The applications of fungal enzymes in
The applications of fungal enzymes in paper industry involve biobleaching of pulp, pulp de-inking, degradation of dissolved and suspended organic compounds in concentrated effluents of mills and enhanced fibrillation. Enzymes usage is encouraged in paper industry in order to reduce the use of chemicals and dapt secretase consumption as well as to improve quality of the products (Bajpai, 2013). A desirable side-effect of processing paper mill waste by WRF enzymes is non-specific degradation of organic environmental pollutants, commonly present in these substrates (Kües, 2015).
Most industrial enzymes currently produced by fungi are products of submerged fermentation (SF) which uses significant amounts of water and generates large quantities of liquid waste stream during the filtration process. Major cost contributor in commercial cellulase production is cost of the feedstock which is mostly glucose and accounts for 50% of the total process cost (Humbird et al., 2011). However, solid state fermentation (SSF) has emerged as an economically attractive alternative for the in situ production of lignocellulolytic enzymes due to lower energy consumption, direct use of low-cost lignocellulosic wastes as substrates, reduction in cost of dewatering in downstream processing, higher concentrations of enzymes and lower demand for the sterility of the equipments (Yoon et al., 2014). At present, the production of lignocellulolytic enzymes by SSF on several agricultural wastes has been reported, such as coffee pulp (Velázquez-Cedeño et al., 2002), spend brewery grains (Gregori et al., 2008), straw and fruit peels (Kurt and Buyukalaca, 2010), rice straw (Khalil et al., 2011) and tomato pomace (Iandolo et al., 2011). Conversely, there are few reports on enzyme production from paper sludge and no report specifically on fungal enzymes production from deinking paper sludge.
The aim of the following work was to untap the potential of DIS as a low-cost substrate for fungal production of lignocellulolytic enzymes via SSF. Fungal strains with the ability to transform the unpretreated DIS to a mixture of industrially relevant lignocellulases were identified. Furthermore, the composition, production dynamics and performance of the extracted enzymes were studied in detail in the most promising of the tested strains (P. ostreatus PLAB). The advantages of lignocellulolytic enzymes production on DIS and their applications in different industries is also discussed from a perspective of cleaner production.
Materials and methods
Results and discussion
Conclusions Enzymes production for lignocellulose degradation is currently a cost intensive process and utilises fresh water and nutrients which in turn results in additional waste stream generation. If combined with efficient and robust microbial enzyme producers, lignocellulosic wastes have an enormous potential for developing a sustainable chemical and energy industry as the most inexpensive feedstock among all the renewable resources. The results of our study have shown that the deinking paper sludge represents a suitable feedstock for the production of lignocelulolytic enzymes by selected Pleurotus strains. The selected strains exhibited outstanding ability to transform untreated and unsterilized DIS to a mixture of alkali-stable enzymes (mainly with endoglucanase, xyalanase and particularly high laccase activities). Production of lignocellulases from unsterilized DIS by SSF should therefore be considered at an industrial level to add value to the major waste stream of paper industry by reducing waste disposal, costs associated with the disposal of wastes to landfill sites and by yielding high value enzymes suitable for application in biorefinery, paper and pulp, detergent and textile industries. Further research should be done to analyse (anticipated positive) effects of the process on the levels and bioavailability of environmental pollutants potentially present in DIS. In addition, the enzymes production should be further optimized and process conditions fine-tuned to increase the yield and productivity of individual enzymes and the cocktail. Major advantages of this process such as less water usage, less energy usage and reduced waste disposal should be studied in detail for its energy, economic and environment benefits.