Preparation of olive pomace soil amendment and its application in heavy metal contaminated soil remediation

Olive pomace is a solid by-product of the olive oil extraction process. It is rich in difficult-to-biodegrade substances such as cellulose, hemicellulose, and lignin, thus limiting the resource utilization of olive pomace. Microbial composting is the main way of agricultural waste treatment in China. However, there are few studies on the microbial degradation of lignin and cellulose in olive pomace, which makes the efficient utilization of olive pomace a major problem. Based on this, in this study, two strains of high-efficiency degrading functional bacteria X4-1 (Enterobacter sp) and M7-2 (Candida tropicalis) of olive pomace cellulose and lignin were obtained through degradation experiments. The above two strains were used in the fermentation process of olive pomace to prepare organic fertilizers that met the application standards of agricultural soil fertilizers. Meanwhile, the effects of organic soil amendment inoculated with heavy metal immobilized bacteria on soil heavy metal remediation, crop growth, and heavy metal enrichment were investigated. The results showed that olive pomace organic amendment promoted the growth of Brassica chinensis and increased biomass. After applying organic amendment to Pb, Cu, and Cd contaminated soil, the plant height, fresh weight and dry weight of Brassica chinensis increased by 4.80%~15.78%, 10.02%~129.85%, and 7.70%~120.41%, respectively. In addition, the application of organic amendment effectively reduced the ecological risk of heavy metals in the soil and inhibited the enrichment of heavy metals by Brassica chinensis. Compared with no fertilization treatment, organic amendment reduced the contents of Cu and Cd in the underground part of Brassica chinensis grown in heavy metal contaminated soil by 85.47% and 34.10%, respectively; and the contents of aboveground part decreased by 42.56% and 54.68%, respectively. The results of the study can provide a reference for the resource utilization of olive pomace and the green remediation of heavy metal contaminated agricultural soils.