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Cadmium Immobilization in the Rice – Paddy Soil with Biochar Additive

Thi Khac Vu, Lan Phuong Dinh Thi, Hang Nga Nguyen Thi, Thanh Hoa Nguyen

Journal of Ecological Engineering

2022

Vol. 23, nr 4

85--95

Cadmium (Cd) is toxic for humans, but its effects on the yield and quality of rice under contaminated irrigation conditions remain uncertain. In this study, paddy soils in the Red River Delta (Vietnam) were selected for experiments with the purpose of understanding the effects of Cd contaminated irrigation water on growth, yields, and grain Cd accumulation. In addition, biochar was produced from rice husk (BRH) and rice straw for preventing Cd infiltration into rice was also studied in this experiment. A field experiment was established with applicated BRH and straw into polluted paddy soil, as a result the Cd content in grains reduced significantly. The Cd contaminated soil was added to the BRH and rice straw (RS) with six ratios, including: (1) RS 2.5%, (2) BRH 2.5%, (3) RS-BRH: 1.25–1.25%, (4) RS 5.0%, (5) BRH 5.0%, (6) RS-BRH: 2.5–2.5%, (w:w). Besides, three content levels 0.01–0.05–0.5 mg/L of Cd in irrigation water were applied throughout crop season. The results showed that the Cd accumulation in rice was in the following order: roots > stems > seeds. With 3 contaminated irrigation levels which were applied, the Cd concentrations of 0.05 mg/L and 0.5 mg/L affected plant height and yield. However, the Cd content in grains under contaminated soil condition can be controlled from 82.47–83.94% by applying a BRH ratio from 2.5–5% (w:w).

Optimization of Copper Removal by Photovoltaic Electrocoagulation from Aqueous Solution Using Response Surface Methodology Towards Sustainable Development

Thanh Hoa Nguyen, Nguyen Lien, Lan Phuong Dinh Thi

Journal of Ecological Engineering

2019

Vol. 20, nr 7

103--111

This research aims at illustrating the optimal functions of removing copper ions in aqueous solution by means of the electrocoagulation process in which portable solar power generators are used as renewable energy. A solar photovoltaic cell (PV), producing approximately 48A current intensity for 4-7 h per day, was sufficient to charge the lithium batteries completely during the day. This system was connected directly to the electrocoagulation tank. The Box-Behnken design (BBD) was applied to evaluate three effects of process factors: current density, the dose of electrolyte (NaCl), and application time. The results showed that an optimal efficiency of 99.01% Cu removal plus an energy savings of 1.039 kWh/m3 were obtained at a current density of 4 A/m2, the dosage of NaCl (electrolyte) of 1.87 g/L, and electrolysis time of 10 min. The chemical components of the sludge produced under these optimized conditions were determined by means of EDX. It was illustrated that the copper ions were the main elements of sludge, and nonhazardous compounds were contained. The PV-lithium battery system is considered to be an efficient alternative energy source toward sustainable development.