An on‐line respirographic biosensor for the characterization of load and toxicity of wastewaters

Abstract

A respirographic biosensor is presented that is capable of monitoring the waste load and potential toxicity of wastewaters, both off‐line in a laboratory or on‐line at the wastewater treatment plant. The principles of the sensors' operation have been developed and implications of the design choices evaluated. Short term BOD values were obtained every 30 min. The linear dynamic range spanned concentrations differing by a factor of 5000. This range could be expanded by a factor of 10 by adjusting the aeration rate of the bioreactor in the sensor. The response time for toxicity detection was approximately 1 h. The use in the sensor of activated sludge from the plant concerned ensured relevant toxicity information was obtained. To check the condition of the sludge, an independent respiration measurement is proposed. When a siginificant activity change is observed, the sludge in the sensor must be replaced. The presence of oxidoreduction chemicals can cause interferences that may lead to measurement errors. Based on a difference in reaction kinetics, their presence can be assessed and the effect eliminated. Both on‐line and laboratory applications in the chemical industry are presented. Special emphasis is given to the usefulness of the sensor data for waste management of production divisions. On‐line assessment of load variations and hydrogen peroxide spills are given as illustrations of the implementation of the sensor on the treatment plant. Attention is drawn to the potential application of the data for process control and improved performance of the treatment plant.

A critical comparison of extant batch respirometric and substrate depletion assays for estimation of nitrification biokinetics

“…Additionally, continuous and automated data acquisition of respirometric and titrimetric assays results in information-rich data, which can translate into high precision of estimated parameters. Respirometric methods have been adopted for various applications including biokinetic estimation of several activated sludge reactions (Chandran andSmets, 2000a,b, 2001;Ellis et al, 1996;Gernaey et al, 2001;Ginestet et al, 1998;Kong et al, 1996;Naziruddin et al, 1995;Surmacz-Gorska et al, 1996;Vanrolleghem and Verstraete, 1993), determining the composition of wastewater streams (Brouwer et al, 1998;Spanjers and Vanrolleghem, 1995;Sperandio and Paul, 2000), detection and measurement of inhibition (Gernaey et al, 1997;Hu et al, 2002;Vanrolleghem et al, 1994;Volskay and Grady, 1990) and monitoring and control of bioreactor performance and kinetics (Gernaey et al, 2001;Spanjers et al, 1998;Surmacz-Gorska et al, 1996). Additionally, optimal design of respirometric assays to facilitate parameter estimation of different biotransformations from resulting respirograms has also been proposed Chandran and Smets, 2005;Petersen, 2000;Vanrolleghem et al, 1995).…”

Error propagation in open respirometric assays

“…Additionally, several on-line respirometer-based biosensors in wastewater treatment plants have been developed. Based on the comparison between the actual respiration rate of the activated sludge with a given set point value (e.g., the historical respiration rate), these biosensors allow the early detection of a toxic wastewater (Sollfrank and Gujer, 1990;Vanrolleghem et al, 1994). However, in order to avoid false alarms, the evaluation of the error associated with the measurement of the actual respiration rate is crucial to distinguish between a real event (e.g., a toxic wastewater) and aleatory fluctuations of the indicator used for toxicity (e.g., the decrease of the respiration rate).…”

A temperature‐gradient sensor for determining the activity of activated sludge

“…The incoming toxicity can be monitored online using respirometry 14 and ATP luminescence. 15 A temperature-gradient sensor can also be used to estimate the effects of toxic chemicals in the influent.…”