Efficiency of Salicornia neei to treat aquaculture effluent from a hypersaline and artificial wetland

In this study we evaluated the potential of Salicornia neei, a halophyte plant native to South America, to treat saline effluents with simulated concentration of ammonium-N (Amm) and nitrate-N (Nit) similar to land-based marine aquaculture effluents. Plants were cultivated for 74 days in drainage lysimeters under three treatments of seawater fertilized with: 1) Nit+Amm, 2) Nit, or 3) without fertilizer (Control). Over 5 repetitions, nitrogen removal efficiency (RE) was high in both treatments (Nit + Amm = 89.6± 1,0 %; Nit 88.8 ± 0.9 %). While nitrogen removal rate (RR) was non linear and concentration-dependent (RRday 1-4: Nit+Amm= 2.9 ± 0.3 mg L−1 d−1, Nit = 2.4 ± 0.5mg L−1 d−1; RRday5-8: Nit + Amm = 0.8 ± 0.2mg L−1 d−1, Nit=1.0 ± 0.2mg L−1 d−1). Effluent salinity increased from 40.6 to 49.4 g L−1 during the experiment, with no observed detrimental effects on RE or RR. High nitrogen removal efficiency and significant biomass production observed, Nit+Amm = 11.3 ± 2.0 kg m−2; Nit = 10.0 ± 0.8 kg m−2; Control = 4.6 ± 0.6 kg m−2, demonstrate that artificial wetlands of S. neei can be used for wastewater treatment in saline aquaculture in South America.


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Aquaculture provides nearly 50% of the world's fish production, and it is expected to increase to 60% by 23 2030 due to the growing demand for marine fishery products [1]. Land-based marine aquaculture systems will 24 play an important role in meeting this demand and will also do so in a more environmentally sustainable way 25 regarding marine aquaculture in the ocean [2, 3]. However, the development of marine recirculating aquaculture 26 systems (RAS) is limited by the ability to efficiently treat saline wastewater, which accumulates a large amount 27 of nitrogen compounds derived from the metabolism of culture organisms [3][4][5]. In these RAS, the removal of 28 nitrogen compounds, mainly ammonium (NH 4 + ) and ammonia (NH 3 -), becomes a priority for elimination 29 because they quickly deteriorate the water quality and cause negative effects on the culture [6,7]. Biofilters that 30 promote the conversion of ionized and deionized ammonium to nitrate (NO 3 -) are usually used for this purpose 31 [8,9]. NO 3 is not very toxic to most cultured organisms [10,11], with tolerable accumulated concentrations 32 reported between 120 mg L -1 of NO 3 and 150 mg L -1 of NO 3 in marine RASs [12].

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Recent developments of integrated systems allow the use of RAS waste products as nutrients, coupling 34 different water loops with the main fish production water system [13].

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The physico-chemical parameters of water quality were recorded directly from the drainage water during 96 the first eight consecutive days after nutrient addition.  Nitrate-N removal was non linear and concentration-dependent for treatments Nit + Ammand Nit ( Figure   155 4). Thus, Nitrate-N removal rates (RR) were reducing when reducing nitrogen loading from 2.9 ± 0.3 mg L -1 d -1 156 (RR day 1-4 ) to 0.8 ± 0.2mg L -1 d -1 (RR day5-8 ) in the treatment Nit +Amm, and from 2.4 ± 0.5 mg L -1 d -1 (RR day 1-4 ) 157 to 1.0 ± 0.2mg L -1 d -1 (RR day5-8 ) in the treatment Nit (Table 2). On the other hand, Nitrate-N removal rates 158 measured between days 1 to 4 (RR day 1-4 ) had a clear tendency to increase as biomass production increased at the 159 treatment Nit but not in the treatment Nit + Amm (Table 2), which is perhaps explained by the greater 160 availability of nitrogen in this last treatment. Without considering these differences in both treatments, the 161 nitrogen removal efficiency was high in each treatment, in and throughout the crop, and varied between 87% 162 and 92% (Table 2)

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The integration of halophytes as a biofilter in recirculating systems in marine aquaculture has been 178 proposed as an adequate alternative to decontaminating waters with increased nitrogen compounds [34].

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Physicochemical parameters of the effluent, such as temperature and pH are especially important in the 186 treatment of saline wastewater because they can affect the determinant processes in the removal of nitrogen 187 compounds [36]. In this study, temperature and pH were maintained within the optimal ranges (20-21 °C and 188 7.8-8.2) and therefore did not affect the nutrient removal processes (