Treatment of Coffee Wastewater with recirculation: optimization and validation

The recirculation of Coffee Wastewater makes it even more polluting and can cause serious impacts if released into the environment without treatment. A very promising technique is electrolytic treatment; however, high hydraulic detention times can make the treatment unfeasible, consuming a lot of electrical energy and increasing the wear of the electrodes. For this reason, the objective of this study was to optimize the treatment time of this effluent based on the efficiency of removing turbidity, total solids and chemical oxygen demand, monitoring the behavior of pH and electrical conductivity. For this purpose, an electrolytic reactor of 1000 cm3 were used, varying the plate distance, current density and effluent collection from the reactor. It was found, which the optimal operating conditions are in average hydraulic detention times intervals of 2614 s, current density of 64 A m−2 and plate distance of 20.66 mm. The adjusted model was designed to overestimate turbidity by 31% and to underestimate total solids by 3%, whereas for chemical oxygen demand there was no change in the prediction. The validation of the treatment in the optimized conditions demonstrated removal of 95.85%, 24.34% and 9.71%, for turbidity, total solids and chemical oxygen demand, respectively. Higher removal rates were evidenced for total solids, turbidity and chemical oxygen demand, in that order, 90.71 mg L−1 min−1, 55.11 NTU min−1 and 41.98 mg L−1 min−1, respectively. The overall electrical consumption was 11.16 kW h m−3, while the operational treatment cost was US$ 0.79 m−3.