A compact treatment apparatus and methodology is provided for scavenging at least H2S from an acid gas stream. The vessel is charged with a batch of an aqueous solution of H2S scavenging treatment liquid. Acid gas is discharged from a sparge bar fit with graduated openings, either graduated from small to large or from a few to many and spaced therealong, for distributed discharge into the treatment liquid. The acid gas percolates up through the liquid and into a vessel headspace, the gas being scrubbed of H2S for producing a treated discharge gas. The treatment solution can be an aqueous solution of incorporating one of several active H2S scavenger ingredients including amine-aldehyde compositions or triazines.