Overview

Thames Water approached 2H Water Technologies for help in refurbishing a trickling filter installation at its STW in Earlswood, Surrey.

The primary works comprised six trickling filters, four of which used structured plastic media, whilst the other two were filled with mineral media. An additional six secondary trickling filters used both mineral and blast furnace slag media.

Thames Water wanted to improve the balance of BOD and ammonia treatment across the primary and secondary stages. After considering several options, Thames Water believed increasing primary treatment capacity would be the most effective approach.

Thames Water could see the difference in quality between the different media – structured plastic and mineral media – used in the primary trickling filters. They decided the best way to improve overall treatment quality was to convert the underperforming trickling filters to structured plastic media. There was an added benefit in upgrading rather than replacing the trickling filters; by re-using the existing asset, Thames Water avoided the inconvenience and expense which would inevitably result from onsite civil construction.

Thames Water appointed Ward & Burke Construction (W&B) as the main contractor.

Collaborative solution

Because W&B wanted to handle the work involved in building the support and installing the media, 2H was left with, what was believed to be at the time, a limited role – i.e. assembling and supplying the BIOdek structured plastic media.

2H could see W&B had committed a lot of their people to the project and were justified in wanting to get the most from a hard-working, highly professional team of people, each of whom took an obvious pride in every aspect of their work.

After discussions with W&B, a fully collaborative approach was agreed; that, after the BIOdek media had been delivered to the site, W&B would provide all the labour while 2H supervised and inspected progress.

W&B carried out the civil works needed to refurbish the walls on the two trickling filters and laid the media support tiles to the base. 2H’s trickling filter design experts confirmed the layout and installation of the support tiles would support the BIOdek media at the same time as allowing discharge of the effluent and sufficient air flow to provide oxygen for the process.

2H supplied 1675m3 of BIOdek structured plastic media for each filter (3350m3 total). W&B handled the installation whilst 2H supervised and inspected progress.

The initial filter installation was signed off in July 2020. At that point W&B refitted the distributor and set the trickling filter to work. Seeding on the first filter started on 2nd July and went so well that, within 3 weeks, W&B had enough confidence in the treatment process to take the second filter offline, ready to remove the mineral media and commence the new installation in early August.

While seeding was underway, 2H had delivered the second batch of BIOdek. 2H carried on inspecting installation of the second trickling filter until it was signed off in August 2020.

Collaboration in action

The two teams quickly established a productive, enjoyable and, above all, collaborative working relationship. The 2H experts who checked the installation at every stage were impressed by the attitude of their counterparts from W&B.