Nitrate removal plant provides flexible water quality solution

Yorkshire Water’s Tophill plant uses a nitrate solution from ACWA.
Yorkshire Water’s Tophill plant uses a nitrate solution from ACWA.

The 24-month design and build contract, core to an overall £7.5 million drinking water improvement scheme lead by Amey, has involved the development of a complete water treatment solution centred around ACWA’s leading Nitreat process, now in use across 25 sites in the UK.

Operational since July this year, the solution enables Yorkshire Water to combat rising nitrate levels from the river Hull, which had previously necessitated costly plant shut downs, providing a solution for improved water quality in East Yorkshire and at the same time removing stress from water supply network.

A flexible solution

The ACWA solution, an Ion Exchange nitrate removal plant, is designed to treat 22 million litres per day in the process reducing nitrates from a maximum of 64 mg per litre to 5 mg per litre.  The treated water is then blended with the remaining drinking water flow to ensure that 68 million litres of water per day are within the target nitrate concentration of 44 mg per litre or below.

The new plant is installed downstream of the plant’s existing rapid gravity filters (RGFs) in a side stream arrangement and consists of two 50% duty Ion Exchange skids to provide a robust and flexible solution able to cope with large variations in flow and nitrate levels, configured to provide the best possible treatment at Tophill Low.

Smallest plant footprint

ACWA’s Nitreat Ion Exchange solution was selected following an extensive evaluation process as the best ‘total expenditure’ solution and one that was already tried and tested at the UK’s largest nitrate removal plant (90 million litres per day) also operated by Yorkshire Water at the Keldgate WTW. The solution also offered the added benefit of the smallest plant footprint. This is important given the existing site constraints and the proximity of an adjoining SSSI, together with the environmental advantages of the lowest waste water flow of all the technologies considered.

Peter Brewer, ACWA Services’ UK General Manager said: “Our focus throughout has been to provide a robust and future proof water quality solution, collaborating with Amey and other contractors to overcome a number of technical challenges to satisfy the demands of both Yorkshire Water and the Environment Agency. We are delighted to be involved with this, our second Nitrate removal project for Yorkshire Water, the largest of their type in the UK.”

“The Nitreat continuous counter current Ion Exchange system is a landmark improvement on conventional ‘batch’ treatment systems, enabling exhausted resin to be continuously regenerated, rinsed and returned to work, with all phases of the cycle occurring simultaneously.”

Constructing the solution off-line made it possible to deal with many of the detailed design elements including process, mechanical, electrical and instrumentation works, and to minimise the impact on the nature reserve. It also meant that fewer shut downs and interruptions to the plant were required particularly those required when connecting to the existing RGF outlet pipework.