WINEP Case Study: Severn Trent Water Ex.1

Nitrate removal trials at Blymhill and Barston Sewage Treatment Works

These trials aim to establish a new technically achievable treatment limit for nitrate removal. Both trials will use treatment processes that don’t require any supplemental chemical application to deliver high levels of nitrate removal.

Barston trial: this involves setting up a new Nereda unit at Barston STW to work alongside the existing units. A Nereda unit is a type of activated sludge wastewater treatment system that uses a special granular purifying biomass to clean the water. The system is designed to biologically remove pollutants like nitrogen and phosphorus from the water in a sustainable way.

Barston STW discharges upstream of a raw water potable abstraction where rising nitrate levels within the watercourse are becoming an issue. Whilst the existing treatment process will meet the UWWTD nitrate condition that is being applied to the discharge permit, additional nitrate removal delivered through this trial will help to safeguard raw water quality.

Blymhill STW will be a full-scale trial of an alternating feed Oxibox (a design variation on conventional oxidation ditches) to achieve full nitrification and denitrification within the same process unit. Nitrification converts ammonia into nitrates so helping maintain healthy soils and supporting nutrient cycling. Denitrification helps to remove excess nitrogen from soil and water, preventing pollution.

Blymhill STW was chosen as a trial site as it is located a few kilometres upstream of Aqualate Mere, a SSSI and Ramsar, and SAC site for which a nitrate environmental quality standard has already been set. Evidence from other oxidation sites within Severn Trent has shown that low levels of nitrate can be achieved with this process. The trial is therefore expected to deliver wider environmental benefits at Blymhill.

Schematic of Blymhill STW. The four circular tanks are the oxibox treatment stream – there are four units to enable different configurations to be trialled. (See image to the right)

Other Examples:

Nitrogen treatment trials are included in the WINEP for Anglian Water, Northumbrian Water, South West Water, Southern Water, Thames Water, United Utilities, Wessex Water, and Yorkshire Water. These trials should help create an improved industry-wide understanding of what innovative solutions are feasible for future improvements to nitrate removal from sewage.

(Banner image: The River Severn(External link) in Shrewsbury(External link), viewed from Shrewsbury Castle(External link) looking downstream. Photo by Chris Bayley(External link).)