Abstract: An improved biofilter design and related methods of utilizing shaped drain assemblies for directing fluid flow though a biofilter media to promote biological interaction. A shaped drain assembly can include a plurality of elongated drain structures having a permeable upper surface, a. lower surface and a drain interior defining a drain cross-section. When configured as a shaped underdrain assembly, each elongated drain structures can be in proximity to a biofilter tank floor such that the lower surface is in fluid communication with one or more flow channels below the floor and with the permeable upper surface supporting the biofilter media. The biofilter can include a shaped drain assembly positioned above the shaped underdrain assembly and located within or above the biofilter media. The shaped drain assemblies can control the flow and mixing of two or more flow species into the biofilter media.