Eutrophication in coastal New Zealand lakes and the mitigation potential of phosphorus immobilization using clay based amendments

Abstract

Water amendments were analysed in-vitro to identify their potential for phosphate sequestration in coastal lakes and water bodies, in an effort to reduce their phosphorus levels. The potential amendments were identified: Allophane, BauxsolTM (re-purposed from aluminium processing) and PhoslockTM (lanthanum treated Bentonite), along with several other clays such as Kaolinite, Bentonite, and Illite as a comparison. Each Amendment was placed in a solution of phosphate, agitated, then left to settle over 24 hours. The remaining phosphate in the solution was measured with a UV spectrometer (880nm, ascorbic acid analysis). The results showed that the common clays (kaolinite, Bentonite, illite) had very low adsorbance potential, with an average of 6.15ppm of phosphate adsorbed out of a total of 50ppm, PhoslockTM adsorbed 33.7ppm while allophane and BauxsolTM adsorbed 11ppm out of 50 ppm. The adsorption experiment was then repeated at variable pHs’. The experiment showed that PhoslockTM was the most effective at adsorbing phosphorus, and has an adsorption coefficient two orders of magnitude above the common clays, and has great potential for use in the lake. Allophane and BauxsolTM also show promise, however at higher pHs’ their adsorption capability was hindered. Further experiments will need to focus on a final evaluation of PhoslockTM’s effectiveness in reducing Phosphorus levels in the lake.