Solar-photovoltaic electrocoagulation of wastewater from a chocolate manufacturing industry: Anodic material effect (aluminium, copper and zinc) and life cycle assessment

Abstract

Wastewater from a chocolate industry with an acid pH (4.38), and a high content of organic matter (Chemical oxygen demand (COD) = 9566 mg/L), Biochemical oxygen demand (BOD5) of 4666.97 mg/L, biodegradability index (BI) of 0.49 and Total organic carbon (TOC) of 1318.7 mg/L, was treated by solar-photovoltaic electrocoagulation. The effects of anodic material (aluminium, copper or zinc), pH (4.38 and 7) and current density (1.781 mA/cm2 and 0.356 mA/cm2) at 60 min of treatment time were studied. The aluminium system exhibited the best results: 50% and 39% removal efficiency of COD and BOD, respectively. The BI increased considerably from 0.49 to 0.59 while TOC diminished only 26.65%. The copper-based cell also showed an acceptable behaviour in the organic removal that was: 43% COD, 53% BOD, 30.7% TOC and the BI was 0.4. The zinc-based system was slightly less efficient than copper and aluminium, where the removal achieved was: 39% COD, 30% BOD5, and 19% TOC. The BI showed an increase to 0.56, improving the biodegradability of wastewater. The quantification and characterization of sludge was carried out using SEM and EDS. Fourier Transform Infrared Spectroscopy (FTIR spectra) proved the removal of organic and nitrogenous matter by the coagulant. Although costs associated with energy savings were estimated, the use of a solar panel, nevertheless, led to energy reductions. According to Life cycle assessment, the Cu anode provided the highest environmental impact and the use of Zn involved a lower effect in all categories, except for marine ecotoxicity, human non-carcinogenic toxicity and human health.