Portrack STW, feeder tank

When Northumbrian Water needed to carry out essential maintenance to three pumps in a sewage treatment works (STW), Selwood were called in to assist. The feeder tanks required draining so that a survey could be carried out. This would allow for the teams to ensure Selwood’s replacement pumps were correctly positioned for the duration of the works. 

Incoming flows at the STW average at 1400 l/s, so the tank drainage and survey would need to take place over night when the incoming flows are at their lowest. Selwood’s solutions team were tasked with draining down the feeder tank within 30 minutes, then carrying out a 
laser scan within one further hour.

The key challenge of the project was ensuring that the tank survey could be carried out within the extremely limited time frame. The three surrounding pump stations which feed the STW had to function as storage tanks, backing up the system to allow for the Portrack site to shut down for 90 minutes. Accuracy of the drainage and tank survey was therefore critical in ensuring the pump stations would not become overwhelmed.

To ensure success of the survey, Selwood called in Academy Geomatics to carry out laser scanning of the surrounding area and The tank. This eliminated the need for anyone to physically enter inside the tank, increasing site safety and speed of the survey process. 

A further challenge arose as the replacement pumps would need to be capable of draining the tank at 230l/s with no room for error, so choosing the most efficient pumps for the works was critical in ensuring success of the project

In order to ensure success of the tank scan and survey, Selwood’s solutions team set up the system a week prior. This ensured that the works could be carried out in dry conditions and reduced the length of time that the station needed to be shut down.

Two Flygt drainer pumps were placed in the rear of the tank to draw down majority of the flows. An additional S150 solids handling pump was chosen to support the process to ensure that the station pumps would not air lock. 

The Flygt pumps were assembled in a Duty/Assist format and were ran off a generator as there was no available power on site. All flows were overpumped via three 
individual suction lines which merged into one common discharge line and stored in an unused storm tank