Synergistic remediation of copper mine tailing sand by microalgae and fungi

Biological soil crusts (BSCs) could strengthen soil particles, increase soil nutrients, and reduce soil erosion. However, available information on stabilizing mine tailing sand by induced BSCs is lacking. In this study, a native microalgae (i.e., Coelastrella sp.) and two fungi (i.e., Aspergillus sp. and Penicillium sp.) isolated from Cu mine tailing sand were inoculated onto the tailing sand in different manners. After being inoculated for 90 days, microorganisms could effectively colonize and form BSCs on the surface of the tailing sand, as proven by scanning electron microscopy images and growth parameters, and the dual inoculation of microalgae and fungi showed synergistic effects on the improved soil properties. Compared with the control treatment, the microorganism co-inoculation group had increased organic carbon, cation exchange capacity, soil moisture, sucrase activity, and microbial biomass carbon by 55.41%, 27.18%, 6.29%, 471%, and 216%, respectively; decreased pH from 9.09 to 8.95; and decreased bioavailable Cu content and bulk density by 15.43% and 6.30%, respectively. This finding indicated that the formation of BSCs could effectively improve the soil properties of mine tailing sand. The composition of dissolved organic matters analyzed by excitation–emission matrix showed that the increase in carbon content in tailing sand was predominantly caused by microalgae and fungi. These results indicated that the use of native microorganisms to construct biological crusts could effectively improve the properties of tailing sand and increase the nutrient content, and it could be used as a new method for tailing restoration.