Effect of pH,ionic strength,and background electrolytes on Cr(VI) and total chromium removal by acorn shell of Quercus crassipes Humb. & Bonpl.

The ability of Quercus crassipes acorn shells (QCS) to remove Cr(VI) and total chromium from aqueous solutions was investigated as a function of the solution pH, ionic strength, and background electrolytes. It was found that Cr(VI) and total chromium removal by QCS depended strongly on the pH of the solution. Cr(VI) removal rate increased as the solution pH decreased. The optimum pH for total chromium removal varied depending on contact time. NaCl ionic strengths lower than 200 mM did not affect chromium removal. The presence of 20 mM monovalent cations and anions, and of divalent cations, slightly decreased the removal of Cr(VI) and total chromium by QCS; in contrast, divalent anions (SO₄ ^2?, PO₄ ^2?, CO₃ ^2?) significantly affected the removal of Cr(VI) and total chromium. The biosorption kinetics of chromium ions followed the pseudo-second-order model at all solution pH levels, NaCl ionic strengths and background electrolytes tested. Results suggest that QCS may be a potential low-cost biosorbent for the removal of Cr(VI) and total chromium from aqueous solutions containing various impurities.     

Freeze survival of the cyanobacteria Microcoleus chthonoplastes without cryoprotector

A Microcoleus chthonoplastes strain SC7B9002-1 isolated from microbial mats in tidal channels from San Carlos, Baja California Sur, Mexico was subjected to short- (15 days) and long-term (2 years) conservation assays in liquid nitrogen (-196 degrees C) using cryoprotective agents, such as 5% DMSO, 20% PVP-40, and 20% glycerol. Survival rate, chlorophyll a, protein, and nucleic acids content were observed in each case. Interesting growth and a significant increase in protein content was observed when no cryoprotectant was used during liquid nitrogen immersion. In the absence of a cryoprotectant, M. chthonoplastes lost their typical shape resembled spheroplasts, and recovery cultivation times after freezing were 5 and 25 days (short and long-term, respectively). Recovery from long-term preservation with 5% DMSO took 15 days. PVP and glycerol did not allow recovery of viable cells. The survival of M. chthonoplastes to freezing without cryoprotectant and the adaptive mechanisms that allow surviving under freezing conditions are discussed.     

An Aerosol Sampler for Determination of Particle Concentration as a Function of Size and Time

A high flow rate four-stage impacfor was developed for the determination of aerosol concentration as a function of both particle size and time. The unit is very useful for long-term sampling intervals (24 hr) and for sampling very dusty atmospheres. Gas-borne particulate matter is collected out on four rotating drums, each with a collection surface area of about 10 sq in.; this allows a large quantity of materials to be collected without danger of particle build-up and blow-off. A particle size-collection efficiency calibration for the unit is presented together with experimental data on wall losses, surface coatings, and other important operational considerations.     

Deducing an upper bound to the horizontal eddy diffusivity using a stochastic Lagrangian model

We present a method for estimating the upper bound of the horizontal eddy diffusivity using a non-stationary Lagrangian stochastic model. First, we identify a mixing barrier using a priori evidence (e.g., aerial photographs or satellite imagery) and using a Lagrangian diagnostic calculated from observed or modeled spatially non-trivial, time-dependent velocities [for instance, the relative dispersion (RD) or finite time Lyapunov exponent (FDLE)]. Second, we add a stochastic component to the observed (or modeled) velocity field. The stochastic component represents sub-grid stochastic diffusion and its mean magnitude is related to the eddy diffusivity. The RD of Lagrangian trajectories is computed for increasing values of the eddy diffusivity until the mixing barrier is no longer present. The value at which the mixing barrier disappears provides a dynamical estimate of the upper bound of the eddy diffusivity. The erosion of the mixing barrier is visually observed in numerical simulations, and is quantified by computing the kurtosis of the RD at each value of the eddy diffusivity. We demonstrate our method using the double gyre circulation model and apply it to high frequency (HF) radar observations of surface currents in the Gulf of Eilat.     

Migration,markets, and mangrove resource use on Kosrae,Federated States of Micronesia

Kosrae, Federated States of Micronesia, is a prototype of an island economy prone to economic crowding. Average family size is large, the habitable land area is small, economic activity is limited, and household dependence on natural resources for fuel and food is high. We analyze how economic crowding--and its mitigation through trade and migration policies--affects mangrove resource use. A comparison of household survey data from 1996 and 2000 indicates that despite decreases in US aid and public-sector jobs, average household consumption of mangrove resources has not increased. Migration and remittances have allowed the purchase of imported fuel and building materials substituting for mangrove wood. Despite changing preferences and shifts toward import consumption, population growth and further declines in US financial support will likely cause aggregate demand for mangrove and upland wood to rise. Moreover, continued emigration may accelerate the export of mangrove crabs to off-island Kosraeans.     

Chlorinated pesticides (2,4-D and DDT) biodegradation at high concentrations using immobilized Pseudomonas fluorescens

Degradation of two chlorinated pesticides (2,4-D and DDT) using a 54-mL glass column packed with tezontle (a low-cost basaltic scoria) was tested. Bacteria were cultured in YPG (yeast, peptone, and glucose) liquid medium at 32 degrees C. The rich medium was pumped during 24 h through the column to inoculate it. Later, the wasted medium was discharged and the pesticide added. Optical densities, TOC, and pesticide concentration were determined. Pesticide removals for 2,4-D (with initial concentration between 100 and 500 mg/L) were about 99%. DDT removal (at initial concentration of up to 150 mg/L) was as high as 55-99%. TOC removals for 2,4-D was in the 36-87% interval, whereas for DDT they were as high as 36-78%.