Treatment of vinasse from sugarcane ethanol industry: H2SO4, NaOH and Ca(OH)2 precipitations, FeCl3 coagulation-flocculation and atmospheric CO2 carbonation

Abstract Vinasse is a key by-product of the ethanol manufacturing industry. Several processes have been studied for the first time in order to treat sugarcane vinasse. Removals of the absorbances (220, 254 and 410 nm) and nutrients (Ca, Mg, P, N, K and Na)≤36% were achieved in the H2SO4 precipitation with the production of a low sludge volume (rich in organic matter and magnesium). A nominal chemical oxygen demand (COD) decline = 12% was also noted when using H2SO4 precipitation, owing to the presence of soluble organic acids in vinasse. Operating pH in the Ca(OH)2 precipitation affected the removal of COD, absorbances and nutrients, obtaining high efficiencies (COD = 51%, absorbances = 88–100%, Mg = 91%, N = 74%, K = 37%, P = 95%, Na = 20%) for high precipitation pH (12–12.5). High depletions in the Ca(OH)2 precipitation can be explained by the formation of insoluble species and polymerization and precipitation of fatty acids, producing a sludge rich in Ca, P, K and Mg. Comparable results were attained for the thermocalcic precipitation. NaOH precipitation treatability for the vinasse decontamination was based on the removals of Ca (80%), P (74%), Mg (64%), N (24%), K (19%), generating a sludge rich in organic matter and nutrients (Mg, K, P and Na). The supernatant produced in the Ca(OH)2 precipitation, under optimal conditions, was subjected to: 1) a coagulation-flocculation step with FeCl3 addition (1 g L−1), improving the removals of absorbance at 410 nm, COD, phosphorus and volatile solids (VS); and 2) a novel green technology (natural carbonation) for the atmospheric CO2 mitigation with treatment and neutralization of the effluent.