Intensified Treatment of Pharmaceutical Effluent Using Combined Ultrasound-Based Advanced Oxidation and Biological Oxidation

The present work investigates the efficacy of ultrasound (US)-based pretreatment methods for the process intensification of biological oxidation (BO) of real pharmaceutical industrial effluent with a high initial COD of 50,000 mgL−1. US, combined with advanced oxidation processes (AOPs), was used to degrade recalcitrant compounds. Conventional BO could only reduce the COD by 3.85% and confirmed the requirement of pretreatment. US, under established optimised conditions of 120 W power, 70% duty cycle, pH 6, and 30 °C temperature, gave a COD reduction of 5.77%. Combining US with oxidants like O3 (2 L/ min), H2O2 (1000 mgL−1), Fenton (1:5 Fe2+:H2O2), and peroxone (2 L min−1 O3 with 1000 mgL−1 H2O2) as pretreatment gave COD reductions of 30.77%, 17.31%, 19.23%, and 42.31%, respectively. Toxicity assays using the agar well diffusion method revealed that the pretreatment techniques reduced the toxicity of the effluent and did not introduce any toxic secondary metabolites into the system. The optimised treatment time for BO was fixed at 30 h, and the COD reduction obtained for the streams pretreated with US, US + O3, US + H2O2, US + Fenton, and US + peroxone were 14.3%, 88.46%, 57.69%, 61.54%, and 94.23%, respectively. The US combined with peroxone method was the best pretreatment for the effluent in terms of overall COD reduction. This work effectively demonstrates the usefulness of US-based methods to intensify the biological oxidation of real industrial effluent with high organic load.