An Eco-Friendly Approach: Incorporating a Xylanase Stage at Various Places in ECF and Chlorine-based Bleaching of Eucalyptus Pulp

Abstract

A potentially more environmentally compatible approach was evaluated, involving the use of an enzyme (X) stage optimally inserted into various bleaching sequences for Eucalyptus kraft pulps. The efficacy of the X stage was evaluated in terms of final brightness, CIE whiteness, post-color number (brightness reversion), effluent characteristics, etc. The results showed considerable benefits with an enzymatic pre-treatment bleaching sequence for improved final pulp brightness (1.6 units higher) and reduced adsorbable organic halogens (AOX) (32% lower), in addition to improved biological oxygen demand (BOD) to chemical oxygen demand (COD) ratio, when using 0.5 kg/t pulp dosage of xylanase; enzymatic posttreatment bleaching sequences were observed to boost final CIE whiteness up to 3.4 units and to reduce post color number by 48% at 0.5 kg/t pulp dosage of xylanase. In addition, approximately 32% reductions in AOX released, as well as appreciable improvement in BOD-to-COD ratio, were observed in the bleach effluents. An improved ratio of BOD-to-COD facilitates possible enhancement in the bio-degradability of discharge effluents in a secondary treatment stage. Nine different bleaching sequences were compared. Three sequences for each category (pre-treatment, intermediate, and post-treatment bleaching sequences) were performed to provide an overview of the influence of xylanase treatment on various pulp properties and environmental sum parameters of the ensuing effluents.

Pulp and Paper Mill Effluent Management

“…FTIR and GC-MS were used to characterize the bleach effluent. Gangwar et al (2016) investigated the use of xylanase as either pretreatment, post-treatment or intermediate treatment together with three bleach sequences. The results were measured in terms of pulp and effluent characteristics.…”

Modelling and optimization of the last two stages of an environmentally-compatible TCF bleaching sequence

“…Hence, bleaching accomplishes the following objectives: (i) to modify the reactivity of the cellulose in the resulting dissolving pulp; (ii) to meet customer requirements that utilize the dissolving pulp; and (iii) to increase brightness and purity of the dissolving pulp (Liu et al 2016;Chen et al 2016). There are numerous bleaching sequences employed to improve pulp reactivity and adjust pulp viscosity, such as chlorinebased bleaching (Gangwar et al 2016), elemental chlorine free (ECF) (Bodhlyera et al 2015;Li et al 2015;Yao et al 2016), catalytic bleaching (Kumar Chenna et al 2016;Afsahi et al 2018); total chlorine free (TCF) (Li et al 2015;Zhou 2015;Veisi and Mahdavi 2016), and bio-bleaching with enzymes, such as cellulases (Duan et al 2017;Hutterer et al 2017), endoglucanase (Quintana et al 2015a), xylanase (Hutterer et al 2017;Zhao et al 2017), or laccase (García-Fuentevilla et al 2015;Quintana et al 2015b).…”

The effect of mechano-enzymatic treatment on the characteristics of cellulose nanofiber obtained from kenaf (Hibiscus cannabinus L.) bark

“…Hence, the remaining fraction of lignin in the cellulose residue obtained from the HTP process must be removed by the process of chemical bleaching, which conventionally employs a large amount of chlorine and chlorine-based chemicals. However, the use of such chemicals liberates several toxic materials and polluting products that contaminate the bleaching effluent, including absorbable organic halides (AOX) (Gangwar et al 2016;Pei et al 2016).…”

“…A recent alternative technique with greater prospects for long-term consequences is xylanase treatment; this technique has been used before the bleaching process to decrease the use of chemicals (Gangwar et al 2016;Saelee et al 2016). The beneficial effect of xylanase during the delignification process is the selective hydrolysis of xylan reprecipitated on the fiber surface, which improves the permeability of the fiber to the bleaching chemicals (Roncero et al 2005;Gangwar et al 2016).…”

“…A recent alternative technique with greater prospects for long-term consequences is xylanase treatment; this technique has been used before the bleaching process to decrease the use of chemicals (Gangwar et al 2016;Saelee et al 2016). The beneficial effect of xylanase during the delignification process is the selective hydrolysis of xylan reprecipitated on the fiber surface, which improves the permeability of the fiber to the bleaching chemicals (Roncero et al 2005;Gangwar et al 2016). Moreover, xylanase treatment increases the extractability of the chromophores associated with lignincarbohydrate complexes (LCCs) and the hydrophobic materials from the fibers, as indicated by an increase in fiber brightness (Shatalov and Pereira 2009;Gangwar et al 2016).…”