A microbial sensing system with the built-in special processing algorithm was developed for detecting the toxicity or over-nutritivity of
physically or chemically pretreated wastewater before been dispensed into a reservoir for further biological treatment. The electrical current
is the output of the system varied according to both bio-chemical and electro-chemical reactions between the bacteria-attached electrode
and wastewater. The toxic substances may inhibit the oxygen uptake of bacteria distinctively sampled from the activated sludge. The
formation of reduction±oxidation reactions on the membrane was considered owing to bio-chemical activities of the oxygen uptake rate,
which induce charge transfer effects. Present microbial sensing system 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 ampli®er, a low pass
®lter, and a data acquisition system. The wastewater reacted with the modi®ed electrode that contained approximately 20 millions of
bacteria controlled under ¯ow culture condition at an optimized interval of ca. 9 h. Experimental results obtained from three varied
concentrations of 40 ml speci®ed 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 suf®cient for
regression calculation and computation to grade the degrees of wastewater's toxicity. Each testing result measured by the newly developed
microbial sensing system was veri®ed with the simultaneous measurement using an oxygen-dissolved analyzer. A highly uni®ed relation
between measurements using the microbial sensing system and oxygen-dissolved analyses was obtained according to slope of the ®tted ®rst
order linear equation to be 0:9921 0:0433. The correlation coef®cient is 0.9767. # 2001 Elsevier Science B.V. All rights reserved.