Ammonia, hydrogen sulphide and methyl mercaptides in Finnish municipal sewage plants and pumping stations.

Ammonia, methane, hydrogen sulphide and methyl mercaptides were analyzed in the atmospheres of 16 Finnish municipal waste water treatment plants and in 18 pumping stations. The sulphides were analyzed on site as it was found that, with the standard 0.5-l laminated plastic bags, significant amounts of the vapours were lost from the gas phase. The relative humidity of the sampled air was the most likely cause. Under normal operating conditions, sulphides varied from less than 0.07 to 53 micrograms l-1, with highest concentrations found at the sludge presses. Pumping stations had sulphide vapours from 0.07 to 0.5 microgram l-1. The presence of ammonia (0.007-3.5 micrograms l-1) and methane (0.7-18 micrograms l-1) confirmed the hypothesis of the anaerobic origin of the offensive gases. Although more effective ventilation without scrubbing the emission gases would reduce the health hazard in the plants it would burden the environment.