Odor reduction using hydrogen sulfide-removing bacteria in sludge filtration systems: Ferrous-oxidizing bacteria and sulfur-oxidizing bacteria.

The preconditioning of digested sludge in sludge filtration systems produces hydrogen sulfide (HS), a major odor-causing source. This study evaluated the effects of adding HS-removing bacteria to sludge-filtration systems. Ferrous-oxidizing bacteria (FOB) and sulfur-oxidizing bacteria (SOB) were mass-cultivated in a hybrid bioreactor equipped with an internal circulation system. In this bioreactor, FOB and SOB effectively removed >99% of HS; however, the acidic conditions created by adding a coagulant during digested sludge preconditioning were more favorable for FOB than for SOB. In batch tests, SOB and FOB removed 94 ± 1.1% and 99 ± 0.1% of HS, respectively; therefore, digested sludge preconditioning proved more suitable for FOB activity than SOB activity. The results revealed that the optimal FOB addition ratio was 0.2%, validated using a pilot filtration system. Moreover, the 57.5 ± 2.9 ppm HS generated in the sludge preconditioning step was reduced to 0.01 ± 0.01 ppm after adding 0.2% FOB. Therefore, the results of this study will be useful because they provide a process for biologically removing odor-causing sources without affecting the dewatering efficiency of the filtration system.