Reinforced Concrete Imhoff Tank

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

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

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 vertical pillars and stainless steel 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.

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.

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

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Article Code

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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)
Article Code	lt.185 for P.E.	lt.200 for P.E.	lt.250 for P.E.	Usable Volume (Sed.+Dig.) (lt)	Width	Length	Height	Tank Weight (ql)	h. 10 cm (B125)	h. 15 cm (C250)	h. 20 cm (D400)
IMHOFF1000	4	4	3	850	125	130	100	13,4	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	6	6	5	1.250	125	130	130	15,7	4,0	6,1	8,1
IMHOFF-MK2A	7	6	5	1.300	120	220	100	27,0	7,0	10,0	13,0
IMHOFF1700	8	7	6	1.500	125	130	150	17,2	4,0	6,1	8,1
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
IMHOFF2000A	10	10	8	2.000	125	180	130	20,0	5,6	8,4	11,2
IMHOFF2500	12	11	9	2.250	125	180	150	21,8	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	14	13	10	2.600	175	180	130	25,2	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	17	15	12	3.150	175	180	150	27,3	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.

Outlet layout

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