Concrete slurry is produced in many places – from construction to the concrete industry. For example, when washing out truck mixer drums. Where to put wastewater full of high-strength concrete? The direct disposal of depressurized concrete via the mains drainage system is a no-go, because it is not only ecologically risky: If concrete slurry settles in the pipes, it can set solid and seal them up. The concrete slurry must therefore be dewatered, i.e. separated from the water.
A solid/liquid separation solidifies the concrete slurry and compresses it to a filter cake with a high level of dewatering. The concrete slurry passes through the filter plates of a filter press. During filtration, the – now purified – water is intercepted. What is left is dry and bonded material that you can now dispose of at the landfill mostly as construction debris. And the water? Can now be used again as mixing water for low concrete grades.
I’m sure you’ve noticed: The environmentally sound disposal of sludge is labor-intensive and costly. Fortunately, there is another way: A self-priming sludge pump conveys residual water from the agitator basin directly into the corresponding filters. How quickly – between about fifteen and twenty minutes – it fills during filtration depends on the solids content. You do not have to monitor the filtration separately: When the filter chamber is full, the concrete slurry pump switches off automatically – a mobile system that works efficiently.
Which way does the wet concrete slurry go?
A – preferably low-wear – slurry pump sends the concrete slurry towards the filter press and feeds it into the filter chambers. In this process, strong inlet pressure initiates filtration: The water penetrates the filter cloths; solids remain on them – gradually a solid filter cake is formed in the filter chambers. In this way, the back pressure in the filter chamber continues to rise, which forces even more water out of the filter cake – the concrete slurry virtually dries out! When filtration is complete, the filter press shuts down and the filter cake falls out of the chambers to be recycled into building materials. And then? If the sludge dewatering goes into the next round, the cycle starts again.
A wide variety of filter presses separate solids from liquids. Filtration as a process has been used to dewater sludge since the 19th century. Dewatering concrete slurry is the task of a special chamber filter press that separates water and cement residues. Substances obtained in this way can then be reused proportionally. A modern filter press works automatically – with the aid of parallel filter plates surrounded by filter cloths. Strong pressure generated by hydraulic cylinders now presses them together, resulting in cavities between them (filter chambers). Fine filtrate discharge pipes drain the filtered water from the filter chamber of the filter press to the outside.
Water treatment systems for the filtration of cement residual water, such as the CWAS, have been developed specifically for the concrete industry to respond to the challenge of increasingly stringent environmental regulations and rising costs of public wastewater and concrete slurry disposal. A water treatment plant such as CWAS treats the residual water with a high treatment capacity. Cleaned in this way, you can then use it again in concrete production. Even the pH value of the return water can be selected as desired. A fully automatic operating program here follows the principle of water density standardization – for a constant water density in the gray water basin. The CWAS water treatment and washout system specifically reduces the water density of the concrete residual water to a freely selectable value. The goal: Nothing less than complete water reuse according to DIN EN 1008! Excessive sediment is avoided during concrete slurry dewatering, but only as much sediment as necessary is removed from the residual water basin. In addition, the patented process allows the sediments taken to be processed: Instead of being disposed of at high cost, they are then used as aggregates.
A clever idea, because a containerized Plug&Play system is so mobile that you can use it at the next location in no time at all and, in winter version, even operate it all year round. These systems are all-rounders: They perform filtration and water recovery as well as volume reduction. The separation ensures fractions such as floating parts, coarse parts, pressed fine parts and clean water; impurities from wood and plastic parts are discharged. In the end, the volume is reduced to a minimum. You decide how dense you want your concrete cake to be. Whereas with a conventional cleaning system, filter cakes or large BigBags have to be disposed of as expensive waste, the new patented process gives you the option of reusing the end product.
Filter cloths become soiled in the course of the separation process: The pressure causes the finest grains to become wedged in the filter cloth. Instead of buying worn filter cloths again and again, it makes sense to clean them professionally on a regular basis. How often depends not only on the nature of the concrete slurry to be dewatered but also on how often the machine is used. Thorough rinsing removes build-up – for longer filter cloth life and overall longer use. To do this, you should remove the filter cloths: Special, highly concentrated cleaning agents such as acidic, odorless basic cleaners (without hydrochloric acid) dissolve out mineral sludge. To do this, cover the filter cloths in a container with undiluted cleaner for a reaction time of 24 to 48 hours. Alternatively, you can also spray on a high-pressure cleaner using a high-pressure gun.
It’s not that complicated to make concrete slurry fit the environmental regulations according to VVEA, is it? These state: Residual materials from drilling and concrete slurries must be disposed of properly, and their recyclable materials must be used as economically as possible. Provided you use efficient process technology that works around the clock with high operational reliability. Time to take environmental protection seriously: Professional filtration reduces environmental impact! Practical solutions take into account the needs of the concrete processing industry for professional disposal.
Products for the treatment of cement residual water, concrete water and concrete slurry provide the ecologically sensible answer, because they conserve natural resources. Filtered water can thus be reused at up to 100 percent – and the disposal of sediment in landfills can be avoided. Innovative technologies are leading the way – with greater efficiency, greater ease of use and water treatment to suit individual needs.
The result?
Better production processes – and a strengthened market position for the user!
Definition of effluent and wastewater