The Donato Gerardi plant draws its water from the nearby Rio de La Plata, and the raw water contains high and variable quantities of suspended solids. In the rainy season, when turbidity levels often rise to 500 NTU, these tanks would accumulate large volumes of sludge that could only be removed manually with hoses, which meant it was common for the sedimentation system to be overwhelmed.
The Zickert bottom sludge scraper uses a reciprocating framework of hydrodynamically shaped profiles mounted on the base of a sedimentation tank. When they move in one direction, these profiles catch the layer of highly concentrated sludge at the bottom of the tank and move it towards a disposal outlet. In the other direction, the shape of the profiles allows them to pass through the sludge with little disturbance.
This method of operation allows the scraper to remove waste with a high concentration of solids, which means less waste for the operator to handle and higher overall process efficiency. The solution’s drive system has only four moving parts, with power provided by a single hydraulic actuator. Energy consumption is low and there are no bearings, gears, chains or other vulnerable mechanical components.
The upgrade is part of a wider programme in which operator Aguas de Buenos Aires SA (ABSA) contracted Veolia to undertake a refurbishment of the facility in 2017.
Constructed in 1950, the treatment plant is said to provide drinking water to 800,000 people in the province.
ABSA has already used the technology at several other plants across Argentina, but the tanks at Donato Gerardi had been built with a v-shaped base profile that was not designed to accommodate a bottom-mounted scraper system.
To resolve the compatibility problem, Nordic Water and Veolia used lightweight concrete to fill the bottom profile of each tank, creating a flat surface ready for the new scrapers. To maintain plant operation during the upgrade, this process was completed one tank at a time, allowing the other 13 units to keep working.
In all, a total of 28 scrapers were supplied to the project, with two installed in each of the plant’s 42-meter by 11-meter tanks. They are claimed to have removed an average of 400 m3 of sludge per hour from the raw water and ensured that turbidity never exceeds 3 NTU at the decanters.
As part of the changes across the site, the new system has almost doubled the capacity of the plant, from 8’000 to 15’000 m3 of clean water per hour.