Inhibition of phosphorus release from sediments of Lake Erhai through argon oxygen decarburisation slag (AOD) and electric arc furnace slag (EAF) capping.

Abstract: The effects of eutrophication in lakes and the open seas has been largely the result of phosphorus (P) that accumulate in the sediment. Eutrophication occurs mainly in the waters in densely populated coastal areas and agricultural dominated areas and occurs when an excess of nutrients reach the soil and water. In situ capping is a proven method to inhibit P and is the method used in this study. A capping is placed on the polluted sediment surface to physically isolate it and reduce the release of P and prevent resuspension, i.e. suspension of already precipitated P. The possibility of inhibiting P by using sediment capping and the reactive filter materials (sorbents) argon oxygen decarburisation (AOD) slag in particle size fractions 0-0.5 mm and 2-8 mm and electric arc furnace (EAF) slag in particle size fraction 1-2.36 mm, have been investigated. Soluble reactive phosphorus (SRP), also called orthophosphates, were the main species of P investigated in this study. A total of three studies were conducted in Lake Erhai in Dali China, during April 2016. One pre-study was conducted at ten different sites in the lake, which aimed to find the most P polluted site. This site was chosen for the main study. The main study aimed to investigate if the aforementioned sorbents managed to absorb  orthophosphates after contact with lake sediment for seven days. The post-study was conducted to see if the sorbents themselves released any orthophosphates into the water. The water samples were tested for pH, conductivity and dissolved oxygen (DO) before and after contact with lake sediment. The slag materials and lake sediment were studied with inductively coupled plasma (ICP) spectroscopy and X-ray diffraction (XRD) to detect elements and compounds. Obtained results showed that the AOD slag (0-0.5 mm) could absorb 96% of the orthophosphates. However, both the AOD slag (2-8 mm) and EAF slag (1-2.36 mm) showed an increase of orthophosphates in the water after contact with lake sediment. The XRD analysis showed contents of silica (Si) and calcium (Ca) compounds in all of the slag materials, which was expected due to the configuration of these materials. The ICP analysis showed that 2% P was absorbed by the EAF (1-2.36 mm) slag, but there were no absorption by the AOD (0-0.5 mm) or AOD (2-8 mm) slag. The conclusion from this study is that AOD slag (0-0.5 mm) can be used successfully in P remediation projects because it absorbs 96% of the orthophosphates. The results are consistent with previous results from (Zuo et al., 2015) and (Renman et al., 2013).