Verder and Naiad Offers Severn Trent the Solution

Naiad Aquatic and Verder pumps were not only able to provide a mechanical and electrical solution but also a detailed understanding of aquatic ecology and the chemicals involved in dosing. With vast experience in saturator system for phosphate removal and a good understanding of the processes involved in sewage treatment, a turnkey lime dosing package was designed, manufactured, installed and commissioned to meet the exact requirements of Severn Trent.

Mike Heap, Sales and Marketing Director of Verder explains what the project involved: “The processes involved in sewage treatment are complex but we were able to help Barston STW because we understand the processes involved and have a range of dosing systems which can provide the perfect solution.”

Dr Philip Kerrison explains: “The Urban Wastewater Treatment Directive imposes a legal obligation on the sewage treatment authorities to remove phosphate from sewage. The phosphate removal is needed to prevent the fertilisation of receiving watercourses and subsequent enhanced risks of eutrophication.

“The process of removing phosphate involves dosing ferric sulphate, an acidic. Lime is then added after the biological treatment phase (phosphate removal) to ensure that the sewage is subsequently able to nitrify successfully before being discharged from the works. The micro-organisms that carry out the nitrification process require pH to be between 7 and 8 and are inhibited by more acid conditions. Lime is dosed to balance the PH of the sewage”

Mike continues: “Barston STW was previously fitted with dosing system comprising of metering pumps and an upstream PH sampling point to allow the system to run automatically. However site operators were unable to use the system automatically because the pH sampling was not quick or accurate enough resulting in over and under dosing of lime. Since its installation the system has only been used in manual mode. As well as having to adjust the system daily operators had no end of problems such as blocked and failing metering pumps and a heavy build up of lime.

“Working with Naiad, Verder engineers installed a completely new system carrying out all the mechanical and electrical works involved. The Verder/Naiad Dose system allowed for fully automatic control with the installation of a new control system and pH monitoring, with special pH probes allowing for quicker response and very minimal maintenance periods.

“The new installation allows, better lime handling and mixing whilst ensuring the lime is dosed correctly and the set pH level is always maintained automatically without the need for any manual adjustment.”