Hemiceluloses catiônicas produzidas a partir da palha de milho e utilizadas como coagulante primário no tratamento de água bruta de abastecimento

Abstract

The cationic hemicelluloses (HC), obtained from the extraction of hemicelluloses from the straw covering the corn cob (PM), is considered an alternative to inorganic coagulants in the treatment of raw water. Since the PM is a renewable source, the conversion of lignocellulosic biomass into added value products is important to a sustainable management of agricultural waste, which is the context of this research. In the initial stage, the hemicellulose extraction of the PM was carried out through the Oxiorganosolv method, using hydrogen peroxide in a basic alcoholic medium. In the cationization of HC, we’ve used 2,3-epoxy-propyl-trimethyl-ammonium chloride (ETA), as a medium basic cationizing agent. The characterization of the hemicellulose and the HC was accomplished through Fourier-transform infrared spectroscopy (FTIR), elemental analysis (EA), and calculation of degree of substitution (GS). The FTIR spectrum showed an increase in the intensity of the methyl group band (-CH3) at 1476 cm-1, with a strong indication of cationization of the hemicelluloses. The AE of the HC showed 2.21 (±0.14) % nitrogen in the structure of the HC and GS of 0.413 (±0.001). The hemicelluloses showed negative zeta potentials, while the HC showed positive zeta potentials, indicating that the ETA was inserted into the hemicelluloses’ structure. The HC were applied as a primary coagulant in raw water supply from Uberabinha River, collected at Renato de Freitas Water Treatment Plant, in the municipality of Uberlândia - MG. In jar test trials we accomplished, with a coagulation pH range of 5 to 11, dosages of 0.5 to 4.0 ppm HC, with sedimentation time of 20 and 30 minutes, and the coagulation diagrams were elaborated using radial basis interpolation. In the treatability tests, the best results were found with a dosage of 3.0 ppm, a sedimentation time of 20 minutes and a coagulation pH of 9.16, with apparent color and turbidity removal of 66.3% and 89.2%, respectively, resulting in apparent color of 13.7 uH and turbidity of 0.9 uT. Therefore, considering this efficiency, we concluded that the HC extracted and synthesized from the PM agro-industrial waste are a promising alternative as a primary coagulant in the treatment of water supplies, since they provided the removal of apparent color and turbidity parameters within the limits established by normative standards - suggesting the advantage in a more sludge with higher biodegradability and of less environmental impact, when compared to the use of inorganic coagulants.