BE1030053B1 - PROCESS AND FACILITY FOR TREATMENT OF WASTEWATER FROM CONCRETE MANUFACTURING PLANTS - Google Patents

Abstract

Process for treating waste water from concrete manufacturing plants, comprising recovery of washing water from mixers and mixer trucks, mechanical separation between, on the one hand, an aqueous phase containing, in suspension or in solution, residues of hydraulic binder and adjuvants and fines from aggregates of said concrete and, on the other hand, a solid phase comprising said aggregates, agitation of the separated aqueous phase in order to prevent settling, filtration of the separated aqueous phase, with obtaining clarified water and a filter cake formed of particles of hydraulic binder and fines from concrete aggregates and recovery of clarified water having a pH between 11 and 13.

Description

PROCESS AND FACILITY FOR TREATMENT OF WASTEWATER FROM

CONCRETE MANUFACTURING PLANTS

The present invention relates to a process for treating waste water from concrete manufacturing plants and to a plant for treating this waste water.

The production and consumption of concrete induce a high production of wastewater. In a concrete batching plant, this is mainly washing water from the mixers of the installation and the interior of the mixer trucks transporting the concrete produced. These wash waters contain fine solid mineral particles and

10 remains of aggregates, such as sands, gravel and gravel of varying grain sizes.

This waste water cannot, or only with difficulty, be evacuated as it is and therefore requires treatment.

The object of the invention is to provide a process and an installation making it possible to treat this waste water obtained in the production of concrete, in a way making it possible to avoid as far as possible pollution of the environment, in particular by providing for recycling of the water worn out.

To solve this problem, provision is made, according to the invention, for a process for treating waste water from concrete manufacturing plants, comprising the following steps: (i) recovery of washing water from mixer trucks and mixers, these recovered washing waters comprising an aqueous phase having a pH of between 11 and 13 and a solid phase formed from excess concrete contained in said washed trucks or mixers, (ii) a mechanical separation between, on the one hand, said aqueous phase of the recovered washing water containing, in suspension or in solution, residues of hydraulic binder and adjuvants and fines from aggregates of said concrete and, on the other hand, said solid phase comprising said aggregates, the aqueous phase separated having a pH of between 11 and 13, (fi) agitation of said separated aqueous phase in order to prevent settling of particles in suspension of said hydraulic binder and adjuvant residues and of said fines from the aggregates and therefore to keep the homogeneous aqueous phase, (iv) filtration of the separated aqueous phase, resulting from the agitation stage, with the obtaining of clarified water as filtrate and of a filtration cake formed of particles of hydraulic binder and fine aggregates which were suspended in the separated, agitated aqueous phase, and (v) Recovery of clarified water which has a pH between 11 and 13.

The process according to the invention does not require the addition of a chemical adjuvant. In particular, it excludes any neutralization of wastewater, the clarified water obtained being very basic, like the wastewater at the start of treatment. Furthermore, the method advantageously allows the separation of three different components, a mixture of aggregates, a filter cake formed of particles of the hydraulic binder and fines from the aggregates and clarified water.

According to a particular embodiment of the invention, the treatment method further comprises recycling of said solid phase comprising the aggregates, resulting from the mechanical separation step, in the manufacture of a lean concrete.

Preferably, the treatment method further comprises

A compacting of the aforesaid filter cake and then its treatment for subsequent recycling, for example in lean concretes. Advantageously, such compacting is carried out during the filtration, using a filter press. The aforementioned treatment may consist of drying the compacted filter cake, crushing it, then screening it.

In another preferred embodiment, the treatment method further comprises a recycling of the clarified water for the production of concretes or for the washing of mixer trucks and concrete mixers. Clarified water can for example be added during mixing to react with hydraulic binder or it can be introduced into high pressure water cleaning tools to wash mixers or mixer trucks after use. It can also be introduced into the rotors of truck mixers to rinse the rotating tanks.

The invention also relates to an installation for treating waste water from concrete production plants. This treatment device according to the invention comprises: - a basin for recovering water from the washing of mixer trucks and concrete mixers, which comprise an aqueous phase having a pH of between 11 and 13 and a solid phase formed from the excess of concrete contained in the said washed trucks or mixers,

* BE2021/6017 - A separation basin for the washing water coming from the recovery basin, a separation device being arranged in this separation basin to extract therefrom in a harvesting chamber said solid phase which contains aggregates and thus separate it of the said aqueous phase of the recovered washing water which contains, in suspension OR in solution, residues of hydraulic binder and adjuvants and fines from concrete aggregates, - A stirring tank for the aqueous phase coming from the separation, in which at least one agitator is arranged to prevent settling of suspended particles of said residues of hydraulic binder and adjuvants and of said fines from the aggregates, - a filtration device for the aqueous phase coming from the agitation tank which is arranged to separate clarified water, as filtrate, from a filter cake, formed of particles of hydraulic binder and fines from the aggregates, - A basin for collecting the clarified water, and - transfer means for communicate pools and devices with each other.

In a preferred embodiment, the aforesaid separation device allowing extraction of the solid phase from the aqueous phase in the separation tank is an endless screw.

Preferably, the aforementioned filtration device is a filter press allowing compaction of the filtration cake.

Advantageously, the treatment installation further comprises a crusher for crushing the compacted filter cake. it should be noted that certain elements of this installation according to the invention can be found on different sites linked together by transfer means. For example, the crushing device or the tools necessary for recycling can be provided on a site located at a distance from the other elements of the installation.

Other modes and embodiments according to the invention are indicated in the appended claims. Other characteristics, details and advantages of the invention will become apparent from the description given below, on a non-limiting basis and with reference to the appended drawings. The single figure represents a flow diagram of the waste water treatment process according to the invention.

The figure schematically illustrates the different steps of an example of a process according to the invention for washing water from truck mixers and concrete mixers. The exterior washing of mixer trucks and chutes preferably takes place with the help of high-pressure water. Washing the inside of the tank of the mixing device or truck mixers consists of filling the tanks and rinsing them while rotating them. The waters resulting from these washes include, in a mixture, the excess concrete removed from the walls of the trucks and the mixers and the water used for the washing. These washing waters, strongly basic, with a pH of around 11 to 13, are recovered in a recovery tank 1, then transferred to a separation tank 2 where a mechanical separation takes place between the aqueous phase which comprises water and, in suspension or in solution, for example cement residues and possible admixtures and fines from aggregates, and the solid phase which comprises aggregates, for example sand, gravel and/or gravel . This mechanical separation can be done, for example, by means of an endless screw immersed in the washing water of the separation tank 2 so as to extract the solid phase therefrom upwards and bring it into a harvest box 3 From this collection box 3, the components of this solid phase can be recycled, for example in the production of lean concrete.

The water and the fine particles making up the aqueous phase are transferred to an agitation basin 4 where one or more agitators prevent the particles in suspension from settling in order to maintain a homogeneous aqueous phase. This homogeneous aqueous phase, which always has a pH of 11 to 13, is then, in the example illustrated, filtered by means of a filter press 5. This can optionally retain particles of material with a fineness of the order of 50-60 µm. It is, for example, made up of about twenty frames sliding on an axis, each equipped with a filter cloth. When the filter press starts a cycle, the frames are automatically positioned against each other and are pressurized by a huge cylinder to ensure the seal between each frame. Then, the loaded aqueous phase is pushed under a pressure of 0.5 to 0.6 MPa between the fabrics supported by the frames. The particles are retained by the fabrics and the clarified water is collected by appropriate channels and returned to a collection basin 7, where it still has a pH of 11 to 13. By dint of accumulating particles in the fabrics, the pressure required to pass the loaded aqueous phase increases. Past a certain pressure threshold, the current cycle is interrupted. The main cylinder is released and the filter cloths are pushed aside. The filter cakes, made up of particles of hydraulic binder and fines from the aggregates which were suspended in the aqueous phase and which have been compacted in the cloths, simply fall under the effect of gravity under the filter press, in a manifold 6.

The clarified water recovered in the collection basin 7 can then be exploited again, for example to rinse the tanks of the mixer trucks. It can also be used to supply water to a mixer during its production of concrete.

As already stated, the filter cakes from collector 6 can be reused, for example by mixing with recycled aggregates, for example after drying, crushing and screening.

/ BE2021/6017

Example

A comparative test was carried out on a concrete produced with mixing water from a catchment well and on a concrete produced in the same way, but with clarified water according to the process according to the invention, which was collected at the output of a filter press, as previously described.

The field of application of the concrete produced is that of reinforced concrete, the aggregates used are of the limestone type, with a Dmax of 20 MM, the minimum cement content (EN 206) is 320 kg/m°.

The fresh concrete thus produced on D-Day in a mixer at a concrete plant was dumped into a mixer truck and then collected using a wheelbarrow, directly from the mixer truck. On each of the fresh concretes, we then proceeded on day D to a measurement of the air content and the wet density using an air meter, to a measurement of the water content by burning the fresh concrete (method by microwave drying) and a measurement of the consistency of fresh concrete using an Abrams cone (measurement of the

Slumps). Then we also proceeded on D-Day to the making of test specimens by molding and their identification.

Further measurements were then taken on hardened concrete.

The specimens were removed from the mold on day D+1 and those to be subjected to later tests were stored under water at 20°C + 2.

The specimens were then crushed on the desired dates (d+1 — d+2 — d+7).

The following standards were followed during the tests: - NBN EN 206-2013+A1-2016 - NBN EN 12350-1 (2009) Tests for fresh concrete —

Sampling

- NBN EN 12350-2 (2009) Tests for fresh concrete - Slump test - NBN EN 12350-6 (2009) Tests for fresh concrete - Density - NBN EN 12350-7 (2009) Tests for fresh concrete - Content of air - Compressibility method - NBN EN 12390-1 (2012) Tests for hardened concrete - Shape dimensions and other requirements specimens and molds - NBN EN 12390-2 (2009) Tests for hardened concrete -

Preparation and conservation of test specimens for resistance tests - NBN EN 12390-3 (2009) Tests for hardened concrete -

Compressive strength of specimens - Test results on fresh and hardened concrete! HO PA

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! Consistency measurement! You! ; 1,200 UIS! Slump measured [mm]! !

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2 | ; 2.2 , p !Air content measured using a! 13 l., = | airmeter [%] ' U 2 ® | Recipe water delta — burning [L] 148 1-48

I I I vossen 1 Mechanical resistance to compression! 1, 10.7 194

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Given the influence of basic parameters, such as the quality of raw materials, the management of humidity in production,

etc we can consider that these results are relatively similar.

The possible influence that the use of recycled water could have had is not apparent in these tests carried out on fresh and hardened concrete.

It can therefore be concluded that the clarified water used in this test is suitable for use in production.

It is understood that the present invention is in no way limited to the modes and embodiments described above and that many modifications can be made thereto without departing from the scope of the appended claims.

Claims (8)

1. Process for treating waste water from concrete manufacturing plants, comprising the following steps: recovery of wash water from mixer trucks and mixers, this recovered wash water comprising an aqueous phase having a pH of between 11 and 13 and a solid phase formed from the excess concrete contained in said washed trucks or mixers, a mechanical separation between, on the one hand, said aqueous phase of the recovered washing water containing, in suspension or in solution, binder residues hydraulic and additives and fines from aggregates of said concrete and, on the other hand, said solid phase comprising said aggregates, the separated aqueous phase having a pH of between 11 and 13, stirring of said separated aqueous phase in order to prevent settling of suspended particles of said residues of hydraulic binder and adjuvants and fines from concrete aggregates and therefore to keep the aqueous phase homogeneous, filtration of the separated aqueous phase, resulting from the agitation step, with obtaining a clarified water as filtrate and a filter cake formed of particles of hydraulic binder and fines from concrete aggregates which were in suspension in the aqueous phase separated, agitated, and recovery of the clarified water having a pH between 11 and 13. 2. Treatment process according to claim 1, further comprising a step of recycling said aggregates, resulting from the mechanical separation step, in the manufacture of a lean concrete. 3. Treatment method according to one of claims 1 and 2, further comprising compacting the aforesaid filter cake and then treating it for subsequent recycling. 4. A method of treatment according to one of the preceding claims further comprising a recycling of clarified water for the production of concrete or for washing truck mixers and concrete mixers. 5. Installation for the treatment of waste water from concrete manufacturing plants, comprising - A recovery tank (1) for washing water from mixer trucks and mixers, which includes an aqueous phase having a pH of between 11 and 13 and a solid phase formed from the excess concrete contained in the said washed trucks or mixers, - A separation basin (2) for the washing water coming from the recovery basin (1), a separation device being arranged in this separation in order to extract therefrom in a harvesting chamber (3) said solid phase which contains aggregates and thus separate it from said aqueous phase of the recovered washing water which contains, in suspension or in solution, residues of hydraulic binder and adjuvants and fines from concrete aggregates, - A stirring tank (4) for the aqueous phase coming from the separation tank (2), in which at least one stirrer is arranged to prevent settling of particles in suspension of said residues of hydraulic binder and of adjuvants and of said fines from the aggregates, - A filtration device (5) for the aqueous phase coming from the agitation basin (4), which is arranged to separate clarified water, as filtrate, from a filter cake, formed from said particles of binder hydraulic and said fines from the aggregates which were in suspension, - A collection basin (7) of the clarified water, and - transfer means for communicating the basins and devices with each other. 6. Installation according to claim 5, characterized in that the aforesaid separation device allowing extraction of the solid phase from the aqueous phase in the separation tank is an endless screw. 7. Installation according to one of claims 5 and 6, characterized in that the aforementioned filtration device (5) is a filter press allowing compaction of the filter cake. 8. Device according to one of claims 5 to 7, further comprising a crusher for crushing the compacted filter cake.