The release mechanism of heavy metals from lab-scale vertical flow constructed wetlands treating road runoff

Leaching of heavy metals from tungsten mining tailings: A case study based on static and kinetic leaching tests

Heavy metal (HM) leaching from tungsten mine tailings is a serious environmental risk. In this study, we assess the HM pollution level of tungsten tailings, determine the HM leaching patterns and mechanisms, and estimate the HM fluxes from a tailings reservoir. The results showed that the comprehensive pollution index (CRSi) values that decreased in order of the HM pollution levels in the tailings were cadmium (Cd) > tungsten (W) > lead (Pb) > copper (Cu) = zinc (Zn) > arsenic (As) > manganese (Mn). This result indicated that Cd, W, and Pb were priority pollutants in tailings. The Res fraction of all HMs was greater than 50%. Pb and Cd had similar species fractions with high Exc fractions, and tungsten had a considerable proportion of the Wat fraction. The general acid neutralizing capacity (GANC) test divides the leaching process of HMs into two stages, and each of stage is affected by different mechanisms. A neutral environment promoted tungsten leaching in the column leching test, while an acidic environment promoted Cd and Pb leaching. In addition, the pH effect was more obvious in the early stage. The kinetic fitting results showed that the second-order dynamic model well simulated the leaching of W, Pb, and Cd in most cases. Based on column kinetic leaching test results and tailings parameters, the annual W, Pb, and Cd fluxes were estimated to be 6.35 × 108, 1.3288 × 109, and 1.012 × 108 mg/year, respectively. The above results can guide the environmental management of tungsten tailing reservoirs, such as selecting suitable repair materials and estimating repair service times.

Design of Constructed Wetland Treatment Measures for Highway Runoff in a Water Source Protection Area

Road runoff contains high levels of pollutants, such as heavy metals and hydrocarbons. If they are directly discharged into sensitive water bodies, they will cause irreversible pollution and damage to the water environment. Furthermore, the leakage of hazardous chemicals into sensitive waters will lead to serious consequences, so determining how to deal with road surface runoff has become an urgent problem. This research adopts a scheme for collecting and processing road runoff in a water source protection area using artificial wetlands. After optimizing and improving the general vertical flow of the wetland structure, a composite wetland structure and a relatively novel tandem wetland structure are proposed. An indoor model is established for experiments on various main wetland structure schemes. The results show that the two newly proposed wetland structures improve the possibility of water level control in general vertical flow structures. At the same time, the movement distance of the water flow in the wetland structure is changed to improve the treatment effect of runoff. The removal effect of composite and tandem wetland structures for heavy metals, petroleum substances, and COD (chemical oxygen demand) is significantly better than that of general vertical flow structures. Among them, the composite structure is better than the tandem structure at removing heavy metals, petroleum substances, and COD. However, due to the water discharge method of the structures, the latter has a better effect than the former in the treatment of suspended substances.

Distributed treatment systems

This section presents a review of the scientific literature published in 2019 on topics relating to distributed treatment systems. This review is divided into the following sections: constituent removal, treatment technologies, planning and treatment management, and other topics. PRACTITIONER POINTS: Highlights changes and innovation in removal techniques and technologies in water treatment. Reviews management systems of distributed treatment systems. Discusses point-of-use treatment systems.

Wetlands for environmental protection

This article presents an update on the research and practical demonstration of wetland-based treatment technologies for protecting water resources and environment covering papers published in 2019. Wetland applications in wastewater treatment, stormwater management, and removal of nutrients, metals, and emerging pollutants including pathogens are highlighted. A summary of studies focusing on the effects of vegetation, wetland design and operation strategies, and process configurations and modeling, for efficient treatment of various municipal and industrial wastewaters, is included. In addition, hybrid and innovative processes with wetlands as a platform treatment technology are presented.

Effects of fillers combined with biosorbents on nutrient and heavy metal removal from biogas slurry in constructed wetlands

The performance of fillers (biochar and zeolite) and their combinations with biosorbents (compound microbial agent and chlorella) in nutrients and heavy metals removal from biogas slurry in constructed wetlands (CWs) planted water spinach (Ipomoea aquatica) and plant uptake of heavy metals was investigated. The results demonstrated that the removal rate of nutrients in CWs was all above 60%. COD removal efficiencies were not significantly affected by fillers and biosorbents, all above 80%. The removal rates of TN and NH₄⁺-N were the highest when the two fillers and two biosorbents were added, and the combination of biochar and chlorella presented the optimal removal effect on TP. The efficiency of removing heavy metals from biogas slurry in CWs was As > Zn > Cu, and their removal rates were 35.38%-83.89%, 8.15%-23.69% and 0.32%-0.88%, respectively. The removal efficiency of As by the combination of biochar and composite microbial agent was high. The combination of the two fillers and two biosorbents had the best effect on reducing Cu and Zn enrichment in the aboveground part of water spinach in each treatment, while biochar alone had the best effect on reducing As enrichment in the aboveground and underground parts of water spinach. This study can provide a basis for the application of fillers and biosorbents in the treatment of biogas slurry in livestock and poultry farms in wetlands.