Science & Technology Development Journal - Science of The Earth & Environment

Chronic effects of domestic and single used plastic leachates on the microcrustacea Daphnia magna

Van-Tai Nguyen — 2021-08-06

Plastic pollution has become one of the most serious environmental issues worldwide. Plastics can contain high amount of additives (e.g., phthalate, bisphenol A, trace metals), and they could be leached out of plastics, enter the aquatic environment and cause toxic effects to aquatic organisms (including microcrustacean). In this study, we investigated chronic effects of plastic leachates from two popular plastic materials (garbage bag and disposable raincoat) on the survival, maturation and reproduction of the microcrustcean Daphnia magna. The results showed that, the plastic leachates from the two materials at the concentration up to 1000 mg/l did not cause negative effect on survival of D. magna. However, exposed to the leachates from the garbage bag (at the concentrations of 10, 100 and 1000 mg/l) and from the disposable raincoat (at the concentration of 10 mg/l), the animals delayed their maturity ages compared to the control. Besides, the two kinds of leachates at the concentration of 1000 mg/l stimulated the reproduction of D. magna, resulting the increase of 17 – 37% of total offspring compared to the control, during 21 days of experiment. The results of this study contribute to the understanding on the toxicity of popular plastic materials to the microcrustacean, D. magna. Additionally, the plastic usage and emission into the environment should be paid more attention to protect the aquatic ecosystems and human health.

Correlation between soil moisture content and reflection value of VV polarization, VH polarization of Sentinel-1 satellite: Study case of dragon fruit farm, Binh Thuan province

Trang Nguyen Dang Khoa — 2021-08-15

Binh Thuan province is one of the driest provinces in the South Central region in particular and Vietnam in general. The scarcity of water for agriculture in this area in the dry season is very serious. Surface moisture is one of the parameters included in the assessment of aridity. In this study, the authors establish the correlation between VV reflectance value, VH reflectance value extracted from Sentinel-1 satellite image and surface soil moisture collected in the study area. Moisture samples in the field will be taken at a depth of 5cm from the surface in at the same time the Sentinel-1 observation through study area. Samples were taken at 4 different days, each day taking 22 samples and 2 samples for calibrated. Reflectance value VV, reflectance value VH at different times are adjusted according to 2 fixed points corresponding to the place where water is saturated and the surface is the driest in the cultivation area of dragon fruit. Besides, the soil moisture value correlated with the reflectance value of VV and reflectance value of VH in research was compared and compared with similar studies in the world in order to increase the reliability of the data. The results of analysis of moisture samples in the field with humidity values ranging from 13.13% to 61.06%, are correlated with the reflectance value of Sentinel-1 image with R2= 0.926 of VV polarization and R2= 0.956 with VH polarization.

Optimizing Electro-Fenton process for removal of atrazine from aqueous solutions using Taguchi method

Loan Huynh Ngoc — 2021-08-18

The purpose of this study is centered on the removal of atrazine, one of the popular organochlorines in Vietnam, from an aqueous solution, using an electro Fenton process with iron and carbon plated steel electrodes at a batch electro reactor. This study had applied the Taguchi method, one of the most uncomplicated cases of design of experiments involving the minimum number of experiments to be performed within the permissible limit of factors and levels through the Signal to Noise ratio. This study design was conducted with five independent factors: initial pH, current density, Fe²⁺ concentration, sodium sulfate and reaction time, at a fixed atrazine concentration of 10 mg/L to find the best condition to eliminate atrazine from the solution. The Signal to Noise ratio results illustrates that the initial pH is the most important factor, followed by the reaction time and Fe²⁺ concentration, while sodium sulfate and current density seem neglectable to the removal of atrazine using electro Fenton process. The optimal Taguchi condition shows that the electro Fenton process reached the best efficiency, approximately 76% atrazine eliminated after 180 min of reaction time at initial pH 3.5, sodium sulfate of 990 mg/L, Fe²⁺ concentration of 2 mM and current density of 2.22 mA/cm². Three confirm experiments at optimal test conditions also indicated good agreement with predicted results with small error variation (1.21 - 3.54%). Thus, the relationship between the removal efficiency and operating parameters could be understood. These obtained results highlight the potential of using the electro Fenton process to eradicate or reduce pesticide contaminants. Electron beam also could be one of the pre-treatment techniques to eliminate persistent organic pollutants before biological treatment systems.

Study of the treatment of leachate after biodigestion using Electro-fenton method

Pham Kieu Tuyet Tran — 2021-08-23

Leachate contains many non-biodegradable organic compounds and nutrients with high concentrations, especially from urban waste landfills with long operating times (> 10 years), which affects the human health and environmental quality. Electro-Fenton is one of the advanced oxidation processes (AOPs) that has been recently studied for the treatment of many persistent organic compounds in water. In this study, post-biological leachate (continuous flow biological tank) was treated using Electro-Fenton method with heterogeneous catalysts as Iron (II) Sulfide and Iron Oxide on two electrodes Ti/IrO₂-Ta₂O₅ and Ti/RuO₂. The effect of different pH conditions on the pollutant removal efficiency in landfill leachate was studied. The results show that Ti/IrO2-Ta2O5 electrode and Iron (II) Sulfide catalyst obtain better leachate treatment performance than the others under the same experimental conditions. The heterogeneous Electro-Fenton process was capable of removing 71% of chemical oxygen demand (COD), 88% of total organic carbon (TOC), 89% of total nitrogen (TN), 93% of ammonium nitrogen N-NH4 + and 99% color at Ti/IrO₂-Ta₂O₅ electrode and Iron (II) Sulfide catalyst at a pH 3, current density 333 mA/cm² after 90 minutes of electrolysis. The results showed that the Electro-Fenton method capable effective treatment of pollutants in the post-biological leachate in the future.

Nutrients recovery from urine through struvite formation using lab-scale fluidized-bed homogeneous crystallization reactor

Dang Bich Phuong — 2021-09-24

Phosphorus (P) is considered the most important micro-element needed for every living thing. Even though they have limited amount, P and nitrogen (N) are responsible for eutrophication in water bodies. This paper aimed to give an insight into the removal efficiency of nutrients and struvite crystallization of slowly soluble fertilizer MgNH4PO4.6H2O, which is also called NH4+-struvite. Besides, using fluidized bed homogeneous crystallization (FBHC) system can reduce impurities in granular struvite generated during the reaction as the advantage function itself. The results showed the changes in pH, magnesium (Mg2+), phosphate (PO43--P), ammonium (NH4+-N), and appearance of spontaneous struvite precipitation over time. Using synthesis urine sample with adjusted pH and Mg2+ concentration to determine the optimal conditions for granular NH4+-struvite recovery to maintain Mg and P removal efficiency up to 99% in steady state. In this study, the removal efficiency of N was about 80 – 85% maximum. The initial results indicated the feasibility of simultaneous crystallizing NH4+-struvite which is mentioned above. It could easily form at pH around 8 – 9. On the other hand, urea hydrolysis makes a pH increase in urine from 6.5 to less than 9.0 at room temperature. This might cause a heavy impact on the NH4+-N crystallization during the formation of granular struvite if there has no suitable NH4+-N pretreatment options. For Mg recovery, the concentration of Mg is detrimental in the creation of struvite. This will bring better removal efficiency if there is an available Mg source in nature which can be reused directly in an environmentally eco-friendly way. The total mass of struvite precipitate obtained in the form of nuclei corresponds to 200 g/m3 of urine during 24 days operation.