Slaughterhouse wastewater treatment by a combined anaerobic digestion/solar photoelectro-Fenton process performed in semicontinuous operation

A new semicontinuous anaerobic digestion/solar photoelectro-Fenton (SPEF) process for the treatment of slaughterhouse wastewater is studied. An Upflow Anaerobic Sludge Blanket (UASB) reactor was used at two different organic load rates (OLR) (3.94 and 8.15 g COD L⁻¹ d⁻¹), while the SPEF was carried out in a photoelectrochemical reactor using a filter press cell with a DSA anode and an air diffusion cathode. The results showed that the UASB reactor achieved up to 70% COD removal for the highest OLR, with a low efficiency of suspended solid removal. The anaerobic effluent was treated by the SPEF process, resulting in 88% and 72% COD removal for the initial concentrations of 195 ± 14 mg L⁻¹ and 867 ± 52 mg L⁻¹, respectively, and a turbidity reduction of up to 80%. The treatment of wastewater by SPEF using a current density of 10 mA cm⁻² was five times less costly than that of 25 mA cm⁻², with an associated cost of 1.4 USD h⁻¹ for the treatment. The proposed semicontinuous processes eliminate at least 91% of the total COD, thus representing a new option for the treatment of slaughterhouse wastewater.