Wessex Water has successfully used the Hydro-Brake® Drop self-activating conveyance and flow control system to protect critical sewer infrastructure by counteracting hydrogen sulfide and drastically reducing related sulfuric acid corrosion and odour issues.

Wessex Water is a regional water supply and sewage treatment company that operates in the south west of England, UK. It supplies around 1.3 million people with around 285 million litres of water every day.

UK regulations require water companies to maintain their sewer networks to a suitable standard. 

Wessex Water engineers had identified a drop shaft in the sewer system serving Bournemouth that had become highly corroded, compromising the integrity of the concrete structure. The shaft, which makes up part of the Coastal Interceptor Sewer (CIS) conveys combined flows from a local sewer and a rising main down to a trunk sewer that runs to the Holdenhurst Treatment Works. Corrosion had probably begun when the system was installed with the rising main.

The tunnel, at 8km in length serves around 34,500 properties, and Wessex Water needed to replace the existing structure before catastrophic damage occurred.

Problem

Sewage can contain high levels of hydrogen sulfide, which is oxidised to sulfuric acid in the presence of water. Sulfuric acid is highly corrosive - this can damage the integrity of sewage structures, potentially leading to catastrophic collapse.

Not only did Wessex Water engineers need to replace the damaged structure, but they needed to replace it with an alternative system that would prevent or reduce the formation or effects of sulphuric acid.

Solution

Nathan Hand, Critical Sewers Engineer at Wessex Water, initiated the project after reading about the Hydro-Brake® Drop on the Hydro International website.

Hydro International’s technical team worked with Nathan to understand his requirements, providing a capability demonstration and supplying test data and case studies to provide evidence for the system’s ability to manage quantity and quality of water - and to mitigate the formation of the sulphuric acid and its corrosive effects. They then designed the system to fit the specific requirements at the site in Bournemouth. 

To increase the robustness of the design Wessex Water also adopted a new, more corrosion-resistant mixture of concrete, containing calcium aluminate, for use in the drop shaft chamber.

Outcome

The Hydro-Brake® Drop system was successfully installed in the new chamber on schedule in May 2018. The project refurbishes 200m of mains sewer network to a safe structural standard, and the network now incorporates technology that mitigates the effects of future hydrogen sulfide corrosion - protecting critical sewer infrastructure and reducing future maintenance and replacement requirements.

“This project is a great example of proactive water network management,” said Phil Collins, Sales Director for Hydro International.

“Wessex Water identified the issue early on and took action before the system failed. They engaged with us at an early stage and throughout the project, so we were able to help them develop the best possible solution. As a result, not only have they resolved the existing issue, but they have improved the network to make it more robust and better protected than it was before.”

All the measures taken should continue to offer mitigation of chemical dosing of the rising mains with sodium nitrate, a more cost-effective renovation and operational intervention.

Proven to mitigate hydrogen sulfide

The Hydro International technical team conducted extensive testing of the Hydro-Brake® Drop at Scottish Water Horizon's specialist Bo’ness Development Centre in Scotland to prove its ability to manage the effects of hydrogen sulfide.

Over 70 hours of testing showed that the system increased dissolved oxygen concentration in flows by up to 400% - counteracting hydrogen sulfide and drastically reducing related sulfuric acid corrosion and odour issues.

Click here to read the report: Hydro-Brake® Drop testing at Bo’ness

Watch the video below to see the system in action