ECOMACCHINE S.p.A.
Via Vandalino 6
10095 Grugliasco (TO)
Tel.: +39.0114028611
Fax: +39.0114028627
Email: ecomacchine@ecomacchine.it
Web: www.ecomacchine.it

GRIT AND OIL REMOVAL SYSTEMS

The second mechanical treatment of the waste water is the grit and sand removal; sometimes the grit removal tank contains also the oil removal system. The grit removal process consists in removing the substances which have a specific weight and hydrodynamic characteristics similar to true sands, such as glass and metal pieces, egg-shells, seeds, fruits-stones, coffee–beans, ashes, clay, mould, etc... Many of these substances are abrasive and may cause damages to the equipments.

There are a few types of Grit Removal Systems:
• channel type, normally aerated and with a lateral oil removal zone;
• “pista” type, in a circular tank;
• detritor type, in a square tank


The size of the solids separated by the Grit Removal System is larger than 200 microns. These solids contain some water. The solids can be separated from water through a sand filter, drying bed type, or by means of solid/water separators.

Our range of production includes the following types of Grit Removal Systems:

Grit and oil removal scraper bridge for rectangular tank, aerated type - mod. EM54
Grit and oil removal scraper bridge for rectangular tank, suction type - mod. EM55
Grit and oil removal system for rectangular tank, suitable for covered tanks - mod. EM52A
“PISTA” type grit removal system mod. EM40A
“PISTA” type grit and oil removal system mod. EM40B
Grit removal system, detritor type, with scraper - mod. EM42

Accessories:

Grit separators:
Screw type grit separator mod. EM39
Reciprocating grit separator with scrapers mod. EM41
Air-lift mod. EM77

OUTLINES OF THE GRIT REMOVAL PROCESS

The waste water often contains a large quantity of inert materials, mainly inorganic, which are generally defined as grit, even if actually the quantity of sand/grit is only a part of this type of materials. In fact, in the waste water treatment field, the words “grit” or “sand” do not refer only to the siliceous sands, of various sizes, but they are more commonly intended as the group of heavy inert materials which can be found in the waste water. The greatest quantity of grit reaches the waste water treatment plant during rainy periods, also because the cities sewer systems usually have a slight slope, and then a slow speed, and the sediments are dragged when the flow rate is rising.

A good grit removal system should sediment all and only the grits, of any size. The sedimentation of the organic materials should be avoided because the presence of putriscible materials in the removed grit would make them unusable or would not allow a direct elimination because it should be thouroughly washed.
Anyway in the grit removal systems, even if well sized and designed, there is always a small quantity of organic material.
To achieve a good grit separation there must be some specific physical conditions which allow to exploit the phenomenon of the difference of sedimentation speed between the particles of inert material, which sediment more quickly, and the particles of organic material.

There are a few types of Grit Removal Systems:
gravity grit removal systems
where the grit separation is achieved only by gravity (channel type systems)
mechanized grit removal systems
where the grit separation is helped by the rotation of a turbine (PISTA type systems)
aerated grit removal systems
where the grit separation is helped by the air blown from the bottom


In the aerated grit removal systems the turbulence due to the air helps the grit separation and the suspension of the organic material.
The addition of a vertical baffle in the aerated grit removal systems makes the oils separation easier. They are collected in a calm zone, after the baffle.
The following table shows the percentage of the grit separation, depending on the granules size and the time of permanence in the tank.

GRIT AND OIL REMOVAL SCRAPER BRIDGE, AERATED TYPE
MOD EM54

Operation description

The water speed in the grit removal channel is lower than 0.3 m/sec., therefore the grit having a larger size than 200 microns settles on the bottom. The air distributed by the diffusers fluidifies the grit before it sediments and removes the organic substances which deposit on it. These organic substances and the other substances in the water, thanks to the air effect, float and flow together to the oil removal zone which is on the channel side and is not aerated, then they are taken away by a surface scraper.
The grit settled on the bottom is conveyed to the hopper by the bottom scraper.
The recommended air delivery is of 10-15 Nm3/h per metre of length of the grit removal channel.

Mechanical solutions for the scraper bridges:

• scraper bridge with concrete runways, equipped with tyred wheels and contrast wheels
• scraper bridge with rails

Technical data

GRIT AND OIL REMOVAL SCRAPER BRIDGE, SUCTION TYPEE
MOD EM55

Operation description

The water speed in the grit removal channel is lower than 0.3 m/sec., therefore the grit having a larger size than 200 microns settles on the bottom. The air distributed by the diffusers fluidifies the grit before it sediments and removes the organic substances which deposit on it. These organic substances and the other substances in the water, thanks to the air effect, float and flow together to the oil removal zone which is on the channel side and is not aerated, then they are taken away by a surface scraper.
The grit settled on the bottom is lifted by a submersible pump or air-lift and conveyed to the lateral channel.
The recommended air delivery is of 10-15 Nm3/h per metre of length of the grit removal channel.

Mechanical solutions for the scraper bridges:

• scraper bridge with concrete runways, equipped with tyred wheels and contrast wheels
• scraper bridge with rails

Technical data

GRIT AND OIL REMOVAL SUBMERSIBLE SYSTEM
MOD EM4953

Operation description

The water speed in the grit removal channel is lower than 0.3 m/sec., therefore the grit having a larger size than 200 microns settles on the bottom. The air distributed by the diffusers fluidifies the grit before it sediments and removes the organic substances which deposit on it. These organic substances and the other substances in the water, thanks to the air effect, float and flow together to the oil removal zone which is on the channel side and is not aerated, then they are taken away by surface blades.
The grit settled is removed by a bottom screw.
The recommended air delivery is of 10-15 Nm3/h per metre of length of the grit removal channel.

Technical data

PISTA TYPE GRIT REMOVAL SYSTEM
MOD EM40A

Operation description

The water flows into the grit removal tank in a tangential way and the blades keep the liquid in motion at any level of flow rate. The tangential flow and the blades rotation make the grit particles sediment on the bottom.
The grit is lifted by an air-lift and is conveyed to a mechanical separator or to a simple draining and filtering bed.
The grit removed is clean enough thanks to the separation of the organic substances due to the effect of the rotary blades.

Sometimes, to avoid the arising of decomposition phenomena due to the inevitable presence of organic material, a certain number of washings by water or air are necessary before extracting the grit.

This type of grit removal system does not separate any oily substances.

Technical data

PISTA TYPE GRIT AND OIL REMOVAL SYSTEM
MOD EM40B

Operation description

The water flows into the grit removal tank in a tangential way. The tangential flow helps the grit particles sedimentation on the tank bottom.
Normally the suspension remains in the tank more than 30 seconds.
The flotation of the organic substances is due to the air blowing.
The grit is lifted by an air-lift and is conveyed to a mechanical separator or to a simple draining and filtering bed.
The oils flow together outside the separation ring and are regularly removed by means of a manual blade or gate valve.
The grit removed is clean enough thanks to the separation of the organic substances due to the effect of the air blowing.

To avoid the arising of decomposition phenomena due to the inevitable presence of organic material, a certain number of washings by water are necessary before extracting the grit.

Technical data

DETRITOR TYPE GRIT REMOVAL SYSTEM
MOD EM42

Operation description

The water flows into the grit removal tank from the side. The water flow must have a laminar motion.
The baffles placed at the entry are installed in such a way to distribute the water homogeneously, all over the tank width.

The grit which sediments on the bottom is scraped and conveyed to the periphery of the tank where it is lifted and evacuated by an air-lift.
The average water level in the tank is 700-1000 mm.

Technical data

GRIT SEPARATOR AND WASHER
MOD EM39

Operation description

The water to be treated is conveyed into the feed hopper where the sand and any other solid particles decantation process takes place.

The screw lifts the solid materials from the hopper to the discharge outlet.

After having been separated from water, the sand is washed with clean water by a spraying nozzle; the dirty water returns to the tank and the washed sand is lifted by the screw.

At the first starting, before the grit is lifted and evacuated outside the machine, the solid materials must begin settling down to form a bed of grit.
When a sufficiently thick bed of grit is formed, the equipment begins evacuating the solid material (grit).

Technical data

RECIPROCATING GRIT SEPARATOR AND WASHER
MOD EM41

Operation description

The water to be treated is conveyed into the feed hopper where the sand and any other solid particles decantation process takes place.

The grit scrapers, thanks to their reciprocating motion, lifts the solid materials from the hopper to the discharge outlet.

After having been separated from water, the sand is washed with clean water by a spraying nozzle; the dirty water returns to the tank and the washed sand is lifted by the screw.

At the first starting, before the grit is lifted and evacuated outside the machine, the solid materials must begin settling down to form a bed of grit.
When a sufficiently thick bed of grit is formed, the equipment begins evacuating the solid material (grit).

Technical data