Abstract
Having been generated with a tremendous amount annually, paper waste (PW) represents a large proportion in municipal solid waste (MSW) and also a potential source of renewable energy production through the application of anaerobic digestion (AD). However, the recalcitrant lignocellulosic structure poses obstacles to efficient utilization in this way. Recently, anaerobic and microaerobic pretreatment have attracted attention as approaches to overcome the obstacles of biogas production. This study was set out to present a systematic comparison and assessment of anaerobic and microaerobic pretreatment of PW with different oxygen loadings by five microbial agents: composting inoculum (CI), straw-decomposing inoculum (SI), cow manure (CM), sheep manure (SM), and digestate effluent (DE). The hints of microbial community evolution during the pretreatment and AD were tracked by 16S rRNA high-throughput sequencing. The results demonstrated that PW pretreated by DE with an oxygen loading of 15 ml/gVS showed the highest cumulative methane yield (CMY) of 343.2 ml/gVS, with a BD of 79.3%. In addition to DE, SI and SM were also regarded as outstanding microbial agents for pretreatment because of the acceleration of methane production at the early stage of AD. The microbial community analysis showed that Clostridium sensu stricto 1 and Clostridium sensu stricto 10 possessed high relative abundance after anaerobic pretreatment by SI, while Bacteroides and Macellibacteroides were enriched after microaerobic pretreatment by SM, which were all contributable to the cellulose degradation. Besides, aerobic Bacillus in SI and Acinetobacter in SM and DE probably promoted lignin degradation only under microaerobic conditions. During AD, VadinBC27, Ruminococcaceae Incertae Sedis, Clostridium sensu stricto 1, Fastidiosipila, and Caldicoprobacter were the crucial bacteria that facilitated the biodegradation of PW. By comparing the groups with same microbial agent, it could be found that changing the oxygen loading might result in the alternation between hydrogenotrophic and acetoclastic methanogens, which possibly affected the methanogenesis stage. This study not only devised a promising tactic for making full use of PW but also provided a greater understanding of the evolution of microbial community in the pretreatment and AD processes, targeting the efficient utilization of lignocellulosic biomass in full-scale applications.
Highlights
In modern society, paper materials have become indispensable consumer products with a wide variety of civil and industrial uses (Bajpai, 2014)
The results indicated that the aerobic or facultative microbes in straw-decomposing inoculum (SI), sheep manure (SM), and digestate effluent (DE) groups were more active or abundant, which might possibly contribute to the higher hydrolysis rate
Results showed the diverse efficacy of these microbial agents and oxygen loadings on the methane production performance of paper waste (PW)
Summary
Paper materials have become indispensable consumer products with a wide variety of civil and industrial uses (Bajpai, 2014). With the unprecedented economic growth and social improvement in the past 20 years, China has become one of the largest paper-producing and paper-consuming countries (NationMaster, 2021), resulting in tremendous production of paper waste (PW) annually. In 2016, the production of PW in China was over 18 million tons, accounting for 9.15% of total municipal solid waste (MSW) (Zhu et al, 2020). The pathway for the environmentally friendly utilization of PW focuses on the recycling and reproduction for new paper products. The PW tainted with glue, paint, food wastes, and other residues cannot be recycled, much of which is discarded as MSW (Ma et al, 2020; Zhao et al, 2020). It is of high significance to develop alternative approaches to make the utmost utilization of PW
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