Evaluation of microplastic bioaccumulation capacity of mussel (Perna viridis) and surrounding environment in the North coast of Vietnam.

This study aimed to identify the presence of microplastics in green mussels (Perna viridis), surface seawater, and beach sediment on the North Coast of Vietnam. The average concentration of MPs in mussels was 3.67 ± 1.20 MPs/g wet weight and 25.05 ± 5.36 MPs/individual. Regarding surface seawater and beach sediments, the MPs concentration was found at 88.00 ± 30.88 MPs/L and 4800 ± 1776 MPs/kg dry weight, respectively. The dominant microplastics shape was fragment with the fractions ranging from 69.86 to 82.41 %. In addition, the size distribution of MPs was mostly in the range of smaller than 50 µm and 1-150 µm (34.17 % and 45.62 % in mussels; 29.65 % and 43.20 % in surface seawater and 40.22 % and 39.40 % in beach sediment, respectively). Polyethylene terephthalate was the major polymer types 49.93-58.44 % of the detected MPs. The risk assessment results based on the polymer types indicated a warning level in several sites.

Selection of a density separation solution to study microplastics in tropical riverine sediment.

Microplastics (MPs) are small (< 5 mm) plastic particles that are widely found in marine, freshwater, terrestrial and atmospheric environments. Due to their prevalence and persistence, MPs are considered an emerging contaminant of environmental concern. The separation and quantitation of MPs from freshwater sediments is a challenging and critical issue. It is necessary to identify the fate and sources of MPs in the environment, minimise their release and adverse effects. Compared to marine sediments, standardised methods for extracting and estimating the amount of MPs in freshwater sediments are relatively limited. The present study focuses on MP recovery efficiency of four commonly used salt solutions (NaCl, NaI, CaCl2 and ZnCl2) for isolating MPs during the density separation step from freshwater sediment. Known combinations of artificial MP particles (PS, PE, PVC, PET, PP and HDPE) were spiked into standard river sediment. Extraction using NaI, ZnCl2 and NaCl solutions resulted in higher recovery rates from 37 to 97% compared to the CaCl2 solution (28-83%) and varied between polymer types. Low-density MPs (PE, HDPE, PP and PS) were more effectively recovered (> 87%) than the denser polymers (PET and PVC: 37 to 88.8%) using NaCl, NaI and ZnCl2 solutions. However, the effective flotation of ZnCl2 and NaI solutions is relatively expensive and unsafe to the environment, especially in the context of developing countries. Therefore, considering the efficiency, cost and environmental criteria, NaCl solution was selected. The protocol was then tested by extracting MPs from nine riverine sediment samples from the Red River Delta. Sediments collected from urban rivers were highly polluted by MPs (26,000 MPs items·kg-1 DW) compared to sediments located downstream. Using a NaCl solution was found to be effective in this case study and might also be used in long-term and large-scale MP monitoring programmes in Vietnam.

Single-step removal of arsenite ions from water through oxidation-coupled adsorption using Mn/Mg/Fe layered double hydroxide as catalyst and adsorbent.

This study developed a layered double hydroxides (Mn/Mg/Fe-LDH) material through a simple co-precipitation method. The Mn/Mg/Fe-LDH oxidized arsenite [As(III)] ions into arsenate [As(V)] anions. The As(III) and oxidized As(V) were then adsorbed onto Mn/Mg/Fe-LDH. The adsorption process of arseniate [As(V)] oxyanions by Mn/Mg/Fe-LDH was simultaneously conducted for comparison. Characterization results indicated that (i) the best Mg/Mn/Fe molar ratio was 1/1/1, (ii) Mn/Mg/Fe-LDH structure was similar to that of hydrotalcite, (iii) Mn/Mg/Fe-LDH possessed a positively charged surface (pHIEP of 10.15) and low Brunauer-Emmett-Teller surface area (SBET = 75.2 m2/g), and (iv) Fe2+/Fe3+ and Mn2+/Mn3+/Mn4+ coexisted in Mn/Mg/Fe-LDH. The As(III) adsorption process by Mn/Mg/Fe-LDH was similar to that of As(V) under different experimental conditions (initial solutions pH, coexisting foreign anions, contact times, initial As concentrations, temperatures, and desorbing agents). The Langmuir maximum adsorption capacity of Mn/Mg/Fe-LDH to As(III) (56.1 mg/g) was higher than that of As(V) (32.2 mg/g) at pH 7.0 and 25 °C. X-ray photoelectron spectroscopy was applied to identify the oxidation states of As in laden Mn/Mg/Fe-LDH. The key removal mechanism of As(III) by Mn/Mg/Fe-LDH was oxidation-coupled adsorption, and that of As(V) was reduction-coupled adsorption. The As(V) mechanism adsorption mainly involved: (1) the inner-sphere and outer-sphere complexation with OH groups of Mn/Mg/Fe-LDH and (2) anion exchange with host anions (NO3-) in its interlayer. The primary mechanism adsorption of As(III) was the inner-sphere complexation. The redox reactions made Mn/Mg/Fe-LDH lose its original layer structure after adsorbing As(V) or As(III). The adsorption process was highly irreversible. Mn/Mg/Fe-LDH can decontaminate As from real groundwater samples from 45-92 ppb to 0.35-7.9 ppb (using 1.0 g/L). Therefore, Mn/Mg/Fe-LDH has great potential as a material for removing As.

Phosphate Adsorption by Silver Nanoparticles-Loaded Activated Carbon derived from Tea Residue.

This study presents the removal of phosphate from aqueous solution using a new silver nanoparticles-loaded tea activated carbon (AgNPs-TAC) material. In order to reduce costs, the tea activated carbon was produced from tea residue. Batch adsorption experiments were conducted to evaluate the effects of impregnation ratio of AgNPs and TAC, pH solution, contact time, initial phosphate concentration and dose of AgNPs-AC on removing phosphate from aqueous solution. Results show that the best conditions for phosphate adsorption occurred at the impregnation ratio AgNPs/TAC of 3% w/w, pH 3, and contact time lasting 150 min. The maximum adsorption capacity of phosphate on AgNPs-TAC determined by the Langmuir model was 13.62 mg/g at an initial phosphate concentration of 30 mg/L. The adsorption isotherm of phosphate on AgNPs-TAC fits well with both the Langmuir and Sips models. The adsorption kinetics data were also described well by the pseudo-first-order and pseudo-second-order models with high correlation coefficients of 0.978 and 0.966, respectively. The adsorption process was controlled by chemisorption through complexes and ligand exchange mechanisms. This study suggests that AgNPs-TAC is a promising, low cost adsorbent for phosphate removal from aqueous solution.

Laterite as a low-cost adsorbent in a sustainable decentralized filtration system to remove arsenic from groundwater in Vietnam.

In the Red River Delta, Vietnam, arsenic (As) contamination of groundwater is a serious problem where more than seventeen million people are affected. Millions of people in this area are unable to access clean water from the existing centralized water treatment systems. They also cannot afford to buy expensive household water filters. Similar dangerous situations exist in many other countries and for this reason there is an urgent need to develop a cost-effective decentralized filtration system using new low-cost adsorbents for removing arsenic. In this study, seven locally available low-cost materials were tested for arsenic removal by conducting batch adsorption experiments. Of these materials, a natural laterite (48.7% Fe2O3 and 18.2% Al2O3) from Thach That (NLTT) was deemed the most suitable adsorbent based on arsenic removal performance, local availability, stability/low risk and cost (US$ 0.10/kg). Results demonstrated that the adsorption process was less dependent on the solution pH from 2.0 to 10. The coexisting anions competed with As(III) and As(V) in the order, phosphate > silicate > bicarbonate > sulphate > chloride. The adsorption process reached a fast equilibrium at approximately 120-360 min, depending on the initial arsenic concentrations. The Langmuir maximum adsorption capacities of NLTT at 30 °C were 512 µg/g for As(III) and 580 µg/g for As(V), respectively. Thermodynamic study conducted at 10 °C, 30 °C, and 50 °C suggested that the adsorption process of As(III) and As(V) was spontaneous and endothermic in nature. A water filtration system packed with NLTT was tested in a childcare centre in the most disadvantaged community in Ha Nam province, Vietnam, to determine arsenic removal performance in an operation lasting six months. Findings showed that the system reduced total arsenic concentration in groundwater from 122 to 237 µg/L to below the Vietnam drinking water standard of 10 µg/L.

Ammonium removal from aqueous solutions by fixed-bed column using corncob-based modified biochar.

This study investigated the potential of removing ammonium ([Formula: see text]) from aqueous solutions using corncob based on modified biochar (MBCC) in the fixed-bed column. Corncob biochar was soaked in a mixture of HNO3 6.0 M and NaOH 0.3 M to prepare active binding sites for ammonium removal. The effect of initial ammonium concentrations (10-40 mg/L), flow rates (1-9 mL/min) and MBCC fixed-bed heights (8-24 cm) on the breakthrough characteristics of the adsorption system were studied. The results showed that the highest adsorption capacity of fix-bed column, the breakthrough time and value of Ct/Co were 12.83 mg/g, 480 min and 0.862 ± 0.025 at 10 mg/L of initial ammonium concentration, 8 cm of MBCC fixed-bed height and 3 mL/min of flow rate, respectively. The breakthrough curve model in this study also indicated that all Yoon-Nelson, Thomas and Adam-Bohart models well fit with the experimental data with a high R2. The results also proved that MBCC can be used as a potential adsorbent for eliminating [Formula: see text] in the fixed-bed column. The saturated MBCC was also regenerated and reused consecutively for four cycles. The usage of mixture of NaOH and NaCl in recovering MBCC was better than NaCl only.

Removing ammonium from water using modified corncob-biochar.

Ammonium pollution in groundwater and surface water is of major concern in many parts of the world due to the danger it poses to the environment and people's health. This study focuses on the development of a low cost adsorbent, specifically a modified biochar prepared from corncob. Evaluated here is the efficiency of this new material for removing ammonium from synthetic water (ammonium concentration from 10 to 100mg/L). The characteristics of the modified biochar were determined by Brunauer-Emmett-Teller (BET) test, Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). It was found that ammonium adsorption on modified biochar strongly depended on pH. Adsorption kinetics of NH4+-N using modified biochar followed the pseudo-second order kinetic model. Both Langmuir and Sips adsorption isotherm models could simulate well the adsorption behavior of ammonium on modificated biochar. The highest adsorption capacity of 22.6mg NH4+-N/g modified biochar was obtained when the biochar was modified by soaking it in HNO3 6M and NaOH 0.3M for 8h and 24h, respectively. The high adsorption capacity of the modified biochar suggested that it is a promising adsorbent for NH4+-N remediation from water.