Recovery of 70 % of waste with new construction material recycling plant
Sodextra S.A., based along the Plateau de Saclay, 15 km south of Paris, operates a major construction waste recycling treatment facility, situated on an 8 ha site, that supports construction professionals to deposit and process waste and rubble in the Paris region. Established in 1975, the business has, for over 45 years, facilitated the diversion of significant tonnages of C, D & E waste from landfill, assisting in the recovery of a variety of high-value construction materials, including recycled sand and aggregate products, and returning them to the sector for use in major public works and infrastructure projects. Its primary market sectors are the recovery of deconstruction concrete, the recovery and treatment of industrial waste and the sale of ready-mixed concrete.
Maximised recovery of inert soil
Currently, the third generation family business recovers one million tonnes of material from waste per year – a significant volume that is set to increase further with the latest investment in CDE technology, which now also enables the recovery of inert soils.
Sacha Bottemanne, managing director of Sodextra S.A. and son of the owner Christian Bottemanne, sees the biggest challenge for the company in the treatment of the highly variable waste that is delivered to the plant. “We used to screen the delivered material and were able to recover about 20 % of the gravel content, which we processed in our crushing plant. The remaining 80 % was landfilled. We realised that in that 80 % there are still materials with high added value, which we can now recover with the CDE plant.”
Based on soil analyses around the Saclay Plateau, Marc Sopransi, CDE’s Business Development Manager for France, quickly recognised the challenge of processing the extremely heterogeneous material, which is heavily contaminated with clay. “The core of the problem was to reduce from a wide range of delivered raw sand qualities to be processed to a uniform, as close as possible and stable product of clean sand of grain size 0 – 4 mm.” The Sodextra team was invited to a CDE reference plant in Germany to see the technology in action. Convinced by the process and the quality of the products that came out the other end, the decision was made to go with CDE.
Samples of feed material to be processed by the plant were tested and analysed by CDE process engineers in its laboratory to determine the reclamation potential of the incoming waste stream and the quality of its output. The final solution incorporates a combination of CDE signature modular technologies, including the AggMaxTM modular logwasher setup for scrubbing and sizing and EvoWash™ sand classification and dewatering systems with integrated patented technologies, including CDE’s Infinity Screen and Counter Flow Classification Unit (CFCU) for density separation, which efficiently separates materials of differing specific gravity to maximise the quality and value of feed stock.
Regarding sand preparation, Marc Sopransi explains that the solution developed for Sodextra is unique: “It consists of a first cyclone pass, attrition cells, a second cyclone pass, an upflow classifier and a third cyclone pass with two main classifying points at 250 µm and 2 mm. Thus, this sand preparation offers a dynamic answer to a dynamic problem. Uniquely, the solution uses technologies usually used in the treatment of industrial sands, a first in Europe.”
Efficient water management
The solution designed for Sodextra not only allows for the recycling of C, D & E waste, but it also maximises water efficiency with CDE’s AquaCycle™. This self-sufficient, compact and user-friendly system can be used for both high and low tonnages in a wide range of market segments. CDE’s AquaCycle is an alternative to the costly direct injection of fresh water into the plant via wells. It is also a highly efficient water management solution that minimises water consumption by ensuring that up to 90 % of process water can be recycled for immediate recirculation.
After the feed material has been washed and classified, the wastewater is sent to the AquaCycle thickener. Here, a small amount of a polyelectrolyte flocculant is added via an automatic dosing system, causing the fines to settle to the bottom of the thickener tank. The clean water at the surface flows over the weir and is stored in the AquaStore tank before being reintroduced into the plant’s water circuit. The result is a highly efficient water treatment system where only 10 % of the water used needs to be replenished. The waste sludge is drained into a buffer tank where agitators operate continuously to ensure that the material does not settle to the bottom and solidify.
For Sodextra, the large amount of sludge involved in processing the feed material meant that a filter press was needed to eliminate the need for settling ponds. Integrating it into the plant made it possible to recover even more water from the process. By recovering filtrates and sending them to the company’s new AquaCycle system, Sodextra was able to achieve a water recycling rate of of approximately 96 %, significantly reducing the need for top-up water supplies.
The plant is processing material that was once destined for landfill, achieving a 70 % recovery rate and producing a range of products, including three different sands: a fine sand 0 – 250 µm, a 0 – 2 mm and a 0 – 4 mm; and three different aggregates: a 4 – 10 mm, a 10 – 20 mm and a + 20 mm aggregates, all ready for use in construction projects in the Paris region.
“Our CDE plant produces high-quality aggregates that we market under the names ‘eco-gravel’ or ‘eco-sand’. These are extremely high-quality materials that are very close to natural materials,” explains Sacha Bottemanne. A filter cake product from the integrated CDE Filter Press also has applications as a waterproofing layer or for pipe bedding and landfill capping. “Our customers are increasingly concerned about protecting the environment. With these new materials, we are contributing to the circular economy and sustainable development,” he continues.
Sodextra’s new plant is the result of over two years of on-site investigations, materials research in the laboratory and joint planning workshops, during which CDE worked with Sodextra’s team to develop a customised solution. The plant has now been in operation for a full year and has successfully met all of Sodextra’s objectives: “to further enhance inert soils, to supply aggregates in grain sizes suitable for concrete, and to realise a plant that requires a minimum of space.”