Abstract
In this work, the treatment of bio-treated coking wastewater (BCW) by catalytic ozonation was conducted in semi-batch and continuous flow reactors. The kinetics of chemical oxygen demand (COD) removal were analyzed using BCWs from five coking plants. An integral reactor with catalytic ozonation stacked by ozone absorption (IR) was developed, and its efficiency was studied. The catalyst of MnxCe1-xO2/γ-Al2O3 was efficient in the catalytic ozonation process for the treatment of various BCWs. The chemical oxygen demand (COD) removal efficiencies after 120 min reaction were 64–74%. The overall apparent reaction rate constants were 0.0101–0.0117 min−1, which has no obvious relationship with the initial COD of BCW and pre-treatment biological process. The IR demonstrated the highest efficiency due to the enhancement of mass transfer and the utilization efficiency of ozone. Bypass internal circulation can further improve the reactor efficiency. The optimal results were obtained with the ozone absorption section accounting for 19% of the valid water depth in the reactor and 250% of circulation flow ratio. The long-term and full-scale application of the novel reactor in a continuous mode indicated stable removal of COD and polycyclic aromatic hydrocarbons (PAHs). The results showed that the system of IR is a promising reactor type for tertiary treatment of coking wastewater by catalytic ozonation.
Highlights
Coking wastewater is a type of typical complex industrial wastewater, in which significant amounts of toxic compounds such as polynuclear aromatic hydrocarbons (PAHs), cyanides, and high concentrations of ammonium salts and chlorides are present [1,2]
The discharge of the bio-treated coking wastewater (BCW) without effective further treatment could result in serious environmental problems
Efforts on advanced treatment processes for coking wastewater to remove the organic matters present in the BCW, especially refractory and toxic compounds, are necessary to guarantee the safety of the water environment [3,4]
Summary
Coking wastewater is a type of typical complex industrial wastewater, in which significant amounts of toxic compounds such as polynuclear aromatic hydrocarbons (PAHs), cyanides, and high concentrations of ammonium salts and chlorides are present [1,2]. Coking wastewater has been effectively treated by the conventional biological treatment process. The chemical oxygen demand (COD) values of the conventional biological treated coking wastewater are generally above 150 mg·L−1 , and most organic compounds in the effluent are refractory, toxic, mutative, and carcinogenic [3]. The discharge of the bio-treated coking wastewater (BCW) without effective further treatment could result in serious environmental problems. Efforts on advanced treatment processes for coking wastewater to remove the organic matters present in the BCW, especially refractory and toxic compounds, are necessary to guarantee the safety of the water environment [3,4].
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