CARPET APPLICATION IN PHOSPHATE REMOVAL AND RECOVERY AS A POLYMERIC LIGAND EXCHANGER

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Abstract

Recycling carpets and phosphorous removal and recovery from water, are two current key environmental concerns. Firstly, the carpets are poorly biodegradable and therefore, they decay slowly to produce little landfill gas (LFG) to generate electricity. However, 500,000 tonnes per year are still sent to landfills. Secondly, phosphorous in water bodies is a major cause of eutrophication with main long term consequence of the depletion of O2, causing therefore a decrease in the amount of aquatic species. For example, in 2008 51 % of the rivers in England were considered to have high phosphate concentration by the Environmental Agency. In this paper, the wool fibres from the carpets adsorb the phosphates by an ion exchange principle. Carpets are formed by amino acids, where many side chains are polar and ionizable, leading to a potential performance as a polymeric ligand exchanger. To increase the efficiency and the affinity towards the anions present in water, different methods namely loading of copper ions or hydrated ferric oxide (HFO) nanoparticles have been studied for carpets. Among the methods tried, the HFO nanoparticles loaded by oxidation of iron (II) sulphate is the one that shows the best phosphate sorption. Moreover it potentially allows the subsequent phosphate recovery by struvite precipitation, which is also one of the key points of the study as the price of phosphorus containing fertilizers is increasing, and also enables the possibility of further reuse of the modified carpets. As the exterior layer of the cuticle’s fibre, i.e. the epicuticle, is formed mainly of fatty acids bound to the protein matrix, it makes the fibre much less ionizable. It was successfully shown that this layer is able to be removed by an alkaline oxidation to greatly enhance the performance as a polymeric ligand exchanger. Recently results show such treatment also greatly improves the binding of HFO to the carpet fibres, and therefore the binding of phosphates from solution.

Aims and Objectives

Headline Findings