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Reinforced Concrete Imhoff Tank

Rectangular Imhoff Pit - CE marking, reference standard: UNI EN 12566-1

Imhoff Pit dimensions: 185 - 200 - 250 lt P.E.

Reinforced Concrete Imhoff Tank

Operating Features and Dimensions

Precast concrete underground Imhoff Tanks (also called Imhoff Pits) with different dimensions, are the very first primary purification step for wastewater, based on the applicable law: they are compulsory in the whole national territory.

Imhoff Tanks are septic tanks made up of two compartments: an upper sedimentation compartment and a lower digestion compartment. The slurry gets into the sedimentation compartment, where settleable suspended solids fall along the inclined hopper walls into the collection compartment underneath and then into the digestion compartment through the longitudinal communication slot.

What's the purpose to an Imhoff Tank? Suspended particles accumulate in Imhoff Tanks and make up for a thick crust, which, must be removed on a regular basis - 1 to 4 times a year. After a specific retention time, water get clarified, as it has had no contact with the compartment underneath. The material accumulated on the tank bottom is digested by anaerobic bacteria, biological gas produced during fermentation are released through the side vents next to the inlet openings, which must be connected to pipes leading to the roof.

It is important to perform a pre-emptive abatement (degreaser-grease separator) before treating wastewater Imhoff tanks, as oils, fats and detergents can cause serious inconvenience during the different treatment phases. For correct tank functioning it is necessary to avoid introducing thick items of any kind, such as: plastic bags, nappies, sanitary towels/tampons, cotton swabs, etc. The structure of the Imhoff tank must be thoroughly checked, with or without aquifer.

The advantages to the monoblock system:

  • if compared to septic tanks made of concrete rings, installation time is much shorter, as there are no joints to be sealed, as the tank is made of just one casting.


Other positive aspects to monolithic tanks in vibrated reinforced concrete against plastic tanks:

  • Installation time is very short, as no filling with water is required, nor other action is required for backfilling;
  • they are carriageable and resist average, heavy and first category traffic;
  • they are self-supporting structures against the ground pressure outside and, therefore, are not subject to crushing during maintenance/draining operations.


More information also from the website: http://www.fosseimhoff.it/

Supply specifications

Delivery and installation of an underground Rectangular Imhoff Tank, CE-marked by notified independent body No. 0407, manufactured in DECLARED SERIES Mod. IMHOFF____ , compliant with UNI EN 12566-1 standard for____P.E. with 185 lt., for____P.E. with 200 lt., for ____P.E. with 250 lt., manufactured by EDIL IMPIANTI 2 S.r.l. with UNI EN ISO 9001 and ISO 45001 management system made of monoblock vibrated concrete, reinforced with stainless steel vertical pillars and horizontal beams, with CE-certified materials, concrete in compressive strength class C45/55 (RCK >55 N/mm²), internal improved-adhesion steel reinforcements checked in our plant, GREESMIX5® steel fibers and electro-welded square mesh B450C, with certification of CHEMICAL RESISTANCE and REACTION TO FIRE (Class A1) issued by an external body based on UNI EN standards.
The CE-marked Imhoff tank is equipped with: inlets/outlets; inlet-side vents; internal hoppers in reinforced concrete or AISI 304 stainless steel (only for specific sizes and/or on demand); sludge extraction ducts where necessary; outer wall protective coating.

Applicable Regulation

UNI EN 12566-1 small wastewater treatment systems up to 50 PE Part 1: precast septic tanks.
The Imhoff tanks must be compliant with the UNI EN 12566-1 standard.

Resolution of the Interministerial Committee for water protection No. 48/77, Legislative Decree Law No. 152/06, Regional Resolution of the Emilia-Romagna Region n. 1053/03, Regional Resolution of the Umbria Region 1171/07, D.A.C.R. Resolution. No. 145/10 Marche Regional Water Protection Plan, Decree of the President of the Autonomous Region of Bolzano No. 6/08.

Imhoff tanks have a primary sedimentation purification performance.

Purification performance table:

  • bod-cod (25- 35 %)
  • settleable suspended solids (from 85 - 90%)
  • total suspended solids (from 55 - 65%)

Dimensions

Dimensions to calculate Population Equivalent
Let us make an example, to try and calculate the dimensions of an Imhoff tank for 20 people. Is the definition "people" correct? Not exactly. It is more appropriate to state you want to define the dimensions for an Imhoff tank for 20 Population Equivalent.
In residential housing as well as in manufacturing or service companies, it would be necessary to assess the effective sludge production to be disposed of to find the right system dimensions. Since this is almost impossible, it is necessary to refer to the Population Equivalent (P. E.), i.e., a standardized measurement unit, which can be determined as follows.

Concrete Imhoff Tank dimensions for:

Civil Residence - counting beds: 1 P.

  • 1 P. E. for bedrooms with up to 13.90 sqm surface
  • 2 P. E. for bedrooms with over 14 sqm surface


Hotel or accommodation structure - the same as for civil residence;
add 1 P. E. every time the room surface has a 6 sqm increase over 14 sqm;
for vacation structures or special situations where the seasonal use causes strong population density, it is necessary to consider the maximum effective potential of the structure.

Factories or artisan workshops - 1 P. E. every 2 employees - permanent and seasonal - during most intense activity times.

Companies, Commercial Offices, stores - 1 A. E. every 3 employees - permanent and seasonal - during most intense activity times.

Restaurants - to calculate the population equivalent, it is necessary to estimate the maximum accommodation capacity of the dining rooms, considering that a person takes around 1.20 sqm, together with the guests, you have to count the staff as well. 1 P.E. every 3 people.

Cafés and Clubs - as under the previous point but calculating 1 P. E. every 7 people.

Cinemas Stadiums Theatres - every 30 users corresponding to 1 P. E.

Schools and Gyms - every 10 people calculated based on maximum potential corresponding to 1 P.E.

Specific cases must be assessed individually, please contact our technical department.

Note
After calculating the Population Equivalent, it is necessary to contact the local authorities (A.R.P.A., Province, HERA) to define which kind of systems should be installed.
The water supply to be calculated can range from 100 lt to 250 lt for every Population Equivalent, depending on local regulation and the activity carried out.

Imhoff Pits

Fields of application

Imhoff tanks are monoblock reinforced concrete tanks
and they are used to treat wastewater, more specifically for housing, hotels, restaurants, hospitals, tourist centers, small towns, small and medium sized water treatment systems located before lifting stations.

Civil residence systems, slaughterhouses, wine cellars, cheese factories, food industry, conservation industry, pasta manufacturers, pastry manufacturers, fish industry, laundry services, civil residence, blocks, restaurants, hotels, hospitals, communities, canteens, catering services, schools, bars, camping sites, bathing establishments, service stations, meal production centers.

Imhoff Tank Outflow

More information

Imhoff tanks are also called septic tanks and stand for an example of compact combined system for water treatment. The typical configuration designed and patented in 1904 is composed of 2 separated but connected compartments: an upper settling compartment and a lower collections and anaerobic digestion compartment (with no oxygen) for settled sludge.

Settleable suspended solids in wastewater collected in the upper settling compartment fall through a slot connecting both compartments down into the lower compartment, where organic materials are subject to anaerobic fermentation and subsequent stabilization.

Imhoff tanks differ from septic tanks due to the separation between upper and lower digestion compartment, which makes it possible to obtain a "fresh" final outflow on the one hand (as it is retained in the settling compartment for a short time) and to digest sludge in the lower compartment in a uniform and controlled manner on the other.

Imhoff tanks treatment performance is equivalent to primary settling tank performance (BOD5 and COD, about 25-35%) - (settleable SS around 85-90%) - total SS about 55-65%).

The production of digested sludge of Imhoff tanks only used for primary treatment ranges from 0.3 and 0.6 l/P.E. a day, with a SS unitary input of about 35 g/P.E. a day. Of course, the input is bigger if the Imhoff tank also collects waste activated sludge coming from secondary treatments placed after the tank itself.

As for septic tanks, sludge must be regularly collected with specific means/ by specialized companies and disposed of in accordance with the law in specific treatment plants.

We always recommend leaving some sludge in the Imhoff tank when collecting it.

Imhoff Tanks Dimensions

Download E.U. dimensions


Select Article Code to access the E.U. dimensions for the product.

Article Code

Data Sheet Download


Select Article Code to access the Data Sheet for the product.

Article Code

Article
Code
Dimensions with
lt. for P.E.
Usable Volume
(Sed.+Dig.)
(lt)
External Dimensions
Imhoff Tank (cm)
Tank Weight
(ql)
Cover slab weight (ql)
lt.185 for P.E. lt.200 for P.E. lt.250 for P.E. Width Length Height h 10 cm B125 h 15 cm C250 h 20 cm D400
IMHOFF1000 4 4 3 850 125 130 100 16,9 4,0 6,1 8,1
IMHOFF-MK1A 5 5 4 1.050 120 170 100 22,0 5,0 8,0 10,0
IMHOFF1400 5 5 4 1.100 125 130 130 20,1 4,0 6,1 8,1
IMHOFF1700 7 6 5 1.300 125 130 150 22,0 4,0 6,1 8,1
IMHOFF-MK2A 7 6 5 1.300 120 220 100 27,0 7,0 10,0 13,0
IMHOFF-MK3A 8 8 6 1.600 120 270 100 32,0 8,0 12,0 16,0
IMHOFF-MK1B 9 8 6 1.700 120 170 150 29,0 5,0 8,0 10,0
IMHOFF-MK4A 10 10 8 2.000 120 320 100 37,0 10,0 14,0 19,0
IMHOFF2500 12 11 9 2.250 125 180 150 27,8 5,6 8,4 11,2
IMHOFF-MK2B 12 11 9 2.300 120 220 150 36,0 7,0 10,0 13,0
IMHOFF3000 13 12 10 2.500 175 180 130 31,5 7,8 11,7 15,6
IMHOFF-MK1C 13 12 10 2.500 120 170 205 37,0 5,0 8,0 10,0
IMHOFF-MK3B 15 14 11 2.900 120 270 150 42,0 8,0 12,0 16,0
IMHOFF3500 16 15 12 3.000 175 180 150 34,1 7,8 11,7 15,6
IMHOFF-MK4B 18 17 13 3.400 120 320 150 48,0 10,0 14,0 19,0
IMHOFF-MK2C 18 17 13 3.400 120 220 205 45,0 7,0 10,0 13,0
IMHOFF4900 21 20 16 4.000 180 180 200 52,4 8,0 12,1 16,1
IMHOFF4900A 21 20 16 4.000 180 240 150 52,1 10,7 16,1 21,5
IMHOFF-MK3C 22 21 16 4.200 120 270 205 52,0 8,0 12,0 16,0
IMHOFF6500 27 25 20 5.000 180 300 150 62,1 13,4 20,1 26,8
IMHOFF-MK4C 27 25 20 5.100 120 320 205 60,0 10,0 14,0 19,0
 
IMHOFF6400A 27 25 20 5.000 180 220 200 60,9 9,8 14,8 19,7
IMHOFF7900A 34 32 25 6.400 180 270 200 70,6 12,1 18,1 24,1
IMHOFF9000 43 40 32 8.000 180 320 200 80,1 14,3 21,5 28,6
IMHOFF10500 48 45 36 9.000 180 370 200 89,6 16,5 24,8 33,1
IMHOFF13000A 62 57 46 11.520 246 320 200 97,5 19,6 29,4 39,1
IMHOFF15000A 68 63 51 12.750 246 370 200 109,0 22,6 33,9 45,2
IMHOFF16500A 78 72 58 14.500 246 420 200 120,5 25,7 38,5 51,3
 
IMHOFF16000 81 75 60 15.000 246 320 250 111,8 19,6 29,3 39,1
IMHOFF19000A 89 82 66 16.530 246 370 250 124,6 22,6 33,9 45,2
IMHOFF21000A 102 94 75 18.900 246 420 250 137,3 25,7 38,5 51,3
IMHOFF24000 114 106 85 21.260 246 470 250 155,5 28,7 43,1 57,4
IMHOFF26000A 129 120 96 24.000 246 520 250 168,2 31,8 47,7 63,6
IMHOFF30000A 140 130 104 26.000 246 570 250 181,0 34,8 52,2 69,7
IMHOFF32000A 153 141 113 28.340 246 620 250 193,7 37,9 * 56,8 * 75,8 *
IMHOFF35000 165 153 122 30.700 246 670 250 206,4 40,9 * 61,4 * 81,9 *
IMHOFF37000 178 165 132 33.000 246 720 250 224,5 44,0 * 66,0 * 88,0 *
IMHOFF40000A 191 177 141 35.430 246 770 250 237,3 47,1 * 70,6 * 94,1 *
IMHOFF42000A 204 189 151 37.800 246 820 250 250,0 50,1 * 75,2 * 100,2 *
IMHOFF45000 217 200 160 40.150 246 870 250 262,8 53,2 * 79,7 * 106,3 *
IMHOFF48000 229 212 170 42.500 246 920 250 275,5 56,2 * 84,3 * 112,4 *
IMHOFF50000 243 225 180 45.000 246 970 250 293,7 59,3 * 88,9 * 118,5 *
IMHOFF52000 255 236 189 47.250 246 1020 250 279,8 ** 62,3 * 93,5 * 124,7 *
IMHOFF55000 268 248 198 49.600 246 1070 250 291,2 ** 65,4 * 98,1 * 130,8 *
IMHOFF57000 281 260 208 52.000 246 1120 250 302,7 ** 68,4 * 102,7 * 136,9 *
 
IMHOFF60000A 297 275 220 55.000 246 970 300 307,5 ** 59,3 * 88,9 * 118,5 *
IMHOFF63000 313 290 232 58.000 246 1020 300 321,0 ** 62,3 * 93,5 * 124,7 *


** The hoppers which form the compartments inside the imhoff tank are in AISI 304 stainless steel
* Cover Slab divided into two parts
The data reported is purely indicative




Marche Region Imhoff Tanks

1 draining a year
Dimensioning: D.P.C.R. Resolution No. 145 of 26/01/2010 Marche Water Protection Plan
100 lt/P.E. for the sedimentation compartment and 150 lt/P.E. for the digestion compartment.
drain twice a year
Dimensioning: D.P.C.R. Resolution No. 145 of 26/01/2010 Marche Water Protection Plan
50 lt/P.E. for the sedimentation compartment and 135 lt/P.E. for the digestion compartment.

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