Electrooxidation studies of swine effluents before and after the anaerobic digestion process

Abstract

The electrochemical behavior of raw and anaerobically pretreated swine wastewater was studied for energy recovery and water treatment. Voltammetric studies using platinum (Pt) electrodes have shown the existence of a characteristic anodic peak, possibly corresponding to the electrooxidation of aromatic compounds in solution. Kinetic parameters taken from Tafel analysis demonstrated the superior performance of Pt for hydrogen evolution reaction in comparison to nickel (Ni). Consecutive electrolysis using Ni electrodes showed that these modestly reduced the chemical oxygen demand (COD) from the wastewater (12.3 ± 1.61 % and 12.7 ± 0.88 % removal for the raw (RW) and digested (DW) wastewater, respectively). On the other hand, graphite anodes achieved degradations of 37.0 ± 1.97 % and 25.5 ± 2.95 % COD removal for RW and DW. The results were confirmed by fitting a pseudo-first-order model and suggest different oxidation mechanisms at the two electrodes. Meanwhile, Fourier-transform infrared spectra demonstrated that biological pretreatment affected the bioavailability of aliphatic compounds, such as saccharides, peptides, and fats, while thermogravimetric analysis reflected the degree of biological stabilization of both swine solutions. These findings indicate that SW offers high potential as an electrolyte solution to following this new electrochemical approach to the valorization of SW.