Abstract | In this study, the complete biodegradation of Acid Orange 7 (AO-7), a mono azo dye, using a novel two-step sequential anaerobic-aerobic system was investigated. The system consisted of a bio-photovoltaic (BPV) coupled with an aerobic bioreactor. The initial anaerobic stage employed a dual-chamber BPV with the photosynthetic purple bacterium Rhodopseudomonas palustris (RP) in the anode, fed with 35 mg/L AO-7. Subsequently, two different aerobic systems were compared: an enzymatic system with immobilized laccase and a photobioreactor with microalgae Chlorella vulgaris. Results demonstrated that RP efficiently degraded AO-7 within 120 hours, achieving 100% dye removal efficiency. The BPV system achieved a remarkable maximum power density of 2.67 mW/m3. Analytical techniques such as GC-MS and FT-IR confirmed the partial degradation of aromatic amines, inhibiting recoloration of the effluent. Moreover, these analyses revealed further oxidation of toxic aromatic amines, as well as reductions in chemical oxygen demand (COD) and biochemical oxygen demand (BOD). Cytotoxicity testing of the final effluent indicated that the photobioreactor system exhibited superior cytotoxicity reduction compared to the laccase system. Overall, our study demonstrated that AO-7 can be completely decolorized and degraded into non-toxic and simpler metabolites. Additionally, the two-step system exhibited a significant reduction in BOD and COD compared to the influent. This work serves as a proof-of-concept for an energy-efficient biological wastewater treatment (WWT) system. Importantly, the two-step system operated at low temperature, requiring less energy compared to conventional biological systems that involve sludge removal, continuous mechanical agitation, and/or heat for anaerobic digestion. Consequently, successful scale-up of this system could significantly contribute to reducing the ecological footprint of WWT plants. |
---|