Rapid detection of toxicity in wastewater: recent developments with manometric respirometry

Manometric respirometry can be used for the direct toxicity assessment (DTA) of wastewater. A first prototype portable system for field use as well as the principle of operation has been reported previously [A. Tzoris, D. Cane, P. Maynard, E.A.H. Hall, Anal. Chim. Acta 460 (2002) 257; A. Tzoris, D. Fearnside, M. Lovell, E.A.H. Hall, Environ. Toxicol. 17 (2002) 284; A. Tzoris, V. Fernandez-Perez, E.A.H. Hall, Sens. Actuators B 105 (2005) 39]. In this report we examine the simple mathematical derivation of the principle and identify some design parameters that could be altered or improved. Hence by changing the geometry of the respiration chamber aiming at a larger surface area and smaller air headspace volume combined with sample stirring for improved aeration, the response of the instrument was improved by at least 50%. Data obtained from real samples as well as data from a comparative study with a lab-based respirometer routinely used in toxicity assessment is presented. Correlation was excellent with the advantage that a test could be completed in 6min or with five repeat measurements the data could be collected within a 10min measurement period. Using a 25% inhibition threshold, all samples found toxic by the standard method were also found toxic by the Baroxymeter method and dilution factors could be estimated for pretreatment of the toxic waste prior to release to a processing plant.