Phosphate removal sediments

Phosphate removal processes from wastewater have been studied by many workers, in order to protect stagnant water area, such as lakes and coastal region from eutrophication. Among conventional phosphate removal processes, the representative one was flocculation and sedimentation process, which was based on precipitation of insoluble metal phosphate or hydroxide. However, the main problem with this process, is to produce large amounts of sludge, which is difficult to dehydrate. 

Table 1 shows the performance of fixed bed type process, in application to various wastewaters. The merit of this process is stability in ability of phosphate removal and low sludge production. Sludge production of this process is from 1/5 to 1/10 lower than that of the conventional flocculation and sedimentation process. 

Martens C. S., Berner R. A., and Rosenfeld J. K. (1978) Interstitial water chemistry of anoxic Long Island Sound sediments 2. Nutrient regeneration and phosphate removal. Limnol. Oceanogr. 23, 605-717. 

CLARIFIER Equipment primarily used to remove suspended solids and/or colloidal materials from a liquid. As applied to sugar, these are normally either flotation (refinery) or sedimentation (factory) devices. See PHOSPHATATION. 

The problem is to calculate the steady-state concentration of dissolved phosphate in the five oceanic reservoirs, assuming that 95 percent of all the phosphate carried into each surface reservoir is consumed by plankton and carried downward in particulate form into the underlying deep reservoir (Figure 3-2). The remaining 5 percent of the incoming phosphate is carried out of the surface reservoir still in solution. Nearly all of the phosphorus carried into the deep sea in particles is restored to dissolved form by consumer organisms. A small fraction—equal to 1 percent of the original flux of dissolved phosphate into the surface reservoir—escapes dissolution and is removed from the ocean into seafloor sediments. This permanent removal of phosphorus is balanced by a flux of dissolved phosphate in river water, with a concentration of 10 3 mole P/m3. 

Several reactions between constituents in As-contaminated groundwater and oxic sediments controlled As mobility in the laboratory experiments. Adsorption was the primary mechanism for removing As from solution. The adsorption capacity of the oxic sediments was a function of the concentration and oxidation state of As, and the concentration of other solutes that competed for adsorption sites. Although As(lll) was the dominant oxidation state in contaminated groundwater, data from the laboratory experiments showed that As(lll) was oxidized to As(V) by manganese oxide minerals that are present in the oxic sediment. Phosphate in contaminated groundwater caused a substantial decrease in As(V) adsorption. Silica, bicarbonate and pH caused only a small decrease in As adsorption. 

The iron-based redox cycle depicted in Figure 18.9 provides an effective preconcentrating step for phosphorus by trapping remineralized phosphate in oxic sediments. The conversion of phosphorus from POM to Fe(lll)OOH to CFA is referred to as sink switching. Overall this process acts to convert phosphorus from unstable particulate phases (POM to Fe(lll)OOH) into a stable particulate phase (CFA) that acts to permanently remove bioavailable phosphorus from the ocean. This is pretty important because most of the particulate phosphate delivered to the seafloor is reminer-alized. Without a trapping mechanism, the remineralized phosphate would diffuse back into the bottom waters of the ocean, greatly reducing the burial efficiency of phosphorus. 

The observed metal phosphate phases agree with thermodynamic models of the ash system described here. These phases control leaching in pH-stat systems and are present after aggressive leaching designed to remove available or leachable fractions. These phases are also similar to ones observed in soil, sediment, smelter dust, industrial wastewater, and slag systems. 

In this work, a chemical demetallization agent was used to convert entrained non-filterable metals into a form which could be effectively removed by filteration or sedimentation. Waste oils were demetallized by diammonium phosphate (DAP). A detailed parametric study was undertaken to map out the process variables so as to identify the most efficient demetallization conditions. 

The effectiveness of zerovalent iron in removing arsenic from water also greatly depends on the properties of the iron. As(III) removal is especially effective with high surface area 1-120 nm spheres of zerovalent iron (Kanel et al., 2005). Provided that interfering anions (such as, carbonate, silicate, and phosphate) are insignificant, colloidal spheres of zerovalent iron could be injected into arsenic-contaminated soils, sediments, and aquifers for possible in situ remediation (Kanel et al., 2005, 1291). 

For blood heparinized venous blood is centrifuged and the upper layer is removed. Wash the erythrocyte sediment three times with 0.9% (w/v) NaCl solution. Haemolyse the washed red cells by adding 4 parts (v/v) of distilled water per volume of packed cells to give a stock haemolysate solution (approx. 5% (w/v)). For assay, dilute the stock solution 1 500 with the phosphate buffer immediately before the assay is to be carried out and determine the haemoglobin content of the solution by the method of Drabkin. The catalase activity is expressed per unit of haemoglobin. 

As was mentioned before, Arey et al. [19] conducted batch equilibration experiments to evaluate the ability of hydroxyapatite to remove uranium from contaminated sediments at the Savannah River Site of DOE and showed that removal of U was due to secondary phosphate minerals that had solubility even lower than autunite (Ca(U02)2(P04)2- IOH2O). The authors suggest formation of Al/Fe secondary phosphate. A similar conclusion was reached by Fuller et al. [20], who showed that uranyl ions can be removed by using hydroxyapatite. 

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