DIN 38405-27:2017-10

Sulfides enter the wastewater through indirect dischargers or can be formed from sulfur compounds in the wastewater under anaerobic conditions, at sufficient water temperatures and through microbiological processes. The potential danger of sulfides in wastewater lies in the formation of life-threatening concentrations of hydrogen sulfide in the sewer system, difficulties in wastewater treatment, odor nuisance from released hydrogen sulfide and the corrosion of construction and other materials. Monitoring the concentration of sulfides in wastewater is therefore of central importance. This document specifies three methods for determining sulfide sulfur in water and wastewater from mass concentrations of 0,04 mg/l. The sample is diluted when using the photometric method for sulfide contents greater than 1,5 mg/l. With the electrochemical method much higher concentrations can be measured without dilution. Both methods can be used to determine higher mass concentrations by reducing the volume of the water sample used. One of the following methods can be used, depending on the type of water and the required information. Method 1 defines a procedure for determining the sulfides in water and wastewater that are easily released at pH 4. Dissolved sulfide is measured completely, while undissolved sulfides are measured either completely or partially, depending on their solubility and state of aging, such as the sulfides of zinc, iron or manganese. Some sulfides are practically not detected, such as copper and mercury sulfide. Under the conditions of the process, organic sulfur compounds can be more or less decomposed to form dihydrogen sulfide and thus be detected as well. Volatile mercaptans are detected to a negligible extent (less than 1 %), while higher-boiling mercaptans are not detected. Method 2 defines a procedure for determining the sulfides in water and wastewater that can be released with strong acids. This procedure detects undissolved sulfides to a greater extent than Method 1, and should therefore be used for the analysis of samples containing heavy metals when particle-bound sulfides should also be detected. Some sulfides are practically not detected, such as mercury sulfide, while others are detected depending on the metal and the state of aging of the precipitate. Method 3 in Annex B defines a method for determining sulfide dissolved in water. The sample shall be filtered since particle-bound sulfides are not to be detected here. This document has been prepared by Working Group NA 119-01-03-01-26 AK "Leicht freisetzbares Sulfid" ("Easily liberatable sulfide") of Working Committee NA 119-01-03 AA "Wasseruntersuchung" ("Water quality") at DIN Standards Committee Water Practice (NAW).