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

Abstract

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.