Evaluation of zeolite/hydrous aluminum oxide as a sediment capping agent to reduce nutrients level in a pond

•Zeolite/hydrous aluminum oxide(ZHAO) was studied as sediment P-capping agent.•ZHAO was efficient to immobilize soluble reactive phosphorus from pond water.•ZHAO could transform release-sensitive P forms in sediment to refractory P forms.•ZHAO performed better than alum to reduce P level in pond water overlying sediment.•ZHAO was able to simultaneously adsorb NH4+ and Mn2+.

Zeolite/hydrous aluminum oxide (ZHAO) has been prepared from coal fly ash and investigated to cap sediment to reduce P concentration in an urban pond using batch and 28-day sediment core incubation experiments. The adsorption isotherm studies illustrated that the maximum adsorption capacity of phosphate, ammonium and manganese (II) ions on ZHAO were 11.88, 7.74 and 13.23 mg/g, which were 7.3, 10.3, and 10.5 times greater than those of sediment, respectively. This suggested that ZHAO was a unique material to block the release of not only anionic P, but also cationic NH4+ and Mn2+ from sediment. ZHAO was able to reduce SRP level from pond water and increasing pH led to decreased removal performance. P fractionation measurements demonstrated that adding ZHAO resulted in the reduction of release-sensitive P fractions (labile-P fraction and reductant-soluble P fraction) in sediment and diminished the release of P under anaerobic conditions. We also found that, during the 28-day sediment core incubation period, ZHAO treatment was more efficient (reducing TP and SRP in the pond water overlying the sediment cores by more than 90%) and durable than the traditional alum treatment which has been used for decades worldwide. ZHAO is a promising sediment amendment material to control the internal P loading in eutrophic lakes/ponds.