Cardiff WWTW aeration optimisation through scientific control

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Aeration optimisation of a 16 basin SBR plant running in ICEAS (Intermittent Cycle Extended Aeration System) mode was under taken by changing the operating parameters from the traditional design of dissolved oxygen (DO) control to a scientific approach using respirometry. Measuring the critical oxygen point for carbonaceous and nitrification bacteria and combining this with in-situ Oxygen Uptake Rate measurements forms the basis of supplying only the correct levels of oxygen for the required amount of time to break down the influent BOD and Ammonia levels. These measures can be used to calculate when treatment is complete and therefore tailor the energy requirements of the site to suit the aeration supply needs. The resultant changes have led to sustainable operational savings of over 20% of aeration energy consumption and reducing carbon emissions whilst maintaining compliance.

INTRODUCTION

This paper will discuss an overall product model that combines a number of pieces of equipment, the expertise of scientists and consultancy support to optimise the aeration process of the activated sludge treatment plants of Cardiff & Afan WwTW, and initial investigations of other top energy sites.

This was achieved using an innovative, cutting edge technology saving Giga Watt hours of energy and assisting Dwr Cymru Welsh Water (DCWW) & Kelda Water Services (Wales) (KWS(W)) in reducing their Carbon footprint. The scientific equipment used by the project was obtained from Strathkelvin Instruments along with their consultancy support working together with the KWS(W) Operations and scientific project teams to deliver savings.

Balancing supply and demand and ensuring sustainable methods is vital to the future of our environment. Water companies use many different methods to treat sewage. One method that is used is Activated Sludge treatment; this has a massive energy demand as air is pumped from large blowers into the treatment process. All sewage ha s an oxygen demand and it is this demand that we want to supply. The treatment process uses bacteria which biodegrade the incoming sewage as food and removes the organic carbons and ammonia from the sewage. It is essential that they receive a supply of oxygen, else they cannot respire resulting in them dying and resultant discharge of untreated sewage to the environment. Therefore to ensure treatment is complete an excess amount of air is pumped into the process, which can be very inefficient and costly under existing methods of dissolved oxygen control. With the prospect of increasing power prices, and the importance of reducing carbon emissions a sustainable solution to this problem must be found.

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