Oleaginous plant seeds and seed by-products for water treatment

The treatment of water is needed for the supply of adequate quantity and quality of drinking water, as well as before the discharge of wastewater to the environment. Treatment technologies are often costly, involve chemicals that may have detrimental effects to health and the environment, or may not be available locally. Consequently, there is a need to find sustainable alternative technologies, adapted for small-scale water treatment units and for developing countries. Oleaginous plant seeds represent a renewable resource available world-wide, basically grown for oil-production, but which has been identified for potential applications in water treatment, such as in the extraction of flocculating proteins (moringa seeds) or for metal biosorption. This thesis consists of a systematic study to investigate the various possible applications of oleaginous seeds and seed by-products for water treatment, with rapeseed (Brassica napus) used as model species. Three main by-products of oilseeds were studied: (i) oil-bodies (OB), the organelles of oil storage in plant seeds, which consist of oil core microcapsules (≈ 1 μm diameter) surrounded by a lipoproteinaceous membrane, (ii) press-cake (PC), the solid residue resulting after seed pressing for oil extraction, composed of fibres, proteins, membrane lipids and residual oil, and (iii) seed husks. OB were shown to have flocculation activity for clay suspensions, comparable to that of the moringa proteinaceous extract1. The flocculation activity of these natural microspheres results from the presence of specific proteins (oleosins) at the surface. Ionic bridging, between oleosins and groups at the surface of clays, is postulated to be the mechanism involved in the flocculation activity. Thus oil-bodies appear as possible candidates for the flocculation of silica or clay laden water (Chapters 1 and 2). Furthermore it was demonstrated that OB and PC constitute novel types of biosorbents for hydrophobic organic pollutants (HOP) based on a liquid-liquid extraction mechanism. Atrazine, which was employed as a model compound for HOP, was shown to partition from an aqueous phase to the oil reservoir of the OB, respectively to the residual oil trapped in the PC matrix. This sorption mechanism (absorption) is in contrast to that for other biosorbents which is generally based on adsorption, and makes PC and OB particularly suited for the treatment of highly laden effluents and hydrophobic compounds (Chapters 3 and 5). Both in the case of OB and PC, the degradation of the sorbed compounds is foreseen by burning of the sorbent material. However, the feasibility of using oil core microcapsules saturated with a HOP for performing two-phase biodegradation was also demonstrated (Chapter 4). The capsules were suspended in a HOP degrading bacterial culture, where the HOP diffused into the aqueous phase and was degraded by the bacteria, leading to further release of the compound into the aqueous phase according to equilibrium partitioning. Thus the concentration in the aqueous phase remains low (below toxicity), but the global concentration in the system, including organic phase, is high, hence greatly reducing the aqueous volume to be biologically treated. Besides the possibility of using PC as biosorbent in a batch system, the feasibility of running sorption experiments in a semi-continuous way was discussed using columns packed with PC (Chapters 6 and 7). Finally the sorption of metal ions on PC was investigated, using copper as a model metal species. The husks of the seeds present as residues in the PC show very interesting sorption properties with complex adsorption mechanisms involving chemisorption and ion exchange (Chapter 7). The results of this thesis demonstrate that oleaginous seed materials exhibit versatile properties for developing novel and sustainable water treatment technologies. ------------------------------ 1Doerries, C (2005). Coagulants of Moringa oleifera Lam. Seeds Purification and Characterisation. Thèse N°3251. LGCB. Faculté des Sciences de Base. Lausanne, EPFL.