Water/Wastewater 37
phosphate which has to be removed. The less phosphate there is; the more difficult removal becomes and the more precipitant is required to eliminate the same amount. For example, more precipitant is required to lower phosphate concentrations from 4 to 2 mg/l than from 6 to 4 mg/l.
Wastewater treatment plants operating an open loop real time control system for phosphate removal have demonstrated considerable savings – a UK works has saved approximately 37% of the ferric sulphate cost and 57% of caustic chemical costs and a plant in Italy has shown 50% cost savings in comparison with a constant dosing system, which represents a 7 month payback.
If closed loop control is applied, the RTC system requires a measurement of phosphate levels immediately after dosing. As a result, the Phosphate concentration can be held at a fixed desired level and the control performance is monitored as indicated in figure 1.
Standard Control
RTC Control
Figure 2: RTC savings
algorithms to optimise the operation of the ASP, leading to greater efficiency and sustainability. Undertaken at full scale, the trial assessed the benefits of RTC at a 250,000 population equivalent (PE) works in the UK and consisted of two identical ASPs (each with four lanes) configured as a 4-stage Bardenpho plant with methanol addition in the secondary anoxic zone.
Standard aeration lanes (fixed DO set-points with fluctuating NH4 effluent concentration) were compared with lanes running an RTC system operating variable DO set-points based on actual load. The RTC lanes deployed extra sensors for dissolved oxygen, ammonium and nitrate.
The trial demonstrated that the RTC system was able to respond quickly to ammonium influent spikes and to maintain a stable effluent ammonium level. The trial also demonstrated that the RTC system was able to reduce methanol consumption by 50% and energy (measured as air flow) by 20% (figure 2). The system has now operated successfully for more than one year.
Summary
The HACH LANGE optimisation system combines process measurement technology with advanced RTC control modules to provide substantial savings in operational costs at wastewater treatment plants, whilst maintaining compliance with consent values.
UK RTC Trial – Activated Sludge Process Control
The results of a trial investigating the benefits of an RTC system on the management of the activated sludge process (ASP) have been published by Thornton, Sunner and Haeck.1
Managed by MWH UK Ltd and employing monitoring instruments from HACH LANGE, the trial employed online sensors and control
Recent advances in sensors, analysers and controllers mean that wastewater treatment no longer has to be managed on a 'worst case scenario' basis. Processes can now be monitored and adjusted instantaneously to maximise efficiency and improve process stability. Cost reduction is obviously a key benefit, but the ability to reduce energy consumption is becoming an important objective in many countries.
[1] Thornton, Sunner and Haeck, 2010. Real time control for reduced aeration and chemical consumption: a full scale study. Water Sci. Technol.61, 2169–2175
AUTHOR DETAILS Dr Michael Haeck,
Manager Product Applications HACH LANGE Düsseldorf, Germany
Tel: +49 (0)211 5288 0 Email:
Michael.Haeck@hach-lange.de Web:
www.hach-lange.com
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Annual Buyers Guide 2010
IET
Aeration (m3
/d)
Savings
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