Seasonal variation of soil enzymes in areas of fluoride stress in Birbhum District, West Bengal, India

AbstractSoil enzyme activities provide a unique biochemical means for assessing soil function as an indicator of soil fertility, which can be altered by a profusion of fluoride in the soil and seasonal changes. Seven sites were chosen in the fluoride-affected area of Nasipur, Birbhum District, West Bengal, India, to compare seasonal changes in enzymes (urease, amylase, cellulase and invertase), fluoride content, physicochemical characteristics and the availability of microbes in the soil with a control. The activity of all the enzymes varied with season. Urease had greater activity in the summer, followed by winter; it showed marginal differences from the control area during the winter (p<0.002) and summer (p<0.110) but a significant (p<0.000) difference during the rainy season. Soil pH had a negative impact on urease activity during both winter and summer. Cellulase activity was accelerated by the organic matter and organic carbon content of the soil. Fluoride therefore had the greatest activity against urease activity during the rainy, summer and winter seasons. The microbial population of the soil also showed a negative impact of fluoride, which may in turn affect the soil enzymes and characteristics

A Switched-Capacitor Multilevel Inverter With Modified Pulsewidth Modulation and Active DC-Link Capacitor Voltage Balancing

Although switched-capacitor (SC) multilevel inverters (MLIs) offer self-voltage balancing of flying capacitors and voltage gain higher than unity, the advantages come at the cost of high current stress and power loss in the SC circuit and dc source. Moreover, the voltage balancing is often restricted to a limited range of modulation indices. Another problem of MLIs with neutral-point clamped (NPC) front end is with dc-link capacitor voltage balancing under unbalanced load conditions, imploring sensor-based closed-loop control. This article proposes a unity gain five-level active-NPC SC-MLI with inrush charging current attenuation and actively balanced dc-link capacitor voltages under all load conditions and over the entire range of modulation index and power factor. The modified pulsewidth modulation (PWM) results in most switches operating at a low switching frequency, minimizing switching losses in the SC circuit. The proposed MLI attains a maximum efficiency of 98.04% at an output power of 510 W. Experiments on a 2 kVA laboratory prototype validate the theoretical analysis. Results from transformerless grid-connected solar photovoltaic (PV) system show that the proposed MLI can inject power into the grid with a unity power factor under conditions of varying irradiance and provide the grid with reactive power as well

Fluoride remediation using floating macrophytes

Six aquatic macrophytes, such as Pistia stratiotes, Ceratophyllum demersum, Nymphoides indica, Lemna major, Azolla pinnata,and Eichhornia crassipes were considered for remove fluoride from aqueous solution. Five different concentrations (10, 30, 50, and 100 ppm) of fluoride solution were taken in 1 L plastic container. Fixed weight (20 g) of macrophytes along with 500 ml fluoride solution was taken in each plastic container for 72 hours observation. Results demonstrated all the macrophytes show highest fluoride removal during 24 h to 48 h, but after 72 h their efficiency reduced drastically. The species N. indica showed better removal efficiency than other experimental macrophytes. In general, pigment measurement data indicated higher concentration at 72 h. However, Pistia sp. showed higher concentration of pigmentation at intermediate time interval (48 h). Higher level of dry weight to fresh weight ratio was recorded for L. major and A. pinnata at all concentrations, excepting at 10 ppm. In addition, all macrophytes showed lower RGR at higher concentration. Isotherm study indicated that macrophyte C. demersum is a good fitted with Freundlich and Langmuir isotherm whereas L. major with Langmuir isotherm during 24 hours