Although entities such as the Colombian Hydrology, Meteorology and Environmental Studies Institute (IDEAM, for its Spanish acronym) or the Regional Autonomous Corporations receive close to 250 annual complaints in this regard, the industries producing many of these gases still do not have the sufficient technology to provide solutions to this problem.
A system composed of biofilters or biological filters that use organic materials and microorganism metabolic processes could be a viable solution to address this issue. These systems are practical for removing foul odors from every industry.
The sense of smell is considered as the most complex of our senses as it not only influences 80% of the taste but it is also in the development of memories; its perception range varies between 5,000 and 10,000 different odors depending on genetic and cultural factors.
This complexity makes bad odors to be especially difficult to detect and measure, as they may be composed of up to 60 gases that are blended and react among each other making it hard to identify them. Although in Colombia these gases were acknowledged as contaminants in 1979, with resolution 1541 of 2013 the authorities pointed out its regulation with the definition for “odor threshold” for 15 substances.
One of the reasons to decontaminate the Bogotá River is its foul odor; in this sense, Wastewater Treatment Plants (WWTP) have a double challenge: decontaminate the water and also eliminate the odors released into the environment.
Universidad Nacional de Colombia (UNal) in Bogotá Biotechnology Ph.D. candidate Diana Vela is heading the development of a biofilter for decontaminating the air coming from these treatment plants. Currently, there are two mega projects of this kind in Bogotá.
Along with the UNal Faculty of Sciences Environmental Negative Impacts Remediation and Mitigation Study Group (Germina, for its Spanish acronym) they have carried out a theoretical, research and a practical project which in its initial stage resulted in a biofilter that removes 100% of the hydrogen sulfide (H2S) and ammonium (NH3), the two main causing gases of foul odors surrounding the WWTP.
Biofilters work closing the area where the contaminated air is present–in this case wastewater– and directing the current using extractors toward a biofiltration system. There, heterotrophic nitrifying, and sulfur-oxidizing bacteria carry out a metabolic process that decomposes the contaminants into innocuous substances, eliminating them completely.
This process involves not only engineering for the design and the adequate operation but also microbiology and chemistry to understand its operation. The importance of assessing technology from different disciplines guarantees the correct operation of the system in real scenarios and sustainability with time.
Due to the lack of information on gas measurement, the group collected data directly at the WWTP of El Salitre, achieving the respective gas measurement as a starting point to establish the problem.
“WWTP confined specific areas reached a concentration of 200 parts per million (ppm) of H2S, a level that makes it difficult to breathe and impacts the central nervous system. To mitigate this gas, researchers tested several natural beds with different combinations of organic materials looking to determine the most appropriate solution,” said Vela.
The first model developed by the team is a system with PVC tubes filled with compost, which helped to select the proper elements and materials to use as a biofilter. In the chosen bed there is residue from other industries such as chicken droppings, which is mixed with sugarcane bagasse or rice hulls. When it turns into compost, these materials have the necessary microorganisms to carry out the biochemical elimination process.
To guarantee the ideal conditions of the process, the time it takes the gas to pass the system must be considered; the least time, a greater quantity of air may be treated and have greater elimination of gases.
“It is important to control the ideal moisture for the microorganisms that carry out the compound breakdown process so they can correctly populate the material,” explained Microbiology Ph.D. and Professor of the UNal Department of Chemistry, Pedro Filipe de Brito Brandão.
During the first tests, they recreated the conditions to decontaminate 9 liters of gas per minute using a biofilter for 4 liters; however, in the United States and different countries in Europe, they have verified that if the prototype works, it will in industrial plant conditions.
Eight cities in Colombia have 41% of the total pollution of the country and generally, the measures to treat pollution are applied to the animal breeding industries, surface linings industries, food, chemistry, and wastewater locations.
The mitigation and elimination methodologies may be physical, chemical, or biological. The first two require high monetary costs as they need constant investment and leave residues that are equally contaminating. The last option progresses and reaches its peak due to different shown benefits, such as the case of use of room temperature, its easy management, operational costs, and because its ecologically cleaner and less susceptible to design parameters and chemical processes.
The use of residue materials boosts ecological, operational, and economic benefits. Maintaining the moisture control in a biofiltration system does not represent greater cost or produce byproducts, and if the compost is depleted it can be replaced partially or completely.
“Although it has an approximate use of two years, through peer researcher experiences we know that the beds that maintain adequate moisture have greater durability, of up to five years,” says Professor De Brito.
To continue the work, they need to consider both the flow as the concentration or the ranges where the system works and the type of degradation in the biofilter, besides determining the physical-chemical properties that it should have to be viable in industrial conditions, for it to not to absorb or adsorb the contaminant permanently, but for the occurrence of less offensive component biodegradation.
To develop the engineering and operation, the associated filters need to be customized to certain contaminants and carry out the correct air transferal. Universidad Santo Tomás in Bogotá Natural Resources and Environmental Ph.D. and Engineer Iván Cabeza and other researchers are involved in this process. Besides, experts of the Physics International Center and the Universidad EAN have also collaborated in the project.
They are currently working on developing a new prototype which looks to go beyond the laboratory environment by eliminating H2S, NH3, acetic acid, and with field projects and overcome the system design and maintenance obstacles, the appropriate useful life, and the implementation of use in industries, beginning with wastewater.
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