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A very great quantity of phosphate present in wastewater, may reach the aquatic environment, and can lead to the pollution of the environment. The phosphate must be removed from domestic and industrial effluents before their dispersion and dilution in the environment. The aim of this paper was to investigate the feasibility of phosphate removal from synthetic wastewater, by precipitation with calcium hydroxide addition, in order to determine optimal operating conditions. The optimal Ca/P molar ratio and the time of precipitation are determined. It was shown that Ca/P ratio and the initial pH are combined and the percentage of phosphate removal obtained is 98% for Ca/P = 2.07. The optimal time of precipitation depends of the initial Ca/P molar ratio; indeed 30 min are sufficient to reach a maximum of phosphate removal (98%) which corresponds to a Ca/P = 2.07. However, for the Ca/P < 0.8, 24 h of precipitation appears insufficient to obtain a phosphate removal = 50%.

In this paper, we have proposed a technique for the removal of phosphate ions from wastewater based on precipitation by calcium hydroxide. The effect of the initial Ca/P molar ratio and the time of precipitation in the phosphate removal process has been investigated. From the experimental study, it was concluded that: (1) Ca/P molar ratio and the initial pH are dependent parameters. For Ca/P equal to 2.07, 98% of phosphorus was removed. (2) The precipitation time plays an important role in phosphate removal. (3) The optimal time of precipitation depends on the initial Ca/P molar ratio. 30 min are sufficient to reach a maximum of phosphate removal (98%) which corresponds to a Ca/P = 2.07. However, for the Ca/P < 0.8, 24 h of precipitation seem to be insufficient to obtain a phosphate removal equal to 50%. (4) The characterization of the obtained precipitate showed that the latter could be a mixture of two phases. The thermal behaviour of this precipitate agrees with our previous conclusion.