Pot experiments were conducted to investigate the impacts of continuous addition of different concentrations of calcium chloride (CaCl₂) and/or low-molecular-weight organic acids (LMWOAs) on soil pH, electrical conductivity (EC), and cadmium (Cd) transformation. These factors subsequently affected Cd phytoavailability in a system consisting of Cd-contaminated soil and Chinese cabbage (Brassica chinensis L.). The results indicate that CaCl₂ addition had a greater impact on reducing soil pH value, increasing soil EC value, and enhancing Cd phytoaccumulation in Chinese cabbage compared to LMWOAs. When soil pH dropped by 0.3 unit and the soil EC increased by 500 µS cm^-1, the Cd concentration in the Chinese cabbage shoots was 3 times higher than that in the control group. Throughout two planting terms of Chinese cabbage, the addition of CaCl₂ (1.6-3.2 g kg^-1) and LMWOAs (≤ 1.0 g kg^-1) led to phytoextracted Cd concentration exceeding exchangeable Cd concentration in soil samples before the pot experiment. Regarding phytoextracted Cd, desorption from carbonate-bound Cd contributes more than desorption from bound to organic matter Cd and adsorption to Fe/Mn oxide Cd. This study underscores the influence of soil pH and EC value variations and Cd transformation on Cd phytoavailability. Special attention should be given to leafy vegetables grown in Cd-contaminated soil, as the phytoavailable Cd concentration reaches approximately 2.0 µg kg^-1, which may lead to Cd levels surpassing acceptable limits for Chinese cabbage.

Dissolved organic matter (DOM) is the major regulated pollutant of landfill leachate in solid waste management industries. Recently, aged-refuse bioreactor (ARB) has received increasing attention for reduction of DOM from mature leachate due to low energy consumption, easy operation, simple maintenance, low cost, and high treatment efficiency. However, the information regarding alternation of the DOM nature during ARB treatment is highly limited. To figure out appropriate posttreatment for effluent of ARB and meet elevated discharge standards, especially in developing countries, this study investigates the characterization of mature leachate DOM during ammonia stripping and two-stage ARB treatment by means of synchronous scanning fluorescence spectra, excitation-emission matrices spectra, and molecular size distribution. The analytical results indicated that ammonia stripping could not significantly remove DOM, though the process was effective in ammonia nitrogen reduction. In contrast, ARB could remove substantial DOM. The first stage ARB preferentially attacked both fulivc-acid-like and humic-acid-like organic molecules and the second stage ARB played a polishing treatment role with a similar treatment fashion. The final effluent after ammonia stripping and two-stage ARB treatment still contained fulvic-acid-like DOM with low molecular weight (<5 kDa) that should be further removed by appropriate posttreatment.

To promote adsorption capacity of biochar as engineering material, pinewood biochar (PC) and bamboo biochar (BC) were prepared by slow pyrolysis (700 °C) and then directly irradiated with UV light at room temperature. The elemental analysis, SEM, FTIR, XPS, and Boehm titration measurements showed that UV irradiation significantly increased the BET surface area, porosity, and surface oxygen functional groups of the biochar. After UV treatment, the BET surface areas of PC and BC were increased by 63.0% and 217%, while the amount of total (acidic) groups increased by 62.0% (155%) and 24.9% (28.2%), respectively. FTIR and XPS measurements suggested that photochemical reactions, including photodegradation and photooxidation processes, may play primary roles in altering biochar the pore structure and surface functional groups of biochar. The Langmuir model capacities (qmax) of modified PC and BC were increased by 94.5% and 50.5% for Pb (II), 18.5% and 13.7% for Cd (II), respectively, compared to their unmodified counterparts. This study examined the effects of UV irradiation on the surface properties of biochar and demonstrate its potential as an effective, simple, and green method for functionalizing biomass material.

This study delves into the pivotal role of biochar particle size and addition ratio in mitigating cadmium (Cd) contamination in paddy-upland soils, with a specific focus on curbing Cd uptake by Chinese cabbage (Brassica chinensis L.) during the pivotal transition from paddy to upland cultivation. Through a meticulously designed laboratory experiment, we uncovered that biochar's adsorption capacity for soil Cd is markedly lower than its maximum adsorptive capacity as determined by adsorption kinetics, potentially due to competitive adsorption by other cationic species present in the soil. This insight underscores the critical need to optimize biochar application rates in Cd-contaminated soils to effectively modulate Cd phytoavailability. Furthermore, our findings demonstrate that biochar not only effectively converts non-residual soil Cd fractions into a more stable "residual Cd" form but also diminishes the uptake of Cd by Chinese cabbage from the soil. Notably, the application of fine biochar (Φ₃ < 0.25 mm) at a 10 % application rate was particularly efficacious, reducing soil non-residual Cd concentration by 28.2 %, equivalent to approximately 1.79 mg/kg. This research introduces a novel perspective on biochar-mediated remediation of soil Cd contamination, emphasizing the critical influence of particle size and addition ratio on regulating Cd phytoavailability and enhancing food safety in agricultural soils under paddy-upland rotation cultivation affected by Cd contamination.