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CP488  Compliance with phosphorus and metal consent requirements Wastewater Treatment
Project Appreciation and Objectives

UK Water Companies are facing more stringent metal consents for phosphate removal at wastewater treatment works (WwTW) and rising chemical costs. Chemical use needs to be reduced to achieve more sustainable wastewater management (Cave Review 2009).

Metal (ferric or aluminium) salts may be unable to precipitate phosphate effectively causing high soluble phosphates / high metal residuals that result in effluent compliance issues at WwTWs. This effect may be linked to seasonal variations in wastewater quality, lack of alkalinity, hydrolysis of organic phosphate to orthophosphate, and organic trade effluents which promote iron complexation. Sites may require tertiary sand filtration to control residual metals in effluent.

This project aims to identify means for improving the effectiveness of metal dosing for both removal of phosphate and control of residual metals, on a site-specific basis, through a greater understanding of the physicochemical processes and the factors which influence precipitation.

Business Benefits to Clients

  • Enable a clear and quantified understanding of optimal chemical dosing to achieve robust compliance with discharge permits.
  • Identify minimum chemical use leading to OPEX savings and more sustainable P removal.
  • Establish a common quality control methodology for chemical use at WwTWs to assist with planning of capital expenditure and ensure effective operation of chemical dosing plant.
  • Identify opportunities for achieving compliance with discharge permits without the need for capital expenditure on tertiary treatment.

Work Programme

  1. Establish theoretical solution equilibrium relationships to predict the behaviour of cations in respect of phosphorus elimination reactions and residual metal concentrations using existing WRc water quality models.
  2. Undertake jar testing to understand the kinetics of the initial dispersion of metal salt and calibrate the theoretical solution equilibrium model.
  3. Complete a site evaluation for each participant to validate the model.
  4. Identify plant improvements required to optimise chemical P removal.

Project Output and Implementation

Spreadsheet tool to assess phosphate solution equilibria, benchmark chemical usage, and assist compliance with phosphorus removal requirements. The tool will be supported by chemical dose control guidelines to enhance asset standards and operational practice.

Related WRc Work

  • CP362b Sustainable options for phosphorus and nitrogen removal, 2011.
  • Iron use in wastewater treatment, Utility Client, 2008.
  • P8103 Water quality and corrosion model, 1999.
WRc's Portfolio Programme
Summary of the £1.5 million per annum research programme

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