Aquatic macrophytes Azolla and Salvinia as biofilters for surfactant decontamination (2014)

The wide range of domestic and industrial applications of surfactants can arise ecological problems when these molecules are present in the aquatic environment in relatively high concentration, exhibiting toxic effects and affecting at different levels the ecosystems. Conventional wastewater treatment plants are not always perfectly designed to remove these contaminants, thus many of them can occur at different concentrations in surface waters and soils. In previous works two species of floating macrophytes, Azolla filiculoides Lam. and Lemna minor L., have been exploited for phytoremediation of sodium dodecyl sulphate (SDS), a commercially important anionic surfactant , that is the core component of several detergent and cosmetic product formulations, contributing significantly to the pollution profile of sewage and wastewater of all kinds. The uptake rates of SDS by duckweed and water velvet showed a potential and remarkably efficient phytoremediation system (Forni et al., 2008). Besides the use of living plants, dried macrophyte biomasses can be used to biosorption of pollutants like a wide range of heavy metals, as demonstrated by Tel-Or and coworkers (Cohen-Shoel et al., 2002; Tel-Or and Forni, 2011 and references therein); this biosorption procedure offers a different approach for reclame of metals from mining waste and industrial discharges. The aim of this work was to verify the applicability of this technology for SDS removal from polluted water in order to offer a possible alternative solution to the use of wetlands and to the burning problem of our industrial society, i.e. to reduce water consumption trying to recycle waste water. For this purpose, biomasses of Azolla filiculoides Lam. and Salvinia natans (L.) All. were dried in oven (70-80° C for 48 hrs) or in the sun and stored at room temperatures until use. 100 grams of mildly crushed dried biomass were rewetted in 500 ml distilled water for 1 hr, and packed in the column (Biorad), according to the procedure of Cohen- Shoel et al. (2002). Solutions, containing 40 ppm SDS were passed through the dried biomass by idrostatic pressure at a flow rate of 5 to 10 mL min−1. The effluent was collected in 250 mL fractions. pH effect on SDS biosorption was tested at pH 2, 7 and 10. The pH of the solution was adjusted by addition of HCl or NaOH. Before starting the filtration, each biofilter was rinsed with double distilled water (DDW) at the same pH of the experiments. The amount of SDS in the eluates was determined according to Forni et al. (2008). The different pH of SDS solution influenced the binding ability of the biofilters, which biosorption rates enhanced along with the increase in pH, being higher at pH 7 than at pH 2. The binding of SDS to insoluble constituents in the fern matrix most probably involves cell wall charged groups, therefore low pH influenced the binding of the anionic surfactant probably because of the negative charged groups of the cell walls. In fact, the dry biomass of both ferns contains very little cellulose and higher amount of pectins, a major component in Azolla (5-7%), and lignin (Cohen-Shoel et al., 2002). These molecules together with polyphenols and phytates may play a role in biosorption. Good binding performances were obtained at pH 7 and 10. Azolla biofilter was better than Salvinia, in some cases 90 -100 % of SDS removal could be obtained. A good rate of the binding already occurred in the first fractions, suggesting that the initial rinsing with DDW at different pH was necessary to adjust the charges of binding groups and a progressive saturation of the binding sites. References Cohen-Shoel N., Ilzycer D., Gilath I. and Tel-Or E. (2002). The involvement of pectin in Sr2+ biosorption by Azolla. Water, Air, and Soil Pollution 135: 195–205 Forni C., Giordani F., Pintore M. and Campanella L. (2008). Effects of Sodium Dodecyl Sulphate on the aquatic macrophytes Azolla and Lemna. Plant Biosystems 142/3: 665-668. Tel-Or E. and Forni C. (2011). Phytoremediation of hazardous toxic metals and organics by photosynthetic aquatic systems. Plant Biosystems 145 (1): 224-235.