Hydrochar (HC) has received increasing attention due to its potential impact on soil amendment. The process parameters of hydrothermal carbonization (HTC) have a significant impact on the characterization of HC, and HC as a soil amendment has effects on soil properties. Therefore, this work summarizes the effects of feedstock type, temperature, residence time, and solid–liquid ratio on the characteristics of HC, and analyzes the effects of HC on soil by HC addition. The feedstock type determined the characteristics of the HC. Temperature had the greatest effect on HC properties, while residence time had a similar but smaller effect than temperature had. The residence time did not affect the characteristics of the HC when HTC was carried out to a certain extent. Solid–liquid ratio determined the characteristics of HC, but research in this area is lacking. Moisture is a crucial factor in plant growth. Compared to other soils, HC significantly increased the water-holding capacity (WHC) in sandy soils. HC is rich in nutrients and micronutrients, making it potentially useful as a fertilizer. The toxicity of HC may inhibit plant growth but may be ignored for poor soil. This review aims to provide recommendations for HC as a soil amendment and to identify areas where further research is needed.

In order to solve the problem of the low treatment efficiency of wastewater containing heavy metals in mining areas, straw biochar and graphene oxide enhanced external pressure ultrafiltration (SGU) was used to treat wastewater containing high concentrations of Pb²⁺. The operation parameters such as pH and temperature were optimized, and the removal efficiency of COD_Cr, NH₃-N, turbidity and Pb²⁺ via SGU, straw biochar ultrafiltration (SU), ultrafiltration (UF), and conventional treatment (CT) were systematically investigated. The results showed that the pH and temperature of polluted water were 4.8–5.2 and 21–30 °C, respectively, the average removal rates of COD_Cr, NH₃-N, turbidity and Pb²⁺ by SGU reached 91%, 97%, 98% and 95%, respectively, and the removal effect was better than that of other processes. In addition, under the backwash conditions of clean water, weak acid, and weak alkali, the membrane flux recovered 65%, 88%, and 89% of the new membrane, respectively. This study provides scientific and theoretical support for the advanced treatment of polluted water in mining areas.