Proceedings

Tertiary DAF combined with i-DOSE for maximum removal of phosphorus from municipal wastewater effluent

Menkveld, H.W.H.1, Broeders, E.1, Mansell, L.2, Fox, E.2, Tolman, M.3

1Nijhuis Industries,  The Netherlands,
2United Utilities PLC, United Kingdom,
3Nijhuis H2OK Ltd, United Kingdom

(free)

Abstract

United Utilities undertook a phosphorus removal trial as part of UKWIR’s Chemical Investigations Programme Phase 2 (CIP2) Innovation Fund trials using Tertiary-Dissolved Air Flotation (T-DAF) technology from Nijhuis Industries. The T-DAF with intelligent real-time control ‘i-DOSE phosphorus’ was constructed for modular installation and trialled for 6 months under the supervision of United Utilities at Macclesfield WwTW located near Manchester in the United Kingdom. Phosphorus removal is achieved by chemical precipitation and flocculation of phosphates prior to dissolved air flotation. The system utilised Nijhuis Industries’ intelligent chemical dosing system (i-DOSE phosphorus) which controls the system in real-time based upon the incoming phosphorus load to ensure efficient phosphorus removal after the clarifiers is achieved for the lowest possible OPEX cost.

The T-DAF in combination with the ‘i-DOSE phosphorus’ is an efficient and robust technology for effluent polishing to remove phosphorus and has the potential to reach an average effluent concentration for total phosphorus (TP) of 0.4 mg/l without exceeding the discharge limits for iron. Also BOD, COD and TSS are greatly removed in the process. The produced sludge is expected to have an average DS% of 4%, which would save sludge processing costs downstream.

The presentation will provide an overview of the process, key design features, treated effluent quality results and operational observations.

Keywords

Tertiary Dissolved Air Flotation, Phosphorus Removal, i-DOSE, UKWIR, CIP2, United Utilities

Introduction

The Chemical Investigations Programme Phase 2 (CIP2) is co-ordinated by UKWIR in response to the challenges of the environmental quality standards (EQS) set out in the Water Framework Directive. In order to address the specific challenge of meeting the EQS for phosphorus, the UK Water Industry (under the co-ordination of UKWIR and in collaboration with the Environment Agency) initiated an evaluation of the likelihood of the effluents from innovative technologies to contribute to a reduction in phosphorus concentrations in wastewaters.

Phosphorus is currently the limiting factor preventing good chemical status under the Water Framework Directive for UK inland surface waters. Typically, aerobic wastewater treatment does not substantially reduce phosphorus concentrations and WwTW’s can become a point source discharge unless additional treatment is applied. Diffuse sources are often also present, although these are often less controlled (for example through fertiliser runoff).

The removal of phosphorus from point source discharges into the water catchment can create real ecological benefits within waterways. This has driven new discharge consents and as a result technologies and methods have been developed to reduce effluent TP concentrations to sub 0.5 mg/l levels.

In 2009 preliminary pilot testing with a T-DAF was conducted for United Utilities at Grasmere WwTW. The results showed an average concentration for total phosphorus of 0.25 mg/l and an average sludge concentration of 4.1% DS can be reached using a T-DAF [Kluit, A, ter Horst, C, Crewdson, C, Crewdson, J., pilot unit test report WwTW Grasmere]. Since 2009 many innovations have taken place to improve the performance of the T-DAF as a separation technology and the first proof of principle for the Nijhuis Industries’ intelligent chemical dosing system ‘i-DOSE phosphorus’ was conducted on raw influent of WwTW Eindhoven the Netherlands in 2014 [STOWA 2014]. Combined with intelligent real-time control ‘i-DOSE phosphorus’ a new T-DAF pilot plant was constructed for modular installation and trialled for 6 months under the supervision of United Utilities at the Macclesfield WwTW located near Manchester in the United Kingdom.

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