Assessment 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

Evaluating environmental requirements for the management of brine discharges in Spain

“…These include: i-ii) the analysis of the quantity and quality of the effluent and marine environment including, at least, salinity and nutrients but also substances that come from the pre-treatment and cleaning of membranes and filters, as coagulants and antifouling or organic matter [5,10,29,30]; iii) the control of the saline plume to determine the area potentially affected by the brine discharge [9]. For this, it is necessary that the implementation of salinity profiles which reach the bottom are used to determine salinity and temperature in a grid of points that cover the potential area of influence, and with seasonal replication to include different oceanographic conditions [9]; iv) to monitor key and protected species if they are present in the area to ensure they are not affected by the discharge [12,15] [13,14,29,32]; vi) the use of salinity-sensitive species of benthic fauna as bioindicators has proven to be useful as sentinel species in order to prevent possible impacts on benthic habitats [20,33] and to discriminate between the effects of desalination and other impacts that may coincide in space [32,34]; vii) it is necessary to carry out a structural monitoring of the submerged outfall for the early detection of possible fractures [8]; viii) in the case of a possible rupture of the outfall (or if the discharge is close to key habitats), the existence of a protocol of action with mitigation measures is convenient, given that this may include the increase of dilution, or the reduction of production [15].…”

“…Consequently, it may intensify the toxicity of the brine discharge, and it would thus induce a localized eutrophication and turbidity of the sea water [10][11][12]. These characteristics of brine discharges impact upon their dispersion mechanisms, which can in turn affect benthic communities such as seagrasses (Posidonia oceanica and Cymodocea nodosa), or benthic fauna [12][13][14][15][16].…”

Impact of brine on the marine environment and how it can be reduced

“…However, in MED and MSF plants, chlorine can be directly discharged with desalination concentrate, acting as an unwelcome biocide in the marine environment and forming mutagenic compounds such as halogenated organic by-products [3,23,50]. Chlorine is neutralized in RO plants using reducing agents such as sodium bisulfite (SBS: NaHSO3); however, a very high SBS dosage can reduce dissolved oxygen levels in the concentrate discharge [4,51]. Chlorine dioxide is also being used as a substitute for chlorine in RO plants because it acts with a shorter contact time and lower dosage and does not form halogenated compounds.…”

Understanding the role of ecological indicator use in assessing the effects of desalination plants

“…Therefore, the coral ecosystems from destructive desalination projects around the food chain damage specific objects like starfish species proliferation, create the phenomenon of avoidance of marine habitats, and biological-genetic-biochemical-morphology development should be made based on the coral ecosystem indicators species for using ecological indicators. Many desalination plants are disinfected by periodic treatment with sodium metabisulphite, sodium perborate, sodium hydrochloride, and use various chemicals that have potentially toxic effects on marine ecosystem, even though no empirical study or experimental evidence for this is yet available [167]. Also, Portille et al [167], evaluated the abiotic and biotic effects of sodium metabisulphite pulses discharged from desalination plant, physico-chemical variables hypersaline, pH, and DOsat on what might be a potential cause of Cymodocea nodosa and other sea grass characteristics of benthic community.…”

“…Many desalination plants are disinfected by periodic treatment with sodium metabisulphite, sodium perborate, sodium hydrochloride, and use various chemicals that have potentially toxic effects on marine ecosystem, even though no empirical study or experimental evidence for this is yet available [167]. Also, Portille et al [167], evaluated the abiotic and biotic effects of sodium metabisulphite pulses discharged from desalination plant, physico-chemical variables hypersaline, pH, and DOsat on what might be a potential cause of Cymodocea nodosa and other sea grass characteristics of benthic community. Various damages on marine ecosystems have been reported near desalination plants located in the shoreline area.…”