The art. 100 of the Lgs.D. dated 04/03/2006 no. 152 part III relative to point 3 cites as follows:

“for the settlements, installations or isolated buildings, that produce domestic sewage waters, the regions identify individual systems or other adequate private or public systems that achieve the same level of environmental protection, indicating the adaptation times of the drainages to said systems, therefore for that which is not expressly legislated from the present the decree, the technical regulations of the deliberation of the interdepartmental committee for the protection of waters of 4 February 1977 and successive modifications and integrations continue to apply, published in the official gazette no. 48 of 21 February 1977”.

The Imhoff system is a system designed for primary sedimentation, for the accumulation and anaerobic digestion of sedimentary sludge, and is applied mainly in the treatment of domestic sewage waters of small isolated communities.

With the exception to the traditional septic pit, the Imhoff system contains a compartment of sedimentation which is separate from that of digestion; therefore the extolled water is almost free from the contamination of the gaseous emissions generated from the fermentation of the sludge.

For this reason, the regulations on the legislation for community drainages that consist of less than 50 lots or 5000 m2, emanate from the Interdepartmental Committee for the Protection against Water Pollution with deliberation of 4 February 1977, which recommends use of the Imhoff system in place of the unacceptable septic retention pit.

The Imhoff systems are particularly effective in dealing with the residential sewage waters of small isolated communities that are unable to use the communal sewage system and have adopted the technique of sub-irrigation for drainage. The Imhoff systems are subdivided on the inside into two distinct compartments: one above (sedimentation unit) where it processes the sewage water, and one below (digestor) where it processes the sludge. The first compartment has the settling of the solid sediments and the flotation of the fats present in the sewage waters; the second compartment has the collection and the anaerobic digestion of sedimentary sludge. Treated as such, the sludge becomes completely stabilized. An Imhoff system can be considered to be built to state of the art regulations if it possesses the following characteristics:

• Hydraulic Seal. The system is always full therefore eventual losses would provoke infiltrations of polluting sewage water and bad odors in the surrounding areas that, most times, is adjacent to the same habitations that are served;
   

• Correct outflow of sewage water: the uniform flow of the sewage water along the sedimentation compartment increases the effective time of permanence and therefore the ability to separate the solid sediments;
   

• Correct accumulation of sludge: the uniform distribution of the sludge on the bottom of the system avoids preferential accumulations and helps to use all the available volume reducing the frequency of purges;
   

• Corrected expulsion of gases: the employment of adequate conducts of expulsion of gases generated from the fermentation of the accumulated sludge considerably reduces the degree of organic pollution in the water extolled in the system exit, and eventually allows it to separate and to carry away the emissions so as to prevent the insurgence of unhealthy smells;
   

• Adequate Dimensions: the dimensioning of the volume of sedimentation (40 ÷ 50 liters per inhabitant, barring exceptions) and of the volume of the accumulation and digestion (100 ÷120 liters per inhabitant barring exceptions) according to the recommendations of the deliberation of the Interdepartmental Committee, which involves the correct operation of the system beyond that of the respective regional legislation still enforced on the matter. However the basins must follow regulations of UNI EN 12255-4: 2002 relative to point 4.3.3.

System “Imhoff” of biological treatment of sewage waters type MUSILLI W100 series realized with monolithic reservoirs prefabricated in reinforced vibrated concrete to high resistance verified for street cargos of 1ª antiseismic category, and suited with cover slab prefabricated in carriageable reinforced vibrated concrete verified for cargos of 1ª antiseismic category with inspections bumper to bumper and D400 class valves. The reservoirs are equipped with separation septa between the settling zone and the sludge digestion zone, and deflectors for the sewage water at the entrance and the exit. The system is dimensioned according to that which is prescribed by the Official Gazette no. 48 of the 2/21/1977. The system is constructed by a company which is in possession of Business Quality System certification of UNI EN ISO 9001:2008 and is ICMQ certified.