Efficiency of chitosans for the treatment of papermaking process water by dissolved air flotation

Abstract

Interest has grown in bio-polymers as being environmental friendly alternatives to synthetic additives. In this work, two native chitosans with different molecular weights have been evaluated on a laboratory scale for their effectiveness for the removal of contaminants from papermaking process waters by dissolved air flotation (DAF). The use of chitosan quaternary derivatives and the use of the native chitosans in combination with anionic bentonite microparticles have also been tested. Results demonstrate a high efficiency of the native chitosan products at intermediate dosages and furthermore, their efficiency is enhanced by the combined addition of bentonite. For an equivalent removal of contaminants, the required dosage of chitosan is about half that the dosage required in absence of bentonite. Quaternary derivatives have not improved the efficiency of the native chitosan in this case. The optimum treatment would be 50 mg/L of native chitosan and 100 mg/L of bentonite where this treatment is capable of the removal of 83-89% turbidity (residual turbidity 210-320 NTU), 68-71% dissolved turbidity (residual dissolved turbidity of 22-24 NTU), 18-22% total solids (residual total solids of 2750-2900 mg/L) and 19-23% COD (1440-1525 mg/L). The low molecular weight native chitosan is more efficient than the medium molecular weight chitosan in all cases. The Focused Beam Reflectance Measurement (FBRM) is used to assess the aggregation process and to predict the separation efficiency of DAF units either with single or dual systems. The efficiency predicted through the FBRM technique is very similar to that obtained later in the DAF tests.

Wastewater Treatment and Reclamation: A Review of Pulp and Paper Industry Practices and Opportunities

“…Rodrigues et al (2008) reported that the chitosan treatment favored settling and the formation of a dense sludge. Miranda et al (2013) showed the efficiency of chitosans for the treatment of process water by DAF. …”

“…The charge demand corresponds to the amount of a strongly charged polyelectrolyte that needs to be added to reach a charge-neutral condition of the surfaces (Rasteiro et al 2008; Blanco et al 2002a,b). This approach has been used to optimize dissolved air flotation systems for pulp and paper mills (Negro et al 2005; Saarimaa et al 2006a,b;Miranda et al 2008Miranda et al , 2009bMiranda et al , 2013. …”

Efficiency of Chitosan and their Combination with Bentonite as Retention Aids in Papermaking

“…It also has a unique set of properties such as natural cationic charge density, biodegradability, biocompatibility, non-toxicity, and antimicrobial activity (Crini and Badot 2008;Renault et al 2009;Thakur and Thakur 2014). These specific properties make it suitable for a large range of applications, including coagulationflocculation processes (Bratskaya et al 2004;Renault et al 2009;Zemmouri et al 2011;Miranda et al 2013;Yang et al 2016). The most relevant characteristics of chitosan in relation to flocculation are charge density (related to its deacetylation degree), molecular weight, and molecular structure (Renault et al 2009;Thakur and Thakur 2014).…”

“…However, there have been no studies regarding the possible combination of chitosan with other typical components of microparticle retention systems, such as bentonite. Some previous works, which focused on process waters and wastewaters, have demonstrated that bentonite improves the size and density of flocs formed with chitosan, thus increasing flocculation rate (Roussy et al 2005a,b;Cai et al 2010;Miranda et al 2013).…”

“…At present, there are only a few applications of chitosan in papermaking, mainly focusing on the surface treatments in the production of specialty paper grades (Kuusipalo et al 2005;Bordenave et al 2010;Reis et al 2011), the improvement of the wet and dry strength of paper (Laleg 2001;Nada et al 2006;Jahan et al 2009;Chen et al 2013), water treatment (Wang et al 2009;Miranda et al 2013), or its possible use in wet end applications as an anionic charge neutralization system (Bobu et al 2002;Li et al 2004b;Belosinschi and Bobu 2008;Nicu et al 2011;Nicu et al 2013).…”