Website: www.waternet.nl and www.agv.nl
Address: Korte Ouderkerkerdijk 7, 1096 AC Amsterdam, The Netherlands
Contact: Wim van Bakel (Tel: +31 (0) 6 52480032, Wim.van.bakel(at)waternet.nl)
Waternet treats waste water and produce drinking water. We maintain water levels and keep surface water clean. We do this on behalf of the Regional Public Water Authority of Amstel, Gooi and Vecht and the City of Amsterdam.
At Waternet about 1.800 people are employed. We operate 12 sewage plants in the triangle of the cities of Amsterdam, Utrecht and Amstelveen. Furthermore we operate about 500 pump stations and 4.000 km of sewage drain in the city of Amsterdam.
Sewage water contains high levels of H2S gas. On the sewage plants, after mechanical cleaning the sewage water settles in concrete vessels, called primary settlement tanks. Here large amounts of H2S are emitted so at regular intervals (roughly every 5 years) the vessels need to be inspected.
In the biological section of the cleaning process sludge is produced. A secondary stream of this sludge is stored in one or more digestion tanks to produce biogas. These steel digestion tanks need to be inspected as well.
Inspections to the primary settlement tanks are done to get a clear picture of the current state of the concrete: Are there any cracks? Is the concrete damaged? Etc.
Furthermore answers are sought what causes the damage. Think of lesser quality of concrete or more aggressive gases or mechanical cause.
In the settlement tanks steal agitators are used. In general large bridges with one or two arms, fitted with scrapers at the bottom of the tanks. These constructions are coated to withstand the aggressive environment and need to be inspected as well. What we are looking for is the state of the coating: is it thick enough? Where is it damaged?
And the mechanical constructions need to be examined as well: Is there any corrosion? Are the welded joints still in good shape? Etc.
A typical settlement tank is several meters in diameter and can be up to 8 meters tall. Depending on the (hydraulic) size of the sewage plant up to 6 can be found. A picture of a cleaned settlement tank, that is also in good shape:
The digestion tanks have no mechanical internal construction. They are prone to corrosion.
In general it can be said that regular inspections are needed to be aware of the state of the equipment: Is it reliable? What are the defects? What are the causes?
For now an inspection means shutting down a treatment stream. Cleaning walls, floors and equipment thoroughly by removing all sludge and other contamination.
After this the enclosed room needs to be ventilated before an inspector can start.
This means shutting down a treatment stream. Cleaning the walls and floors thoroughly, ventilates and then human inspection can start.
If a robotic solution is able to do the kind of inspection without the ventilating and cleaning it will mean a considerable reduction in shut down time and investment.
A civil inspection will cost between 50.000 and over 100.000 euro per vessel, depending on volume and measurements taken to ensure the primary process, i.e. by passes.
If cleaning and ventilation can be omitted, the shutdown time will be shortened by about 1 or 2 days per vessel. Savings in terms of money can be up to 20%.
This cost reduction will eventually lead to a lower tax rating. And because of the mechanical inspection to a better quality of the inspection.