Removal of organic contaminants and toxiciy from industrial effluents using freezing processes

Removal efficiency of organic contaminants and reduction of toxicity (Microtox) in the secondary petroleum refinery and pulp mill effluents using two freezing processes, unidirectional downward freezing (UDF) and the spray freezing, was evaluated in this experimental study. The effect of the freezing temperature, initial feed water impurity concentration, mixing of the freezing liquid and the duration of freezing on the impurity removal efficiency was examined. Effective removal of chemical oxygen demand (COD) and total organic carbon (TOC) causing materials from both effluents, color causing materials in the pulp mill effluent, and removal of linoeic and abietic acids in the meltwater of the spray ice was achieved by freezing only 70% of the feed water. Close association of effluent toxicity with TOC and COD concentrations was observed when EC20 was used to measure the toxicity. Mixing of the freezing liquid significantly improved the impurity removal efficiency of the UDF process, reduced the influence of freezing temperature and initial feed water impurity concentration. Greater impurity removal efficiency was observed for the spray ice with longer storage time. The impurity removal efficiency of the spray freezing process was similar to that of the UDF without mixing.