Energy savings by reduced mixing in aeration tanks: Results from a full scale investigation and long term implementation at Avedoere wastewater treatment plant

The aim of this project was to investigate the potential of reducing number of mixers in the biological treatment process and thereby achieve energy and economical savings and contribute to cleaner environment. The project was carried out at Avedoere wastewater treatment plant and a full scale investigation was conducted to study the effect of reduced mixing on flow velocity, suspended solid sedimentation, concentration gradients of oxygen and SS with depth and treatment efficiency. The only negative effect observed was on flow velocity; however the velocity was above the critical velocity. The plant has been operating with 50% of its designed number of mixers since September 2007 and long term results also confirm that reduced mixing did not have any negative effect on treatment efficiency. The estimated yearly electricity saving is 0.75 GWh/year.</jats:p

Modelling and control strategy testing of biological and chemical phosphorus removal at Avedore WWTP

The biological phosphorus removal process is often implemented at plants by the construction of an anaerobic bio-p tank in front of the traditional N removing plant configuration. However, biological phosphorus removal is also observed in plant configurations constructed only for nitrogen removal and simultaneous or post-precipitation. The operational experience with this "accidental" biological phosphorus removal is often mixed with quite a lot of frustration, as the process seems to come and go and hence behaves quite uncontrollably. The aim of this work is to develop ways of intentionally exploiting the biological phosphorus process by the use of instrumentation, control and automation to reduce the consumption of precipitants. Means to this end are first to calibrate a modified ASM2d model to a full-scale wastewater treatment plant (WWTP), including both biological and chemical phosphorus removal and a model of the sedimentation process. Second, based on the calibrated model a benchmark model is developed and various control strategies for biological phosphorus removal are tested. Experiences and knowledge gained from the strategies presented and discussed in this paper are vital inputs for the full-scale implementation of a control strategy for biological phosphorus removal at Avedore WWTP, which is described in another paper. The two papers hence show a way to bridge the gap from model to full implementation

Aeration tank settling and real time control as a tool to improve the hydraulic capacity and treatment efficiency during wet weather: Results from 7 years' full-scale operational data

This paper investigates the aeration tank settling (ATS) operation in combination with real time control (RTC) as a tool for increasing the hydraulic capacity and improving the treatment efficiency of a wastewater treatment plant (WWTP) during wet weather flows. Results from 7 years' full-scale operational data at the Avedøre WWTP, Denmark, show that ATS operation in combination with RTC increases the hydraulic capacity of the treatment plant with up to 150 and 67% of the design capacity during winter and summer respectively. Compared to the conventional wet weather operation, the ATS in combination with RTC operation resulted in lower effluent concentrations for total phosphate (40–50%), suspended solids (30–60%) and chemical oxygen demand (30–50%), whereas no significant effect was observed on total nitrogen. Apart from the reduced effluent concentrations, the RTC resulted in economic savings in the form of reduced costs for electricity and green taxes. However, in very few cases the ATS operation in combination with RTC was not able to handle design capacity, and some overflows occurred at flows below the design capacity. The frequency of these overflows may increase in the future due to increased rain intensity resulting in shorter prediction time available for ATS.</jats:p

On-line estimation of nitrification and denitrification capacity at Avedøre wastewater treatment plant

In this paper, on-line nitrification and denitrification rate estimation in an alternating wastewater treatment plant is discussed. The nitrification/denitrification rates are estimated on-line using continuous measurements of ammonia and nitrate. From the rate estimates, the plant capacity is derived. This information is useful in various ways: for early warning to prevent severe disturbances such as nitrification inhibition; for optimising phase lengths and distribution of the phases in the alternating operation; and directly for the control system of the treatment plant. The estimation is based on the derivatives of the measurement signals combined with a simplified model of nitrogen dynamics of the plant. In the paper, we show examples of a successful application of the estimation methods to full-scale operation of the treatment plant and are today incorporated in the control system

Introducing biological phosphorus removal in an alternating plant by means of control: a full scale study

In this paper, a control strategy for introducing enhanced biological phosphorus removal (EBPR) in an alternating plant designed for enhanced biological nitrogen removal (EBNR) is presented. Alternating aerobic and anaerobic conditions to promote EBPR are provided by controlling the phases of the operational cycle, instead of a separate anaerobic volume. By utilising the control schemes already built in the STAR((R)) control system for nitrogen removal, the control strategy is fully integrated in the system. The control system relies on on-line measurements of nitrogen (ammonia and/or nitrate) and orthophosphate. The control strategy has been implemented in full-scale operation at the Avedore wastewater treatment plant in Denmark and the results show clear indications of success. The control strategy has operated robustly for several months with a 60% decrease in use of precipitation chemicals