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

Emulating nature for better engineering

UK researchers describe a novel approach to making porous materials, solid foams, more like their counterparts in the natural world, including bone and wood in the new issue of the International Journal of Design Engineering.

According to Carmen Torres-Sanchez of the Department of Mechanical Engineering, at Heriot-Watt University, Edinburgh and Jonathan Corney of the Department of Design, Manufacture and Engineering Management, at the University of Strathclyde, Glasgow in the natural world, the graduated distribution of porosity has evolved so that nature might transfer forces and minimise stresses to avoid whole structure failure. For instance, a crack in the branch of a tree will not lead to the felling of the tree in the same way that a broken ankle will not lead to collapse of the whole leg. “Porosity gradation is an important functionality of the original structure that evolution has developed in a trial and error fashion,” the team explains.

It is not just tree trunks and bones that have evolved graduated porosity, beehives, marine sponges, seashells, teeth, feathers and countless other examples display this characteristic. Researchers would like to be able to emulate the way in which nature has evolved solutions to the perennial issues facing engineers. In so doing, they will be able to develop structures that use the least amount of material to gain the lowest density structure and so the maximum strength-to-weight ratio.

“Many engineering applications, such as thermal, acoustics, mechanical, structural and tissue engineering, require porosity tailored structures,” the team says. If materials scientists could develop porous materials that closely mimic nature’s structural marvels, then countless engineering problems including bridge building and construction in earthquake zones, improved vehicle and aircraft efficiency and even longer-lasting more biocompatible medical prosthetics might be possible.

Unfortunately, current manufacturing methods for making porous materials cannot mass-produce graduated foams. The collaborators in Scotland, however, have turned to low power-low frequency ultrasonic irradiation that can “excite” molten polymers as they begin to foam and once solidify effectively trap within their porous structure different porosity distributions throughout the solid matrix. This approach allowed the team to generate polymeric foams with porosity gradients closely resembling natural cellular structures, such as bones and wood. The technology opens up new opportunities in the design and manufacture of bio-mimetic materials that can solve challenging technological problems, the team adds.

The researchers anticipate that using more sophisticated ultrasound energy sources as well as chemical coupling agents in the molten starting material will allow them to fine tune the formation of pores in the material. This is an area of current interest because it would facilitate the design of novel texture distributions or replicate more closely nature porous materials, the team concludes.

Sanchez, C., & Corney, J. (2011). A novel manufacturing strategy for bio-inspired cellular structures International Journal of Design Engineering, 4 (1) DOI: 10.1504/IJDE.2011.041406

The ignored virus that causes liver cancer

Hepatitis G virus was identified in 1995. Some little research was carried out on the virus and the US Food and Drug Administration (FDA) declared it a non-harmful virus in 1997. Researchers in Saudi Arabia, writing in the International Journal of Immunological Studies present evidence to suggest that this may have been the wrong decision. They claim that transmission of the virus through donated blood that was not screened for the virus as well as infection through other routes has led to an increase in cirrhosis of the liver and liver cancer.

Hepatitis G virus (HGV) was renamed as GB virus C (GBV-C) and is a virus in the Flaviviridae family but has not yet been assigned to a genus. Intriguingly, some evidence suggests that co-infection with the AIDS virus, HIV, somehow enhances the immune system in those patients. However, it is the effects of the virus on the livers of otherwise healthy patients that is of concern to Mughis Uddin Ahmed of the King Abdulaziz Hospital (NGHA) in Al-Ahsa, Saudi Arabia. He points out that since the FDA declared the virus not to cause health problems to humans in 1997, no donated blood has been screened for this virus.

However, Mughis Uddin Ahmed has carried out a review of the scientific literature for the last 16 years that show the virus to be quite prevalent around the globe. Moreover, there is a correlation with infection with this virus and hepatitis, cirrhosis of the liver and it is possibly linked to hepatocellular carcinoma. Mughis Uddin Ahmed also found an apparent link with hematological disorders and hematological malignancies.

For this reason, he suggests that research should be carried out into this virus to determine whether it is a true human pathogen and a viral carcinogen. He also advises that screening of donated blood for this virus should be reinstated urgently rather than healthcare workers continuing to transferring the virus ignorantly to blood recipients and risking the same morbidity and mortality outcomes seen with hepatitis C virus transferred from donor to recipient until screening for that virus was adopted.

Ahmed, Q. (2011). Hepatitis G virus (HGV): where we stand and what to do? International Journal of Immunological Studies, 1 (3) DOI: 10.1504/IJIS.2011.041723