Wastewater application, phosphate

Precipitation is often applied to the removal of most metals from wastewater including zinc, cadmium, chromium, copper, fluoride, lead, manganese, and mercury. Also, certain anionic species can be removed by precipitation, such as phosphate, sulfate, and fluoride. Note that in some cases, organic compounds may form organometallic complexes with metals, which could inhibit precipitation. Cyanide and other ions in the wastewater may also complex with metals, making treatment by precipitation less efficient. A cutaway view of a rapid sand filter that is most often used in a municipal treatment plant is illustrated in Figure 4. The design features of this filter have been relied upon for more than 60 years in municipal applications. 

To cope with these problems, we have developed phosphate removal process using crystallization, which can minimize the amount of sludge and recover phosphate. Mechanism of this process is crystallization of calcium phosphate on the surface of phosphate rocks by contacting supersaturated solution with them. In case of application to wastewater containing 1-3 mg/jg phosphate as P, we proposed fixed bed type process, which has demonstrated excellent performance in the sewage treatment. 

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. 

We have reported only the results of the last investigation of fundamental properties of this process. But there are many problems remaining unsolved such as growing mechanism of calcium phosphate, the reason of difference in phosphate removal efficiency between application to wastewater and tap water, and also how contaminants include into growing calcium phosphate. 

Several examples of the applications of SLMs in the removal of antibiotics from wastewater are shown below. Kawasaki et al. [154] studied the application of the flat-sheet SLM in the removal of erythromycin A from aqueous matrices. The feed phase consisted of citric acid (concentration = 0.025 mol dm 3), boric acid (concentration = 0.100 mol dnr- j, and sodium phosphate (concentration = 0.050 mol dm ). The SLM was prepared from PTFE flat sheet porous with 1-decanol as the diluent. 

Chloride, nitrate, phosphate and sulphate in wastewater, IC Application Note No. S-7, Metrohm Ltd. CH-9101 Herisau, Switzerland. 

The formation of many low-soluble compounds with commonly occurring cations in waters causes very low concentrations of phosphates in both natural and wastewaters. The concentration of phosphates in surface waters can be several tenths mg 1. More rich in phosphates are waters from peat moors which can sometimes contain as much as 1 mg 1. Due to detergents and application of phosphates in agriculture their content is continually increasing in natural waters. To prevent further undesirable increase of phosphates in surface waters their application in the production of synthetic detergents is now limited. 

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