It constitute a series of important processes of biological nature of treatment of the waste water that have jointly the utilization of microorganisms (between that the bacteria stand out) to carry out the elimination of organic biodegradable matter, so much colloidal as solved, as well as the elimination of compounds that contain elements nutrients (N and P). In most of the cases, the organic matter constitutes the source of energy and of carbon that the microorganisms need for their growth. In addition, also there is necessary the presence of nutrients, which contain the essential elements for the growth, specially the compounds that they contain N and P, and finally, in case of aerobic system, the presence of solved oxygen in the water. The latter aspect will be key at the moment of choosing the most suitable biological process.
The aerobic processes are based on the elimination of the organic pollutants by its transformation on bacterial biomass, CO2 and H2O. The anaerobic processes transform the organic substance into biogas, mixture(mixing) of methane and CO2.
BACTERIAL BEDS
Also named biological filters. They are based on the biological aerobic processes. It consists of putting the residual water in touch with an inert material or support where the microorganisms stick fast. They are in the habit of being fixed beds of great diameter, stuffed with rocks or pieces of plastic or ceramics with special forms to develop a great surface on that the water is sprayed to treating. On the surface there grows a thin cap of biomass, on which the residual water disperses to treating, that it wets in its decrease the surface. At the same time, sufficient space has to stay in order that it circulates air, which ascends of natural form. The growth of the biomass provokes that it departs from the microorganisms part with the surface, and therefore, a later sedimentation will continue being necessary for his separation of the effluent one.
BIOLOGICAL ROTARY CONTACTORES: BIODISCS AND BIOCILINDERS
Are based on the biological aerobic processes. These need an intimate contact between the residual water, the biomass activates and the oxygen.
They consist of a series of plates or discs placed in a horizontal axis that turn slowly inside the tank that contains the residual water, with 49 % of the plunged surface. On the surface of the discs there is fixed the biomass that one finds alternative in touch with the residual water and the air. This makes possible the ingestion of the organic matter on the part of the microorganisms and its later degradation in presence of the oxygen of the air.
The biocilinders are a variant of the biodiscs. Its principal difference is the substitution of the discs for biocilinders. These are formed by a metallic malle whose interior is refilled of pieces of plastic that use as support to the biomass.
In these systems it is produced an excess of biomass that parts with the contactor. This one is kept in suspension in the tank thanks to the movement of the material support. To regulate the quantity of present microorganisms in the system it arranges of a clarifier or secondary decanter. It is produced the sedimentation of the excess of biomass.
ACTIVE SLUDGES
It is an aerobic process of suspended biomass, which needs an intimate contact between the residual water, the biomass activates and the oxygen. It consists of contacting in an aerobic way, normally in a raft with air or in a tank of aeration, the residual water with floc biological before formed, in that adsorbed the organic matter and where it is degraded by the present bacteria (there is kept a certain concentration of aerobic microorganisms). To accelerate the natural processes oxygen is given them solved increasing this way the capacity of treatment beside obtaining a better quality of effluent and minor quantity of mires.
They qualify in processes of complete mixture or slug flow.
The processes of complete mixture are characterized by the uniformity of the characteristics of the liquor in the tank of aeration or raft with air.
The processes of slug flow, nevertheless, support a gradient of concentration depending on the distance at the entry of the process. In these processes mixture does not exist.
The model of complete mixture can adopt the following variants:
Long aeration. It consists of a tank of aeration, with a system of aeration for turbines, aireators submersible or ceramic diffusers. These support the biomass in suspension and introduce the necessary oxygen. These processes are characterized by its low load and low production of mires. In addition, its utilization is interesting when compounds try to be eliminated by nitrogen simultaneously by the organic matter.
· Contact - stabilization. This process develops in two tanks. The first one called of contact in that the effluent one is mixed by the re-circulated mire, in it exists aeration and mixture completes. After the contact the sedimentation takes place re-circulating the mire to the tank of stabilization. In the tank of stabilization there develops the new biomass, which is sent to the tank of contact and this way to initiate again the cycle.
DISCONTINUOUS SEQUENTIAL REACTORS (SBR) The biological sequential reactors (SBR) are discontinuous reactors in which the residual water is mixed by a biological mud with aeration.
The unitary processes that intervene are identical to those of a conventional process of activated mires. In both systems the aeration and the sedimentation intervene. Nevertheless, an important difference exists between both. In the conventional plants, the processes are carried out simultaneously in separated tanks, whereas in the SBR, the processes take place sequentially in the same tank. The employment of the only tank reduces substantially the necessary space and the investment.
GREEN FILTERS
Green filters are based on the property that has the soil of purifying physics and biological the waters that are applied to it in the shape of irrigation. The principal processes that develop in the soil are: physical filtered, biological, adsorption and rainfall, ionic exchange and assimilation of nutrients and trace elements.
The culturing more personnel are the capable ones of assimilating big quantities of water and nutrients.
ANAEROBIC DIGESTION
Is an anaerobic process of suspended biomass. It is in use specially when the waste water has a great pollutant load. It consists of the decomposition of the organic matter, which generates as final product a gas of contained energetic high place, called biogas, formed fundamentally by methane (60-80 %), carbon dioxide (40-20 %) and traces of other elements as sulphur of hydrogen. This biogas is capable of being used as fuel for the generation of thermal and / or electrical energy.
The process of anaerobic digestion is realized in completely closed tanks in those who control several types of microrganisms. Between(among) the most important and specifics of this process are on the one hand the producing bacteria of acids and for other one the producing bacteria of methane. The producing bacteria of acids transform the organic complex matter, in intermediate products. The producing bacteria of methane act on the above mentioned intermediate products transforming them into gases and stabilized by-products. The process that originates is slow and needs a few certain conditions. The first phase of the process is named an acid phase, with pH below 6,8, the second phase names methanic, which increases the pH to values of 7,4, these bacteria are very sensitive to the values of pH and keep out with lower values than 6.
BIOLOGICAL REACTOR OF MEMBRANE (MBR) consists of two parts integrated to the alone one: on the one hand, the biological reactor responsible for the biological purification and for other one, the physical separation of the biomass and the water by means of a system of direct filtration with membranes. The system has a major aptitude to eliminate colloidal DQO, since on not having crossed the membrane it has a time of very much major contact with the biomass.
