Chemical and spectroscopic characterization of water extractable organic matter during vermicomposting of cattle dung
Highlights
► Vermicomposting degraded the protein-like groups while increased the humic acid-like compounds in the WEOM. ► Fluorescence regional integration (FRI) can reveal the transformation and humification process during the vermicomposting. ► WEOM is very useful to monitor the organics transformation and assess the maturity in the vermicomposting.
Introduction
In China, the intensification of cattle breeding has resulted in an increase in the production of biodegradable organic wastes, which need to be efficiently recycled due to the environmental problems associated with their indiscriminate application to agricultural fields (Bernal et al., 2009). Vermicomposting is a popular technique characterized by the combined action of earthworms and microorganisms, thereby accelerating the stabilization of organic matter and greatly modifying its physical and biochemical properties (Aira et al., 2002, Lazcano et al., 2008). This method is easy to operate, odorless, cost effective, pathogen free and environmental friendly (Khwairakpam and Bhargava, 2009, Lazcano et al., 2008, Li et al., 2011). Additionally, the significant higher nitrogen, phosphorus and humic contents in the end products of vermicomposting can help to improve soil fertility and stimulate plant growth (Arancon et al., 2005).
Although earthworms accelerate the vermicomposting process by modifying the substrate and stimulating the microbial metabolic activity (Lazcano et al., 2008), the biochemical degradation of the organic matter is carried out by the microorganisms, either living free and/or dwell in the earthworm gut (Aira et al., 2002, Benitez et al., 1999). Since most of the organic matter is transformed by microorganisms in the water-soluble phase (Caricasole et al., 2010), WEOM stands for the most active fraction of the organic waste. Moreover, WEOM was most subject to change and it could directly reflect the organic matter transformation processes (Said-Pullicino et al., 2007, Caricasole et al., 2010). Consequently, the composition of WEOM has been suggested as a better indicator of stability for the organic matter than that of the solid phase (Caricasole et al., 2010). For example, the evolution of WEOM extracted from aerobic composting has been regarded as a good indicator of the overall transformation and maturity of organic matter (Said-Pullicino et al., 2007). Therefore, studying the changes of WEOM is very helpful to understand the bio-stabilization process.
Previous studies on vermicomposting focused on the stabilization of various solid wastes, the application of vermicompost as a soil organic amendment or fertilizer and the earthworm population dynamics (Garg et al., 2006, Aira et al., 2007, Renuka Gupta, 2008). In addition, the characteristics of WEOM in the initial and final vermicomposts of sewage sludge and cow dung were also reported (Xing et al., 2012). However, the chemical and spectroscopic behaviors of WEOM during vermicomposting process have not been fully understood.
WEOM consists of a heterogeneous mixture of compounds with different molecular sizes and complexities, ranging from simple sugars and organic acids to complex proteins and humic colloids (Traversa et al., 2010). An integration of various techniques is a prevalent way to characterize the features of WEOM. Many indices, including dissolved organic carbon (DOC), specific ultra-violet absorbance (SUVA), and fluorescence excitation–emission matrix (EEM) spectroscopy etc., were used to investigate the properties of WEOM (Shao et al., 2009, He et al., 2011a). DOC can act as a general indicator of WEOM, while SUVA254, E4/E6 and Fourier transform infrared spectra (FT-IR) can provide more detailed information on WEOM, such as the aromaticity and humification degree of derived compounds (Weishaar et al., 2003, Saadi et al., 2006, He et al., 2011a). Furthermore, fluorescence excitation–emission matrix (EEM) spectroscopy combining with fluorescence regional integration (FRI) technique can provide an overall view of fluorescent properties of WEOM in a selected spectral range, which has been employed in structural identification and stability assessment of organic wastes (Zhu et al., 2011).
Keeping in light of the above facts, we hypothesized that the WEOM could show obvious changes during the vermicomposting process and be also very helpful to understand the stabilization process in the vermicomposting. Therefore, the aims of this study were to examine the chemical and spectroscopic characteristics of WEOM at different stages during vermicomposting of cattle dung by using various analytical approaches, as well as to investigate the transformation of WEOM and the vermicompost stability based on the WEOM information obtained.
Section snippets
Vermicomposting process and sampling
The fresh cattle dung (FCD) was obtained from a cattle farm in Pudong district, Shanghai, China. In order to avoid the damage of the high moisture content and anaerobic fermentation to earthworms, the cattle dung was naturally dried under sunlight for 1 week with periodic turning over before used. Eisenia fetida maintained in the laboratory with cattle dung as culturing substrate were randomly picked from several stock cultures. E. fetida was chosen because it had wide tolerance of environmental
DOC
DOC is the most biological and chemical active fraction in organic waste (Caricasole et al., 2010). As the DOC content of the WEOM decreases, the substrates become more stable (He et al., 2011b). The concentrations of DOC extracted from different stages are shown in Table 1. In the initial 14 days, the DOC concentration showed no significant change, after then the DOC decreased rapidly from 4.30 to 2.70 g kg−1 until the day 60, which was possibly attributed to the fast degradation of easily
Conclusions
WEOM extracted from different vermicomposting stages were characterized by chemical and spectroscopic techniques. The DOC concentration kept steady around 2.7 g kg−1 after day 60. Moreover, the aromaticity of WEOM significantly increased and the fraction with molecular weight between 103 and 106 Da became the main part of WEOM. Vermicomposting decreased the aliphatics, alcohols, protein-like materials and polysaccharides, whereas increased the humic-like and fulvic-like materials in the WEOM.
Acknowledgements
The research was funded by the National Natural Science Foundation of China (NSFC, No:51109161), the PhD Programs Foundation of Ministry of Education of China (20110072120029), the Fundamental Research Funds for The Central Universities (0400219187), the Open Analysis Fund for Large Apparatus and Equipments of Tongji University (No. 2012055), the National Spark Program of China (2010GA680004). The author would like to thank Shaobo Liang (University of Idaho) for reading through the manuscript
References (35)
- et al.
How earthworm density affects microbial biomass and activity in pig manure
Eur. J. Soil Biol.
(2002) - et al.
Investigation of organic matter dynamics during in-vessel composting of an aged coal-tar contaminated soil using fluorescence excitation–emission spectroscopy
Chemosphere
(2006) - et al.
Effects of vermicomposts produced from cattle manure, food waste and paper waste on the growth and yield of peppers in the field
Pedobiologia
(2005) - et al.
Enzyme activities as indicators of the stabilization of sewage sludges composting with Eisenia foetida
Bioresour. Technol.
(1999) - et al.
Composting of animal manures and chemical criteria for compost maturity assessment. A review
Bioresour. Technol.
(2009) - et al.
Changes in labile phosphorus forms during maturation of vermicompost enriched with phosphorus-solubilizing and diazotrophic bacteria
Bioresour. Technol.
(2012) - et al.
Chemical characteristics of dissolved organic matter during composting of different organic wastes assessed by 13C CPMAS NMR spectroscopy
Bioresour. Technol.
(2010) - et al.
Stability and composition of different soluble soil organic matter fractions – evidence from δ13C and FTIR signatures
Geoderma
(2005) - et al.
Vermicomposting of different types of waste using Eisenia foetida: a comparative study
Bioresour. Technol.
(2006) - et al.
Spectroscopic characterization of water extractable organic matter during composting of municipal solid waste
Chemosphere
(2011)
Physicochemical and spectroscopic characteristics of dissolved organic matter extracted from municipal solid waste (MSW) and their influence on the landfill biological stability
Bioresour. Technol.
Chemical and spectroscopic analysis of organic matter transformations during composting of pig manure
Environ. Pollut.
Vermitechnology for sewage sludge recycling
J. Hazard. Mater.
Comparison of the effectiveness of composting and vermicomposting for the biological stabilization of cattle manure
Chemosphere
Compositional and functional features of humic acid-like fractions from vermicomposting of sewage sludge and cow dung
J. Hazard. Mater.
Dissolved organic matter fractions formed during composting of winery and distillery residues: evaluation of the process by fluorescence excitation–emission matrix
Chemosphere
Humic acid-like fractions in raw and vermicomposted winery and distillery wastes
Geoderma
Cited by (124)
Studies on the humic acid structure and microbial nutrient restriction mechanism during organic-inorganic co-composting
2024, Journal of Environmental Management