Small-scale sour starch agroindustry in Colombia suffer from absence of water treatment. Although starch processing plants produce diluted wastewater, it is a source of pollution and cause environmental problems to the nearby rural population. A laboratory scale anaerobic horizontal flow filter packed with bamboo pieces was evaluated for the treatment of cassava starch extraction wastewater. The wastewater used in the experimentation was the draining water of the starch sedimentation basin. The reactor was operated for 6 months. It was inoculated with a semi-granular sludge from an anaerobic UASB reactor of a slaughterhouse. Maximum organic loading rate (OLR) applied was 11.8 g COD/L d without dilution of the wastewater. At steady state and maximum OLR applied, 87% of the COD was removed and a gas productivity of 3.7 L/L d was achieved. The average biogas yield was 0.36 L/g COD removed. Methane content in the biogas was in the range of 69-81%. The total suspended solids (TSS) removed were 67%. The relative high lactic acid content did not negatively influence the performance of the reactor. No perturbation due to cyanide (3-5 mg/L) was observed during the reactor operation. The results obtained indicated that the anaerobic horizontal flow filter could be used efficiently for the treatment of wastewater from Colombian starch processing small-scale agroindustry. (c) 2006 Elsevier Ltd. All rights reserved.