Evolution of Lignocellulosic Macrocomponents in the Wastewater Streams of a Sulfite Pulp Mill: A Preliminary Biorefining Approach

Abstract

The evolution of lignin, five- and six-carbon sugars, and other decomposition products derived from hemicelluloses and cellulose was monitored in a sulfite pulp mill. The wastewater streams were characterized and the mass balances throughout digestion and total chlorine free bleaching stages were determined. Summative analysis in conjunction with pulp parameters highlights some process guidelines and valorization alternatives towards the transformation of the traditional factory into a lignocellulosic biorefinery. The results showed a good separation of cellulose (99.64%) during wood digestion, with 87.23% of hemicellulose and 98.47% lignin dissolved into the waste streams. The following steps should be carried out to increase the sugar content into the waste streams: (i) optimization of the digestion conditions increasing hemicellulose depolymerization; (ii) improvement of the ozonation and peroxide bleaching stages, avoiding deconstruction of the cellulose chains but maintaining impurity removal; (iii) fractionation of the waste water streams, separating sugars from the rest of toxic inhibitors for 2nd generation biofuel production. A total of 0.173 L of second-generation ethanol can be obtained in the spent liquor per gram of dry wood. The proposed methodology can be usefully incorporated into other related industrial sectors.

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

“…A recent study with the Z(EOP)(PO) bleach sequence (Llano et al 2015) showed an increase of intrinsic pulp viscosity from 560 mL after the Z stage to 610 mL/g after the (EOP) stage. The study also showed that the hemicelluloses in the AS eucalypt pulp decreased from 5.1% to 2.2%, and the xylan decreased from 4.5% to 1.7% when going through the (EOP) stage.…”

“…Some processes that are being investigated to produce dissolving pulp are the SO2-ethanol-water (SEW) process (Iakovlev et al 2011;Yahamoto et al 2014) or the direct purification of paper-grade pulp (Roselli et al 2014;Duan et al 2017). Other well-known processes already manufacture dissolving pulps, such as prehydrolysis kraft (PHK) (Duan et al 2015;Matin et al 2015;Chen et al 2016), prehydrolysis soda-anthraquinone (SAQ) (Sixta and Schild 2009) and acid sulfite (AS) (Llano et al 2012;Llano et al 2015).…”

“…These stages were investigated to see how they affected the physico-chemical properties of the resulting dissolving pulp prior to their conversion into viscose or nanocellulose pulp grades. In a previous publication (Llano et al 2015), the entire Z(EOP)(PO) bleach sequence for the acid sulfite mill located in northern Spain was analyzed in general for viscose production. The authors concluded that the bleaching process could be improved to avoid molecular weight degradation of the cellulose.…”

Detoxification of a Lignocellulosic Waste from a Pulp Mill to Enhance Its Fermentation Prospects

“…In any case, a pH adjustment of the lignocellulosic hydrolyzate has to be done in order to create a medium where yeasts can be grown and survive. Biofuel potentials [29,43] would increase significantly after detoxification in comparison with the untreated SSL. This phenomenon is due to the separation of the inhibitors from the SSL whom hinders the ability of microorganisms to produce bioethanol or biogas.…”

“…This phenomenon is due to the separation of the inhibitors from the SSL whom hinders the ability of microorganisms to produce bioethanol or biogas. However, calculations performed by Thomsen et al [43] and implemented to the untreated SSL by Llano et al [29] do not take into account the inhibition caused, for instance, by the presence of acetic acid. Olsson and Hahn-Hägerdal [44] reported that acetic acid concentrations above 4.3 g/L inhibit fermentation by 50% with S. cerevisiae at pH of 5.5.…”