Direct determination of molecular hydrogen sulfide in sewage effluents

In wastewater, dissolved sulfide is a mixture of molecular hydrogen sulfide (H₂S) and hydrosulfide ions (HS^-) existing in equilibrium with hydrogen ions. The standard analytical methods for sulfide determination in solution (e.g. Iodine method) permit measurement of total sulfide (H₂S + HS^-) rather than the direct measurement of H₂S. In this work, the direct determination of H₂S in sewage samples was determined using a method which was similar to that of Broderius and Smith Jr. The procedure involves bubbling nitrogen through the aqueous sulfide solution to strip all the H₂S which could escape to the gas phase and measure it by an H₂S-gas detector. The amount of molecular H₂S was determined from the calculation of the total area under the curve relating the volume of nitrogen (L) and H₂S concentration (mg/L) in the gas phase. The area was calculated using the Trapezoidal Numerical Method. The H₂S for the same sewage sample was also determined by using the standard iodine method.