Effect of combined iron and calcium treatment on phosphorus release from sediments

Abstract Iron (Fe) and calcium (Ca) are two commonly used sediment phosphorus (P) inactivators. However, both have limitations when used alone, and few studies have investigated the effectiveness of their combined use. In this study, two sediments with different nutrient levels (high-nutrient sediment, HS, and low-nutrient sediment, LS) were selected to study the effects of adding ferric chloride alone (Fe treatment), calcium hydroxide alone (Ca treatment), and their combined addition (Fe&Ca treatment) on the P release flux and P fractions in the sediments. The results showed that Fe treatment significantly inhibited P release from HS and LS, and their P fluxes at the end of the experiment were −0.137 mg·m −2 ·d −1 and −0.135 mg·m −2 ·d −1 , respectively. In terms of P removal and fluxes, the efficacy of Fe&Ca treatment was comparable to that of Fe treatment alone. However, Fe&Ca treatment exhibited superior inhibitory effects on total nitrogen and ammonia nitrogen compared to Fe treatment alone. In addition, the Fe&Ca and Ca treatments significantly increased the sediment apatite P content and decreased the non-apatite inorganic P content, whereas the Fe treatment significantly decreased the apatite P content. The inhibitory effects of Fe&Ca on P in both sediments were greater than that of Ca alone, and there was no significant difference between the Fe&Ca and Fe treatments. This study showed that the combined treatment of Fe and Ca can effectively make up for the deficiencies of the single treatment method, demonstrating significant synergistic effects, thus providing a practical and efficient method for in situ control of the release of nutrients in lake sediments.