Simultaneous removal of Cu and PAHs from dredged sediments using flotation

Purpose

This study addresses the feasibility of a flotation technique, using a lab-scale flotation cell, to simultaneously remove both metals and polyaromatic hydrocarbons (PAHs) from fine sediment fractions (<250 μm) that are potentially contaminated with copper (Cu).

Materials and methods

A multiple flotation process with three consecutive flotation stages was performed on three sediments (13S, 14B, and 24A) with different particle size distributions, Cu and PAH concentrations, and organic matter contents.

Results and discussion

Flotations performed under selected conditions allowed for significant removal of both Cu (61–70 %) and PAHs (75–83 %) with acceptable froth recoveries of approximately 23–29 %. Removal rates for arsenic, lead, and zinc were 48–61, 40–48, and 32–36 %, respectively. Flotation selectivity of Cu was greatly influenced by the contents of fine particles and organic matter of the sediments. The maximum flotation selectivity was obtained for the 53–125-μm size fraction. The high flotation selectivity of Cu (2.5–3.2) and PAHs (3.0–3.6) demonstrated the feasibility of flotation to treat soils or sediments containing both organic and inorganic pollutants.

Conclusions

Overall, the flotation results showed a high selectivity for both Cu and PAHs and demonstrated the feasibility of flotation to treat media contaminated with organic and inorganic contaminants.     

Nitrogen use efficiency and drought tolerant ability of various sugarcane varieties under drought stress at early growth stage

ABSTRACT

The experiment was conducted under glasshouse conditions to evaluate nitrogen use efficiency and drought tolerant ability of the five different sugarcane varieties (including NiF3, Ni9, Ni17, Ni21 and Ni22) under early growth stage from 60 to 120 days after transplanting. The results showed drought stress reduced the photosynthetic rate, growth parameters including plant height, leaf area; partial and total dry weights; and nitrogen use efficiency (NUE) traits including photosynthetic NUE, nitrogen utilization efficiency and biomass NUE of measured sugarcane varieties. The significant differences were found among varieties in growth parameters, dry weights, NUE traits and drought tolerant index (DTI). The significant positive correlations among NUE traits and DTI suggested higher NUEs could support better a tolerant ability to drought stress at the early growth stage. Because of larger contributions, DTIs for aboveground and stalk dry weight could be used as the important DTIs to evaluate drought tolerant ability in sugarcane varieties.     

Impacts of climate change on snakehead fish value chains in the Lower Mekong Basin of Cambodia and Vietnam

ABSTRACT

The productive fisheries of the Lower Mekong Basin of Cambodia and Vietnam are essential to the food security and nutrition of 60 million people. Yet these fisheries, both culture and capture, are susceptible to the impacts of climate change. This article reports on a study undertaken to examine the vulnerability, as perceived by snakehead (Channa striata) fish farmers in Vietnam and fishers in Cambodia, to the impacts from climate change. Perceived impacts on various actors in the value chain are identified, as well as adaptation strategies currently being utilized and planned for the future. Recommendations are suggested to contribute to assisting snakehead farmers and fishers in adapting and preparing for the impacts of climate change.     

Operation of the Ba Lai irrigation system in the Mekong Delta, Vietnam

Ba Lai Irrigation Project is located at coastal area in the Mekong Delta. In dry season when the flow rate decreases and the strong east wind blows into the delta, the salinity intrusion increases and seriously affects agricultural and domestic water use. Intakes of Ba Lai system have to be closed for 1–3 months depending on their locations, and no water supply during this period often causes water pollution in the project area. In order to solve such problems, this study aims to seek gate operation procedures for salinity control and water environment improvement. A numerical model is developed to simulate water movement, salinity concentration and duration of remaining water (water age) within the system under three scenarios: (1) without control structures, (2) with available control structures, (3) with the full control structures. Through the numerical simulations, control structures are confirmed to be an effective measure for the salinity control and suitable gate operation schedules are proposed to improve the water environment in the project.     

Isolation of Sesquiterpenoids and Steroids from the Soft Coral Sinularia brassica and Determination of Their Absolute Configuration

Two undescribed rearranged cadinane-type sesquiterpenoids (1–2), named sinulaketol A-B, together with one new chlorinated steroid (3), one new gorgosterol (4), one known sesquiterpene (5), one known dibromoditerpene (6) and two known polyhydroxylated steroids (7–8) were isolated from the soft coral Sinularia brassica. The structures of these compounds were established by extensive spectroscopic analysis, including HRESIMS, 1D, and 2D NMR spectroscopy. Their absolute configurations were also determined by the ECD calculations and DP4+ probability analysis. Antileishmanial activity of compounds 1–8 was evaluated in vitro against the amastigote forms of Leishmania donovani, in which compounds 3, 6, and 7 inhibited the growth of L. donovani by 58.7, 74.3, 54.7%, respectively, at a concentration of 50 μM. Antimicrobial effect of the isolated compounds were also evaluated against Candida albicans, Staphylococcus aureus, and Escherichia coli. Compound 6, a brominated diterpene, exhibited antimicrobial effect against S. aureus.     

Residual Organic Compound Removal from Aqueous Solution Using Commercial Coconut Shell Activated Carbon Modified by a Mixture of Seven Metal Salts

The modified activated carbon (MAC) derived from commercial coconut shell activated carbon (AC) with mixture of seven metal salts was used as an adsorbent to remove target residual organic compound (sucrose) from aqueous solutions in batch modes. The results indicated that the highest adsorption capacity of sucrose onto MAC reached when the AC was modified at the ratio of impregnation of AC with mixture of seven metal salts, including nitrate silver (AgNO₃), manganese nitrate (Mn (NO₃)₂), potassium bichromate (K₂Cr₂O₇), nitrate cobalt (Co (NO₃)₂·6H₂O), nitrate copper (Cu (NO₃)₂·3H₂O), nitrate nickel (Ni (NO₃)₂·6H₂O) and nitrate iron (Fe (NO₃)₂·9H₂O) of 3% (w/w). The most appropriate conditions for sucrose adsorption onto MAC in batch experiments obtained at pH 7, contact time of 120 min, 800 mg MAC/50 mL of sucrose solution with initial concentration of 1500 mg/L. At this condition, the highest adsorption capacity of sucrose onto MAC reached 28.28 mg/g. The Langmuir, Freundlich, and Sips adsorption isothermal equilibrium models can adequately describe the adsorption properties of sucrose on MAC. The adsorption kinetic of sucrose onto MAC obeyed pseudo-first-order and pseudo-second-order models with the chemical sorption process. The saturated MAC was recovered by heat from an oven. The highest recovery efficiency of saturated MAC obtained at 180 °C in 120 min. The highest adsorption capacity of sucrose onto recovered MAC was 24.31 mg/g, appropriately adsorption capacity of initial MAC.     

Applying Activated Carbon Derived from Coconut Shell Loaded by Silver Nanoparticles to Remove Methylene Blue in Aqueous Solution

This study developed a new adsorbent, specifically activated carbon-loaded silver nanoparticles (AgNPs-AC) by coating the silver nanoparticles (AgNPs) onto activated carbon (AC). The obtained AgNPs-AC were characterized by scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), Fourier transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET). The ability of AgNPs-AC to remove methylene blue (MB) was evaluated using different experimental factors, these being pH solution, contact time, adsorbent dose, and initial MB concentration. Results indicated that the highest adsorption capacity of MB onto AgNPs-AC was obtained when the AC was loaded onto AgNPs at the impregnation ratio of 0.5% w/w for AC and AgNPs. The best conditions in which AgNPs-AC could remove MB were as follows: pH 10, contact time lasting 120 min, and adsorbent dose being 250 mg/25 mL solution. In this scenario, the maximum adsorption capacity of MB onto AgNPs-AC was 172.22 mg/g. The adsorption isothermal equilibrium was well described by the Langmuir, Freundlich and Sips models. The Sips equations had the highest correlation coefficient value (R²?=?0.935). The pseudo-first-order and pseudo-second-order kinetic models agree well with the dynamic behavior of the adsorption of dye MB on AgNPs-AC.     

Better management practices and their outcomes in shrimp farming: evidence from small-scale shrimp farmers in Southern Vietnam

Despite the growth of aquaculture exports from developing countries to developed countries in recent years, a high percentage of these products are rejected at developed countries’ ports because of non-compliance with international standards. This paper presents a case study of the shrimp aquaculture sector in Vietnam to examine the factors behind the persistence of such port rejections. In particular, we focus on why the so-called better management practices (BMPs) are not appropriately adopted by many farmers and examine whether the number and types of information sources matter in farmers’ decisions on BMP adoption and whether BMP adoption actually leads to better performances. On the basis of our estimation using primary data collected in Southern Vietnam, we find that information sources and training experiences indeed matter in the adoption of a higher number of BMPs and that BMP adoption indeed reduces the possibility of disease outbreaks. These results prove the effectiveness of BMPs and suggest the importance of disseminating knowledge regarding them to farmers through experts.     

Effects of soil type and water saturation on growth,nutrient and mineral content of the perennial forage shrub S<Emphasis Type="Italic">esbania sesban</Emphasis>

Sesbania sesban (L.) Merr is a perennial N₂-fixing tree with high potential for use in agricultural production systems as a green manure and livestock forage. We studied the interactive effects of soil type and water level on the growth, biomass allocation, nutrient and mineral content of S. sesban. Four-week old seedlings of S. sesban were grown for 49 days (n = 5) in a factorial mesocosm set-up with six soil types (sediment, sand, alluvial, acid-sulfate, saline and clay) and three water levels (drained, water-saturated and flooded). The soils tested represent the predominant alluvial soil types of the Mekong delta, Vietnam. Sesbania sesban grew well with relative growth rates (RGR) around 0.08 g g^?1 d^?1 in all studied soil types, except the saline soil where plants died. In the low-pH (3.9) acid sulfate soil, that constitute more than 40 % of the Mekong delta, the RGR of the plants was slightly lower (0.07 g g^?1 d^?1), foliar concentration of calcium was 3–6 times lower, and concentrations of iron and sodium up to five times higher, than in other soils. The nutrient and mineral contents of the plant tissues differed between the soils and were also affected by the flooding levels. Foliar concentrations of nitrogen (50–74 mg N g^?1 dry mass) and phosphorus (5–9 mg P g^?1 dry mass) were, however, generally high and only slightly affected by water level. The results show that S. sesban can grow well and with high growth rates on most wet soils in the Mekong delta, except saline soils where the high salt content prevents establishment and growth. The nutrient and mineral contents of the plants, and hence the nutritional value of the plants as e.g. fodder or compost crops, is high. However, soil type and water level interactively affect growth and tissue composition. Hence, optimal growth conditions for S. sesban differ in the different regions of the Mekong delta.     

Biopore history determines the microbial community composition in subsoil hotspots

Biopores are hotspots of nutrient mobilisation and shortcuts for carbon (C) into subsoils. C processing relies on microbial community composition, which remains unexplored in subsoil biopores. Phospholipid fatty acids (PLFAs; markers for living microbial groups) and amino sugars (microbial necromass markers) were extracted from two subsoil depths (45–75 cm ; 75–105 cm) and three biopore types: (I) drilosphere of Lumbricus terrestris L., (II) 2-year-old root biopores and (III) 1.5-year-old root biopores plus six 6 months of L. terrestris activities. Biopore C contents were at least 2.5 times higher than in bulk soil, causing 26–35 times higher Σ PLFAs g^-1 soil. The highest Σ PLFAs were found in both earthworm biopore types; thus, the highest soil organic matter and nutrient turnover were assumed. Σ PLFAs was 33% lower in root pores than in earthworm pores. The treatment affected the microbial community composition more strongly than soil depth, hinting to similar C quality in biopores: Gram-positives including actinobacteria were more abundant in root pores than in earthworm pores, probably due to lower C bioavailability in the former. Both earthworm pore types featured fresh litter input, promoting growth of Gram-negatives and fungi. Earthworms in root pores shifted the composition of the microbial community heavily and turned root pores into earthworm pores within 6 months. Only recent communities were affected and they reflect a strong heterogeneity of microbial activity and functions in subsoil hotspots, whereas biopore-specific necromass accumulation from different microbial groups was absent.