Lin Luo

Aged landfill leachate is difficult to treat biologically because of its low biodegradability and limited carbon availability. Carbon-rich transfer station wastewater is a potential co-substrate, but its use in staged biological co-treatment requires evaluation. This study examined coagulation pretreatment of transfer station wastewater followed by co-treatment with aged leachate in a two-stage anoxic/oxic system. Water-quality and optical analyses showed differences in biodegradable-carbon availability and dissolved organic matter composition: protein-like components were more prominent in transfer station wastewater, whereas humic- and fulvic-like components predominated in aged leachate. During 60 d of operation, average removal efficiencies for chemical oxygen demand, ammonium nitrogen, and total nitrogen were 93.4%, 91.12%, and 85.0%, respectively. Amphiplicatus was among the dominant bacterial taxa, and unclassified groups dominated the fungal community. Defluviicoccus was relatively more abundant in the first anoxic compartment, whereas Candida was more abundant in the final oxic compartment. The results support the use of transfer station wastewater as a carbon-rich co-substrate for biological treatment of aged leachate.

Various metal ions in acid mine drainage (AMD) cause environmental pollution. Due to the unique advantages of heavy metal treatment and gelling properties, previous concretes incorporating red mud have attracted extensive attention in AMD passive treatment, which utilises naturally occurring chemicals to cleanse contaminated mine waters with low operating costs. This study aims to develop red mud–based geopolymer pervious concrete as an eco–friendly method to remove heavy metals in AMD. Compared with raw pervious concrete, red mud–based geopolymer pervious concrete improves the purification efficiency of heavy metals. The high rate of acid reduction and metal removal by the geopolymer is attributed to the dissolution of portlandite in red mud. Precipitation of metal hydroxides seems to be the dominant metal removal mechanism. Under optimal conditions (influent pH = 4.0 and the hydraulic retention time = 24 h), red mud–based geopolymer pervious concrete could completely remove Cu(II), Mn(II), Cd(II) and Zn(II) by up to 10 mg/L, 10 mg/L, 1.6 mg/L and 16 mg/L, respectively. When the influent pH is 2.5, the hydrolysis of Fe(III) released from red mud increases the consumption of OH⁻. Moreover, when the influent pH is 4.0, the precipitation of CaSO₄ promotes the dissolution of portlandite and metal removal. Therefore, red mud has demonstrated feasibility in the manufacturing of geopolymer–based pervious concrete for purification AMD.

In this study, we conducted field experiments to assess the effects of the combined application of Chinese milk vetch (Astragalus sinicus L., CMV) and red mud (RM) to remediate the cadmium-polluted acidic paddy soil. The results showed that the combined application increased the yield component index and improved the grain yields, compared with the control, RM1, RM2, and CMV treatments. However, the increased range of soil pH values in the CMV-RM1 and CMV-RM2 treatments was smaller than that of the RM1 and RM2 treatments at the different rice growth stages. The soil organic matter (SOM) contents of the RM-only treatments did not differ throughout the whole period, but were significantly different (p < 0.05) between CMV-RM2 and the control. Compared with the control, the combined application decreased the concentration of exchangeable Cd in the early rice soil. The combined application of CMV and RM substantially decreased the rice uptake of Cd. However, we found no significant difference (p < 0.05) between the CMV-RM1 and CMV-RM2 treatments. Therefore, compared with remediation with RM or CMV alone, we recommend the combined application of CMV and RM as an economical, highly effective, and replicable amendment for remediating acidic, Cd-polluted paddy soil. Considering the restorative effect and proper use of RM, we recommend CMV-RM1 treatment.

The resource utilization of excess red mud produced from aluminum production is a current research focus. In this study, novel nano-Fe₃O₄ modified high-iron red mud material (HRM@nFe₃O₄) was fabricated using the method of co-precipitation to remove Sb(III) from the aqueous phase. The HRM@nFe₃O₄ at a nFe₃O₄:HRM mass ratio of 1:1 had optimal adsorbing performance on Sb(III) in water. Compared with others, the synthetic HRM@nFe₃O₄ sorbent had a superior maximum Sb(III) adsorption capacity of 98.03 mg·g⁻¹, as calculated by the Langmuir model, and a higher specific surface area of 171.63 m²·g⁻¹, measured using the Brunauer-Emmett-Teller measurement. The adsorption process was stable at an ambient pH range, and negligibly limited by temperature the coexisting anions, except for silicate and phosphate, suggesting the high selectivity toward Sb(III). HRM@nFe₃O₄ retained more than 60% of the initial adsorption efficiency after the fifth adsorption-desorption cycle. The kinetic data fitted by the pseudo-second-order model illustrated the existence of a chemical adsorption process in the adsorption of Sb(III). Further mechanism analysis results indicated that the complexation reaction played a major role in Sb(III) adsorption by HRM@nFe₃O₄. This HRM@nFe₃O₄ adsorbent provides an effective method for the removal of Sb(III) in wastewater treatment and is valuable in the reclamation of red mud.

The increasing usage of zinc oxide nanoparticles (ZnONPs) inevitably leads to their release into the environment. To understand their fate and toxicity in water systems, a reliable method for the quantitative analysis of ZnONPs in environmental waters is urgently needed to be established. In this study, a quantitative analytical method of ZnONPs in environmental waters was developed by cloud point extraction (CPE) combined inductively coupled plasma mass spectrometry (ICP-MS). To obtain high recoveries of ZnONPs, the CPE parameters including pH, surfactant concentration, salt concentration, bath temperature, and time were optimized. The results demonstrated that the addition of β-mercaptoethylamine could significantly reduce the interference of Zn²⁺ on the extraction of ZnONPs, while the CPE approach was not affected significantly by the typical environmental inorganic ion and ENMs (such as Au, TiO₂, and Al₂O₃). The extraction method of ZnONPs with different diameters was also assessed, and satisfactory extraction efficiency was obtained. The results of ZnONP concentration in collected environmental water were in the range of [ ]-[ ] μg/L. And the recoveries of ZnONPs in different environmental waters were [ ]-[ ] at low concentration spiked levels (12.57-54.68 μg/L), demonstrating that it is efficient to extract trace ZnONPs from real environmental waters. This established method offered a reliable method for the quantitative determination of ZnONPs in environmental waters, which could further promote the study of the environmental behavior, fate, and toxicity of ZnONPs in an aqueous environment.