The challenges of Total Nitrogen removal: PRESENTATION ONLY
Banfield, P.1, Anderson, M.1 and Butterfield, M.2, 1Veolia, UK, 2Hach, UK
(free)
Tidworth WWTW is a small site serving a population of 15,000 PE. The site consists of a typical treatment process stream of screening, primary settlement, surface aeration and final settlement, with the effluent discharging to a series of soakaway lagoons. When the site was subject to a licence change from a 15 mg/l Ammonia consent to a 9.4 mg/l Total N consent, this prompted evaluation of the treatment plant process to ensure compliance with the new, more stringent discharge consent. A variety of upgrades were evaluated and a trial implemented on the preferred option of configuring the nitrification aeration stream to a nit/denit pre-anoxic MLE configuration. The trial demonstrated the ability for the assets to deliver robust Total N removal, which subsequently meant that there was a requirement to tightly control the aeration, loading and nitrate returns to deliver maximum efficiency. To deliver this, real time control of the assets was evaluated.
Amongst the challenges faced with implementation of the real time control system, there was no existing site PLC to provide control loops to the infrastructure, exchange data with the real time controller or take back control If an error occurred. A solution was identified where the instrumentation controller network took over that function and provided the necessary fall-back conditions. The real time controllers HMI provided a schematic of the plant for operators to see the critical plant parameters with the software controlling load to the ASP, aeration for nitrification and internal recirculation for denitrification.
Since implementation of the control system, the plant has achieved an annual TN average value below consent.
