Microorganisms Clean the Air around the Bogotá River
May. 10 de 2012
By: Hermann Sáenz, Unimedios
When traveling along the road leading to the Salto del Tequendama waterfall (in the Department of Cundinamarca), one normally detects an aroma similar to rotten eggs that seems to come from the waters of the Bogotá River. It actually comes from a gas known as hydrogen sulfide (H2S), which is produced not only by contamination of the aquifer but is also emitted by meat processing industries and electric power generation along the river banks.
To control these odors, companies some years ago resorted to installing water-based biological filters, aimed at decreasing the number of parts per million (ppm) of H2S in the environment. However, the expected results did not materialize: the reduction of sulfide was minimal and the biofilters lasted just eight months.
That is why in 2009 they decided to issue an invitation to submit innovative ideas aimed at finding a solution. At that point, researchers from the International Center for Physics (Centro Internacional de Física – CIF), which is part of the Universidad Nacional, presented a pilot program that was able to mitigate 97% of the gas emanations. “During the critical moments of H2S emission, concentrations had hitherto reached between 300 and 800 ppm. Now, using the biofilter that we have invented, they have been reduced to 24 ppm and sometimes even less”, says Martha Guardiola, director of the Biotechnology Group at the CIF.
Initially, the mechanism made using organic materials (molasses, cow and sheep manure, sugarcane bagasse and vegetable material among others) would process very high concentrations of sulfide for a week and a half, but then became exhausted. The CIF experts decided that they would have to improve the system.
The explanation as to how it works is simple: the biofilter is colonized by microorganisms, which paradoxically come from the sulfide and are responsible for biological degradation of the volatile contaminants. “When a gas molecule enters the layers of the biofilter, it begins an extensive journey that takes it to the organic material, where the microorganisms find the perfect food for their reproduction. There, using their enzymes, they decompose the H2S and eat one of its main compounds: the sulfur. That is why the product subsequently emitted into the environment is no longer a sulfide”, according to José Enrique García, director of the Group for Applied Physics for Technological Development at the CIF.
What is new about this process is that, to improve the action of the microorganisms, the application of water was eliminated, because its high pH levels (acidity) not only affected the food but also shortened the filter’s useful life. “Now they can reproduce without any problem and unceasingly help to eliminate the bad odors”, adds researcher Guardiola.
A gas that must not be underestimated
H2S irritates the eyes, dries out the nasal mucus and leads to colds, frequent symptoms among those who must put up with this odor on a daily basis. If the concentration in the air exceeds 300 ppm, it can even cause dizziness and fainting. That is why professor Guardiola says that hydrogen sulfide must not be underestimated. “If concentrations go beyond 500 ppm, it can be imperceptible to the nose while generating brain damage”.
The biofilter for the pilot project carried out by the CIF was installed at a company located between San Antonio del Tequendama and Mesitas de Colegio (Cundinamarca), whose emissions affect four villages with a population of around 1500 inhabitants. In this area, H2S concentration tends to rise between 3:00 and 5:00 a.m.
Another characteristic of this gas is its highly corrosive action. According to the CIF researcher, “even when concentrations are low, iron or any other element alloyed with it is destroyed. In many cases, industries seek the benefits from the biofilters not only to reduce toxicities emitted into the environment but also to lower maintenance costs for their equipment, which tends to suffer deterioration from the H2S. Among local farmers, the corrosion damages roofs and fences”.
The system created by the CIF makes it possible to measure the environment in real time and monitor it through a webpage in order to calculate the entry and exit of the gas. This part of the system was not easy to achieve.
“It implied designing a mechanism that would constantly measure the quantity of gas entering and leaving the filter, and that would be sufficiently robust to not corrode due to aggressive conditions from the medium and high H2S concentrations”, recalls José García.
In accordance with the estimated time frames, the biofilter should last a bit longer than a year, but has actually now been in operation for nearly two years. Despite the rugged conditions, the measurement mechanisms remain intact, which shows the success of the system as a whole.
Currently, researchers at the CIF are designing a new biofilter for another company, also near the Bogotá River. “We need to adjust it to the characteristics of the particular company, because there are differences between a paper producer or an electric power plant and a meat processor. Each biofilter is a world in itself due to the type of distribution that it applies to the gas. Also, the H2S never appears on its own but is always accompanied by another type of gas, depending on the particular kind of industrial process. We even have to redesign the biological material used to nourish the microorganisms”, concludes Professor Martha Guardiola.