized compounds in low water volumes, issue that requires large volumes of fresh water intake to avoid lethal concentrations, and the subsequent discharge of important wastewater volumes. In order to minimize the environmental impact and fulfil with law regulations, continuous efforts addressed to develop new water treatment technologies aimed to permit significant water reclamation and reuse with minimal cost.

Based on Electrochemical Oxidation Technology, and advanced oxidation process (AOP) this paper presents an innovative water treatment concept specially developed to improve the productivity and environmental impact of marine recirculating aquaculture systems (RAS) used by the exponentially growing aquaculture industry, ELOXIRAS [4]. The process allows the efficient destruction of all the highly concerned pollutants in RAS (ammonia, nitrite, organic matter, bacteria and viruses, etc.) without the addition of chemicals and with no change in water composition. It only requires electricity and the catalytic properties of the electrode materials to achieve water purification.

Removal efficacies up to 99% were validated at pilot plant scale that consisted in a 1 m³ fish tank and a 170 cm² electrochemical reactor based on DSA electrodes. Post-electrochemical treatment were carried out in an activated carbon column. As an illustrated case study, the experimental conditions included 4.8 kg of gilthead bream fingerlings (3g each), a recirculating flow of 600 L h^-1, salinity of 33 g l^-1, inlet temperature of 24 ºC and initial pH of 7.4. Evolution of total ammonia nitrogen over time was kept in the range of 0-1 mg L^-1 with variable current densities in the range of 150-450 A m^-2 adjusted as a function of the hourly variable pollution rate from the fish metabolism. Similar behaviour was found for nitrites with values in the range of 0-0.2 mg L^-1. pH was kept in optimal values around 7 and electrolyte composition of the sea water was unaltered. 100% of fish survival was found after 72 h, proving nontoxic effects on the fish farmed.

ELOXIRAS introduces a new advanced marine RAS water quality control and purification system that overcomes the main limitations of the current conventional technologies (bio-filter technologies as main competitor in the market) such as: i) significant water uptake requirements; ii) limited efficacy in contaminant removal; iii) restricted culture density.

The novelty of ELOXIRAS system is the ability to increase the production of different marine species: 1) Allowing higher cultured densities within the purification controlled limits (30% more production); 2) Reducing up to 20% the new water intake consumption (and thus, proportional wastewater generation); 3) Eliminating almost completely the key pollutants (>90%), and 4) Increasing by a minimum of 30% the estimated potential benefit (â?¬/year) of the overall process.

The next innovative characteristics provide the key points for the market application of ELOXIRAS: a) High efficacy and removal of the targeted pollutants, including bacteria and virus; b) Compact and modular design; c) Low energy requirements; d) Easy to operate with adaptable capacity to required productivity. The following market applications with competitive edge have been developed based in this technology:

ELOXIRAS HYBRID focuses on new or existing large RAS facilities, offering an increment of common or actual productivity with lower water and energy use.

ELOXIRAS MINI focuses on small scale RAS facilities for final commercialization of adult aquaculture species, offering compactness and adaptable treatment capacity.

ELOXIRAS LOGISTIC focuses on typical truck or well boat transport operations from hatcheries to growing facilities, offering extended range of distances and bigger biomass capacity due to the compactness design of ELOXIRAS water treatment system that allows its installation in the trucks.

ELOXIRAS BIO focuses on quarantine and bio-security facilities of any RAS scale, offering control of pathogens (bacteria and viruses) due to the disinfection capabilities and contributing to high isolation levels.

 

Acknowledgements

This project has received funding from the European Unionâ??s Horizon 2020 research and innovation programme under grant agreement No 698494. This contribution reflects only the author's view and that the Agency is not responsible for any use that may be made of the information it contains.

REFERENCES

[1] Food and Agriculture Organization of the United Nations, Statistics Division, 2016. http://faostat3.fao.org/, last accessed 6-5-2016.

[2] European Comission, Eurostat, 2016. ec.europa.eu/eurostat/, last accessed 6-5-2016.

[3] FAO, 2014.The State of World Fisheries and Aquaculture. Opportunities and Challenges. ISBN 978-92-5-108275-1; Rome.

[4] ELOXIRAS, 2016. http://www.eloxiras.com/, last accessed 6-5-2016.