Observation on some of the environmental parameters of selected shrimp farms in Khulna, Bangladesh

In recent years, the ecological degradation, loss of technological sustenance and other multidimensional consequences caused by shrimp farming have made the experts and authorities bound to rethink about the development of the industry. The present study describes the water and sediment quality, and culture and management techniques in five selected shrimp farms at Paikgacha, Khulna throughout a production cycle from March to September 1997. The water quality parameters were found to be more or less suitable throughout the cycle. The concentration of the limiting major nutrients such as nitrogen and phosphorus and minor nutrients such as calcium and magnesium were satisfactorily high, concentrations of the organic matter content were also high. Remarkable negative correlation of shrimp production with secchi depth was observed among the farms. Production per cycle ranged between 273 kg/ha and as low as 63 kg/ha.

Studies on arsenical creosote as a wood preservative for marine structures. Part 2. Observation on leaching, corrosion and resistance to borer attack

A detailed study on arsenical creosote with reference to leaching, corrosion and anti-borer properties was carried out. Results showed that aging had very little effect on the preservative which suggested better fixation of the preservative into the wood. Corrosion of mild steel, galvanised iron, aluminium-magnesium alloy (M57S) and copper panels in the preservative was found to be negligible. Normal creosote and low temperature creosote of Regional Research Laboratory, Hyderabad, both fortified with arsenic trioxide resisted borer damage on wooden panels for a period of over five months in the port of Cochin. The performance of low temperature creosote fortified with arsenic was found to be equally satisfactory when compared to normal creosote fortified in the same manner. A loading of 208.6 Kgs/ml³ for Haldu (Adina cordifolia) and 138 Kgs/m³ for Mango (Mangifera indica) in the case of normal creosote and 177 Kgs/m³ for Mango the case of RRL creosote were found to be sufficient for treating the wood.

Effect of organophosphate, diazinon on some immunophysiological, haematological and histological variable of Rutilus frisii kutum (Kamensky,1901)

The acute toxicity and effects of diazinon on some haematological parameters of kutum (Rutilus frisii kutum, Kamensky, 1901) weighing 613.33 g±157.06 g were studied under static water quality conditions at 15°C ± 2ºC in winter and spring 2009. The effective physical and chemical parameters of water were pH= 7-8.2, dh= 300mg/L (caco3), DO= 7 ppm and T= 15°C±2ºC. The first test was primarily to determine the effects of acute toxicity (LC5096 h) of the agricultural toxicant diazinon (emulsion 60%) on kutum male brood stocks. For this purpose, 4 treatments were used to test toxicity; each treatment was repeated in 3 tanks with 9 fish per treatment and with 180 litres water capacity. After obtaining the final results, the information was analysed statistically with Probit version 1.5 (USEPA, 1985), and we determined the LC10, LC50 and LC90 values at 24 hours, 48 hours, 72 hours and 96 hours; the maximum allowable concentration value (LC5096 h divided by 10) (TRC, 1984); and the degree of toxicity. The second stage of testing consists of four treatments: LC0= 0 as experimental treatment, treatment A with a concentration of LC1= 0.107 mg/L, treatment B with concentration of LC5= 0.157 mg/L, treatment C with concentration of MAC value= 0.04 mg/L. Male brood stocks of kutum were treated with these concentrations for 45 days. Experiments were carried out under static conditions based on the standard TRC, 1984 method over 45 days. Our results show that long-term exposure to diazinon causes a decrease in the erythrocyte count (RBC), haemoglobin (Hb), haematocrit (PCV), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC), leucocyte count (WBC), lymphocyte, testosterone, iron (Fe), sodium (Na), lactate dehydrogenase (LDH), and cholinesterase (CHeS). In addition, diazinon also causes an increase in prolymphocyte, aspartate aminotransferase (AST), cholesterol, alkaline phosphatase (ALP) and adrenaline (P<0.05). There are no significant effects on monocyte, eosinophil, magnesium (Mg), chloride (Cl), glucose (BS), urea (BUN), uric acid (U.A), triglyceride (TG), calcium (Ca), albumin (Alb), total protein (TP), cortisol, noradrenaline and high density lipoprotein (HDL) levels in kutum male brood stocks (P>0.05). Pathology results showed toxin diazinon no effect on average weight and fish body length, the average weight of heart, brain, spleen, liver, kidney and liver index but caueses decrease of gonad weigth and gonad index and also, cause complications of tissue necrosis, vascular congestion, inflammation in the liver, a sharp reduction in the number of glomeruli, necrosis, vascular congestion and haemorage in the kidney, capsule thickening and fibrosis, atrophy, vascular congestion, macrophages release increased, increasing sediment Hemosiderine and thickening of artery walls in the spleen, atrophy, fibrosis and necrosis in testis , vascular congestion, increased distance between the myocardium and fibrous string in heart and neuronal loss, vascular congestion and edema in the brain of kutum male brood stocks.

Composition of waters of lakes and rivers in east and west Africa

Thirty-three groups of geochemically related natural lake and river waters collected from 368 sites scattered over East and West Africa, were investigated to determine correlations between their various ions and the patterns of change in their ionic composition across the African continent. The following nine significant correlations were found to exist in the entire area or in a major part of it: sodium and potassium; sodium and chloride; sodium and sulphate; potassium and ammonium; potassium and chloride; ammonium and nitrate; calcium and magnesium; magnesium and chloride; sulphate and chloride. When compared with the world average composition. The concentration of potassium in these waters was found to be high, that of calcium and nitrate was low. With respect to the area of East Africa only, trends in the pattern of change involving the ionic composition of the lake and river water and the longitude at which the sites were present, were found to exist for the ratio of sodium: conductivity (which showed an increase in the direction of West to East), magnesium: conductivity, and for the sum of calcium and magnesium: phosphate was generally found to increase in East Africa in the direction of west to East.

MgB2 sample tests for possible applications of superconducting fault current limiters

Cheap to make and easy to shape, Magnesium Diboride (MgB2) throws the field of applied superconductivity wide open. Great efforts have been made to develop a super-conducting fault current limiter (SFCL) using MgB 2. With a superconducting transition temperature of 39 K, MgB 2 can be conveniently cooled with commercial cryocoolers. A cryogenic desktop test system, an ac pulse generation system and a real time data acquisition program in LabView/DAQmx were developed to investigate the quench behavior of MgB2 wires under pulse overcurrents at 25 K in self-field conditions. The experimental results on the current limitation behavior show the possibilities for using MgB2 for future SFCL applications. © 2007 IEEE.

Preliminary laboratory-scale model auger installation and testing of carbonated soil-MgO columns

This paper presents details of the installation and performance of carbonated soil-MgO columns using a laboratory-scale model auger setup. MgO grout was mixed with the soil using the auger and the columns were then carbonated with gaseous CO2 introduced in two different ways: one using auger mixing and the other through a perforated plastic tube system inserted into the treated column. The performance of the columns in terms of unconfined compressive strength (UCS), stiffness, strain at failure and microstructure (using X-ray diffraction and scanning electron microscopy) showed that the soil-MgO columns were carbonated very quickly (in under 1 h) and yielded relatively high strength values, of 2.4-9.4 MPa, which on average were five times that of corresponding 28-day ambient cured uncarbonated columns. This confirmed, together with observations of dense microstructure and hydrated magnesium carbonates, that a good degree of carbonation had taken place. The results also showed that the carbonation method and period have a significant effect on the resulting performance, with the carbonation through the perforated pipe producing the best results. Copyright © 2013 by ASTM International.

Thermogravimetric study on the hydration of reactive magnesia and silica mixture at room temperature

The synthesis of magnesium silicate hydrate (MSH), which has wide applications in both construction and environmental fields, has been studied for decades. However, it is known that the characteristics of magnesia (MgO) vary significantly depending on their calcination conditions, which is expected to affect their performance in the MgO-SiO2-H2O system. This paper investigated the effect of different MgO and silica sources on the formation of magnesium silicate hydrate (MSH) at room temperature. The hydration process was studied by mixing commercial reactive MgO and silica powders with water and curing for 1, 7 and 28 days. The hydration products were analysed with the help of X-ray diffraction (XRD) and thermogravimatric analysis (TGA). The results showed the continuous consumption of MgO and the existence of MSH and brucite and other minor phases such as magnesite and calcite. It is found that the Mg and Si sources have significant effect on the hydration process of MgO-SiO2-H2O system. The reaction degree is controlled by the availability of dissolved Mg and Si in the solution. The former is determined by the reactivity of MgO and the latter is related to the reactivity of the silica as well as the pH of the system. © 2013 Elsevier B.V. All rights reserved.

Carbonating magnesia for soil stabilization

This paper investigates the potential for carbonating reactive magnesia (MgO) to serve as a more sustainable soil stabilization method by providing rapid and significant strength development of the stabilized soil through absorbing substantial quantities of CO2. Gaseous CO2 was forced through laboratory-prepared reactive MgO-treated soil samples in a triaxial cell set-up, and their resulting mechanical and microstructural properties were investigated using unconfined compressive strength, X-ray diffraction, and scanning electron microscopy. The results showed that adequately carbonated MgO-treated soils could, in a few hours, reach a similar strength range to corresponding 28 day Portland cement (PC)-stabilized soils. Hydrated magnesium carbonates, namely nesquehonite and hydromagnesite-dypingite, were the main products of the carbonated MgO in the soil, and were responsible for the significant strength development.

Effects of micronutrients on biological treatment efficiency of textile wastewater

Micronutrients play a very important role in biological processes for wastewater treatment. Many industrial wastewaters lack in nutrients (macronutrients and micronutrients) required for microbial growth, and this is one of the main problems at many activated sludge plants treating industrial wastewater. The microbial community structure is one of the important factors controlling the pollutant-degrading capacity of biological wastewater treatment system. In this study, the concentrations of micronutrients of the textile wastewater discharged from a textile plant were determined, and the effects of micronutrients on treatment efficiency and microorganism community structure of the biological treatment system were studied. The results showed that the optimal concentrations of magnesium, molybdenum, zinc, thiamine and niacin in the textile wastewater were 5.0, 2.0, 1.0, 1.0 and 1.0mg/L, respectively. The COD removal rates when magnesium, molybdenum, zinc, thiamine and niacin were added individually to the wastewater in their optimal concentrations were 1.8, 1.4, 1.3, 1.6 and 2.2 times of that of the control, respectively. The improving effects of combinations of zinc and thiamine, zinc and niacin, thiamine and niacin were better than single micronutrient. The diversity of quinones (DQ) changed significantly after the micronutrient was added into the wastewater treatment system. This indicated that there was probably a feasibility of optimizing the biological treatment performances and microorganism community structure of textile wastewater treatment system through micronutrient supplement.

Development of low-pH cements for immobilisation of intermediate level radioactive waste: Achievements and challenges

Although cementation is a widely recognized solidification/ stabilization process for immobilisation of Intermediate Level Radioactive Waste (ILRW), the low resistance to hyperalkaline pore waters compromises the effectiveness of the process when Portland Cement (PC) is employed. Moreover the manufacture of PC is responsible for significant CO2 emissions. In this context, low pH cements are environmentally more suitable and have emerged as a potential alternative for obtaining secure waste forms. This paper summarises the achievements on development of low-pH cements and the challenges of using these new materials for the ILRW immobilisation. The performance of waste forms is also discussed in terms of radionuclides release. Reactive magnesium oxide and magnesium phosphate cements are emphasised as they feature important advantages such as consumption of available constituents for controlling acid-base reactions, reduced permeability and higher density. Additionally, in order to identify new opportunities for study, the long-term modelling approach is also briefly discussed. Copyright © 2013 by ASME.

Strength and hydration products of reactive MgO-silica pastes

The reaction between MgO and microsilica has been studied by many researchers, who confirmed the formation of magnesium silicate hydrate. The blend was reported to have the potential as a novel material for construction and environment purposes. However, the characteristics of MgO vary significantly, e.g., reactivity and purity, which would have an effect on the hydration process of MgO-silica blend. This paper investigated the strength and hydration products of reactive MgO and silica blend at room temperature up to 90 days. The existence of magnesium silicate hydrate after 7 days' curing was confirmed with the help of infrared spectroscopy, thermogravimetric analysis and X-ray diffraction. The microstructural and elemental analysis of the resulting magnesium silicate hydrate was conducted using scanning electron microscopy and energy dispersive spectroscopy. In addition, the effect of characteristics of MgO on the hydration process was discussed. It was found that the synthesis of magnesium silicate hydrate was highly dependent on the reactivity of the precursors. MgO and silica with higher reactivity resulted in higher formation rate of magnesium silicate hydrate. In addition, the impurity in the MgO affects the pH value of the blends, which in turn determines the solubility of silica and the formation of magnesium silicate hydrate. © 2014 Elsevier Ltd. All rights reserved.

Effect on nitrogen acceptor as Mg is alloyed into ZnO

Our Raman measurement indicates that the intensity of the peaks (510 and 645 cm(-1)) related to nitrogen concentration is enhanced in MgZnO compared with that in ZnO. Using first-principles band structure methods, we calculated the formation energy and transition energy level for nitrogen acceptor in ZnO and random MgxZn1-xO (with x=0.25) alloy. Our calculations show that the incorporation of nitrogen can be enhanced as Mg is alloyed into ZnO, which agrees with our experiments. The acceptor energy level deeper in the alloy ascribes to the downward shift of the valence-band maximum edge in the presence of magnesium. (c) 2008 American Institute of Physics.

Determination of MgO/AlN heterojunction band offsets by x-ray photoelectron spectroscopy

MgO is a promising gate dielectric and surface passivation film for GaN/AlGaN transistors, but little is known of the band offsets in the MgO/AlN system. X-ray photoelectron spectroscopy was used to measure the energy discontinuity in the valence band (Delta E-v) of MgO/AlN heterostructures. A value of Delta E-v=0.22 +/- 0.08 eV was obtained. Given the experimental band gap of 7.83 eV for MgO, a type-I heterojunction with a conduction band offset of similar to 1.45 eV is found. The accurate determination of the valence and conduction band offsets is important for use of III-N alloys based electronic devices.

MOVPE growth of GaN and LED on (111) MgAl2O4

The growth of wurtzite GaN by low-pressure metalorganic vapor-phase epitaxy on (1 1 1) magnesium aluminate (MgAl2O4) substrates have been studied. The morphological, crystalline, electrical and optical properties are investigated. A p-n junction GaN LED was fabricated on the MgAl2O4 substrate. (C) 1998 Elsevier Science B.V. All rights reserved.