Haile et al. Bioresour. Bioprocess.
(2021) 8:35
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the fly ashes used in concrete systems utilized in hostile environments. The inorganic wastes from pulp and paper mills have been engineered for different applications (Fig. 7). Green liquor dregs have shown promising effects for correct- ing soil acidity and fertilizer. Dregs have also been used in wastewater treatment. The inorganic grits are mainly composed of calcium carbonate and can be used for the replacement of calcareous raw materials such as in build- ing and construction (Quina and Pinheiro 2020). Agriculturalists already investigated the lime mud can be used in soil healing such as for fertilizing and remedial agents. Compositionally lime mud is similar to the com- mercially available calcium carbonate and can be used as a potential substitute and replacement in building mate- rials. The crude carbonate component of lime mud pro- vides high alkalinity which makes the use of lime mud in precipitation and immobilization of heavy metals in watery streams, removal of phosphorus, and stabilization of sewage sludge. Utilization of pulp and paper waste: future prospects Most of the pulp and paper mill wastes in developing countries adopt recycling for lower grade paper; recy- cling being the only used pulp and paper mill waste utilization method. The scope and technology for utili- zation of the different wastes for other industrial appli- cations are practically not available and not attempted (Raut et al. 2012; de Alda 2008). The biomass from pulp and paper mill is composed of different ingredients. The major wastes of biomaterial concern from these mills are
The incinerated black liquor in recovery boilers is used in pulp and paper mills as an optional energy source as it provides steam. It is also possible to reclaim pulping chemicals for reuse. The current and alterna- tive technology for reuse is the gasification of black liquor. This process has the potency to replicate the amount of production energy used in the pulp and paper mill (Naqvi et al. 2010b). The sawdust as well can be used as a secondary raw material for pulp produc- tion and recycled for paper manufacturing (Srinivasa- kannan and Bakar 2004). It can also be used as filler for the manufacturing of bricks and cement material in the field of construction. The sludge from pulp and paper mills can be recycled via different routes. Mainly the sludge can be used in construction and energy and as a chief source of energy. The suitability of sludge for utilization in power genera- tion is the inherent compounds present in the sludge that are organic with a high degree of combustibility. Commonly cement plants use fly ash as their raw mate- rial together with other ingredients. Fly ash is also used as fertilizer in modern agricultural practice. The suitabil- ity especially in cement application is due to the inherent high strength to weight ratio of fly ash as compared with other cement materials. This is also supplemented by car- bon footprint and minimal energy consumption which makes fly ash a replacement for cement in cost-effective construction and eco-efficient geotechnical applica- tions (Cherian and Siddiqua 2019). It can also be used as an immobilizer of pollutants. Their physical proper- ties such as mechanical resistance and durability make
Fig. 7 Current utilization of pulp and paper mill inorganic wastes ( GLD green liquor dregs, SG slacker grits, LM lime mud, BFA boiler fly ash)
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