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Anbarasan Anbalagan (talk) 22:58, 1 March 2017 (UTC)

Microalgae and activated sludge symbiosis

Microalgae are a photosynthetic unicellular organism which is green (e.g., Chlorella sp. and Scenedesmus Sp.) and brownish (e.g., Nitszchia) in nature. They are commonly found in freshwater, brackish and seawater either branched or unbranched form. In natural conditions, they utilise nitrate through carbon dioxide from the atmosphere or bacterial metabolism during organic matter decay. In return, photosynthetic oxygen is always available in nature for other microbial processes. The interaction between microalgae and bacteria is termed as microalgae and bacteria symbiosis. This kind of interaction is very common in marine, estuaries and freshwater environment. Similar interaction happens in the wastewater environment which is termed as microalgae and activated sludge symbiosis. Activated sludge is composed of microorganisms from human faecal microcosm and soil microbiota. These organisms are defined as a mass of the aerated precipitated portion of sewage which is consisting of bacteria, archaea, protozoa and fungi as dominant microbes along with other multicellular organisms. Out of which bacteria plays the significant role in degrading organic matter and in the presence of oxygen converts ammonium into nitrate and nitrous oxide via nitrite oxidation. This process is termed as activated sludge process or activated sludge metabolism. Overall, microalgae-based activated sludge process is termed as microalgae and activated sludge symbiosis.

Why is nitrate uptake important by microalgae? In general, microalgae constructs its biomass based on the following elements, carbon, nitrogen, phosphorus and sulphur similar to bacterial biomass. In the case of microalgae, the biomass to nitrogen uptake is higher due to its need for cell organelles. Therefore, during photosynthetic growth inorganic carbon, phosphorus and nitrogen are utilised during its growth. Microalgae prefer ammonium to promote direct assimilation into the cells however ammonium is not readily available in its natural environment due to nitrifying bacteria in its environment.Thus, microalgae are utilised energy intensive nitrate uptake through conversion of nitrate to nitrite and then to ammonium again to synthesis amino acids. However, the assimilation of nitrate-nitrogen is dependent on two bacteria, namely ammonium oxidising bacteria and nitrite oxidising bacteria, if either one of them is slower, the whole process will be slower, which results in slow-growing microalgae because microalgae cannot process nitrite from their environment.

Is it a new method or existing method to treat wastewater?

Microalgae bacterial process has been studied by many authors in different parts of the world to treat wastewater. For instance, mixed microalgal communities and activated sludge communities originating from its environment has been studied at Mälardalen University, Sweden. This process is called MAAS process which is abbreviated as microalgae-activated sludge process