Sewage treatment plants (STP) based on activated sludge often cover large surface areas, necessitated mainly by the large settling tanks. To build compact STP's, biomass can be grown as biofilms on a carrier material, or as fast settling aerobic granular sludge without a carrier.  Recent research showed the advantages of a discontinuously fed system, in which it is possible to grow stable granulated sludge under aerobic conditions.
Simultaneous Chemical oxygen demand, and Nitrogen and Phosphorus removal, can be easily integrated in a discontinuous fed system.  Because of the high settling capacity of the granules, the use of a traditional settler is unnecessary.  Therefore, the installation can be built very compact, needing only 20% of the surface area of conventional activated sludge systems.