Coupling thermophilic composting and vermicomposting processes to remove Cr from biogas residues and produce high value-added biofertilizers

• Published in: Bioresource technology Vol. 329; p. 124869
• Main Authors: Ning, Jing-Yuan, Zhu, Xiao-Dong, Liu, Hai-Gang, Yu, Guang-Hui
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.06.2021
• Subjects: Animals; Biofuels; Biogas residues; Composting; Oligochaeta; Soil; Soil Pollutants - analysis; Synchrotron radiation spectromicroscopy; Trichoderma guizhouense; Vermicomposting; Vermicomposting; Biogas residues; Composting; Trichoderma guizhouense; Cr; Synchrotron radiation spectromicroscopy
• ISSN: 0960-8524; 1873-2976
• DOI: 10.1016/j.biortech.2021.124869

•The total content of Cr in biogas residues markedly increased after composting.•Organic or inorganic functional groups contributed the binding sites for Cr.•23–31% of Cr was removed under 60 g earthworm/kg and with worms of 0.7 ~ 1.0 g.•Co-fermentation process of biogas residues and Trichoderma was optimized. Removing pollutants and producing high value-added products are essential steps for sustainable disposal and utilization of biogas residues. Here, a coupled thermophilic composting and vermicomposting process was used to remove Cr from biogas residues, and the composting products were co-fermented with the plant growth-promoting fungus Trichoderma to produce high value-added biofertilizers. The results showed that thermophilic composting for 37 d markedly increased the total content of Cr but decreased the percentage of available Cr fractions. Synchrotron-radiation-based observations further provided direct evidence of the binding sites to support the results from traditional sequential extraction. At a density of 60 g earthworm/kg biogas residues, vermicomposting removed 23–31% of Cr from biogas residues. After vermicomposting, co-fermentation of biogas residues and Trichoderma was optimized, in which Trichoderma spores were 2–5 × 108 cfu/g substrates. Together, coupling thermophilic composting and vermicomposting processes is a promising technique to remove a portion of heavy metals from biogas residues.