An article published in the magazine Environmental technology describes a new low-cost anaerobic reactor model, which works with a bacterial biofilm attached to a polyurethane foam, capable of reducing the concentration of nitrogen compounds in sanitary wastewater by up to 70%.
To achieve these results, the scientists perfected a mathematical model that allows them to understand and predict the nitrogen removal mechanism in the biofilm formed by bacteria that transform nitrogen compounds into nitrogen gas, which is harmless to the environment.
Under the guidance of Professor Eugenio Foresti, of the São Carlos School of Engineering of the University of São Paulo (CESE-USP), and with a grant from the São Paulo Research Foundation (FAPESP), the work was carried out by a team led by the environmental engineer Bruno Garcia Silva for his doctoral thesis in hydraulic and sanitary engineering.
“Nitrogen removal is still done in some wastewater treatment plants in Brazil, while in Europe and the United States it is already done more easily. The idea is to bring the necessary infrastructure into our reality, “Garcia said in a statement by Agência FAPESP.” Here the anaerobic reactor is generally used, which generates an effluent with low organic load, and this makes the process of nitrogen removal “.
According to the researcher, the removal of nitrogen compounds (including nitrites, nitrates and ammonia) from both domestic and industrial sewage is essential, as they can contaminate surface water bodies (lakes, dams, streams and streams) and underground (such as large aquifers). aquifers), promoting the uncontrolled growth of bacteria, algae and plants, in a process called eutrophication.
Additionally, Garcia explains that consuming nitrate-contaminated water can lead to the development of diseases such as methemoglobinemia, known as blue baby syndrome. More common in children, the condition can cause headaches, dizziness, fatigue, lethargy or even shock, as well as severe respiratory depression and neurological changes, such as seizures and coma, in severe cases.
“When algae flourish, one of the consequences we have seen in dams like Billings, for example, is the death of fish from lack of oxygen in the water. An area that could be for supply, recreation or both is lost due to the excess of algae, which are very difficult to remove from the liquid environment, ”stresses Foresti.
The main differentiator of the new reactor model is the biofilm, which is formed by a biological process in which bacteria create a kind of film on a polyurethane foam. The configuration of the equipment allows for what the researchers call “counter diffusion”, that is, the introduction of oxygen from the opposite side to the contaminants.
“The oxygen will be transported into the foam because it remains only where it is needed for the reaction to take place. We did not want this gas to always be in contact with the organic matter, as the bacteria would have consumed all the oxygen to degrade it and there would be nothing left. to consume nitrites and nitrates, “explains Garcia. “That’s why we put oxygen on the other side of the biofilm. The idea is that the organic matter that reaches the biofilm from the opposite side can be oxidized not only by oxygen, but also by nitrites and nitrates. “
According to the researcher, when there is no oxygen entering the reactor, the ammonia remains unchanged. However, when it gets to the part where oxygen enters, it begins to turn into nitrites and nitrates. “Since the only way out is through the biofilm, the compounds cross this barrier by diffusion in the opposite direction to that of organic matter. The meeting of organic matter in countercurrent creates the optimal conditions for the removal of these nitrites and nitrates, because there is no more oxygen and there is the organic matter necessary for denitrification ”.
Foresti explains that anaerobic reactors (in which organic matter is degraded by bacteria that don’t need oxygen to live) are increasingly used by Brazilian municipalities due to the country’s climate, which is warmer than that of the Northern Hemisphere.
High temperatures allow for increased activity of bacteria to decompose organic matter. In Europe and the USA it is the opposite, because at low temperatures the process is different: the organic matter present in the liquid phase, after the sludge has been removed, is oxidized by an aerobic process (which involves oxygen).
Due to the cost, according to Foresti, nitrogen compounds are not completely removed here in Brazil and end up being released directly into nature. “This new reactor model aims to develop a second phase for the treatment of sewage systems, simpler and cheaper, focusing on future technologies and partnerships”.
Garcia had the collaboration of scientists from the laboratory of Professor Robert Nerenberg, at the University of Notre Dame, in the US state of Indiana, where he was a visiting researcher between 2019 and 2020.
“The difference between my design and theirs is that instead of using polyurethane foam, they use a semipermeable membrane, similar to a straw filled with air inside,” he explains. “In contact with water, this straw allows oxygen to pass through, but not water, and the biofilm sticks to this surface. In other words, it is through the walls of this straw that oxygen is supplied to the bacteria. So the oxygen comes from within and the water supplies the ammonia and organic matter. It is the same system of contradiction. The difference is that here we use a simpler and cheaper material “.
According to him, in the biofilm, bacteria grow by adhering to the surface. “But it wouldn’t be a filter in itself, because it doesn’t offer mechanical resistance to the passage of a particle. What this reactor actually does is serve as a support material to allow bacteria to grow and consume soluble organic matter and nitrogen compounds. “
In a cooperation program between the Basic Sanitation Company of the State of São Paulo (Sabesp) and FAPESP, the researchers intend to test the new model with real sewage from the city of São Carlos, which has already passed through an anaerobic reactor at the treatment facility managed by the Autonomous water service of São Carlos (SAAE). Researchers from the Federal University of São Carlos (UFSCar) and the Instituto Mauá are also part of this cooperation program and will develop other systems for testing.
According to Garcia’s research consultant, this method is the first to use the counter-diffusion process in this way here in Brazil. “He demonstrated the concept of synthetic wastewater. The efficiency found with this reactor configuration was much higher than that observed in previous research, but we still have to evaluate several factors. “
For now, the new setup has been lab tested. New designs have yet to validate efficiency, as it is not possible to predict how equipment with large amounts of effluent will behave. In addition, it is necessary to test the plant using real, domestic and industrial sewage, since, until then, the samples were of synthetic sewage, prepared by the team itself.
“Maybe we need to improve the design and geometry. How can I optimize this design to have more surface area per reactor volume to make it more economical? This work provides the foundation, the foundation for continuing to think about this process and also the tool, which is the mathematical model, ”concludes Garcia.
The Brazilian post creates an affordable and less harmful wastewater treatment system that first appeared on Olhar Digital.
Source: Olhar Digital