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 Ca(2+) 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 Ca(2+). However, the peak ADMI value in calcium-contained solution is lower than that without Ca(2+). 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 Ca(2+) is faster than that without Ca(2+). The optimal initial calcium dosage shows linear relationship with the initial phenol concentration, which is useful for practical application.

The effects of preozonation on the biodegradability of mixed phenolic solution using a new gas-inducing reactor.

In this study, the effects of preozonation on the biodegradability of mixed 2-chlorophenol/4-cresol solution were investigated using a new gas-inducing reactor, which can provide high ozone utilization efficiency. The decomposition rate of phenolic mixture, COD removal and TOC removal increases with increasing pH. A half-order overall kinetic model can correctly describe the decomposition of phenolic mixture. The BOD(5)/COD ratio of the preozonized solutions increases with increasing preozonation time, indicating that preozonation can enhance the biodegradability. Based on high ozone utilization rate, it is concluded that the best characteristic time can be chosen at the rapid increase of ozone gas outlet concentration. Since the ozone gas outlet concentration can be easily monitored, it is a useful real-time control parameter in preozonation.

The enhancement of the biodegradability of phenolic solution using preozonation based on high ozone utilization.

In this research, the effects of preozonation on the biodegradability of 4-cresol, 4-nitrophenol and 2-chlorophenol solutions were investigated using a new gas-inducing reactor with high ozone utilization rate. The extent of preozonation may be monitored by determining the characteristic ozonation behaviors of preozonized phenolic solutions, such as residual phenolic concentration, ADMI value and ozone gas outlet concentration. Experimental results showed that as the initial phenolic compounds decomposed completely, the ozone gas outlet concentration rapidly increases. In addition, at pH 7, a peak ADMI value appears during the preozonation of 4-cresol and 2-chlorophenol, while for 4-nitrophenol the ADMI value decreases monotonically. Based on the characteristic ozonation behaviors and the ozone utilization rate, three characteristic times were chosen in order to have better control on the extent of preozonation. The effect of preozonation on the biodegradability of preozonized phenolic solution was studied based on these characteristic times. The intermediate products during the preozonation were also identified. The variation of BOD5 is strongly dependent on the accumulation of intermediate products. It is suggested that the best characteristic time is as the rapid increase of ozone gas outlet concentration in this study. The biodegradability (BOD5/COD) of preozonized 4-cresol, 2-chlorophenol and 4-nitrophenol solutions increase to 0.18, 0.26 and 0.33, respectively, for the best characteristic time.

The effectiveness of a new gas-induced reactor in treating phenolic wastewater by ozonation and hydrogen peroxide.

A new Gas-Induced Reactor (GIR) has been developed to improve the efficiency of ozone utilization in water treatment. In this study, the GIR was used to investigate the behavior of ozonation of aqueous phenol solution by means of O3 and O3/H2O2 processes in order to explore the feasibility and efficiency of treating such wastewater using the new GIR. The study observed the decomposition of phenol, utilization of ozone, and variation of TOC during ozonation, varying pH values, phenol initial concentrations, ozone input concentrations, and hydrogen peroxide dosages. The study concluded that the new GIR was capable of performing effective and efficient ozonation of phenolic wastewater, maintaining high ozone utilization ratios at all experimental pH values and initial phenol and ozone concentrations. The optimal pH condition for phenol removal was around 11. The best molar ratios of initial hydrogen peroxide over input ozone among the performed experiments were about 20 at pH 7 and 10 at pH 9 and 11. The primary operational energy used for treating a tonne of wastewater was 66 MJ, giving treatment costs of about USS1.0 per tonne.