Evaluation of three types of limes for the primary treatment of coffee wastewater Evaluación de tres tipos de cal para el tratamiento primario de las aguas residuales del café

In order to find an alternative for the primary treatment of coffee wastewater to optimize the functioning of biological systems and the conditioning of water for subsequent treatments with chemical products,  neutralization and precipitation processes were evaluated. Three types of lime (agricultural, dolomite and slaked) were added to the residual water, selecting the one with which the lowest absorbance and pH values were obtained in the ranges required for secondary treatment. For the selected lime, the efficiency in the removal of organic load was evaluated in terms of chemical oxygen demand (COD) and TSS. For the evaluations, five doses of lime and 2 concentrations of COD (12,500 and 25,000 mg L-1) of wastewater were used. Slaked lime (calcium hydroxide) was found to be the most appropriate for primary treatment of coffee wastewater, with the lowest absorbance values (between 0.392 and 1.089), as well as pH values in pretreated water between 5.6 and 12.0. Additionally, with slaked lime, removal percentages were achieved in the organic pollutant load, expressed as COD, close to 50% and TSS higher than 75%. The optimal doses for the primary treatment with slaked lime, under the evaluated conditions, were 2.60 g of lime per liter of wastewater with COD of 12,500 mg L-1 and 4.63 g of lime per liter of wastewater with COD of 25,000 mg L-1.