Hydrothermal carbonization is a promising strategy for the resource utilization of agricultural wastes. However, the effect of hydrochar on ameliorating saline–sodic soil remains unclear. In the present study, a novel hydrochar amendment was prepared from spent mushroom substrate (SMSHC), followed by an incubation study of saline–sodic soil samples with different pH values (A, pH 9.83; B, pH 8.98; C, pH 8.21). The results demonstrated that SMSHC reduced the adverse effects of saline–sodic soil effectively, and the best effect was obtained when 6% SMSHC was added. Soil pH and ESP decreased by 0.34–0.75 units and 1.0–13.0% at 6% SMSHC loading, respectively. The maximum percentage increase in the soil’s available N, available P, and DOC was 72.3, 221, and 408%, respectively. In the subsequent rice pot seedling experiment, decreased malondialdehyde (MDA) content and increased K⁺/Na⁺ ratio, proline, soluble sugar, total N, and total P in plant samples were observed. This study verifies hydrothermal carbonization as an alternative method, except for the widely used pyrolysis, to recycle biomass wastes into valuable products for soil remediation.

Carbonate mineralization based on urea hydrolysis by bacteria has a significant implication in the remediation of heavy metals polluted environment, but a huge quantity of ammonium released due to the addition of urea may lead to non-point source pollution. In this study, a lead-resistant strain ZN5, identified as Brevibacillus laterosporus, which could induce different carbonate precipitations of Pb (II) through ammonification and nitrate assimilation processes without the addition of urea, was isolated. The maximum of pH values of bacterial fermentation suspensions were 9.07 and 9.22 during ammonification and nitrate assimilation processes, respectively. The minimum inhibitory concentrations of Pb (II) to strain ZN5 in two processes were 150 and 100 mg/L, respectively. Strain ZN5 could rapidly remove 94% and 70% of Pb (II) at an initial concentration of 15 mM through two processes, respectively. Furthermore, the induced carbonate precipitates of Pb (II) in ammonification and nitrate assimilation processes were dense spherical crystal of Pb₃(CO₃)₂(OH)₂ and loose irregular crystal of PbCO₃, respectively, based on XRD and SEM-EDS. Besides, these two biominerals were relatively stable in dilute acid solution, especially the biomineral formed during nitrate assimilation process. These results showed that strain ZN5 had promising application in remediation of Pb-contaminated environment.