Treatment Of Chemical Wastewater By FOP-EGSB-MBR Combined System

Treatment efficiency of conventional processes is poor because of the special characteristics of chemical wastewater. Nowadays the trend in development of treatment technology of toxic non-biodegradable wastewater is the application of highly efficient and novel technology as well as the integrated process with multi-unit techniques.In this study, the efficient combined system with Fenton Oxidation (FOP), Expanded Granular Sludge Bed (EGSB) and Membrane Biological Reactor (MBR) process is developed for the treatment of chemical wastewater. And the pollutants were synthetic wastewater from 2-naphthol production process. The treatment effects and process of single technique including FOP, EGSB and MBR are investigated respectively. The main idea and objective of this study is that partial COD are removed and some toxic organic compounds are converted into biodegradable compounds by Fenton oxidation process; and that most of COD in the wastewater is removed effectively in the anaerobic process, which ensures high loading and low cost in the whole treatment system; and quality of effluent meeting discharge standard after the aerobic membrane bioreactor. Research results of this paper are of practical value to achieve low investment, low operating cost, strong stability and high quality of effluent for treatment of chemical wastewater. Based on the results of these investigations, the major conclusions are shown as following:1. The optimum experimental conditions for the COD removal of the simulated 2-naphthol wastewater were established as follows: H2O2/COD=2, H2O2/Fe2+=12 and initial pH = 4 at room temperature (T = 20℃), which yielded an overall COD removal efficiency of 86%; and the optimum conditions for the value of BOD/COD as follows: H2O2/COD = 2, H2O2/Fe2+ = 16 and initial pH = 4 at room temperature (T = 20℃), which yielded a high BOD/COD value of 0.67.2. Further increase in temperature did not improve oxidation and oxidant consumption rates. H2O2 consumption ran parallel to COD removal; at approximately 2.3 times faster rate than COD abatement.3. According to the activated sludge inhibition test (ISO 8192), the EC50 value obtained for untreated 2-naphthol wastewater was 329 mg/L in terms of COD, whereas the pre-treated samples of 2-naphthol wastewater exerted no inhibition, indicating that the inhibitory effect of the 2-naphthol was totally eliminated with Fenton's pretreatment. Biocompatibility of the 2-naphthol wastewater was restored to that of readily biodegradable effluent of domestic character upon exposure to Fenton's pretreatment under optimized reaction conditions.4. COD value in wastewater treated by the procedure of Fenton oxidation was 5000 mg/L, and after EGSB and MBR treatment the values in the effluent were below 100 mg/L,respectively,the water quality satisfied the standard of grade 1 in Integrated Wastewater Discharge Standard (GB-8978-1996).5. The COD removal rate reaches to 99% by the combined processes. It showed the system was technically feasible for the treatment of chemical wastewater.