Calcium enhanced COD removal for the ozonation of phenol solution

in order to improve the chemical oxygen demand (COD) removal rate for the ozonation of phenol solution, ozonation combined with calcium binding was investigated. The results show that the addition of Ca2+ can effectively enhance the COD removal rate. During the ozonation, calcium ion can bind with some of the intermediate products of phenol, including high molecular weight products, maleic acid and oxalic acid, to form insoluble precipitates. These calcium binding effects are responsible for the enhancement of COD removal. The variations of ADMI value during ozonation are similar for solutions with and without Ca2+. However, the peak ADMI value in calcium-contained solution is lower than that without Ca2+. As the phenol was completely decomposed, the ozone gas outlet concentration rapidly increases. The increasing rate of the ozone gas outlet concentration for ozonation with the presence of Ca2+ is faster than that without Ca2+. The optimal initial calcium dosage shows linear relationship with the initial phenol concentration, which is useful for practical application. (c) 2006 Elsevier Ltd. All rights reserved.