Haile et al. Bioresour. Bioprocess.
(2021) 8:35
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Table 3 Potential pulp and paper mill waste types Type of waste
Source of waste
Black liquor
Chemical pulp manufacture (kraft process) All types of pulping mainly chemical and mechanical methods of pulp manufacturing Stock preparation for paper machine, kraft pulp- ing, and recycling route for paper manufac- turing
Wood/bark residues [Saw dust and others]
Screening and other rejects
Semi-mechanical sludge
Effluent and water treatment
Biological sludge
Effluent treatment utilizing biological technique
Sludge from de-inking treatment
Recycled paper de-inking treatment
manufacturing of different paper products varies from 20 to 40% on a dry mass. The grade of paper and the specific type of process adopted for the manufacturing of the paper product determines the amount of sludge generated. (Quina and Pinheiro 2020). In comparison, the amount of waste sludge generated from industries that utilize the recycled paper approach produces a large amount of sludge than the conventional approach through virgin raw materials. From each one tonne of reclaimed paper, a total of 300 kg sludge is generated. Depending on production capacity and the type of pulping a large amount of fly ash is released annually from pulp and paper mills (Environmental 2007; Mik- kanen 2000). A recent report in Finland indicated a release of 240,000 tonnes of ash every year. As an illus- tration of the availability of waste biomass from pulp and paper mills, it is reported that the collective fly ash and wood ash produced from Canadian mills is 1 mil- lion tonnes per year. Most of the pulp and paper mill wastes have an impact on the environment and create health prob- lems. The major sources of pollutants at different stages of pulping and paper manufacturing are summarized (Table 5) (Gavrilescu et al. 2012). The environmental impact generated by the manufacture of pulp and paper results mainly from wood pulping and pulp bleaching. In pulping processes, sulfur compounds and nitrogen oxides are emitted into the air, and during pulp bleach- ing, chlorinated and organic compounds and nutrients are discharged to the wastewaters (Gavrilescu et al. 2012; Singh and Chandra 2019). The pulp paper industries release very complex organic and inorganic pollutants mainly from pulping and bleaching stages. Particularly, sulfur compounds and nitrogen oxides are emitted into the air, and chlo- rinated and organic compounds and nutrients are dis- charged to the wastewaters (Gavrilescu et al. 2012; Bank 1999). The pollutants are gaseous, inorganic, and organic type. The major pollutants include hydrogen
Table 4 Generation of solid waste from kraft mill (Gavrilescu 2004; Bajpai 2015b; Quina and Pinheiro 2020) Type of waste Yield (kg/t of dry pulp)
Sawdust
10–30
Bark
100–300 50–100
Pins and fine
Woody fragments/wood yard/
0–20
Knot
25–70
Recovery boiler salts
5–10
Dregs
10–30 15–40
Grits
is also very wide. Due to internally established treatment and utilization routes for generated waste along with the manufacturing process by different pulp and paper mills, there is limited quantitative data on the total amount of waste generated from the mills. Estimated data on the quantity of solid waste from sample pulp and paper mill is reported. The potential woody wastes and rejects are from the preparation of pulpwood and contribute to solid waste generation (Table 4). The predominant biomass available in large quantities in pulp mills is the black liquor. It is reported that kraft mill producing bleached paper engenders around 1.7–1.8 tonnes of black liquor per one tonne of pulp on a bone dry basis (Leponiemi 2008). This highly viscous liquor is a result of the conversion of almost half of the raw chips used in the hopper of the pulping operation. A report of IEA revealed about 170 million tonnes of black liquor per year is released from pulp and paper mills worldwide. Another portion of the waste involves sludge of dif- ferent types namely primary, secondary, and deinking sludge. From a total sludge of 40–50 kg per tonne of the virgin paper production, the primary sludge accounts for 70% and the rest 30% is the secondary sludge. On a glance approximation, the sludge generated from the
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