Sludge Buffer Tank Internal Inspection using Elios 2


AREA: Scotland

SERVICES: Drone visual examination

CLIENT: Scottish Water Horizons

Background Information:

Interior examinations in GPS-denied environments have been problematic as “conventional” drones must be flown in manual mode and due to their size, are difficult to control and have only limited capability. To that end, GeoAccess invested in leading-edge technology in 2019 and acquired the Flyability Elios 2 confined-space inspection drone.

With the ability to fly in GPS-denied environments, the drone is enclosed in a collision-resistant cage and can be used safely in tight spaces where obstacles are present. A dual camera capability in both video and infra-red allows a broad range of examinations to be conducted. Still images captured from the video footage can be used to construct photogrammetry models and low-density point-clouds, enabling engineers to view assets in 3D and take relative measurements of the structure and defects.

Our examiners have at least 5 years of experience conducting examinations of a broad range of structures including airshafts, bridges, culverts, retaining walls and tunnels; they are also Dynamic Risk Assessment and First Aid trained. GeoAccess pilots have carried out numerous examinations of a range of structures with the Elios 2.

 Elios 2

GeoAccess Services

Our expertise in carrying out visual inspections in confined spaces using the Elios 2 was brought to the attention of Scottish Water Horizons (SWH). We were asked to submit a proposal for the internal inspection of an 18,000 litre sludge buffer tank at their Deerdykes facility near Cumbernauld in Scotland. The facility is used to process food waste by anaerobic digestion and the by-product methane gas is used to power the facility. The tank had not been inspected since its installation and had been in continuous use for many years.

The usual method of inspection is to drain and clean the tank. Once this stage has been completed a mobile scaffold tower is erected inside the tank for the inspector to use. This is a lengthy and expensive process as the components for the tower have to be fed through an access hatch which is c.700mm in diameter. The tower is then moved around the tank allowing the inspector to examine the interior.

buffer tank exterior

However, this can be problematic as there have be incidences where the tower has moved and collided with the tank interior, damaging the glass panels that line the tank walls. This has resulted in expensive repairs and a major reduction in the facility’s capacity to process the waste.

The inspection also takes several days and the down-time impacts both operations and incurs financial loss. There are also the risks involved to personnel when working at height. In order to minimise disruption to the running of the facility SWH decided to trial a drone inspection to determine the feasibility and effectiveness for future tank inspections.

Using the Elios 2 we were able to carry out a visual examination in several hours, with a particular emphasis on difficult access areas such as the underside and recessed elements of the structure. This represents a significant reduction in time, resources and costs when compared to traditional methods, which would have taken several days at the very least. A total of nine flights were completed, with each flight focussing on a particular area and elements of the structure, and 70 minutes of 4K video footage was obtained.

Tank visual examination
This represents a significant reduction in time, resources and costs when compared to traditional methods, which would have taken several days, during which time the facility would be operating at reduced capacity with an increasing backlog of food waste to be processed.


Defects Tank Ring

Upon completion of the site works the video footage was uploaded to Flyability Inspector, a software application that is used to view and analyse the video. Points of interest, including defects and areas of concern, were then created by selecting individual frames from the video by the tank inspector. These frames were then annotated, with approximate measurements of features taken from the image where appropriate.

A number of defects were identified, including degradation of the sealant between glass panels and heavy corrosion of the tank ring on the roof. Using the Inspector software results in less time being spent on analysis and reporting. The normal approach would have involved the tank inspector analysing hundreds of images captured by camera. As a result delivery of the report to SWH was achieved in several days, rather than in weeks.

Successful delivery of the project, by using a drone for the examination of the tank and specialist software for analysis and reporting, resulted in a much reduced timescale, the resumption of operations earlier, cost savings for the client and importantly, reduction in risk to the personnel carrying out the work.


The Old Dairy
Pessall Lane
B79 9JL

T: 0333 772 2315



Company Reg No 09229168
Registered in England & Wales
VAT No 230959695