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.MethodsDifferent mixed materials including P sorbent, natural organic carbon (C), and an oxidizing agent were applied in a 1-year pilot-scale experiment.ResultsThe addition of iron-rich (IR) clay and Phoslock agent promoted the formation of iron bound P (Fe(OOH)~P) and calcium bound P (CaCO3~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 (EPC0). 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.ConclusionWe 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.
Highlights
Eutrophication has become a worldwide environmental problem and a threat to humanity, and it is partly caused by excessive nutrients especially phosphorus (P) and nitrogenResponsible editor: Haihan Zhang (N) (Paerl et al 2011; Schmidt et al 2013; Schindler et al 2016; Li et al 2021)
In this study, compared with applications of Phoslock agent and IR treatment, the addition of SU significantly promoted the reduction of Fe(OOH)~P levels (Fig. 1), implying that the addition of SU led to the formation of an anaerobic state and further accelerated the desorption and release of Fe(OOH)~P
We suggest that P adsorbent material and organic C combined with oxidizing agent should be used as an effective mixed material for sediment remediation, which would increase P adsorption and provide electron donor for denitrification and avoid the generation of anoxia
Summary
Eutrophication has become a worldwide environmental problem and a threat to humanity, and it is partly caused by excessive nutrients especially phosphorus (P) and nitrogenResponsible editor: Haihan Zhang (N) (Paerl et al 2011; Schmidt et al 2013; Schindler et al 2016; Li et al 2021). To decrease the internal loading of nutrients in sediments and the risk of nutrient release, various remediation technologies have been developed These methods mainly include dredging, in situ capping, in situ chemical applications (e.g., injecting Fe, Ca, or Al-based agents) and bioremediation (e.g., microorganism strengthening) (Jiao et al 2011; Liu et al 2014; Alvarado et al 2020; Hu et al 2020; Lin et al 2020; Rochera et al 2020). These techniques all exhibited results in laboratory or field sediment remediation experiments. The in situ capping method is more effective and easier to implement and has been widely used
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