• Nopens, Ingmar
• Van Langenhove, Herman
• Demeestere, Kristof
• Weemaes, Marjoleine
• Wieland, Arne
• Ried, Achim
• Stapel, Harald
• Chys, Michael
• Van Hulle, Stijn
• Audenaert, Wim

Abstract

During secondary effluent ozonation, real-time control of the ozone dose based on the water quality is essential to minimize operational costs and by-product formation (i.e. two of the main hurdles hindering a fast implementation of the technology). In this pilot-scale study, the ozone dose was controlled via online UV absorbance (UVA(254)) measurements. Only one sensor was used although a AUVA(254)-based control strategy was applied. The practical implications of online spectral sensors and the effect of effluent dynamics in terms of load (i.e. Dissolved Organic Carbon or DOC concentration) and composition (i.e. reactivity) was studied in relation to the applied control strategies. The one sensor approach - presented for the first time to the best of the authors' knowledge - reduced the negative impact of sensor fouling. The use of manual and ultrasonic cleaning is recommended as it results in significantly less fouling (i.e. a factor of 6 difference). Additionally, the variable effluent reactivity showed to be more influential than the effluent load in determining the ozone dose. The use of AUVA(254) ensured the supply of the required ozone doses during varying water quality and weather conditions, and at lower operational costs than more common control strategies (up to 22% of savings). Flow or load proportional strategies were not able to cope with the dynamic ozone demand of the effluent. However, the required additional response time of the AUVA(254)-strategy might be a disadvantage and could be tackled using hybrid control approaches including load-based dosing (i.e. O-3:DOC ratio based) and the use of a combined feedback-feedforward system.

Topics

• impedance spectroscopy
• Carbon
• laser emission spectroscopy
• ultrasonic