When wastewater have a high concentration of dissolved organic matter, the most competitive option is biological treatment, due to its simplicity and low costs.
The only requirements for satisfactorily applying this technology is that the pollution be biodegradable and that there no biocidal compound be present in the effluent to be treated. The biological treatment of wastewater is based on the ability of a set of microorganisms that are capable of degrading the organic matter present in the wastewater for its own growth. Apart from organic matter, microorganisms need water containing nutrients, basically nitrogen and phosphorus, to grow. Subsequently, the separation of these microorganisms from water is simple and economical. Thus, microorganisms are responsible for removing the organic matter present in water, both particulate and soluble.
The set of microorganisms is very varied and rich in species and its exact composition depends on the properties of the wastewater being treated and the process conditions; as it is a kind of ecosystem that adapts continuously to changing external conditions.
The removal of biodegradable organic matter, as well as nitrogen and phosphorus, through wastewater biological treatment is the most economical and simplest way to treat effluents. For this reason, it is the treatment applied mostly for both urban and industrial wastewater.
The limitations of this type of treatment are related to the biodegradability of the contaminants and the presence in the effluent of substances inhibiting the growth of microorganisms (biocides).