Use of different coagulants for cassava processing wastewater treatment

The processes necessary for transformation of cassava into starch generate several residues, among them cassava wastewater (manipueira) that has high pollutant load. For the effluent treatment system it is essential to remove sedimented suspended solids, which can be performed by the coagulation/flocculation/sedimentation process (C/F/S), requiring a comparative study between coagulants for the successful selection of the coagulant and its dosage. Therefore, the aim of this work was to investigate the efficiency of different coagulants in color and turbidity removal of starch industry effluent. In this way, jar-test experiments were conducted. Four natural commercial coagulants (Acquapol WW, Acquapol S5T, Tanfloc SL, Tanfloc SG) and a chemical coagulant (Al2SO4) were tested at concentrations of 160, 320, 480, 640 and 800 mg L−1, setting the fast mixing stage for 2 min at 120 rpm and the slow mixing stage for 15 min at 20 rpm, at natural pH of the effluent. Among the studied coagulants, natural commercial coagulants presented greater efficiency of color and turbidity removal when compared to chemical coagulant, besides having the advantage of being non-toxic and from renewable source. All coagulants had a minimum sedimentation time of 15 min. The best natural coagulant (Acquapol S5T and Tanfloc SL) concentration determined from statistical analysis (ANOVA, p-value <0.05; Turkey's test, p-value >0.05) was 320 mg L−1, capable in removing color (≥77.5%) and turbidity (≥88.5%) parameters for treatment of the studied effluent. The C/F/S process employing these two selected coagulants proves to be an effective physico-chemical method for primary treatment of this type of effluent, contributing to the improvement in wastewater quality.