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

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) 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 from several industries, when compared to traditional synthetic flocculants with a significant environmental footprint. Moreover, LDS proved to be a feasible technique to monitor flocculation processes, even when a real industrial effluent is being tested

Pre-treatment of industrial olive oil mill effluent using low dosage health-friendly cationic polyelectrolytes

Olive oil production involves a significant annual release of industrial olive oil mill effluent (OME) to the environment. These discharges bring serious environmental problems since they are extremely hazardous for the aquatic environment due to their organic matter and high turbidity levels. The present study comprises the development of new, hydrophobically modified, cationic flocculants directed to oily effluents application. A health-friendly formulation was used in their synthesis process, performed by inverse-emulsion. In particular, Poly(AAm-MAPTAC) was synthesized in two different polymer compositions and, as well, with the presence of a hydrophobic monomer (Poly(AAm-MAPTAC-SMA)) at several compositions up to 8wt%. The obtained polyelectrolytes were characterized in terms of final composition, hydrodynamic diameter, zeta potential and molecular weight. Their flocculation performance was evaluated in an industrial oily effluent from an olive oil mill. Results revealed that the hydrophobic modification improves noticeably the flocculation performance of cationic polyelectrolytes in the treatment of olive oil mill effluents. In the best conditions, it was possible to achieve 90% turbidity reduction, 47% COD removal and 34% total solids removal with only 53mg/L of flocculant. Moreover, 79% of turbidity was reduced after addition of 13mg/L

Evaluation of Anionic Eco-Friendly Flocculants Prepared from Eucalyptus Pulps with Diverse Lignin Contents for Application in Effluent Treatment

Modification of cellulosic-rich materials for the production of cellulose-based polyelectrolytes (PELs) can bring several benefits, such as high biodegradability and low or no toxicity, for numerous applications, when compared with the use of traditional, synthetic PELs. Moreover, cellulose-based PELs originating from wood wastes, contribute to the valorisation of such wastes. In this work, Eucalyptus pulps with diverse lignin contents, extracted from Eucalyptus wood wastes, were anionized by a two–step reaction procedure (periodate oxidation followed by sulfonation). Applying different reaction times (24–144 h) in the sulfonation step allowed for producing a range of cellulose-based anionic PELs with different characteristics. PELs obtained after 24 and 72 h of sulfonation were thoroughly characterized (Fourier transform infrared and 1H nuclear magnetic resonance spectroscopies, anionic group content (elemental analysis), zeta potential and hydrodynamic diameter (dynamic light scattering)) and subsequently evaluated as flocculants in decolouration processes of model effluents (Methylene Blue and Crystal Violet) and an industrial effluent from a textile industry. Furthermore, possible flocculation mechanisms induced by the use of the various PELs are discussed. Results are compared with those obtained with a commonly applied, synthetic flocculant (polyacrylamide). It is demonstrated that it was possible to obtain water-soluble lignocellulosic PELs starting from raw materials with different degrees of purity and that those PELs are promising eco-friendly alternative flocculation agents for the decolouration of effluents

Flocculation Treatment of an Industrial Effluent: Performance Assessment by Laser Diffraction Spectroscopy

Flocculation processes are extensively used as separation methods to remove suspended and dissolved solids, colloids, and organic substances in effluents. As flocculation performance affects the economy of many industrial processes, it is important to understand the underlying mechanisms, as well as the predominant flocculant properties influencing the final results. In the present study, a strategy based on the use of laser diffraction spectroscopy was developed to screen different flocculants performance in an industrial potato crisps manufacturing effluent, using anionic polyelectrolytes as flocculants. The flocculation process was monitored over time, and information on floc average size and structure was obtained. The effect of flocculants properties, including their hydrophobic content and concentration, on the flocculation process and on flocs density was investigated. With this methodology for continuous monitoring of the flocculation process in real effluents, it is possible to obtain simultaneously information about the kinetics of floc size evolution and also about the evolution of floc structure with time. This is an important proof of concept, since it will allow in the future to perform prescreening of polymers to be used in the flocculation treatment of a specific effluent, minimizing in this way pilot trials. The highest polyelectrolyte concentration studied leads to the largest flocs obtained, which were, however, very sensitive to the turbulent environment. This agrees with the low scattering exponent values obtained for all the flocs, which indicate an open and porous floc structure. Characteristics of the polymers used proved to have an important role in the floc size. Higher zeta potential, hydrodynamic diameter, and molecular weight of the flocculant resulted in larger flocs. The presence of hydrophobicity in the polyelectrolyte also was showed to influence the floc properties, although an optimum content could be identified above which flocculation was hindered

Cationization of Eucalyptus wood waste pulps with diverse lignin contents for potential application in colored wastewater treatment

Modification of cellulosic-rich materials such as Eucalyptus wood waste and production of cellulose-based polyelectrolytes (PELs) presents several advantages for a variety of applications, when compared to the utilization of synthetic PELs, due to the nature, availability, high biodegradability and low or no toxicity of cellulosic materials. Moreover, valorization of the cellulosic waste itself to provide end products with higher added value is also an important aspect. In the present work, the objective was to evaluate the possibility of cationizing more complex and heterogeneous chemical pulps, obtained from Eucalyptus wood waste, with different cellulose purity and a relatively high lignin content (up to 4.5%). A two-step reaction (with sodium periodate and Girard's reagent T) was employed and a range of cellulose-based cationic polyelectrolytes were produced with different degrees of substitution. The final products were characterized by several analytical techniques and the bio-PELs with the highest and the lowest substitution degree by cationic groups were evaluated in a new application, as flocculants in the decoloration of model effluents, bentonite having been used as an inorganic aid. Also, possible mechanisms of flocculation were discussed and the results compared with those of a synthetic flocculant, often used in these treatments, cationic polyacrylamide. Lignocellulosic-PELs proved to be very favorable eco-friendly flocculation agents for the decoloration of dye-containing waters with potential application in several industries

Anionic Polyelectrolytes Synthesized in an Aromatic-Free-Oils Process for Application as Flocculants in Dairy-Industry-Effluent Treatment

The wastewater generated from many industries contains suspended and dissolved solids, including organic and inorganic particles, metals, and other impurities. Direct flocculation is regularly used to neutralize the charge of the colloidal particles and bridge the destabilized particles together to form flocs in a cost- and time-effective way. This work refers to the development of new anionic flocculants (co- and terpolymers) tailored to be used in dairy-effluent treatment, using a synthesis process in which new oil phases free of aromatics are applied. Regarding the terpolymers, anionic polyacrylamides were synthesized in the presence of three different hydrophobic monomers at different concentrations. Flocculation performance was evaluated using an effluent from dairy industry. Results show that the developed polyelectrolytes are very promising additives for the treatment of the mentioned effluent. For optimized conditions, 95% turbidity reduction, 44% chemical-oxygen-demand removal, and 57% total-solids removal were achieved with only 53 mg/L of flocculant

Analysis and prediction of cluster formation

An experimental and theoretical analysis of the interaction of titanium dioxide particles during coagulation was performed, using laser light dynamic scattering (LDS) and both von Smoluchowski and reversible coagulation approaches. For cluster formation, different initial particle numbers and different shear rates were investigated and the experimental data were fitted to a mathematical model based on aggregation and disaggregation processes. The primary particle size was less than 1 micrometre, but in all cases the LDS information showed that primary clusters of 3.5 micrometres were rapidly formed, which then went on to cluster further to provide larger aggregates. Hence, the modelling approach was one of cluster-cluster aggregation and disaggregation, rather than primary particle aggregation