Operation Tagus 2018
In Vila Velha de Ródão, a layer of sediments, with a high organic load, has been signposted, which covers the bottom on both sides of the Portas de Ródão, in the heart of the Natura 2000 site and the UNESCO natural park.
Dredging began to remove the sludge and Geotube treatment and dewatering technology was the option chosen. Although applied in many other treatment projects at a national level, within the scope of environmental remediation, this is a pioneering project in the use of Geotube technology in Portugal.
The sediments were collected by a suction dredger that was operated by a Portuguese team of experienced divers. This is the most accurate way to ensure that only the sediment is removed and that the sand and rock remain in-situ. The sludge was pumped along 1.2 km of pipe to a platform where as much water as possible was separated from the contaminated sediments and returned to the water environment.
This process took place on a temporary platform built for this purpose with specific geosynthetic materials supplied by TenCate Geosynthetics, a world leader in this field.
The essential function of the platform is dewatering that takes place in giant permeable bags, capable of receiving large amounts of sludge. A coagulant is added to the dredged material consisting of an environmentally safe polymer, previously prepared in a dedicated unit and built for this purpose. This unit acts in such a way as to react dynamically in relation to both the concentration and the amount of polymer added, depending on the flow rate of the dredge and its suspended solids content. This unit was built and operated by Ambitrevo, Lda. and Geosin International, Lda, and reacts in real time to the oscillations verified. The coagulant will thus aggregate the suspended solids into larger particles, a phenomenon that will allow them to be filtered. The mixture of dredged and coagulant material is then sent to a flocculator, which allows the residence time of said mixture to be increased before being sent to the geotube.
As soon as the sludge enters the “bags”, the special textile configuration of the filter traps the particles, while the clean water is drained and returned to the river.
In Portugal, this type of operation is pioneering, but technology has led the options worldwide. Awareness of the need for a clean environment is still growing in Europe. TenCate Geotube® dewatering technology has been used in various industries and remediation projects around the world.
