Removal of dyes from industrial effluents using combination of Advanced Oxidation Processes (AOPs) and biological treatment
Che Zulzikrami Azner, Abidin
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Nowadays, the removal of dyes from industrial effluents is still far away to a satisfactory solution. Even though the AOPs are known strong technologies for wastewater treatment, it still requires further advancement and extent. Hence, a new promising treatment is their combination with biological treatment, by taking the advantages of the individual potentials. Therefore, this research evaluated four treatment techniques, namely ozonation, ozone/hydrogen peroxide (O3/H2O2), ultraviolet/hydrogen peroxide (UV/H2O2), and a combination of ozonation-biological for synthetic dyes, consist of monoazo Methyl Orange (MO), disazo Reactive Red 120 (RR120) and anthraquinone Reactive Blue 19 (RB19). Finally, the treatments are evaluated with batik wastewater as a real wastewater sample from industries. The finding revealed that ozonation, O3/H2O2, UV/H2O2, and ozonation-biological become an effective treatment for monoazo, disazo, anthraquinone, and real wastewater. The treatments accomplish, under appropriate conditions, a full decolourization and a substantial mineralization. However, O3/H2O2 and ozonation works well with the dyes, in contrast to UV/H2O2. It reveals that complete decolourization by ozonation and O3/H2O2, with less than 20 min contact. Two decolourization curves of ozonation and O3/H2O2 almost overlapped suggesting that H2O2 hardly affects decolourization rate. Contrariwise, it takes more than 60 min for complete decolourization with UV/H2O2 for RR120, but requires more than 120 min for MO and RB19. Nevertheless, there was a significant difference for COD and TOC removals. It is apparent that O3/H2O2 showed higher removal, suggesting that the presence of H2O2 promote the oxidation reaction. The final COD removal of O3/H2O2 reached 100% within less than 10 min for RR120 and RB19, while 15 min for MO. Likewise, the higher TOC removal was observed for O3/H2O2 in comparison to ozonation and UV/H2O2. On the whole, the COD removal was similar to TOC removal for each treatment. It is obvious that high decolourization from the start of biological was contributed from ozonation pre-treatment. In addition, the results indicate that 59.6 and 69.4% COD removal from ozonation and ozonationbiological, respectively for MO. While, resulted about 40.7 and 72.9% removal for RR120, and 51.4 and 59.8% for RB19, respectively. Thus, it represents small organic molecules that contribute considerably to the COD that cannot be completely removed by ozonation-biological treatment. Similar to COD, the results indicate that 49.1 and 73.7% TOC removal from ozonation and ozonation-biological, respectively for MO. While it leads to 39.3 and 64.3% removal for RR120 and 37.5 and 70.8% removal for RB19, respectively. It is clear that the biological further degrades the dyes from ozonation. In addition, each dye shows different decolourization pattern and degradation behaviour according to its chemical structure. The change in UV-vis and FT-IR spectra indicated the evidence of dye structure cleavage and intermediates formation. While, the NO3 -, SO4 2- and Cl- anions formed indicate dye mineralization. The decolourization conform first-order kinetics, with R2 values greater than 0.92. The O3/H2O2 performs better with the batik wastewater, as compared to ozonation and UV/H2O2. Therefore, the results for synthetic wastewater support its application for real wastewater, even though the batik wastewater was more difficult to be decolourized and degraded because of its complex composition.