Sono- and Zeolite-Assisted Electrocoagulation for Compost Wastewater Treatment: Does Ultrasound Power Make a Difference?

This study builds on previous research that investigated the triple hybrid wastewater treatment system combining electrocoagulation (EC), zeolite (Z), and ultrasound (US), and it examines the effects of different ultrasonic powers on compost wastewater treatment by analysing several process parameters. In the first part, two levels of US power intensity, corresponding to 20% and 100% of intensity, with and without zeolite addition, were investigated on three different electrode materials. Although satisfactory chemical oxygen demand (COD) reduction was obtained (81.42%–88.90%), better results were obtained for Al and Zn electrodes at 20% US power intensity, while for Fe better resulted were obtained at 100% US power intensity. Deteriorations of the anodic and cathodic surfaces, which were analysed using optical microscope images at 50× and 200× magnification, are generally less pronounced at higher US power intensities. Energy consumption in the range of 3.86–18.78 kWh/m³ showed an increased sequence—Fe < Zn < Al. In the second part, Taguchi optimisation was used to study the influence of US intensity (0%, 20%, 100%), the electrode materials (Al, Fe, or Zn), contact time (10, 20, and 30 min), and mixing speed (150, 250, 350 rpm) on COD decrease, electrode consumption, settling velocity, and voltage (power) consumption. The result shows that increased US power enhances COD reduction, electrode mass preservation, and voltage while decreasing the settling velocity.