Combined use of calcium nitrate, zeolite, and anion exchange resin for controlling phosphorus and nitrogen release from sediment and for overcoming disadvantage of calcium nitrate addition technology.

Ca(NO3)2 addition has proved to have a high potential to immobilize internal phosphorus (P) in sediments; however, it cannot effectively stop the release of ammonium-nitrogen (NH4+-N) from sediments into overlying waters (OL-waters). Additionally, the addition of Ca(NO3)2 alone has high risk of nitrate-nitrogen (NO3--N) releasing into OL-waters. To overcome the shortcoming of the Ca(NO3)2 addition method, we reported an integrated method, i.e., a combined method based on Ca(NO3)2 injection, zeolite capping, and anion exchange resin (AERN)-contained floating system suspending (Ca(NO3)2/zeolite/AERN). The effectiveness and mechanism of the Ca(NO3)2/zeolite/AERN method for simultaneously controlling the release of soluble reactive P (SRP) and NH4+-N were investigated, and the NO3--N releasing risk of this method was evaluated. It was found that the joint use of Ca(NO3)2 injection, zeolite capping, and AERN-contained floating system suspending not only could effectively suppress the release of SRP and NH4+-N from sediments into OL-waters simultaneously, but also had much less risk of NO3--N releasing into OL-waters as compared to the single Ca(NO3)2 injection method and the combined Ca(NO3)2/zeolite method. The inhibition of the reductive dissolution of the P-bound Fe(III) oxides/hydroxides by the presence of nitrate and the adsorption of ammonium on the zeolite played very important roles in the interception of SRP and NH4+-N releasing into OL-waters by the Ca(NO3)2/zeolite/AERN method. After the sediment remediation using the Ca(NO3)2/zeolite/AERN approach, the increase in the content of residual P in the sediment layer of 0-50 mm, the decrease of mobile P in the sediment layer of 0-10 mm, and the increased NH4+-N adsorption capacity for the sediment layer of 0-10 mm would be conductive to the interception of SRP and NH4+-N liberation in the long run. Results of this research suggest a promising application potential of the Ca(NO3)2/zeolite/AERN method in the simultaneous control of the release of SRP and NH4+-N from sediments.