Synthesis and characterization of ZnO–activated carbon composite derived from battery waste and coffee grounds for palm oil mill effluent degradation

Abstract The increasing area of oil palm plantations indirectly causes environmental problems in the form of waste, namely palm oil mill effluent. One method that can be used to reduce the concentration of palm oil mill effluent is photodegradation. In this study, the adsorbent was a composite of coffee grounds, activated carbon as a precursor, and ZnO battery waste as a semiconductor. The coffee grounds/ZnO waste battery-activated carbon composite was characterized using X-ray Diffraction (XRD) and UV-Vis Diffuse Reflectance Spectroscopy (UV-Vis DRS). The XRD patterns exhibited the same diffractogram, characterized by a hexagonal wurtzite structure. The UV-Vis DRS results showed band gap energy values of 1.17, 4.69, and 1.61 eV. The results of the photocatalytic activity test showed a decrease in COD concentration with increasing UV-C light radiation time at contact times of 1, 3, and 5 h, corresponding to degradation percentages of 3.94%, 7.88%, and 16.66%, respectively. The BOD concentration decreased at contact times of 1, 3, and 5 h, with degradation percentages of 2.21%, 6.63%, and 15.48%, respectively.