Investigação de hemiceluloses catiônicas obtidas de cascas de amendoim como coagulante primário no tratamento físico-químico de efluente sintético de laticínio

Abstract

Natural organic coagulants are presented as an alternative to the use of inorganic coagulants derived from aluminum and iron metal salts. Moreover, they have advantages in terms of possible safety for human health and ecosystems. In this direction, the main objective of this research was to investigate the synthesis of cationic hemicelluloses (CH), extracted from peanuts shells, and applied as an organic coagulant potential. Notice, the CH is a primary coagulant agent in the treatability process (coagulation, flocculation, and sedimentation) of a synthetic dairy effluent (SDE). The efficiency of CH was compared with a commercial coagulant well-established in the literature and industry, which is Tanfloc SG (TSG) - a polymer composed of cationic tannin purchased from the company TANAC Brasil S/A. The present work is divided into two phases, the synthesis of the CH and application in SDE. Initially, the hemicelluloses were cationized by etherification reaction in alkaline medium with 2,3-epoxy-propyl-trimethyl-ammonium chloride (ETA). Characterization was performed by Fourier transform infrared spectroscopy (FTIR), elemental analysis (AE), and degree of substitution (GS). The FTIR analyzes were also accompanied by a theoretical study by computational chemistry. In the second phase, the coagulant materials were applied by Jar Test, ranging from 5 to 11 coagulation pH and in dosages from 100 to 900 ppm. The assays generated coagulation diagrams, plotted by the spatial interpolation method of the Kringing regression model. The composition of the generated sludge was also analyzed using X-ray energy dispersive (EDS/SEM). The analysis of the floc morphology was performed by applying the non-intrusive method of image capture. Experimentally and theoretically FTIR analysis shows an increase in the intensity of the methyl groups band (-CH3) at 1475 cm-1, a serious indicator of cationization. The elemental analysis showed 1.92% (±0.09) of nitrogen in the structure of CH and GS of 0.32 (±0.01), close to the literature data. The optimal point selected experimentally from the coagulation diagrams, occurred for neutral cationic hemicellulose (NCH) and TSG at 400 ppm at coagulation pH 9.00 and 7.38, respectively. Removal efficiency with NCH and TSG was: 94.79 and 98.67% in turbidity; 56.72 and 65.21% for apparent color; 79.76 and 97.22% SST; 47.83 and 62.50% COD and 73.93 and 62.39% BOD5.20, in sequence. Previous information about the particles in the flocculation process showed a low variation of the fractal dimension (Df) of the flocs of 1.319 (±0.02) and 1.871 (±0.001), for NCH and TSG, respectively. During the analysis time, was occurs a stabilize tendency after 15 minutes of flocculation. It was also verified the formation of smaller and less dense flocs for NCH with diameters from 0.023 to 0.254 mm, justifying the slower sedimentation and dispersed flocs; while for TSG, it was obtained 0.032 to 5.718 mm. The statistical of the central composite design, indicated by the Pareto charts, that the coagulation pH contributes most significantly to the performance of both coagulants in SDE treatment, among the independent variables (coagulation pH and dosage). Consequently, the cationic hemicellulose, extracted and synthesized from an agro-industrial residue of peanut shells, are a promising alternative for application as primary coagulants. Forasmuch, as the NCH provided efficiency in the removal of the treatment investigated parameters and indicated a sludge with predominantly organic composition, which has advantages of biodegradability and final disposal.