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

How low can you go?

We’re repeatedly advised to switch off electrical devices, like TVs and DVD players at the mains outlet rather than leaving them in standby mode, to turn to compact fluorescent bulbs and to turn them off when illumination is no longer necessary, to do our laundry at lower temperatures, to run the dishwasher only when it’s full, and to avoid using energy-hungry power showers. All those kilowatts add up to a lot of power wasted if we don’t.

According to a new study into energy use in the UK, by following this advice we might be reducing our carbon footprint a lot more than we thought. Conversely, those who don’t follow the advice might be wasting far more energy than the government thinks and so contributing more to carbon dioxide emissions and so anthropogenic global warming and climate change. Writing in the journal Energy Policy this month, Adam Hawkes, of the Grantham Institute for Climate Change at Imperial College London, has calculated that the figures used by government advisors to estimate the possible carbon dioxide reduction possible might be 60% too low.

Hawkes points out that power stations that supply electricity vary in their carbon dioxide emission rates, depending on the fuel they use: those that burn fossil fuels (coal, gas and oil) have higher emissions than those driven by nuclear power and wind. In general only the fossil fuel power stations are able to respond instantly to changes in electricity demand. He says that the government should keep track of changing carbon emission rates from power stations to ensure that policy decisions for reducing emissions are based on robust scientific evidence.

Hawkes used 60 million data points for electricity production each half-hour period by each power station in Great Britain from 2002 to 2009 and calculated the emissions for each different type of generator by examining government data showing their average annual fuel use. He then calculated emissions rates attributed to a small change in electricity demand from these two data sets.

SPT86-montalto-power-station (Credit: David Bradley)
Montalto power station (Credit: David Bradley)

His new study suggests that excluding power stations with low carbon emission rates, such as wind and nuclear power stations, and focusing on those that deal with fluctuating demand would give a more accurate emission figure. Hawkes’ calculations show that, 0.43 kilograms of carbon dioxide per kilowatt hour of electricity consumed is 60 percent lower than the actual rates observed between 2002 and 2009 (0.69 kilograms of carbon dioxide per kilowatt hour), meaning that policy studies are underestimating the impact of people reducing their electricity use.

“One way governments are trying to mitigate the effects of climate change is to encourage people to reduce their energy consumption and change the types of technologies they use in their homes,” Hawkes says. “However, the UK government currently informs its policy decisions based on an estimate that, according to my research, is lower than it should be.”


Energy Policy, 2010, online

Black gold

An estimated 513 billion barrels of “technically recoverable” heavy oil lie in Venezuela’s Orinoco Oil Belt, a 50,000 square kilometre region in the East Venezuela Basin Province.

Worldwide consumption of petroleum was 85.4 million barrels per day in 2008. The three largest consuming countries were United States with 19.5 million barrels per day, China with 7.9 million barrels per day, and Japan with 4.8 million barrels per day. So the Venezuelan heavy oil represents a potential supply that could last a decade at the current rate of consumption.

The United States Geological Survey (USGS) has carried out the first assessment that identifies how much oil might be technically recoverable using currently technology and standard industry practices. According to USGS Energy Resources Program Coordinator Brenda Pierce, this part of the world has one of the world’s largest recoverable oil accumulations. The USGS’s report is part of its program directed at estimating the technically recoverable oil and gas resources of priority petroleum basins worldwide. This is the largest accumulation ever assessed by the USGS.

“Knowing the potential for extractable resources from this tremendous oil accumulation, and others like it, is critical to our understanding of the global petroleum potential and informing policy and decision makers,” explains Pierce. “Accumulations like this one were previously very difficult to produce, but advances in technology and new understandings in geology allow us to assess how much is now technically recoverable.”

USGS team member and a co-author of the report, Christopher Schenk explains further: “Heavy oil is a type of oil that is very thick and therefore does not flow very easily. As a result, specialized production and refining processes are needed to generate petroleum products, but it is still oil and can generate many of the same products as other types of oil.”

The estimated petroleum resources in the Orinoco Oil Belt, range from 380 to 652 billion barrels of oil (at a 95 and 5 percent chance of occurrence, respectively). Schenk says that the estimates are based on a rate of oil recovery of between 40 and 45 percent.

Orinoco (Credit: USGS)
Credit: USGS


However, others are sceptical that these oil reserves are economically or environmentally viable. Venezuelan oil geologist Gustavo Coronel told the Associated Press that he doubted the recovery rate could be much higher than 25 percent given the nature of the crude oil. More intriguing is that the USGS announcement seems to have been timed to coincide with an international auction for drilling rights in the Orinoco Belt which took place on 28th January, with results to be announced on 10th February.

Moreover, there are no little energy and environmental costs to be considered in recovering heavy crude oil as it is not necessarily as easy to extract as conventional crude oil. Moreover, the existence of such reserves while perhaps saving us from short-term oil shortages does not address the issues of carbon emissions and potential climate change.


USGS Assessment

Energy Resources Program

Auction news

Crude claims

AP report