Studies on the early detection of wastewater's toxicity using a microbial sensing system

A microbial sensing system with the built-in special processing algorithm w as developed for detecting the toxicity or over-nutritivity of physically o r chemically pretreated wastewater before been dispensed into a reservoir f or further biological treatment. The electrical current is the output of th e system varied according to both bio-chemical and electro-chemical reactio ns between the bacteria-attached electrode and wastewater, The toxic substa nces may inhibit the oxygen uptake of bacteria distinctively sampled from t he activated sludge. The formation of reduction-oxidation reactions on the membrane was considered owing to bio-chemical activities of the oxygen upta ke rate, which induce charge transfer effects. Present microbial sensing sy stem is capable of measuring different degrees of toxicity correlated with the inhibition rates of the bacteria. The system is a portable and compact design primarily including a sensor, a signal amplifier, a low pass filter, and a data acquisition system. The wastewater reacted with the modified el ectrode that contained approximately 20 millions of bacteria controlled und er how culture condition at an optimized interval of ca. 9 h. Experimental results obtained from three varied concentrations of 40 mi specified toxic solutions indicated that the degree of toxicity in different wastewater was roughly correlated with their electro-induced bioactivities within 8 min. Only data acquired between 1 and 500 s were empirically found to be suffici ent for regression calculation and computation to grade the degrees of wast ewater's toxicity. Each testing result measured by the newly developed micr obial sensing system was verified with the simultaneous measurement using a n oxygen-dissolved analyzer. A highly unified relation between measurements using the microbial sensing system and oxygen-dissolved analyses was obtai ned according to slope of the fitted first order linear equation to be 0.99 21 +/- 0.0433. The correlation coefficient is 0.9767. (C) 2001 Elsevier Sci ence B.V. All rights reserved.