Cyclic and safety utilisation of Cu polluted biogas residue in saline-alkali soil

The proper disposal of copper (Cu) polluted plant residues after phytoremediation has attracted extensive attention. In this study, the Cu-polluted biogas residue produced through anaerobic digestion was applied directly. Wheat, soybean and pakchoi were grown in pots for four seasons over two years. The application dosage of Cu-polluted biogas residue was evaluated by measuring growth conditions of crops, Cu content in edible parts, and amelioration of saline-alkali soil. The results showed that the biomass of the crops, the content of soil organic matter, total N and available P and microbial diversity can be improved, and the Cu concentration of the edible parts was all lower than limit standard. Amendment with 2% biogas residue enhanced the growth of beneficial bacteria and fungi, and decreased the relative abundances of potentially pathogenic fungi in the saline-alkali soil. The results of this study provide a basis for the safe utilisation of copper-polluted plant residues.