Degradation of paper mill wastewater sludge and cow dung by brown-rot fungi Oligoporus placenta and earthworm (Eisenia fetida) during vermicomposting

Highlights

• The decomposition of PPMS in vermicomposting and vermibed added with brown-rot fungi is assessed.

• The combination of E. fetida and O. placeta caused more humification in PPMS.

• The PPMS in 50–75% proportion with CD showed higher nutrient mineralisation.

• The earthworm growth and microbial population in waste mixtures also influenced by the treatment type.

Abstract

To evaluate the effect of brown-rot fungi Oligoporus placenta and earthworm Eisenia fetida on decomposition of paper mill sludge, the paper mill sludge was mixed with cow dung in 0, 25, 50, 75, and 100% proportions and changes in physicochemical quality of waste mixtures was carried out for 28 days. All waste mixtures were treated with: Setup-I (E. fetida), Setup-II (O. placenta) and, Setup-III (E. fetida + O. placenta). A decrease in total organic carbon, C/N ratio and cellulose but an increase in total kjeldhal nitrogen, total phosphorus, total potassium and pH was recorded. The paper mill sludge in 50–75% proportion in feedstock showed the better results and rate of mineralisation were in order: Setup-III > Setup-I > Setup-II. The proportion of CD has direct role in waste mineralisation. The microbial population (bacterial, fungal and actinomycetes) and earthworm biomass were also high in Setup-III, suggesting the influence of brown-rot fungi on paper mill sludge humification. Results indicate that fungal inoculate in vermicomposting was effective in decomposing cellulose-rich industrial sludge.

Introduction

The pulp and paper pulp industry is one of the fastest growing industries in India and the demand for paper is expected to grow 21.0 million tons by 2020. The environmental pollution is one of the prime issues associated with this industry apart from fresh water utilization (Thompson et al., 2001). Such industries produce millions of tonnes of solid wastes, which include ashes from the boiler and furnace units and toxic sludges from high rate biological wastewater treatment systems, etc. The solid waste from a paper mill includes around 45% wastewater sludge (20–60% solid fractions, pH ≈ 7), 25% ash, 15% wood cuttings and wastes, and 15% other materials as solid waste in a typical paper mill sludge (Nurmesniemi et al., 2007). Due to higher lignin content, about 0.3–1 m³ sludge is produced during per ton paper production (Priadi et al., 2014). The wastewater sludge disposal is a growing problem in paper industries due to strict environmental norms and scarce landfill space. Decreasing land availability for disposals and growing public concerns over adverse impacts of insanitary disposals have drawn the attention of policymakers to find an alternative strategy for safe disposals or meaningful utilization of such specific wastes. On the other hand, landfilling is not a feasible approach for low-income countries because of economic realities (high capital and operation costs) and environmental concerns (Hackett et al., 2009). This triggered to develop an economically viable, environmentally safe and technologically feasible system. Most preferred technologies are those that have the potential to produce a saleable product (Hackett et al., 2009).

Numerous studies have shown the potential applications of pulp and paper mill sludge (PPMS) in various useful processes of energy and materials production: anaerobic digestion (Meye and Edwards, 2014, Lopes et al., 2018), pyrolysis (Cho et al., 2017), ethanol production (Boshoff et al., 2016), composting (Hackett et al., 2009; Hazarika et al., 2017), material preparation (Goel and Kalamdhad, 2017), vermicomposting (Kaur et al., 2010; Negi and Suthar, 2013; Sahariah et al., 2014). Vermicomposting has been appeared as a vital process to convert toxic industrial sludges into products with high plant nutrients and less toxic substances (Kaur et al., 2010; Sahariah et al., 2014; Soobhany et al., 2017). Vermicomposting is better than composting in terms of processing time and quality of end product. The aerobic microbes play an important role in both composting and vermicomposting system as they drive the degradation process by providing extra-cellular enzymes in decomposing wastes (Aira et al., 2007; Gomez-Brandon et al., 2011). The limitation of paper mill sludge vermicomposting is the slow degradation of high chain polysaccharides like cellulose, lignin and other fibers. Earthworm occupied materials which have an appropriate environment for the growth of some cellulose producing fungal species (Pramanik and Chung, 2011) excess of; cellulase activity can be accomplished in vermicomposting by supplementing the waste with an appropriate cellulose degrading fungi. Few studies have shown a significant effect of Trichoderma, Aspergillus, white-rot fungi (Phanerochaete sp., Trametes sp., Fomes sp., etc.) on the degradation of cellulolytic and lignolytic waste in composting process (Awasthi et al., 2014; Voberkova et al., 2017). Pramanik (2010) pre-composted water hyacinth biomass for 7 days using three different fungal species Trichoderma viridae, Aspergillus niger and Phanerochaete chrysosporium and then vermicomposted further. This resulted in increased activities of cellulase, protease and acid and alkaline phosphatase in vermicomposting trails. Very limited data on the impact of fungi inoculation have been reported on vermicomposting of industrial wastes in published literature. The brown-rot fungi belong to the group Basidiomycota, mostly wood-decaying fungi. Typically, the brown-rot fungi degrade cellulose and hemicellulose after a partial modification of lignin (demethylation, partial oxidation, and depolymerization) by a non-enzymatic Fenton-type catalytic system (Anastasi et al., 2013), thus helps in cellulose-rich waste humification. Application of such fungi in vermicomposting of PPMS could enhance the PPMS degradation process.

To our best knowledge, however, the degradation of PPMS using brown-rot fungi or any other fungi and earthworm under combined treatment, has not been studied yet by previous researchers. Although, significance of vermicomposting in decomposition of PPMS and production of toxic-free vermifertilizers has already been reported (Kaur et al., 2010; Elvira et al., 1996; Negi and Suthar, 2013), but information on use of cellulosic fungi in vermicomposting of primary sludge from a pulp and paper mill is still not investigated. The aim of this study was to investigate the effect of cellulose and lignin-degrading brown-rot fungi Oligoporus placenta and earthworm on the degradation of PPMS spiked with cow dung (CD). To achieve the aim of the study, different mixtures of PPMS and CD were prepared and then decomposed using three experimental setups with: (i) E. fetida, (ii) O. placenta and, (iii) E. fetida + O. placenta. The literature suggests that cow dung (CD) or any other animal dung not only enhances the palatability of industrial sludges for inoculated worms (Suthar and Singh, 2008) but also enriches the feedstuff with beneficial microbes and nutrients. In general, sludges have a high load of fibres and hard to degrade substance, therefore; less preferred by earthworms (Negi and Suthar, 2013), which can be compensated by mixing of a bulky agent like CD in industrial sludges in specific proportions for successful vermicomposting operations. Despite improving the physicochemical conditions for decomposing biota in the waste pile, the bulky material enriches the feed with essential nutrients (Suthar, 2012) and microbial flora, which helps in fast mineralisation of industrial sludges. Thus we have mixed PPMS with CD in different proportions in this study to see the impact of a bulky material of sludge stabilisation during the treatment by fungi and earthworm. Previous reports also suggested the use of CD as bulky material for easy mineralisation of paper mill sludge (Butt, 1993; Kaur et al., 2010; Negi and Suthar, 2013).

During this study, we observed the changes in physicochemical characteristics, earthworm biomass and microbial properties in all the waste mixture trials.