Phosphate recovery from wastewater with magnetic particles and enrichment of the reclaimed solution as a source for struvite precipitation

Abstract

In this study phosphate was recovered from different wastewaters (WW) by using magnetic particles modified with layered double hydroxides (LDH). Afterwards, the enriched reclaimed solution was used for the precipitation of struvite. Adsorption and desorption cycles were performed in four types of raw wastewaters (LFKW (10 L), MBA, DSLF and UASB) by using the LDH-composite particles. After the different enriched reclaimed solutions were obtained, struvite precipitation kinetics were performed in order to find the optimum parameters of pH value and molar ratio of NH4+:Mg+2:PO4-3, for further struvite precipitation. From the complete adsorption/desorption cycles, it was found that the LFKW (10 L) wastewater had the best adsorption total efficiency (96.6 %) and from this 85.4 % was desorbed, whereas the DSLF showed the lowest adsorption total efficiency (75.4 %) and from this 53.4 % was desorbed. In addition, it was found that the carbonate presence in the DSLF wastewater had a significant contribution to the low yield. Regarding the struvite precipitation kinetics and struvite precipitation measurements in synthetic WW and in the different reclaimed solutions, working at pH 8.5 revealed high phosphate uptakes in the kinetic reactions, regardless of the molar ratio of Mg+2:NH4+:PO4-3. It was observed that at higher Mg+2:NH4+:PO4-3 molar ratio higher phosphate precipitation occurs, regardless the matrix type. Moreover, the color of the enriched reclaimed solutions revealed the color of the resulting struvite solid products, which can be attributed to the presence of the contaminants. Additionally, the experimental Mg+2:NH4+:PO4-3 molar ratios of the actual struvite precipitation were calculated and they were lower than the theoretical.