Mechanisms and risks of joint control of nitrogen and phosphorus through sediment capping technology in a pilot-scale study

Abstract

Purpose Nitrogen (N) and phosphorus (P) are the key elements leading to eutrophication, and it is important to jointly control N and P release from sediments into the water column. Methods Different mixed materials including P sorbent, natural organic carbon (C), and an oxidizing agent were applied in a 1-year pilot-scale experiment. Results The addition of iron-rich (IR) clay and Phoslock agent promoted the formation of iron bound P (Fe(OOH)~P) and calcium bound P (CaCO 3~P ) in sediments, respectively. IR clay offered more advantages in immobilization of phosphorus as refractory P, and the Phoslock agent more effectively reduced the risk of P release into water, which was expressed as a low equilibrium P concentration (EPC 0 ). Mixtures of sugarcane (SU) detritus and IR clay exhibited high carbohydrate (CHO) contents, which further fuelled both denitrification and dissimilatory nitrate reduction to ammonium (DNRA). This indicated that the SU dosage should be controlled to avoid DNRA over denitrification. Attention should be given to the fact that SU introduction significantly promoted the generation of an anaerobic state, leading to the desorption and release of Fe(OOH)~P, which could be alleviated by using Oxone. Multienzyme activity analysis showed that P and N transformation shifted from P desorption to organic P hydrolysis and from ammonification to denitrification and DNRA, respectively. Conclusion We recommend the use of P sorbent and organic C combined with oxidizing agents as effective mixed materials for sediment remediation, which could enhance P adsorption and provide electron donors for denitrification, while also avoiding the generation of anoxia.

Control of Endogenous Phosphorus Release at the Sediment–Water Interface by Lanthanum-Modified Fly Ash

“…Substrate dredging [14,15] might result in secondary pollution and complicated subsequent treatment. The active material cover method [16][17][18] reduces the risk of phosphorus overlying the sediment by placing blunt phosphorus materials at the sediment-water interface to form an active cover layer, with technical difficulty derived from identifying green, environmentally friendly, and economical active cover materials [19,20]. In situ chemical methods [21,22] can add iron, aluminum, and calcium salts to form precipitates with phosphate, but too high a dosage can cause pollution.…”