From Solid Waste to Technosols: Evaluation of Aggregate Stability, Microbial Community and Biotoxicity

To meet the requirements for the efficient utilization of bulk solid wastes, technosols were cultivated using solid wastes as raw materials and their aggregate stability, bacterial community, mineralization process, and biological toxicity were investigated. A proportional mixture of four types of solid wastes (fly ash, sludge, straw, and earthworm manure) resulted in the formation of aggregates with excellent pore structure after two months of cultivation and four samples were obtained. Their soil organic matter (SOM) and total nitrogen (TN) contents were higher than those in Chinese surface soil. A total of 215 genera were common to all four samples. The high organic matter content in straw, along with its lignin content and the fine organic particles generated during the straw degradation process were conducive to the formation of highly stable aggregates, making the quality with added straw superior to that with added vermicompost. Furthermore, the addition of straw was more beneficial for increasing potential mineralized organic carbon. Amongst the four tested samples, sample 3# exhibited the best soil nutrient supply capacity along with strong mineralization but weak carbon sequestration. A seed germination test confirmed that four samples were all biologically safe. This study marked a shift from “pollution control” towards “resource utilization” in dealing with bulk solid wastes. Additionally, applying technosols for soil remediation could present an effective solution to ecological restoration challenges in soil degradation such as mining sites.