Brazil: New Anaerobic Reactor Removes 70% of Nitrogen from Wastewater

wastewater treatment brazil
Microscope image of the polyurethane foam, taken right after the formation of bacterial biofilm. Credit: Bruno Garcia Silva

A group of Brazilian researchers developed an anaerobic reactor that is capable of removing up to 70% of harmful nitrogen compounds from wastewater. The reactor comprises bacteria on a thin layer of polyurethane foam. The biofilm of bacteria processes nitrogen-containing compounds and releases pure nitrogen, which is environmentally harmless. The novelty is the result of work of Bruno Garcia Silva’s doctoral research at the University São Paulo (USP) in Brazil, with Eugenio Foresti as thesis advisor. Foresti is a professor at the São Carlos School of Engineering (EESC-USP).

The wastewater treatment conditions in Brazil are far from perfect: Nitrogen removal is still achieved by only a few wastewater treatment plants in Brazil, whereas it’s regularly performed in Europe and the United States, for example. The idea of Garcia’s research was to adapt the existing infrastructure to the Brazilian reality. 

While nitrogen as such is environmentally harmless, removal of nitrogen compounds from both domestic sewage and industrial wastewater is essential. Nitrites, nitrates, and ammonia, among other compounds contaminate surface water as well as aquifers and other groundwater, letting the growth of bacteria, algae, and plants spiral out of control. Furthermore, consumption of water contaminated by nitrate can lead to diseases such as infant methemoglobinemia, which may cause neurological alterations such as seizures and coma in severe cases.

“When algal blooms proliferate, as seen in reservoirs like Billings, for example, lack of oxygen in the water leads to the death of fish and loss of water supply as well as leisure areas. It’s very hard to remove algae from reservoirs,” – Eugenio Foresti, professor at Sao Paulo University.

How It Works

A unique part of the new reactor is the biofilm – a thin layer of bacteria – laid onto a layer of polyurethane foam. Another is the configuration of the equipment to permit what the researchers call counterdiffusion, where oxygen is introduced on the opposite side to the contaminants.

“Oxygen is transported into the foam because this ensures that it remains only where it’s needed for the reaction to occur,” Garcia explains. “We don’t want oxygen to come into contact with organic matter all the time. If it did, the bacteria would use up all the oxygen to break it down and nothing would be left over to consume the nitrite and nitrate. So we insert the oxygen on the other side of the biofilm. The goal is for the organic matter that reaches the biofilm on the opposite side to be oxidised not just by oxygen but also by nitrite and nitrate.”

When oxygen does not enter the reactor, the ammonia remains unchanged. When ammonia enters the site of the reactor with oxygen input, however, it is converted into nitrite and nitrate.

“The only way out is via the biofilm, and the compounds cross this barrier by diffusion in the opposite direction to the organic matter. Their collision with organic matter in contraflow creates optimal conditions for nitrite and nitrate removal because there’s no longer any oxygen and there’s enough organic matter for denitrification,” – Bruno GArcia Silva, University of Sao Paulo.

The anaerobic nitrogen extraction technology is especially effective in the warm climate of Brazil. Bacteria decompose organic compounds faster in warm water. Unlike Brazil, in Europe and North America, where average temperatures are lower, the process is different. The organic matter present in the liquid phase after sludge removal is often oxidised aerobically. Regardless, the nitrogen extraction technology is still a rarity for Brazilian wastewater treatment facilities for cost reasons. Garcia’s novel reactor is relatively inexpensive and highly efficient. It means this reactor can solve Brazil’s nitrogen extraction problem at wastewater treatment facilities of any level.

Next Steps in Wastewater Treatment

The new reactor has been tested in the laboratory. Efficiency will be measured in further projects, and the optimal configuration will be chosen for large-scale wastewater treatment facilities.

According to Foresti, the new configuration of the reactor is inspiring further research by the group. In a program of cooperation between the Sao Paulo State Basic Sanitation Corporation (SABESP) and the Sao Paulo Research Foundation, the researchers plan to test the new model with real sewage that has been through an aerobic reactor in the treatment plant operated by SAAE, the municipal sanitation service in Sao Carlos. Researchers at UFSCar and IMT are also part of the program and will develop other systems to be tested.

Credit: Water World