The most recent plant solutions also provide the degradation of other nutrients (N and P).
The nitrogen is found in the sewage, mainly in the form of ammonia: initially combined in molecules of various complex organic substances, which are key components of the cells of living organisms; the transformation occurs by oxidation by biological means and degradation of these substances, with consequent solubilization into ammonia. The ammonia nitrogen is subsequently oxidized, always for biological pathway, to "nitrites" and further oxidized to "nitrate", according to the following simplified scheme:
N (organic substances) +O2
(ammonia) + CO2
(ammonia) + O2
- (nitrites) + H2
(nitrites) + O2
These reactions occur in the oxidation basin by specific strains of bacteria (Nitroso monas and Nitrobacter) using the dissolved oxygen available in the tank, introduced by means of a suitable system.
In the aerobic nitrogen transformation process we are witnessing the conversion of the same from the reduced form of ammonia nitrogen to the oxidized form of nitrate nitrogen. The latter may be present in the final effluent in a limited concentration and therefore will have to undergo further processing.
The purpose is a step of denitrification in the anoxic tank, in which numerous specialized bacterial strains fix the oxygen present in the molecule of the nitrates by using it for endogenous needs about the metabolization of the organic substances; In fact, these strains (heterotrophic) are facultative aerobes, that is, if the surrounding environment there is the presence of dissolved oxygen using it directly, while in case of anoxia can use the oxygen present in the nitrate.
This phase, with the aim of accelerating the reaction kinetics and consequently the necessary volumes, is usually carried out upstream of the compartment oxidation-nitrification, and for this reason is defined pre-denitrification.
The control of phosphorus discharged from municipal and industrial wastewater treatment plants is a key factor in the prevention of eutrophication of surface waters.
The municipal waste waters can contain from 5 to 20 mg / l of total phosphorus, of which 1-5 mg / L are organic and the remainder is inorganic.
The removal of phosphates is currently used mainly by chemical precipitation with the addition of a coagulant, in which the chemicals are fed directly into the aeration tank or before it.
The most commonly used multivalent metal ions are iron and aluminum.
The continuous recirculation of the sludge, together with the adsorption processes and coagulation-flocculation due to activated sludge, allow a reduction in chemical consumption.
Ultimately the result that is obtained with an activated sludge system is the elimination of the biodegradable organic matter by means of transformation into inert material and in a muddy concentrated solution of the organic substance which must be subjected to further treatment before final disposal.
The plant scheme provides for:
- A pretreatment section (if any);
- A denitrification tank;
- A nitrification tank and bio-oxidation of carbon;
- A recirculation circuit (sludge and aerated mixture) and a removal system of excess biomass;
- Adequate mixing and aeration systems;
- A sub-fund for the separation of the sludge from the waters "purified".
- Domestic and urban wastewater treatment;
- Industrial waste water treatment:
- Agro-food industries;
- Paper industries;
- Textile industries;
- Chemical and pharmaceutical industries;
- Petroleum and petrochemical industries;
- Metallurgical and mining industries;
- Agricolture animal husbandry.