An example of a wastewater treatment project for high concentrations of benzene, xylene, acetophenone, and DOPO generated in the production of phosphorus flame retardant

ABSTRACT Wastewater generated in the production of phosphorus flame retardants contains benzene, xylene, acetophenone, and 9, 10-dihydro-9-oxa-10-phosphoxanthine-10-oxide (DOPO) with larger benzene rings, which are more difficult to biodegrade directly. In this study, the wastewater generated in the production of phosphorus flame retardants applied for high-temperature nylon and reactive phosphorus flame retardant was first treated by the combined process of lime emulsion–flocculation reaction and precipitation–ozone oxidation reaction for degradation of benzene, xylene, acetophenone, and DOPO, and then processed by the secondary combined process of upflow anaerobic sludge bed anaerobic digestion–air flotation–membrane bioreactor bio-contact oxidation; thus, the final concentration of pollutants in the wastewater can reach the relevant limit either for external discharge or as the supplemental water for other production devices. In addition, the detailed chemical degradation mechanisms and removal effects of benzene, xylene, acetophenone, and DOPO in an ozone reactor were explored. After the project had been normally operated for half a year, the test results of the effluent were as follows: chemical oxygen demand, 50 mg/L; BOD5, 20 mg/L; NH3-N, 5.0 mg/L; total phosphorus, 0.5 mg/L; benzene ≤ 0.1 mg/L; xylene ≤ 0.4 mg/L; acetophenone ≤ 0.4 mg/L; and DOPO ≤ 0.02 mg/L. Ultimately, the cost was 2.1 $/m3. It provides a useful process for wastewater treatment related to phosphorus flame retardants.