Crude Sewage rapid chemical mixing for phosphorus removal – can you help?

1 April 2021

Challenge update Autumn 2021: Having reviewed the submissions and requested further information where required, we are now exploring the possibility of trialling some of the solutions.  We’ll provide further updates in due course.

We are required to remove phosphorus (P) from the effluent discharges of many of our water recycling centres (WRCs). For AMP7 (2020-2025) there are a number of new or tightened discharge permits for us to meet, as identified in the Water Industry National Environment Programme (WINEP).

Our conventional approach for P removal is to employ coagulant dosing, often at the front-end of the works into crude sewage. Rapid mixing of the coagulant is key to successful P removal. We are looking for alternative mixing technologies for cases where our design standard mixing options are not suitable.


In AMP7 we have 53 sites where we will be introducing new coagulant chemical dosing into crude sewage for phosphorus removal. The sites have an FFT (flow to full treatment) from 400 m3/d to 123,000 m3/d, and population equivalents from 444 PE to 167,000 PE.

Due to the complexities of some WRCs, our conventional, design standard mixing options (detailed below) are not always suitable, or can be disproportionally expensive, or carry higher risk. In addition to the dosing point infrastructure, significant upgrades are often required to the existing site process to ensure good performance of the mixing technology, including improved screening or grit removal, or new chambers. Separate slide packs give details of example sites and the constraints for mixing faced at each – see example scenarios onetwothree and four, with the dataset information giving some background information on the examples as a whole.

Therefore, we want to explore if there are any alternatives that may be more cost effective and robust than the existing design standard technologies used.

Existing design standard mixing options:

  1. Dosing shall be into highly turbulent areas to ensure very rapid mixing of the chemical and at the last point of high turbulence prior to the primary tanks or treatment plant. A suitable level of turbulence will be created by a free drop of the flow over a 150mm high weir.
  2. If no area of high turbulence can be located, then a non-ragging channel mixer shall be considered.
  3. If there is not sufficient depth for a channel mixer then a mechanical mixer will be considered to be installed in a suitable chamber, with a valved bypass arrangement.
  4. Where the dosing is into a rising main there shall be adequate means of mixing immediately downstream of the dosing point using a static mixer. The dosing point shall be made via a withdrawable dosing lance with isolation valves to permit lance removal while the process main is in operation and under pressure. The mixer shall be designed to achieve a CoV (coefficient of variation) of 0.05 at the mixer outlet under all flow conditions.
  5. The crude sewage coagulant dosing point shall be prior to the primary tanks (after any storm separation) or into the ASP (activated sludge process) if the process does not have primary tanks.

What are we looking for?

We are looking for alternative crude sewage chemical mixing technologies.

The suggested technologies must be:

  • Suitable for overcoming the constraints at the example sites detailed in the example scenario slide packs and dataset information at the links above.
  • Available to install in AMP7 – i.e. are available on the market without further research/development required.
  • At a lower whole life cost than installing a pumping station to lift all the flows in order to give a 150 mm minimum free drop (costs will be assessed on both an upfront capital cost, and a 20 year ‘whole life’ cost).
  • Small in terms of carbon footprint.

How to get involved

We are very happy to answer any queries you may have in order to consider responding. Please send queries to by Friday 16 April (11.59pm) – we will respond to them all here (unless there are questions that wouldn’t be appropriate to share answers to that may relate to specific IP of an organisation).

We then ask for interested parties to submit their proposals by Friday 14 May (11.59pm) – please email them to

Submissions should include:

  • Details on the mixing technology proposed
    • Type of technology
    • Footprint required
      • typical proposal drawing
    • Process or operational specific requirements – i.e:
      • minimum screening requirements
      • grit removal requirements
      • flow rates
      • energy requirements
      • washwater requirements
      • chamber/channel/pipe requirements
    • Provide any details of headloss
    • Any scientific evidence verifying the ability to achieve a CoV of 0.05 at the mixer outlet under all flow conditions, or complete mixing within 5 seconds of chemical dose application
  • Case studies of any UK/worldwide installations
  • Your expertise in this area
  • Operating and maintenance regime and costs
  • Indicative costs
    • Capital costs
    • Ongoing operational and maintenance costs

We look forward to hearing from you!

We will review all the submissions and see if there are any we would like to discuss and explore further, and feed back to companies accordingly. We’ll aim to get back to you by early July but will keep you informed if further time is needed. We also intend to feed back more generally on the challenge via our blog page.

If you want to hear about other Marketplace challenges over a range of areas when they are released you can sign up to our mailing list.

Important points

– Taking part in this Marketplace challenge does not guarantee a contract at the end for provision of P removal technologies. A tender may be required, and Wessex Water reserves the right to stop the project at any time.