Hydrogen sulfide effects on ammonia removal by a biofilter seeded with earthworm casts

Ammonia (NH₃) removal efficiencies were evaluated when hydrogen sulfide (H₂S) and NH₃ in binary mixture gases were supplied to a ceramic biofilter seeded with earthworm (Lumbricus terrestris) casts. The effect of inlet H₂S concentration and space velocity (SV) on the removal of NH₃ was investigated after the acclimation of the biofilter with NH₃ gas. When NH₃ was singly supplied to the biofilter, NH₃ removal was maintained at almost 100% until inlet NH₃ concentration was increased up to 600 μL L^-1 and SV up to 330 h^-1, at which the elimination capacity of NH₃ was 148 g N m^-3 h^-1. When H₂S was supplied simultaneously, however, the accumulation of toxic sulfide ions showed dual effects on NH₃ removal efficiencies. First, no effects were observed at inlet H₂S loading below 60 g S m^-3 h^-1; however, inhibition by H₂S at higher loading was observed above 60 g S m^-3 h^-1. The point at which loading achieved a maximum of more than 99% NH₃ removal efficiency was 139 g N m^-3 h^-1, when inlet H₂S concentration was held under 100 μL L^-1, but it dropped to 76 and 30 g N m^-3 h^-1 when the inlet H₂S concentration increased to 220 and 460 μL L^-1, respectively. The critical points of inlet H₂S loading that guaranteed over 99% NH₃ removal were determined as 100, 100, 60, and 40 g S m^-3 h^-1 at inlet NH₃ concentrations of 100, 200, 400, and 600 μL L^-1, respectively. Inlet NH₃ loading had synergic effects of increasing the inhibition of inlet H₂S loading on the NH₃ removability of the biofilter.