76 A. Klitkou et al.
There exist different approaches to producing advanced biofuels from
wooden material, including residues, but these approaches are mostly integrated into the production of other products in biorefineries (Gregg et al.,
2017). Mainly we distinguish between an anaerobic digestion pathway to
produce biogas, a thermo- chemical pathway for biodiesel or bio- oil and a biochemical pathway to produce bioethanol (Fevolden & Klitkou, 2016). The
thermo- chemical approach involves heating the biomass either with oxygen (gasification for producing syngas and later through a Fischer- Tropsch processcreated biodiesel) or without oxygen (pyrolysis for producing bio- oils).
Manufacturing of pulp and paper
The amount of waste in the pulp and paper industry is substantial: around
40–50 kg of dry sludge is generated during the production of one tonne of
paper while as much as 300 kg results from one tonne of recycled paper
(Najpai, 2015). The composition of waste from pulp and paper mills depends
on the final products, production methods and equipment. Waste from
mechanical pulping includes rejects (bark and wood residues, sand), ash from
energy production, green liquor sludge, dregs and lime mud, primary and
biological sludge and chemical flocculation sludge. Papermaking using virgin
fibres results in waste in the form of rejects from stock preparation and sludge
from water treatments (sludge from chemical pre- treatment, from clarification, biological treatment and chemical flocculation). Papermaking from
recovered paper requires many cleaning processes, resulting in more waste,
especially deinking sludge composed of cellulose fibres, printing inks and
mineral components (Monte, Fuente, Blanco & Negro, 2009). Most of these
wastes can be used and valorised, largely eliminating the use of landfills.
One of the most common waste treatment methods in the European pulp
and paper industry is the incineration of residues (rejects and sludge) by
power and steam generation (Monte et al., 2009; Oral et al., 2005). Other
thermal processes, such as pyrolysis, steam reforming, wet oxidation or gasification, are also possible but the technologies for sludge application are still
being improved. In the cement industry, both material and energy residues
from pulp and paper production can be used to improve products and production processes. Wastes and sludge can be used as soil improvers, through
anaerobic digestion converted to biogas and humus (Monte et al., 2009).
Other interesting valorisation pathways are cat litter and other absorbents
from dried sludge, pesticide/fertiliser carriers or conversion to fuel components (Najpai, 2015). Research on waste from the pulp and paper industry
confirms useful elements for both value- added products and industry.
While some producers ‘capitalise on these opportunities’, current best practices are still ‘far from gaining the maximum value from paper resources’
(CEPI, 2013).
There exist different approaches to producing advanced biofuels from
wooden material, including residues, but these approaches are mostly integrated into the production of other products in biorefineries (Gregg et al.,
2017). Mainly we distinguish between an anaerobic digestion pathway to
produce biogas, a thermo- chemical pathway for biodiesel or bio- oil and a biochemical pathway to produce bioethanol (Fevolden & Klitkou, 2016). The
thermo- chemical approach involves heating the biomass either with oxygen (gasification for producing syngas and later through a Fischer- Tropsch processcreated biodiesel) or without oxygen (pyrolysis for producing bio- oils).
Manufacturing of pulp and paper
The amount of waste in the pulp and paper industry is substantial: around
40–50 kg of dry sludge is generated during the production of one tonne of
paper while as much as 300 kg results from one tonne of recycled paper
(Najpai, 2015). The composition of waste from pulp and paper mills depends
on the final products, production methods and equipment. Waste from
mechanical pulping includes rejects (bark and wood residues, sand), ash from
energy production, green liquor sludge, dregs and lime mud, primary and
biological sludge and chemical flocculation sludge. Papermaking using virgin
fibres results in waste in the form of rejects from stock preparation and sludge
from water treatments (sludge from chemical pre- treatment, from clarification, biological treatment and chemical flocculation). Papermaking from
recovered paper requires many cleaning processes, resulting in more waste,
especially deinking sludge composed of cellulose fibres, printing inks and
mineral components (Monte, Fuente, Blanco & Negro, 2009). Most of these
wastes can be used and valorised, largely eliminating the use of landfills.
One of the most common waste treatment methods in the European pulp
and paper industry is the incineration of residues (rejects and sludge) by
power and steam generation (Monte et al., 2009; Oral et al., 2005). Other
thermal processes, such as pyrolysis, steam reforming, wet oxidation or gasification, are also possible but the technologies for sludge application are still
being improved. In the cement industry, both material and energy residues
from pulp and paper production can be used to improve products and production processes. Wastes and sludge can be used as soil improvers, through
anaerobic digestion converted to biogas and humus (Monte et al., 2009).
Other interesting valorisation pathways are cat litter and other absorbents
from dried sludge, pesticide/fertiliser carriers or conversion to fuel components (Najpai, 2015). Research on waste from the pulp and paper industry
confirms useful elements for both value- added products and industry.
While some producers ‘capitalise on these opportunities’, current best practices are still ‘far from gaining the maximum value from paper resources’
(CEPI, 2013).