| dc.description.abstract | The objectives of this study are aimed to investigate the performance of biodegradability enhancement in an industrial wastewater by preozonation process. Effect of ozone dosage, reaction time of preozonation and initial pH was studied. The biodegradability of wastewater was evaluated by BOD curve, COD fractionation and dissolved organic carbon molecular weight (DOC MW) distribution. This study also investigated the color removal in this wastewater by preozonation process and corresponding variation in biodegradability.
Experimental results showed that this industrial wastewater contains 50% biorefracotry organic compounds and the value of BOD5/COD was 0.27. Moreover, the average concentration of sulfate and chloride are as high as 236mg/L and 764mg/L respectively. The biodegradability of wastewater could be enhanced apparently with 116.2 mg/min of ozone dosage due to the mineralization of COD and the increase of BOD5. However, within 120min of preozonation time, biodegradability enhancement in this wastewater was also observed, but the optimal reaction time of preozonation and the increase of BOD5/COD were depended on the initial pH of wastewater. The value of BOD5/COD increased at 7.5 of initial pH as a result of the partial oxidations of biorefractory organic compounds and the generation of biodegradable organic compounds. When the initial pH was controlled at 5.0, the phenomena of partial oxidation and COD mineralization occurred simultaneously. In addition, although the BOD5 of wastewater was mineralized in the initial preozonation time at 9.0 of initial pH, but the biodegradability of wastewater could be eventually enhanced as the reaction time of preozonation approached 120 minutes.
The analysis of COD fractionation and BOD curve showed the particulate biorefractory organic compounds were mineralized at low ozone dosage when initial pH was at 7.5 and 9.0 respectively, but could be converted to soluble biodegradable organic compounds with the increase of ozone dosage. Also, the biorefractory organic compounds were converted to particulate and soluble biodegradable organic compounds when initial pH was maintained at 5.0. Additionally, biodegradability enhancement in this wastewater was primarily resulted from the conversion of high MW DOC (>500kD) to low MW DOC by means of DOC MW distribution analysis.
Results also revealed that color of wastewater could be effectively removed by preozonation, and the color removal could be over 90% when ozone dosage and preozonation time was 42.0mg/min and 60min respectively. In particular, biodegradability enhancement in this wastewater was obtained along with the color removal. This implied that the color of this wastewater was one source of biorefractory organic compounds. | en_US |