6th December, 2016.- The discovery in the early 90s, in sewage sludge, of a set of bacteria capable of eliminating ammonia without oxygen, opened the door to the development of new purification techniques with significant energy savings and lower CO2 emissions.
The power of the anammox
Actually, anammox bacteria had begun to be studied in the 1930s, to try to explain how the elimination of nitrogen was taking place in a series of effluents, “but the metabolic pathway of these microorganisms was still unknown».
The above is the explanation given by María del Mar Micó, Project Manager of Life Celsius -developed by Acciona Agua with the support of EFE News Agency Efe Agency- to demonstrate the feasibility of a waste water treatment system in warm climates with the premise of energy saving.
Anammox have been found in all the aqueous environments of the world and are, in fact, responsible for the highest percentage of nitrogen removal in the ocean, which they protect from eutrophication or excess nutrients.
María del Mar Micó, Chemical Engineer at Acciona Agua, says: “And we know that these bacteria can grow both in lakes to ten degrees as well as in geysers, which indicates that they can grow in a wide temperature range».
They get the name of anammox for the type of metabolism that they realize, the anaerobic oxidation of ammonium by nitrite or nitrate and in the absence of oxygen, a process that contributes to fix CO2 and emits to the atmosphere nitrogen gas, which is «the main component of the air we breathe”.
The experience on Life Celsius
According to the Life Celsius Project Manager, the partial nitrification tank of the plant, developed for the project and installed in the Water Waste Treatment Plant (WWTP) of Archena (Murcia) has already demonstrated the feasibility of this system.
Two types of bacteria work together in conventional nitrification: ammonioxidants, which convert ammonium into nitrites, and nitrite oxides, which convert it into nitrate, both of which require oxygen for their metabolic functions.
Micó explains that: «In our partial nitrification we want the ammonioxidants to survive over the nitrite oxidizers and we achieve this by minimizing aeration as much as possible; while in another reactor, the anammox combine the ammonium with the nitrate and turn it into nitrogen gas without need of oxygen; the combination of both «results in significant savings in aeration».
The perfect climate
The plant developed by Life Celsius corresponds to the second phase of the project led by Acciona Agua, which began with the installation at the Archena WWTP of an anaerobic membrane digester for the removal of organic matter without oxygen and without the need for an external heat source, since the effluent reaches the sewage treatment plant around 15-20 degrees.
Micó points out that: «The Spanish Mediterranean is characterized by mild temperatures throughout the year and this can be used to improve the development of biological processes, which in other latitudes would require external heating”.
The second stage started last June with the implementation of the different biological processes of the Celsius plant: partial nitrification. For this, bacteria were inoculated from the water treatment plant in Archena itself, and the anammox phase was successful due to the contribution of microorganisms of other Acciona Agua plants.
The anammox «had to adapt themselves to the climate and to the type of effluent that reaches the water treatment plant and so far, we have managed to keep it running smoothly». Now,»we initiate the next phase of the project, which consists in optimizing the process».
Therefore, «once the reactors have been stabilized, we will try to improve the quality of the effluent output». This phase will last for twelve months, after which the optimum conditions will have been obtained to operate the plant for one more year, during which we will attempt to optimize oxygene consumption as well as other processing type parameters.
Micó assures that: «The results obtained will be significant enough to enable their full-scale implementation».
Traducción: Carmen Gilson