The evolution of water extractable organic matter and its association with microbial community dynamics during municipal solid waste composting
Introduction
The production of municipal solid waste (MSW) is an inevitable consequence of today’s consumer society. Finding safe, sustainable and cost-effective alternatives to the disposal and usage of MSW has recently become a significant issue for solid waste management (Hong et al., 2010). Composting as an attractive waste management option is defined as the biological decomposition of organic matter under controlled conditions to form a stable, humus-like end product (Fialho et al., 2010). Thus it can be seen that humification process is the primary mechanism during composting and can be successfully allowed to assess the stability and maturity of compost (Said-Pullicino et al., 2007, Shao et al., 2009). Water-extractable organic matter (WEOM) has been demonstrated to be more easily utilized by microbes versus solid-phase organic matter during composting (Chefetz et al., 1998, Said-Pullicino and Gigliotti, 2007). Water-soluble phase is also an important reaction interface for the transformation of solid-phase organic matter by microbial metabolism (Chefetz et al., 1998, He et al., 2014, Said-Pullicino et al., 2007). Moreover, characterization of the composition of WEOM has been regarded as a better indicator of the overall transformation of the organic matter than solid-phase (Chefetz et al., 1998).
With the composting time, the content polysaccharide structure of WEOM decreased during MSW composting and a higher content of macromolecules that related to humic substances were formed in WEOM at the final stage of composting (Chefetz et al., 1998). Thus, WEOM characteristics measured by spectroscopy could be used to monitor the compost maturity during composting (Chefetz et al., 1998, Hsu and Lo, 1999, Tian et al., 2012). The humification of WEOM during composting is facilitated by a diverse community of microbes, whose community dynamics vary greatly temporally, and generally involves the development of thermophilic temperatures as a result of biologically produced heat (De Gannes et al., 2013a, de Gannes et al., 2013b, Goyal et al., 2005, Ishii et al., 2000).
Many studies have focused on the influence of environmental factors on microbial community (Wang et al., 2015, Zhang et al., 2011). Nevertheless, the mechanism with respect to the links of bacterial and fungal community dynamics and the humification parameters of WEOM was also worth researching. Previous studies demonstrated that WEOM humification with increasing in molecular weight and aromatic and alkyl structures was driven by microbes decomposing the fulvic acids, protein and water soluble carbon (WSC) of WEOM during composting (Senesi et al., 1989). However, the heterogeneous role of bacterial and fungal community during composting was not clear.
This study will therefore illuminate the evolution of WEOM and its association with bacterial and fungal community dynamics during MSW composting. The different driving roles of bacterial and fungal communities on WEOM humification process are also investigated. The purpose of this study is to provide basic information for improvement of MSW composting for through regulating microbial community dynamics.
Section snippets
Composting process and sample collection
Composting samples were obtained from Beijing Asuwei Composting Plant, China. The factory disposes 800–1000 t of organic solid waste every day. The composting pile was 1.6 m high, with 2.5 × 3 m wide, containing more than 2 t of organic solid waste. The composting pile was turned every 2 d by forklift before 21 d. The curing stage took 30 d to complete, and then the pile turned mechanically every 7 d. To ensure the composting was successful, the initial water content was adjusted to 65–70%, the C/N ratio
The humification process of WEOM during composting
The data of humification parameters of WEOM in the course of composting was shown in Table 1. Moisture content was declined 14% by C28, further dramatically decreased to the lowest value at C51. The dry basis of WSC decreased 70.4% during composting. SUVA254 and E253/E203 gradually increased during sequential composting and reached the highest at the end of composting (C90). This result suggested that abundance of aromatic carbon and oxygen-containing functional groups increased during the
Conclusion
The temporal variation of bacterial and fungal community composition was significantly related to humic-like materials and oxygen-containing functional groups while humification parameters of WEOM affecting each species were different. Based on RDA analysis, humic-like materials, humification degree, molecule weight, abundance of aromatic carbon and oxygen-containing functional groups explained the most variation in distribution of bacterial, and the protein-like materials, abundance of and
Acknowledgments
This study was supported by the National Natural Science Foundation of China (Nos. 51325804 and 51508540) and the Scientific Research Foundation of the Higher Education Institutions of Henan Province (No. 16A570001).
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