In wastewater treatment, flocculation is a widely used solid/liquid separation technique, which typically employs a charged polymer, a polyelectrolyte (PEL). Polyelectrolytes features, such as charge type, charge density and molecular weight, are essential parameters affecting the mechanism of flocculation and subsequent floc sedimentation. The effectiveness of the process is also influenced by the characteristics of the system (e.g., type, size, and available surface area of suspended particles, pH of the medium, charge of suspended particles). Thus, a good understanding of the flocculation kinetics, involved mechanisms and flocs structure is essential in identifying the most adequate treatment conditions, having also into consideration possible subsequent treatments. In this study, Eucalyptus bleached pulp and a cellulosic pulp with high lignin content (∼4.5 wt%) obtained from Eucalyptus wood waste were used for bio-PELs production. Firstly, a pre-treatment with sodium periodate increased the pulps reactivity. To produce cationic cellulose the oxidation step was followed by the introduction of cationic groups in the cellulose chains, through reaction with Girard's reagent T. Applying different molar ratios (0.975 and 3.9) of Girard's reagent T to aldehyde groups led to cationic PELs with diverse charge density. On the other hand, to obtain anionic cellulose a sulfonation reaction with sodium metabisulfite was applied to the intermediate dialdehyde cellulose-based products, during 24 or 72 h, and anionic-PELs with diverse features were obtained. The developed water soluble, anionic and cationic bio-PELs were characterized and tested as flocculation agents for a textile industry effluent treatment. Initially, jar-tests were used to tune the most effective flocculation procedure (pH, flocculant dosage, etc.). Flocculation using these conditions was then monitored continuously, over time, using laser diffraction spectroscopy (LDS). Due to the small size of the dyes molecules, a dual system with an inorganic complexation agent (bentonite) was essential for effective decolouration of the effluent. Performance in the treatment was monitored first by turbidity removal evaluation (75-88% with cationic-PELs, 75-81% with anionic-PELs) and COD reduction evaluation (79-81% with cationic-PELs, 63-77% with anionic-PELs) Grenda et al.Evaluation of Anionic and Cationic Pulp-Based Flocculants in the jar tests. Additionally, the evolution of flocs characteristics (structure and size) during their growth and the flocculation kinetics, were studied using the LDS technique, applying the different PELs produced and for a range of PEL concentration. The results obtained through this monitoring procedure allowed to discuss the possible flocculation mechanisms involved in the process. The results obtained with the bio-PELs were compared with those obtained using synthetic PELs, commonly applied in effluents treatment, polyacrylamides. The developed bio-PELs can be competitive, eco-friendly flocculation agents for effluents treatment fro...
Eucalyptus wood waste has been used to produce cationic lignocellulose-based polyelectrolytes (PELs) and the new PELs proved to be efficient flocculants in the decoloration of dye-containing waters with potential application in several industries.
Natural-based polyelectrolytes (PELs), with all the advantages coming from being produced from renewable and biodegradable sources, are a potential solution for the removal of dyes from wastewater. In this work, surplus Eucalyptus bleached cellulose fibres from a paper mill were modified to increase the charge and solubility of cellulose. First, reactive aldehyde groups were introduced in the cellulose backbone by periodate oxidation of cellulose. Further modification with alkylammonium produced positively charged cellulose-based PELs. The final products were characterized by several analytical techniques. The PEL with the highest substitution degree of cationic groups was evaluated for its performance in decolouration processes, bentonite being used as aid. This was found to be effective for colour removal of either anionic or cationic dyes. Bio-PELs can thus be considered as very favourable eco-friendly flocculation agents for decolouration of harsh effluents from several industries, considering their biodegradable nature and thus the ability to produce less sludge.
Bark tannin extract from Acacia mearnsii (Mimosa ME) was modified at laboratory and pilot plant scales via the Mannich condensation reaction using formaldehyde and dimethylamine hydrochloride. Several conditions were varied during the modification procedure (heating rate, formaldehyde dosage, and Mannich solution activation time) to evaluate their influence on the shear viscosity and shelf life of the resulting products. It was possible to tune these properties with the reaction conditions. Modified condensed tannins with five distinct shear viscosities (30 cP to 430 cP) were selected to test the colour removal of anionic (Duasyn Direct Red and Acid Black 2) and cationic (Methylene Blue and Crystal Violet) dyes. The performance was monitored by ultraviolet spectroscopy. Colour removal was studied over different pH levels (1 to 14). Good decolouration results (85% to 96% reduction) were obtained with the simultaneous introduction of other additives to the process, which were bentonite and a cationic or anionic polyacrylamide, with minimal dosages of the latter additives. An improvement to decolouration performance with an increase in the biocoagulant viscosity was typically observed. However, for practical applications, modified condensed tannins with a lower viscosity may be preferred because they exhibited a longer shelf life and presented reasonable removal efficiencies.
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