The sedimentation stage of the cassava-starch extraction process generates the largest pollutant load in terms of quantity and quality of wastewater. In the north of Cauca department, there are several anaerobic filters for wastewater treatment which have shown deficiencies associated with environmental and operational factors. The evaluation of start-up and the performance of full-scale anaerobic filter evidenced the need to adjust chemically the wastewater with a minimum dose of 2180 mg NaHCO 3/L and the Buffer Index (BI) was shown as a simple and efficient tool for process control since allowed to determine instability conditions when its value was higher than 0,35. In stable conditions (TRH theoretical 12 hours; TRH real 10,2 hours), with chemical adjusting and BI inside the appropriate range (0,20 -0,30), the reactor reached COD and TSS removal efficiencies more than 77 and 76% respectively .