Mining activities has generated large amounts of mine tailings each year, and these tailings usually contain high concentrations of heavy metal pollutants, which not only cause serious damage to the local and surrounding soil ecosystems, but also harm human health via the transmission of food chain. Phytoremediation is treated as environmentally friendly, long-term effective and low-cost restoration method. However, tailing soil acidification, low organic matter content, poor water holding capacity and compaction make plant struggle to survive. Biochar, a soil conditioner can promote plant growth by improving the physical, chemical and biological properties of soil, thus strengthening the ability of phytoremediation in the contaminated tailings. This review elaborates how the physicochemical properties of biochar affect phytoremediation; and summarized how the raw materials of biochar affect the physicochemical characteristics. Finally, the future research directions are prospected.

The precipitation of struvite (MgNH₄PO₄·6H₂O) is considered to be a promising method for the recovery of phosphate from wastewater. In this review, the kinetic models, which are commonly used to explain the process of struvite crystallization, are described. The mixed-suspension mixed-product removal (MSMPR) model is based on the population balance equation (the size-dependent growth model and the size-independent growth model). Thereafter, the first-order kinetic fitting model that aligned with concentration changes in the substrate is summarized. Finally, the several physical and chemical factors that affected the efficiency of struvite crystallization are determined. The supersaturation ratio, which is seen as the driving force of struvite crystallization, is the main factor that influences crystallization; however, it cannot be used in practical applications of engineering because it is indirectly associated with the following factors: pH, the molar ratio of Mg:N:P, and the interference of foreign impurities. In this study, we present conclusions that should be used to guide further research studies, and encourage the engineering practice of wastewater treatment with struvite precipitation.

The use of vegetable greenhouse production systems has increased rapidly because of the increasing demand for food materials. The vegetable greenhouse production industry is confronted with serious environmental problems, due to their high agrochemical inputs and intensive utilization. Besides this, antibiotic-resistant bacteria, carrying antibiotic-resistance genes (ARGs), may enter into a vegetable greenhouse with the application of animal manure. Bacterial communities and ARGs were investigated in two typical vegetable-greenhouse-using counties with long histories of vegetable cultivation. The results showed that Proteobacteria, Firmicutes, Acidobacteria, Chloroflexi, and Gemmatimonadetes were the dominant phyla, while aadA, tetL, sul1, and sul2 were the most common ARGs in greenhouse vegetable soil. Heatmap and principal coordinate analysis (PCoA) demonstrated that the differences between two counties were more significant than those among soils with different cultivation histories in the same county, suggesting that more effects on bacterial communities and ARGs were caused by soil type and manure type than by the accumulation of cultivation years. The positive correlation between the abundance of the intI gene with specific ARGs highlights the horizontal transfer potential of these ARGs. A total of 11 phyla were identified as the potential hosts of specific ARGs. Based on redundancy analysis (RDA), Ni and pH were the most potent factors determining the bacterial communities, and Cr was the top factor affecting the relative abundance of the ARGs. These results might be helpful in drawing more attention to the risk of manure recycling in the vegetable greenhouse, and further developing a strategy for practical manure application and sustainable production of vegetable greenhouses.

The aim of this study is to evaluate the anaerobic digestion and biogas production of plant biomass under high salinity by adopting a theoretical and technical approach for saline plant-biomass treatment. Two completely mixed lab-scale mesophilic reactors were operated for 480 days. In one of them, NaCl was added and the sodium ion concentration was maintained at 35.8 g-Na⁺·L⁻¹, and the organic loading rate was 0.58-COD·L⁻¹·d⁻¹–1.5 g-COD·L⁻¹·d⁻¹; the other added Na₂SO₄–NaHCO₃ and kept the sodium ion concentration at 27.6 g-Na⁺·L⁻¹ and the organic loading rate at 0.2 g-COD·L⁻¹·d⁻¹–0.8 g-COD·L⁻¹·d⁻¹. The conversion efficiencies of the two systems (COD to methane) were 66% and 54%, respectively. Based on the sulfate-reduction reaction and the existing anaerobic digestion model, a kinetic model comprising 12 types of soluble substrates and 16 types of anaerobic microorganisms was developed. The model was used to simulate the process performance of a continuous anaerobic bioreactor with a mixed liquor suspended solids (MLSS) concentration of 10 g·L⁻¹–40 g·L⁻¹. The results showed that the NaCl system could receive the influent up to a loading rate of 0.16 kg-COD/kg-MLSS·d⁻¹ without significant degradation of the methane conversion at 66%, while the Na₂SO₄–NaHCO₃ system could receive more than 2 kg-COD·kg⁻¹-MLSS·d⁻¹, where 54% of the fed chemical oxygen demand (COD) was converted into methane and another 12% was observed to be sulfide.