Thames Water Use Watson-Marlow Pumps for Ferric Dosing Flocculating Application

Leading the way with new sewage treatment methods, Thames Water South East Provinces Waste Water site in Cranleigh is using ferric chloride as a flocculating agent in order to meet the AMP 3 biochemical oxygen demand parameter. For a totally reliable pump that could deal with this highly corrosive chemical, they turned to Watson-Marlow Bredel and their new 520UN/R2 peristaltic pump.

Moving into the AMP 4 period means tighter consent requirements for water and waste treatment plants, which involves meeting three parameters, including the reduction of biochemical oxygen demand (BOD). In order to do this, Thames Water opted for chemical dosing using ferric chloride.

The 520UN/R2 from Watson-Marlow was selected because of its reliability, critical for meeting the requirements of AMP 3 & 4. Peter Packham, Process Coordinator for Thames Water South East Provinces Waste Water comments: “The ability to handle this aggressive substance, while being 100 per cent reliable is paramount.”

After screening and grit removal, ferric chloride is dosed into the sewage on its journey towards the primary settlement tank. Here the ferric hydrolyses into electropositive ferric hydroxide, attracting negatively charged colloidal substances and thereby forming flocs that clump together and precipitate out.

Through this mechanism, ferric chloride reduces BOD as well as removing heavy metals, larvae eggs, pathogenic content, suspended solids and colloidal content. After this process, the sewerage continues through to the primary settlement tanks and onto the secondary and tertiary treatment stages.

With the impending introduction of further phosphorus consents, Thames Water has big plans to expand their use of ferric chloride alternative chemical pumps. Using ferric chloride for primary waste treatment has proved to be very successful at this site. It’s ability to be an effective coagulant and remove odour-inducing sulphides more efficiently and cost effectively than alum, explains the growing movement towards this method.