Theory

• Our online toxicity monitoring system using sulfur oxidizing bacteria (SOB) relies on the production of hydrogen ions (H⁺) which lowers the medium pH, and SO₄²^- which increases the electrical conductivity (EC) of the medium.
• The increase in EC and the decrease in pH indicate that SOB attached to the So particlesandoxidizedthe So to H₂SO₄ using O₂ providedas the electronacceptor.
• In the presence of toxic chemicals, the activity of SOB will be inhibited, which will cause an increase in pH and a decrease in EC.
• Thus, toxicity can be detected using simple EC and pH meters.
• It is simple, uses little energy, and its sensitivity is not reduced by turbid waters.
• Long term operation (months) compared to other sensors that have to be maintained for feeding every week.
• Periodic calibration of pH and EC meters is not needed.
• No toxic byproducts are produced - the total mass of sulfate produced is low.
• High sensitivity - contaminants are detected in the low ppb range due to the low operating pH.
• High accuracy and stability since three different sensors are simultaneously operated.
• Since the SOB biosensor gives a biological response to toxicity, the response is to the additive and synergistic effects of multiple contaminants which is likely a better predictor of overall toxicity than the measurement of individual chemicals.

Comparison of different biological species for toxicity monitoring.

	Sulfur Oxidizing Bacteria (EC50)	Vibrio fischeri (EC50)	Fish, 96-h (LC50)	Daphnia, 48-h (EC50)	Ostracod (EC50)	Algae (EC50)
Zn²+	0.05	0.5-55	0.55-7.2	0.76-8.1	3.4	0.06
Cd²+	0.01	0.015-3.7	1.0-100	0.035-1.9	3.2	0.04
Pb²+	0.05	2.56	1.4-8.0	3.6	-
Cr⁶+	0.01	-	11.2-133	0.26-1.8	20.1
Hg²+	0.005	0.064	0.01-0.9	0.03-0.05	0.37
Benzene	0.005	2.0	-	-	-
Phenol	0.005	-	-	3.1	-

Specification

Model	SBTOX-WW	SBTOX-RW
Applicable water	Domestic wastewater Industrial wastewater	Drinking water River water
Test Organism	Sulfur oxidizing bacteria (SOB)
Detection time	2-30 minutes
Measurement	pH and EC
End point	Decrease in EC due to inhibition of SOB
Detection range	0.005~10 ppm depending on toxic substances
Operating Temp	30-40℃
Operating mode	R1 : continuous mode	R2, R3 : semi-continuous mode
Electrical power	1 kW
Size dimension	50 cm (W) x 66 cm (D) X 115 cm (H)
Weight	60 kg
Output	TCP/IP, 4-20 mA, RS-232
Display	TCP/IP, 4-20 mA, RS-232

Examples

• Swine wastewater

  

  

• Cr⁶⁺

  

  

• NO₂^-

  

  

Applications

• Drinking water intake
• Monitoring of rivers, lakes, reservoirs
• Monitoring of industrial effluents and influents
• Monitoring of ground water
• Monitoring of the influent and effluent of wastewater treatment plants
• Sediment and soil testing

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