Analysis and Design for Final Clarifiers in England

The Budds Farm Wastewater Treatment Works operated by Southern Water Services Ltd. treats waste water from the Portsmouth and Havant catchments. Prior to 2006, the Wastewater Treatment Works at Budds Farm had eight final clarifiers of 35m internal diameter. In order to meet the requirement of projected AMP4 flows, the existing settlement tanks were modified and two new 35m diameter clarifiers were built to operate alongside the existing eight tanks.

Geosyntec Scope of Services

Geosyntec was commissioned by 4D and Southern Water to undertake a program of computational modeling and hydraulic analysis for eight existing and two new clarifiers. The objective of this work was to calculate the performance of the clarifiers and to confirm the solids loading with and without internal modifications.

A verified and validated computational fluid dynamics (CFD) modeling technique was used to determine the internal hydrodynamic performance of the final settlements tanks [1]. The simulations were performed in two dimensional, axi-symmetric co-ordinates with models for sludge settling, mixture density and viscosity.

It was found that the existing tank with Ø7m diameter stilling well (as built) would only work up to 70% of flow to full treatment (FFT).

Notable Accomplishments

The Geosyntec designed McKinney baffle modification improved high solids loading and stirred sludge volume index (SSVI), enhancing the capacity and performance of the existing tanks by up to 26% in flow. The proposed new tank with Ø10m diameter stilling worked well up to 70% of FFT, but the McKinney baffle influent modification enhanced the capacity and performance of the new tank by up to 20% in flow. Geosyntec provided the capability to optimize the internal modifications prior to construction. In this case, the investigation revealed that the influent design had a significant impact on the clarifier performance. A modified influent, designed by Geosyntec, and incorporating a sloped McKinney baffle plus deflection ring gave >20% improvement in the site maximum forward flow. The recommended design of influent has been incorporated on all 10 tanks at Budds Farm.

Burt, D. and Ganeshalingam, J., Design and Optimisation of Final Clarifier Performance with CFD Modeling, Presented at the CIWEM / Aqua Enviro joint conference on Design and Operation of Activated Sludge Plants, Leeds, UK, 19th April 2005.

Project Overview

  • Location: England
  • Client: Southern Water Services Ltd.
  • Project Practice Areas: Water and Wastewater System Planning, Engineering, and Design, Waste Management Planning, Engineering, and Design
  • Type of Facility: Wastewater Treatment
  • Company: MMI Engineering

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