In Japan, three deaths were reported at an inert solid waste landfill site after exposure to hydrogen sulfide (H 2 S) generated at the site. H 2 S gas is produced when sulfate-reducing bacteria (SRB) convert sulfate derived from waste gypsum board under anaerobic conditions. The recommended countermeasure is to supply oxygen by installing gas venting pipes. However, a large cost is necessary for pipe installation and the pipes are not applicable to coastal landfill sites. On the other hand, H 2 S generation suppression by nitrate (NO 3 ) addition has been reported in sewage systems. In this study, in order to develop a method to suppress H 2 S generation by NO 3 addition at a landfill site, the extent of suppression was quantitatively estimated. When NO 3 reagent was added at the rate of 0.46 mmol-NO 3 /(L•d) into a liquid from which H 2 S gas was generated at the rate of 0.21 ± 0.05 mmol-H 2 S/(L•d), H 2 S generation rate was decreased to approximately 1/4 of the original rate. Although it was difficult to maintain the concentration of NO 3 because it tended to disappear rapidly, the frequent addition of NO 3 reagent to maintain the concentration of approximately 430 mg-NO 3 /L enabled us to control H 2 S concentration to below 1000 ppmv for one month and H 2 S generation rate to below 1/20 of the original rate.

H 2 S generation suppression by the addition of NO 3 from reagent (NR) or compost (NC), and O 2 supply (OX) was quantitatively estimated in column percolation experiments. The cumulative amounts of oxygen added exceeded 300 mmol-O/L in NR and NC, and approximately 2 mmol-O/L in OX on day 75. The cumulative amounts of H 2 S generated on day 60 in control, NR, NC, and OX were 69, 26, 71, and 31 mmol-H 2 S/L, respectively. The amounts in NR and OX were half of that in control, whereas the amount in NC was almost the same as that in control. The H 2 S generation rates from day 50 to day 60 in control, NR, NC, and OX were 0.86, 0.019, 0.75, and 0.041 mmol-H 2 S/(L·d), respectively, and the rates in NR, NC, and OX were 0.02, 0.9, and 0.05 times that in control. In this way, the H 2 S generation suppression effects of NO 3 reagent addition were observed. In NR, although NO 3 was injected from the top of the column, the suppression effect reached the deep layer.