WaterSulf Process H2S in Water Analyser

Measures H2S and sulphides in waste water, including quench towers, waste water treatment plants and stripped sour water.

WaterSulf Process H2S in Water Analyser

Duty: To measure the concentration of dissolved H2S in a waste water stream and to calculate total dissolved sulphides.

Process water flows through a sensor equipped with a propriety membrane. Due to the partial pressure effect, the membrane is only pervious to gases, not to ions, liquids or solids.

The sensor contains a buffer solution with a redox catalyst and 3 electrodes. A polarisation voltage is applied to the electrodes to give a ratio of the oxidised/reduced redox catalyst. The H2S reacts, first chemically in presence of the redox catalyst to form a reaction product and then the electrochemical oxidation of the reaction product takes place at the measuring electrode. This causes a flow of current proportional to the concentration of dissolved H2S present in the sample.

The measurement is compensated for pH, pressure and temperature changes on a real time basis, and these can be reported as separate 4-20mA outputs (optional) if required.

The benefits of this technology can be summarised as follows:


  • As the measurement is specific to H2S, there will be no interference from other sulphur components
  • Fast response (seconds) compared to ion-selective electrodes (hours)
  • The instrument has a wide range capability, measuring between 0-2ppm to 0-1% H2S
  • Configuration of the system is via a touch screen which eliminates the need to open the enclosure.
  • Real time compensation for pH, pressure and temperature
  • Optional analog outputs for pH, pressure and temperature
  • Suitable for gas group IIC environments.

The measurement of dissolved H2S in water is important as it can be highly toxic and foul smelling. Also, H2S can biologically degrade to sulphuric acid which can cause corrosion in concrete and metal pipes and sewage systems.

Applications can be found in:

·          Ethylene quench towers

·          Waste water treatment 

·          Sewage systems 

·          Coke oven quench towers 

·          Steel plant scrubbers 

·          Sour water plants 


·          Well-head injection.    





Measurement principle 


Measurement of HS and calculation of dissolved sulphides using an electrochemical cell with pH, temperature and pressure compensation 






C++ Windows XPe based

 Measurement range




0 - 100 mg/l HS. Other ranges on request 






± 2% full scale


Response time




T90 < 10 secs    




 4-20mA for both HS and dissolved sulphides

Optional outputs for pH, pressure or temperature






1 x measurement alarm



1 x instrument failure alarm


Area classification 


ATEX approved, Ex d [ia] IIC T4 


Ambient temperature 


5°C to +30°C 


Weather protection 


IP66 (IEC 60529)









120 / 240 VAC 50 / 60 Hz, 49VA






Pressure 1.5 to 10.0 barg



Flow 0.2 to 0.5 l/min



Temperature 30°C max







Process connections


¼” NPT female  



35 Kg



550(w), 1100(h), 235(d) mm