Assessment of the anaerobic filters starting-up process for the treatment of instant coffee wastewaters

Abstract

The soluble coffee production process considers the stages of roasting, grinding, extraction, centrifugation, evaporation and drying, where approximately 10.62 L of wastewater / kg of soluble coffee produced are generated. They are characterized by having a high content of suspended and dissolved organic matter, high chemical and biochemical oxygen demand (COD, BOD). Considering that anaerobic digestion is an alternative for the treatment of these residuals, the adaptation of a bovine manure inoculum for anaerobic reactors in a semi-continuous regime was evaluated. Four up-flow reactors, two mesophilic (35+2ºC) and two thermophilic (55+2°C), were used for a total period of 49 days. The inoculum was characterized as a function of pH and SSV, while dissolved oxygen, salinity, pH, tannins and COD were determined for the substrate. For the inoculum, a pH close to neutrality and SSV higher than 50% on a dry basis were obtained. The characterization of the substrate showed a decrease in pH probably caused by the presence of volatile fatty acids that contributes to acidogenesis. The highest total methane production during the whole experiment was 12.4 mL CH4 corresponding to one of the thermophilic reactors. Despite the presence of inhibitory compounds such as tannins, stable behavior was evident in the anaerobic digestion process and adaptation of the inoculum to the substrate, thus representing an alternative for the digestion of instant coffee wastewater.