Ground glass solution for cleaner water

British science has led to a use for waste glass that cannot be recycled that could help clean up polluted waterways by acting as an ion-exchange filter to remove lead, cadmium and other toxic metals. Details are published in a forthcoming issue of the International Journal of Environment and Waste Management.

Only a fraction of waste glass bottles and jars can be recycled, partly because much of the glass is coloured, brown or green, and partly because the market sustains only a limited weight of recyclable glass. Millions of tonnes of waste container glass is generated across Europe. As such, large amounts of waste glass, purportedly for recycling, are shipped to China and elsewhere to be ground up and used as hardcore filling materials for road building.

Now, Nichola Coleman of the University of Greenwich, London, has developed a simple processing method for converting waste container glass, or cullet, into the mineral tobermorite. Tobermorite is hydrated calcium silicate, silicate being the main material that can be extracted from glass. In the form produced, the phase-pure 11-angstrom form – the mineral can be used as an ion-exchange material that can extract toxic lead and cadmium ions from industrial effluent, waste water streams or contaminated groundwater.

To make the tobermorite, Coleman simply heats a mixture of ground cullet, lime (as a calcium source) and caustic soda (sodium hydroxide solution) to 100 Celsius in a sealed Teflon container. Initial tests show that uptake of lead and cadmium from solution are rather slow, so Coleman suggests that, at this stage of development, the synthetic mineral might best be used in the in situ remediation of groundwater rather than in industrial ex situ effluent filtration processes. The concept is now being extended to create other classes of ion exchange filter from unrecyclable and low-quality waste glass.

“The cullet-derived sorbent could be used in reactive barriers to prevent the lateral migration of pollutants in groundwater, rather than as a remediation material for waterways,” says Coleman. “Heavy metal-contaminated land and groundwater are global problems, arising from industrial and military activities and also from the natural leaching of heavy metal-bearing minerals,” she adds.

Nichola Coleman (2011). 11 Å tobermorite ion exchanger from recycled container glass Int. J. Environment and Waste Management, 8 (3/4), 366-382

Nanotech Viagra patch

Sildenafil citrate, commonly known as Viagra, is currently the first choice drug for erectile dysfunction but despite its success oral delivery of the drug is hampered by numerous side effects, the long delay before it starts working and the short amount of time it lasts. Researchers in Egypt think they may have a solution via nanotechnology.

Writing in the International Journal of Nanotechnology, the team describes tests on different formulations for sildenafil citrate transdermal nanocarriers as the delivery agent on human skin rather than the user having to swallow a pill. The benefits of such nanocarriers are that the drug gets into the bloodstream through the skin much more quickly than having to be ingested. Moreover, 70% of an oral dose of sildenafil citrate is wasted as it is metabolized by the liver without having any effect. Improved delivery via the transdermal route would avoid several side-effects as well as making onset of activity much quicker.

Pharmaceutical scientist Yosra S.R. Elnaggar of Alexandria University and professors there and at Alexandria and Pharos University, explain how previous attempts to create a Viagra transdermal application have been hampered by the properties of the drug itself. The drug has low oil and water solubility and is loathe to cross membranes, such as human skin, because of this. However, it is possible to encapsulate the drug in nanoemulsion based systems that can cross membranes readily. As such, the team has investigated two types of nanocarriers made using fat-like lipid molecules – the first made by forming an emulsion with the drug using a surfactant compound to allow the lipid molecules and drug to mix, much as soap will emulsify oil and water. The second option is a self-emulsifying nanocarrier that has its own inbuilt surfactant.

The team demonstrated in the laboratory that both formulations would have benefits for oral drug delivery, whereas only the nano-emulsion, rather than the self-emulsifying formulation, shows promise for a Viagra patch, in other words.

Elnaggar, Y., Massik, M., & Abdallah, O. (2011). Sildenafil citrate nanoemulsion vs. self-nanoemulsifying delivery systems: rational development and transdermal permeation International Journal of Nanotechnology, 8 (8/9) DOI: 10.1504/IJNT.2011.041443

Biofilters cut old landfill carbon footprint

Researchers in the US are testing biofilter systems as a viable alternative to releasing methane from passive landfill vents into the atmosphere. The technology could reduce the overall impact of old landfills on global warming. Details are reported in the current issue of the International Journal of Environmental Engineering.

Organic matter rotting in smaller, old landfill sites generates a slow trickle of the potent greenhouse gas, methane, into the atmosphere, amounting to just 2 or 3 kilograms per day per vent. In contrast to controlled methane generate for biofuel from modern, managed landfills, tapping this slow stream of the gas is not viable technologically or economically. However, methane has an infrared activity 21 times greater than carbon dioxide and so represents an important anthropogenic source of this greenhouse gas when attempting to balance the climate change books. Indeed, landfills contribute 12% of worldwide anthropogenic methane emissions due to the decomposition of organic waste.

Old landfills typically have passive gas vents. Methane is simply released into the atmosphere from these vents, or if the rate of emission is high enough it can be burned, or flared. According to Tarek Abichou and Jeffery Chanton of the Florida State University, Jose Morales of Environmental and Geotechnical Specialists, Inc., Tallahassee, Florida and Lei Yuan of Geosyntec Consultants in Columbia, Maryland, methane oxidation has recently been viewed as a more benign alternative to venting or flaring of landfill methane.

The researchers tested two biofilter designs capable of oxidizing methane gas to carbon dioxide and water. Both are packed with so-called methanotrophic bacteria, microbes that digest methane. They found that the radial biofilter design gave a much higher methane oxidation rate than a vertical biofilter. The higher surface area exposed to methane flow led to greater oxygen penetration into the biofilters, essential for microbial digestion. The radial biofilter has a surface area of well over 1.2 square meters whereas the vertical biofilter amounts to just 0.3 square meters area.

The team also found that the average percent oxidation rate of 20% and higher for the radial biofilter was possible when the air temperature was 20 to 36 Celsius, indicating the optimal soil temperature for methanotrophic bacteria to oxidize methane. Vertical biofilters averaged a little over 12% oxidation.

Abichou, T., Yuan, L., Chanton, J., & Morales, J. (2011). Mitigating methane emissions from passive landfill vents: a viable option for older closed landfills International Journal of Environmental Engineering, 3 (3/4) DOI: 10.1504/IJEE.2011.041354