Release characteristics and control of hydrogen sulfide during thermal drying of municipal wastewater sludge

Hydrogen sulfide (H2S) is the most predominant malodorous gas released during the thermal drying of municipal wastewater sludge. Experiment using a laboratory-scale tube furnace was conducted to determine the characteristics of H2S release and the changes of sludge moisture content. The addition of calcium oxide (CaO) in the original sludge was also tested and evaluated for its inhibitory effect on the H2S release. The results showed that the amount of H2S released increases with the increase of temperature in the tested range of temperature from 80 to 280 °C. The critical temperature range defined as the turn point of temperature at which the H2S or other odorous gases release starts to drastically increase was determined to be 200–240 °C. It was found that the drying process could be divided into two stages according to the changes of H2S release speed and the corresponding moisture content, and the majority of H2S release was detected in the second stage. The reduction of element sulfur in sludge was approximately proportional to the H2S released in the temperature range from 80 to 280 °C. The addition of CaO in the sludge could significantly repress the release of H2S during thermal drying. This inhibitory effect was observed to last for the entire drying process and not be changed with the change of temperature.