Hazardous peak concentrations of hydrogen sulfide gas related to the sewage purification process

The concentration of hydrogen sulfide in the atmosphere of a sewage purific ation plant in Norway was studied. Continuous measurements over several 3-w eek periods showed that the concentrations generally were lower than 2 ppm, but peak concentrations over 100 ppm were discovered. Rapid onset and decl ine characterized these peak concentrations, which occurred at regular inte rvals. Through evaluation of the time pattern of these peaks compared with plant operations, a specific process was identified as the likely causative factor of the spikes. Through simple remedial actions the hydrogen sulfide concentration associated with this activity was reduced from above 100 ppm to less than 2 ppm. Olfactory fatigue to hydrogen sulfide and strong offen sive odors from other compounds in the sewage makes smell ineffective for s ignaling high concentrations. Peak concentrations may therefore pass unnoti ced unless detected with continuous measuring equipment. The risk for expos ure may be reduced by enclosing processes and through the use of spot extra ction ventilation in areas with compacted anaerobic waste material.