Upgrade of Scottish Water’s Wastewater Treatment Plant (WWTP) mixing operation in St Andrews.

Following an intricate operation using divers, ESD (the joint venture involving Galliford Try, MWH Treatment and Black & Veatch) has completed the successful upgrade of its mixing operation at Scottish Water’s Wastewater Treatment Plant (WWTP) in St Andrews, Scotland.

In 6m-deep zero-visibility wastewater, three divers (and a dive manager) ensured that there was no interruption to the crucial aeration process in the oxidation ditches, which since 2002 has been served by three very low rpm Landia mixers.

Situated close to where the sport of golf was first played in the 15th century, just a few miles from the oldest golf course in the world, the WWTP, which has UV filters for its final effluent, is in an extremely sensitive area that welcomes visitors from all over world. At just 34 rpm, the 4kW Landia mixers very gently mix sludge so as not to cause any process-damaging floc shear.

“The Landia mixers have always worked well”, said St Andrews WWTP Site Manager, Alan Mearns. “This is the type of reliable equipment we want as ESD delivers improvements to Scotland’s water and wastewater infrastructure”.

He added: “Working purely by touch in such a challenging environment wasn’t easy at all for the divers, but over the 3-day installation that included new guide rails, they did a great job in ensuring that we could still maintain sufficient flow for our process”.

In addition to the three adjustable-pitch submersible Landia units in the main oxidation ditch, there is also one Landia mixer in the Sludge Holding tank for SAS (Surplus Activated Sludge) and one in the anoxic Inlet Tank.

Apart from a 10-minute stop every 4 hours, the three Landia mixers in the oxidation ditch run 24/7, sustaining a required gentle flow of just 0.3 metres per second. Landia’s in-house team will also service the mixers every 6 months.