Synthesis of a ternary microscopic ball-shaped micro-electrolysis filler and its application in wastewater treatment

[Display omitted] •High COD removal efficiency was obtained around 80%.•Good reusability and stability were proved after 10 cyclic experiments.•Unique microscopic ball-shaped structure was synthesized to play a vital role in removal mechanism.•Synergistic effects of electrochemical oxidation, adsorption, and coprecipitation of iron hydroxides. Oil refineries produce a variety of relatively intricate and biodegradable wastewater streams. A ternary micro-electrolysis filler (iron (Fe)-biochar (BC)-copper (Cu)) was synthesized using BC produced from waste Lycium barbarum L. branches by high-temperature anaerobic calcination, and was then used to treat oil refinery water. To evaluate the applicability of Fe-BC-Cu, the effects of various reaction parameters, including the initial pH of wastewater, Fe-BC ratio, and Fe-BC-Cu ratio, were investigated. A comparative study was conducted using three different kinds of fillers (BC, Fe-BC, and Fe-BC-Cu) to determine the reaction behavior, which was characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area analysis, scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and EDS mapping. The results of batch studies revealed that the maximum chemical oxygen demand (COD) and total organic carbon (TOC) removal efficiency was 77.11% and 68.71%, respectively, under the optimal conditions of an initial wastewater pH of 4.0, Fe-BC ratio of 1:1, and Fe-BC-Cu ratio of 1:1:1. The reusability of the Fe-BC-Cu filler was measured to ensure that the COD removal efficiency was maintained at around 80% during 10 cycles. The results of a heavy metal analysis of the effluent indicated that the application of the Fe-BC-Cu filler in wastewater treatment presented no risk of heavy metal release. The microscopic ball-shaped structure revealed by SEM facilitated a suitable micro-electrolysis reaction rate. The removal mechanism of organic pollutants in the wastewater by the Fe-BC-Cu micro-electrolysis filler could be due to the synergistic effects of electrochemical oxidation, adsorption, and coprecipitation of iron hydroxides. The extraordinary performance of the Fe-BC-Cu micro-electrolysis filler for organic pollutant removal indicated its practical potential for industrial applications.