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United UIilities: Treatment Process Mathematical Modelling


United Utilities


North West England

Key Services

Mathematical Modelling of Treatment Operating Costs

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Project Overview

Sweco was commissioned to assist with United Utilities’ Unit Cost of Treatment project. The objective of the project was to calculate the theoretical and actual operational expenditure relating to energy and chemical use so as to inform the budgets for their Business Plan.


The Challenge

Sweco created a modular mathematical modelling tool using MATLAB/Simulink to enable United Utilities operational staff to select individual process components of a site, connect them, and populate them with site-specific parameters such as tank dimensions, and control settings, etc.

We created process models for both clean water and wastewater treatment works to calculate a theoretical cost of treatment. These costs were then compared with the actual costs. The model was designed to link with site telemetry to model the asset and cost performance of the site.

Our Approach

For the Phase 1 study, Sweco data analysts created dynamic process models using MATLAB/Simulink of the highest cost components at four sites. We utilised static equations developed in partnership with United Utilities and an independent contractor. The innovative models included a wide range of available telemetry and lab results to set a moving target. This provided a more accurate cost estimate than United Utilities’ original internal calculations, which could not account for varying influent conditions or the impact of one process unit on another downstream process unit. TOTEX costs were estimated to calculate and assess the favourability of proposed interventions at the sites modelled.

The success of this work led to Phase 2, where we modelled several additional sites and developed a software tool using MATLAB/Simulink which would allow United Utilities to build models of other sites themselves.


led to Phase 2 as UU asked us to model several additional sites and to develop a generic software tool using MATLAB/Simulink which would allow the UU to build models of other sites themselves.

Sweco designed and implemented the underlying architecture for the software tool, checked and validated the data inputs, designed and built the site-specific process models, verified the results and returned the completed site models to United Utilities. Our collaborative approach with the client and other stakeholders, provided the ability for United Utilities to continue to use this tool to drive further operational savings.

The Results and Benefit to the Client

The models developed by Sweco were used to identify opportunities to reduce chemical dose rates and energy use, while continuing to meet consent levels. A total of £500k in annual savings was identified.


Examples of the savings identified included:

  • Refurbishing and optimising the chemical dosing in the coagulation stages at Clean Water Site A would save in excess of £140k per year
  • Refurbishment of the inter-stage pumps at Clean Water Site B would save £30k per year while refurbishing just the worst performing pump would save £10k annually
  • A delay in repairing a broken ammonia sensor at Wastewater Site C was found to have incurred costs of £14k over a 70 day period
  • Improved control of the blowers on Wastewater Site D’s BAFF plant would save at least £3k annually

In addition to these savings, United Utilities received a modelling library which will allow them to build their own models, monitor the performance of their sites using telemetry data, and identify additional opportunities for TOTEX savings from interventions on energy and chemical use.

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