The Removal of Heavy Metal, Phosphate, and COD Substances from Wastewater by the Lime Sulfurated Solution (Calcium Polysulfide) Process

Abstract

Abstract A new chemical precipitation process that had been developed for the removal of heavy metals was extended to the removal of phosphate and COD substances. For simulated wastewater contaminated with heavy metal, phosphate, and COD substances, removal experiments were undertaken in a batch, stirred vessel by using the lime sulfurated solution as a single coagulant. The coagulant, the main component of which is CaSx, decomposes in water on contact with air or CO2 gas, and liberates H2S, CaS2O3, CaCO3, CaSO4, and solid sulfur particles. While heavy metals are precipitated as metal sulfides or hydroxides, phosphate is precipitated as calcium phosphate and COD substances are sorbed on the surfaces of the precipitates and they removed. The experimental findings are as follows: (1) The simulated wastewater contaminated simultaneously with phosphate and cadmium ions can be treated better than that contaminated only with the phosphate ion. Also, the CaSx process is found to be more effective than the Ca(OH)2 process for the removal of phosphate. (2) The removal percentages of COD substances ranged from 40% to 90% according to the sort of substance. The COD removal can be attained by the sorption of the substances mainly on the liberated solid sulfur particles, and partly on the calcium salts.