Combination treatment of corn starch wastewater by sedimentation, microfiltration and reverse osmosis

Combination treatment of sedimentation, microfiltration and reverse osmosis was investigated to recover solids from wastewater produced during the washing of corn starch. Sedimentation was carried out in a column 2.55 m high using a simulated solution of dry corn starch and real corn starch wastewater effluent. Microfiltration using a 0.2 mu m PVDF membrane of 7.5 m(2) was carried out in a real production plant on wastewater solutions with and without a prior sedimentation step. The permeate of the microfiltration was subjected to reverse osmosis stage in a laboratory flat cell. The sedimentation showed that the settling velocities were very slow, and depended strongly on the molecular structure of the modified starches and the composition of the wastewater, especially when salt was present because cationic starch production. The highest concentration factor achieved by microfiltration was 8.25 in the case of oxidized starch with prior sedimentation. The highest volumetric reduction percentage and the highest flux were obtained with cationic starch without sedimentation. A sedimentation was useful in the case of oxidized starch but did not improve the processing of cationic starch. When the reverse osmosis stage was included, BOD(5) in the discharge water was reduced to just 31.2 mg O(2)/L. (C) 2011 Elsevier B.V. All rights reserved.