Italiano
English
Deutsch
Français
Residential buildings and similar
WASTE WATER TREATMENT AND TYPES OF DISCHARGE
The characteristics of waste water from residential buildings and similar are comparable to those of households. Suitable parametrisation coefficients translate the pollutant load from these types of users into 'population equivalents'.
The pollutant content is basically expressed in terms of discharged BOD* and nitrogen, with possible presence of suspended solids and floating materials, such as fats and oils from food.
For the treatment of the waste water from this type of urban building there are different system schemes depending on the type of discharge: discharge into sewers, discharge into receiving water body, dispersion onto land, possible re-use of the treated water, for example for irrigation.
Primary treatment layouts can be used for removal of sedimentable suspended solids, fats, oils and floating materials in case of connection to the sewage network, in compliance with local regulations and the provisions of the managing body.
In the case of direct discharge to a receiving body of water, secondary treatments must be provided, aimed at reducing BOD below the legally established limits: aerobic or anaerobic percolating filter plants and activated sludge plants.
*BOD: Expresses the amount of oxygen needed by aerobic micro-organisms, to break down organic material present in a given water sample therefore it is an indirect measurement of the bacterially degradable organic substances present in the water.
Primary treatment
Primary treatment refers to all treatments aimed at removing macroscopic pollutants in waste water.
Coarse and heavy solids, such as sand, soil, gravel, which are sedimentable, are separated by gravity sedimentation and are collected on the bottom of the treatment tank.
Light solids, such as grease and oil of a food or mineral nature, rise to the surface of the liquid in the tanks and are skimmed off. The primary treatments are mainly composed of physical systems, even though in the tanks biological degrading mechanisms can be developed to break down the substances that settle on the bottom and are removed, in the form of sludge.
Primary treatments encompass all the phases of the processes that are responsible for the gravimetric removal of suspended sedimentable and floating solids.
The products used consist of tanks, the size and shape of which are designed to facilitate the sedimentation and/or floating processes. Tanks are generally free of moving parts and electromechanical equipment as the static processes that take place within them involve the gravimetric separation of the solids present in the waste water with differing specific weights.
Grease separator
The grease separator is required in the preliminary stage of the treatment of effluents containing organic fats and oil from residential users, or from commercial businesses with similar waste water: community kitchens, restaurants, hotels, motorway catering areas, fast food restaurants, steakhouses, and similar.
Imhoff septic tank
The special geometry of the Imhoff tank ensures that the sewage remains inside it long enough to trigger a series of biological mechanisms, through which the suspended substances are dissolved or precipitate to the bottom, where they sediment and undergo partial stabilisation by anaerobic bacteria. When light substances are present, they separate by flotation, accumulating on the surface of the liquid.
Separation of settleable solids and light liquids can be achieved with these products: some of the organic material is decomposed by a septic-type anaerobic fermentation process. The tanks must also guarantee an adequate storage capacity to prevent floating substances from being dragged outside with the clarified liquid in any way.
Septic tank
Used for the treatment of black water that is substantially free of fats and floating substances, the septic tank consists of a sedimentation tank where static sedimentation of the suspended solids contained in the sewage takes place.
Secondary treatment
The various secondary treatments available aim to reduce organic pollution (expressed in terms of BOD) in effluent waste water and the simultaneous reduction by bacterial assimilation of the other micropollutants (phosphorus and nitrogen).
The removal of BOD is made possible through biological synthesis by means of bacterial populations whose growth is promoted by the particular conditions and microclimate that are established inside the purification tank, which becomes, in all respects, a biological reactor.
The various treatments proposed differ according to the way in which the biological reactions take place and, ultimately, in relation to the different types of bacterial population selected, depending on whether the bacterial population have been grown in the indistinct mass of the reactor (suspended biomass) or whether development is favoured on a solid support (adherent biomass) consisting of a series of plastic type filling media.
The adoption of a secondary treatment plant is generally preceded by one or more primary treatment units (grease separator, Imhoff, septic tank) aimed at the removal of the solid and coarse floating materials that could otherwise interfere with the correct performance of the biological reactions and with the transfer of oxygen (for aerobic type plants), as well as clogging the pipes and hydraulic connections
Anaerobic percolating filter
The anaerobic percolating filter is an extremely simple but effective biological purification system (it is completely free of electromechanical elements), which reaches such a high degree of purification that the treated waste water, predominantly of a domestic or similar origin, can be discharged directly into a surface body of water.
Aerobic percolating filter with natural convection of air
The aerobic percolating filter with natural convection of air is an extremely simple biological purification system, free of electromechanical elements, which reaches such a high degree of purification, that the treated waste water, predominantly of a domestic or similar origin, can be discharged directly into a surface body of water.
The aerobic percolating filter is generally installed downstream of an Imhoff tank
Total oxidation activated sludge plant
Total-oxidation activated sludge plants are complete waste water treatment systems for small communities with which conditions for the assimilation and thorough removal of the organic substances contained and the almost complete oxidation of the biomass produced are realised. The purified waste water is compatible with direct discharge into the receiving water body.