Use Of Zirconium-modified Zeolites To Control The Release Of Nitrogen And Phosphorus From Sediments In Surface Water Bodies

Eutriphication of surface water bodies such as rivers, lakes, reservoirs and coastal seas has become a serious environmental problem in China. Eutrophication of surface water bodies can result in excessive growth of algae and aquatic plants, and subsequently lead to increased dissolved oxygen depletion and fish toxicity. Nitrogen(N) and phosphorus(P) are widely recognized as two limiting nutrients for phytoplankton growth, and excessive N and P in surface water bodies can cause their eutrophication. Therefore, it is necessary to reduce the concentration of N and P in the overlying water. Sediments in surface water bodies are considered as a sink as well as a source for N and P. The release of N and P from sediments may have a significant impact on the concentration of N and P in the overlying water. Therefore, the control of the release of N and P from sediments into the overlying water is an important issue to protect surface water bodies from eutrophication.In situ treatment of sediments with sorbents, which involves introducing sorbent amendments into contaminated sediments that alter sediment geochemistry, increase contaminant binding, and reduce contaminant exposure risks to people and the environment, is a novel and promising approach for in situ sediment remediation that minimizes or eliminates some of the problems of the conventional techniques. In situ sediment capping with an active barrier system using sorbents, which involves placement of a layer of sorbents at the sediment-water interface to create a adsorbing layer between the sediment and the overlying water column, has gained more attention in recent years and is considered as a potentially effective method for controlling nutrients release from sediments into overlying waters. One of the key points of the successful application of the in-situ sorbent treatment technology or the in-situ active capping technology to control N and P release from sediments is to select the suitable sorbent materials. Natural zeolite has high selectivity to the cationic pollutants such as ammonia-nitrogen due to its high cation-exchange ability. In order to improve the phosphate sorption capacities for zeolite, modification of natural zeolites is necessary. In this study, a zirconium-modified zeolite was prepared, characterized and used as sediment amendment materials and sediment active capping materials to control nutrients(e.g. N and P) release from sediments in surface water bodies.The zirconium-modified zeolite(Zr MZ) was used as an adsorbent to remove phosphate from aqueous solution. The adsorption characterization of phosphate on Zr MZ from water was investigated through batch experiments. The sequential extraction methods were used to investigate the forms of P in the phosphate-adsorbed Zr MZ. Results showed that the Zr MZ was effective for the removal of phosphate from water. The phosphate adsorption capacity for Zr MZ decreased with increasing water p H. The adsorption of phosphate on Zr MZ followed a pseudo-second-order kinetic model. The equilibrium adsorption data of phosphate on Zr MZ could be well described by the Langmuir isotherm model with a maximum monolayer adsorption capacity of 10.2 mg P/g at p H 7 and 25 oC. The sequential extraction of P from the phosphate-adsorbed Zr MZ under laboratory conditions suggested that about 6% of P bound by Zr MZ was release-sensitive, while about 94% of bound P was unlikely to be released under reducing and common p H(5~9) conditions. Sequential extraction of P from the phosphate-adsorbed Zr MZ suggested that most of P bound by Zr MZ existed as the Na OH extractable P(Na OH-P) and residual P(Res-P), and were unlikely to be released under natural p H and reducing conditions.The immobilization of phosphate in Taihu Lake sediment-water systems using aluminium-modified zeolites(Zr MZs) and zirconium-modified zeolites(Al MZs) as amendment was comparatively studied. The sorption of phosphate-P from Taihu Lake sediment-water systems on Al MZ and Zr MZ was investigated through a series of experiments. The Langmuir and Freundlich isotherm models were found to be quite useful to describe the sorption equilibrium data of P on the raw and amended sediments at a high initial P concentration(1~10 mg/L). The sorption kinetics of phosphate on the raw and amended sediments followed a pseudo-second-order model. Based on the Langmuir isotherm model, the maximum phosphate-P sorption capacities for the raw, Al MZ-amended and Zr MZ-amended sediments were 395, 613 and 1009 mg/kg, respectively. Sequential extractions of P from the raw and amended sediments after phosphate sorption indicate that most of phosphate sorbed by Al MZ existed in the form of Na OH-P(P extracted with Na OH) and most of phosphate sorbed by Zr MZ existed in the forms of Na OH-P and Res-P(Residual P). Phosphate-P could be released from the raw and amended sediments at a very low concentration of P in water. The amount of phosphate-P released from the modified zeolites-amended sediment was less than that from the raw sediment. The contents of bioavailable P including water-soluble P(WSP), readily available P(RDP), Na HCO3-extractable P(Olsen-P) and algal-available P(AAP) in the sediments reduced after the sediments were mixed with Al MZ or Zr MZ, making P in the sediments more stable. The content of NH4Cl-P(P extracted with NH4Cl) in the modified zeolites-amended sediment was less than that in the raw sediment. The content of BD-P(P extracted with bicarbonate dithionite) in the raw sediment was higher than that in Zr MZ-amended sediment, but was no significant difference to that in the Al MZ-amended sediment. Results of this work indicate that Al MZ and Zr MZ are promising amendments for controlling phosphate-P release from Taihu Lake sediments, and Zr MZ are more suitably used as sediment amendments to control phosphate-P release than Al MZ.The immobilization of phosphorus from sediment using zirconium-modified zeolites(Zr MZs) was investigated in batch mode. The addition of Zr MZ into sediments reduced the inorganic P activity in the sediments by transforming BD-P to Na OH-P and Res-P. The contents of bioavailable P such as WSP, Olsen-P and AAP in sediments reduced after the sediments were mixed with Zr MZ, making P in the sediments more stable. The addition of Zr MZ into sediments significantly reduced the releasing flux of P from the resuspended sediments to the water column under different p H values, ionic strengths, Si O32- concentrations, or sediment’s organic matter(OM) content conditions. In the anaerobic static systems, the addition of Zr MZ into sediments also reduced the flux of P released from the sediments to the water column.The efficiency and mechanism of sediment capping with active barrier system(ABS) using zirconium-modified zeolite(Zr MZ) to control phosphate and ammonium release from sediments in heavily polluted river was investigated through batch and sediment incubation experiments. The phosphate adsorption capacity for Zr MZ decreased with increasing p H. The ammonium adsorption capacity for Zr MZ increased with increasing p H from 4 to 5, was relatively high at p H 5~8, but decreased with increasing p H from 8 to 10. The adsorption kinetics of phosphate and ammonium on Zr MZ followed a pseudo-second-order model. The equilibrium adsorption data of phosphate and ammonium on Zr MZ could be described by the Langmuir and Freundlich isotherm models. The maximum phosphate and ammonium adsorption capacities for Zr MZ derived from the Langmuir isotherm model were found to be 7.75 and 9.59 mg/g at p H 7 and 25 °C, respectively. The phosphate and ammonium removal efficiencies of Zr MZ increased with increasing adsorbent dosage. The main mechanism for phosphate adsorption onto Zr MZ is ligand exchange. The main mechanism for ammonium adsorption onto Zr MZ is cation exchange. About 82.5% of phosphate adsorbed onto Zr MZ existed in Na OH-P form, and was relatively stable and unlikely to be released under low dissolved oxygen conditions. The percentage of water-soluble phosphorus(WSP), readily desorbable phosphorus(RDP), or Na HCO3 extractable phosphorus(Olsen-P) to total phosphorus(TP) adsorbed onto Zr MZ was very low, and algal available phosphorus(AAP) accounted for only 29% of TP adsorbed onto Zr MZ. The phosphate-phosphorus(PO43--P) and ammonium-nitrogen(NH4+-N) could be released from the sediments used in this study into the overlying water under low dissolved oxygen conditions. The PO43--P and NH4+-N fluxes from the sediments to the overlying water under low dissolved oxygen conditions were significantly reduced by the ABS using the Zr MZ. Results of this work indicate that Zr MZ is suitably used as a capping material for preventing PO43--P and NH4+-N release from sediments in heavily polluted river under low dissolved oxygen conditions.Bellamya quadrata shell alone, fish bone alone, mixture of Bellamya quadrata shell and fish bone were used to remove phosphate from aqueous solution. The removal of phosphate from aqueous solution by Bellamya quadrata shell alone, fish bone alone, and mixture of Bellamya quadrata shell and fish bone was investigated using a series of batch experiments. The mixture of Bellamya quadrata shell and fish bone was effective for the removal of phosphate from aqueous solution, and it exhibited much higher phosphate removal efficiency than Bellamya quadrata shell alone and fish bone alone. The kinetics of phosphate removal by the mixture of Bellamya quadrata shell and fish bone followed a pseudo-second-order model. The amount of phosphate removed by the mixture of Bellamya quadrata shell and fish bone increased with increasing initial phosphate concentration. Solution p H has little influence on the removal of phosphate by the mixture of Bellamya quadrata shell and fish bone. Coexisting Cl-, SO42-, Na+, K+, or Mg2+ in solution has little influence on the removal of phosphate by the mixture of Bellamya quadrata shell and fish bone, while coexisting HCO3- in solution reduced the removal of phosphate by the mixture. The mechanisms for the removal of phosphate by the mixture of Bellamya quadrata shell and fish bone include the surface adsorption of phosphate on Bellamya quadrata shell and fish bone, and the precipitation of calcium phosphate. The precipitation of calcium phosphate occurred according to two consecutive phases: first, the dissolution of bellamya quadrata shell and fish bone produced an increase in the concentration of Ca2+ ions in solution; then the Ca2+ reacted with the phosphate ions to form the precipitate of calcium phosphate. The precipitation of calcium phosphate took place at the surface of fish bone, which acted as substrate for the heterogeneous nucleation of calcium phosphate. The presence of Ca2+ ions in solution represented a further source of Ca2+ ions that were available for the precipitation of calcium phosphate, thereby leading to an increase in the phosphate removal efficiency of mixture of bellamya quadrata shell and fish bone. Thus, the mixture bellamya quadrata shell and fish bone is a promising sorbent for the removal of phosphate from wastewater.The above conclusions revealed that the use of zirconium-modified zeolites as sediment amendment materials can efficiently control P release from sediments, and the use of zirconium-modified zeolites as sediment active capping materials can efficiently contro ammonium-N and phosphate-P releae from sediments.