Haile et al. Bioresour. Bioprocess.
(2021) 8:35
Page 9 of 22
Table 5 Potential pollutants from pulp and paper mill waste S. N Main input Process step
Pollutants
1 2 3 4 5 6
Raw material/wood Chemicals/energy
Wood preparation Pulp manufacture
Solid wastes and wastewater Air emissions and used water
Process water
Pulp washing/screening
Dissolved material, residual chemicals, and wastewater
Chemicals/energy
Pulp bleaching
Air emissions, dissolved material, residual chemicals, and wastewater
Energy
Pulp drying
Air emissions
Energy/water/chemicals
Paper manufacture
Solid wastes, dissolved material, residual chemicals, and wastewater
compounds mainly soluble salt ions (Fig. 5a) (Viel et al. 2020). Black liquor is separated from the pulp in washing (Fig. 5b). The biorefinery approach can be used for the conversion of lignin and hemicellulose in black liquor into biomaterials (Vakkilainen and Välimäki 2009; Vak- kilainen 2016). Black liquor being the major waste other potential wastes include sawdust, sludges of different types, waste paper, and fly ash. The major inorganic type wastes from pulping and after-treatment stage include the dregs, lime mud, and grits. The different wastes are obtained as extracted from different pulp and paper industries are summarized (Fig. 6). The sawdust (Fig. 6a) as woody material is composed of cellulose, lignin, and hemicelluloses (Bajpai 2018a). The cellulose composition of sawdust is by far higher than the lignin content. Accordingly, the interest in biomaterial synthesis relies on the cellulose component of the saw- dust. The current preferably adapted extraction of cel- lulose from sawdust involves the preparation of sawdust (drying, cutting, and conditioning); dissolution of wood
sulfides, sodium sulfide, sulfur, chlorine dioxide, fer- rous, copper, hexadecanoic acids, octacosane, phenol, and β-sitosterol. It has been reported that the differ- ent pollutants cause environmental and health impacts in terms of respiratory disorder and irritation to the skin, neurotoxicity, and direct toxicity of effluent to the reproductive system in aquatic flora and fauna are reported. Several of these pollutants are reported to contain endocrine-disrupting chemicals. Furthermore, the environmental pollution caused by the pollutants poses a threat to aquatic life as well as to plants and human beings (Bank 1999; Gavrilescu et al. 2012; Singh and Chandra 2019) . Current utilization of pulp and paper mill waste Characteristic components of major by-products The wastes from pulp and paper mills are both of organic and inorganic types. Most of the biomass generated from pulp and paper mills is organic residues. Black liquor consists of organic polymers (lignin, polysaccharides, and resinous compounds of a low molar mass) and inorganic
Fig. 5 Black liquor: a Gross structure of black liquor; b Black liquor separation
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