Assesment of the abiotic and biotic effects of sodium metabisulphite pulses discharged from desalination plant chemical treatments on seagrass (Cymodocea nodosa) habitats in the Canary Islands

Reverse osmosis membranes at many desalination plants are disinfected by periodic shock treatments with sodium metabisulphite, which have potentially toxic effects to the environment for marine life, although no empirical and experimental evidence for this is yet available. The aim of this study was to characterise for the first time, the physico-chemical modification of the marine environment and its biological effects, caused by hypersaline plumes during these membrane cleaning treatments. The case study was the Maspalomas II desalination plant, located in the south of Gran Canaria (Canary Islands, Spain). Toxicity bioassays were performed on marine species characteristic for the infralittoral soft bottoms influenced by the brine plume (Synodus synodus and Cymodocea nodosa), and revealed a high sensitivity to short-term exposure to low sodium metabisulphite concentrations. The corrective measure of incorporating a diffusion system with Venturi Eductors reduced nearly all the areas of influence, virtually eliminating the impact of the disinfectant.

This study was conducted as part of the Project “Technical feasibility study of Venturi Diffusers in desalination plant brine discharges to enhance the dilution process and reduce the environmental impact on marine ecosystems”, under the National Programme for Experimental Development Projects, within the Ministry of the Environment and Rural and Marine Affairs, Environment and Eco-Innovation Sector, Management and Sustainable Uses of Natural Resources Subsection. The authors would like to thank Canaragua-Aqualogy, Elmasa Tecnologia del Agua, CEDEX and ECOS for their support and assistance, A. Arencibia and F. Roch, from General Electrics, and J. McGrath for translation of the manuscript. This research was also funded by other two Projects granted by the Ministry of the Environment and Rural and Marine Affairs (OSMOGRASS Project no. 021/SGTB/2007/1.3) and the Science National Plan of the Ministry of Science and Innovation (OSMOGRASS II Project no. CTM2009-08413MAR) to J.M. Ruiz of the Spanish Oceanography Institute.

Peer reviewed