Evaluation of Anionic and Cationic Pulp-Based Flocculants With Diverse Lignin Contents for Application in Effluent Treatment From the Textile Industry: Flocculation Monitoring

Abstract

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...

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“…The turbidity is sometime applied for determination of color removal, e.g., in wastewater treatment from the textile industry: where R d is dye removal (%) and T o and T f are the turbidity of the initial wastewater and after treatment at a given time, respectively [ 49 ].…”

“…The transformation of cellulose into a more useful soluble form is possible by chemical reactions leading to ionic character. There are numerous studies on cellulose derivatives of anionic [ 49 , 98 , 99 , 102 ], cationic [ 49 , 103 , 149 ] and amphoteric [ 104 ] nature, as high-performance polymer flocculants.…”

“…Grenda and co-workers [ 49 ] described the chemical modification of cellulose leading to cationic and anionic polyelectrolytes with different charges. The raw materials for obtaining flocculants were Eucalyptus bleached pulp and a cellulosic pulp with high lignin content (∼4.5 wt%).…”

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“…In cellulose, the reaction occurs on the hydroxyl groups of the beta-glucan units (Figure 11), thus allowing the potential grafting of new functional groups and extending the range of practical applications [74]. SE parameter provides a mean of expressing the degree to which primary particles fill the space within the nominal volume occupied by an aggregate, that is, its compactness [68,70]. This strategy allows pre-screening the best flocculants for a certain application, without requiring expensive pilot tests.…”

“…It has been show that the flocculation process can be followed by laser diffraction spectroscopy (LDS), which monitories the mean size distribution of the flocs, over time, enabling the evaluation of the kinetics of the flocculation phenomena [ 68 ]. Additionally, it allows inferring on the flocs structure, either by assessing their time resolved fractal dimension or their scattering exponent (SE) [ 69 ].…”