Sequential biological treatment including ozonation for persistent organic compounds

Abstract

2,4,6-trichlorophenol is widely used as insecticides, herbicides and fungicides as well as preservatives for wood, glue, paint, vegetable fibers and leather. It is included in the effluent from pulp mills and contaminate soils around wood-preserving industries and groundwater environment due to surface runoff or direct industrial waste discharges. PVA (polyvinyl alcohol) and HEC (hydroxyethyl cellulose) have been used in the chemical industry, especially in the expandable polystyrene manufacturing process. They remained in the environment for a longtime and could not be effectively destroyed by conventional wastewater treatment processes. Molecular weights of PVA and HEC are more than 25,000 amu. The objectives of this research are as followed. First, it is to determine the parameters and performance of anoxic-oxic process used for complete degradation of persistent organic compounds, esp. PAV and HEC in petrochemical wastewater and 2,4,6-TCP. Second one is to suggest the method for determining biodegradability. The third is to evaluate the effects of ozonation on biodegradability. Last one is to define the toxic effect of 2,4,6-TCP under anoxic condition and find out the parameters of inhibition model. In the study of biodegradation using anoxic-oxic process, 2,4,6-TCP was completely removed at recycle rate of 1.5Q and HRT of 18 hours. However, the removal efficiency of 2,4,6-TCP decreased as recycle rates increased. The wastewater from expandable polystyrene (EPS) process was treated using anoxic-oxic process. PVA was completely removed and the removal efficiency of COD and HEC reached to 83% and 89.4% at recycle rate of 2.5Q, HRT of 30 hours and organic loading rate of 0.9 g COD/L·day. When ozonation was applied to petrochemical wastewater, post-ozonation was more effective than pre-ozonation. The removal efficiencies of COD and HEC increased to 92% and 93% at ozone feed rate of 0.18 mmole/min. Biodegradability was estimated using methane potential,...