Moving bed type reactors are bio-film processes utilizing small, plastic biomass carriers that mix in the water. The use of biomass carriers is becoming common world-wide, for many applications, some of which are: compact low operation units, industrial wastewater roughing filters, retrofit and upgrade of municipal wastewater treatment plants. The AGARTM Process (Attached Growth Airlift Reactor) belongs to this category, with the addition of: airlift-based mixing and process staging. As development of the scientific basis of this technology unveils the variety of applications of the process, different configurations are standardized for different purposes. Design and operation allow manipulation of the nature of the bio-film that develops on the protected surfaces of the bio-mass carriers, in order to achieve the required process performance. Process configuration is chosen in design according to site conditions. For example: many small wastewater treatment plants require a process with low operation and maintenance; this requirement practically dictates a process without circulation of activated sludge.