Date Published: January 25, 2017
Publisher: Public Library of Science
Author(s): Xiaoqiang Gong, Le Wei, Xin Yu, Suyan Li, Xiangyang Sun, Xinyu Wang, Daniel Cullen.
The effects of adding the biosurfactant rhamnolipid, the lignolytic and cellulolytic fungus Phanerochete chrysosporium, and the free-living nitrogen-fixing bacterium Azotobacter chrococcum on vermicomposting of green waste with Eisenia fetida was investigated. The addition of rhamnolipid and/or either microorganism alone or in all combinations significantly increased E. fetida growth rate, the number of E. fetida juveniles and cocoons, the population densities of cellulolytic fungi and Azotobacter bacteria, and cellulase and urease activities in the vermicomposts. The quality of the final vermicompost (in terms of electrical conductivity, nutrient content, C/N ratio, humic acid content, lignin and cellulose contents, and phytotoxicity to germinating seeds) was enhanced by addition of rhamnolipid and/or microorganisms. The physical characteristics of vermicomposts produced with rhamnolipid and/or microorganisms were acceptable for agricultural application. The best quality vermicompost was obtained with the combined addition of P. chrysosporium, A. chrococcum, and rhamnolipid.
The city of Beijing has more than 47,000 ha of green space that annually produces more than 2.37 million tons of green waste . The green waste has been traditionally eliminated by deposition in landfills or by incineration but these disposal methods cause problems. The deposition of green waste in landfills subtracts from the available cultivated land and also pollutes surface and ground water . Incineration of green waste leads to the formation of the greenhouse gases carbon dioxide and methane . In addition, both methods result in the loss of green waste as a biomass resource. Therefore, safe and environmentally friendly methods of green waste disposal are needed.
The results of the present study indicate that the efficiency of vermicomposting and the quality of the vermicompost were highest with the combined addition of rhamnolipid, P. chrysosporium, and A. chrococcum. This optimal combination enhanced E. fetida growth and fecundity during vermicomposting, increased microbial numbers and enzymatic activities, accelerated the decomposition of lignin and cellulose, increased the nutrient concentrations in the vermicomposts, and increased the GI value. The combination also resulted in a vermicompost with physical characteristics that were in the optimal ranges for agricultural use. Based on these results, we suggest that vermicomposting of green waste can be enhanced by the combined addition of rhamnolipid, P. chrysosporium, and A. chrococcum.