Abstract: An apparatus and a method for removing constituents from an influent. The apparatus includes a biological processor that receives a water mixture as influent and outputs a liquor, a solid-liquid separator that receives the liquor and separates the liquor into a liquid and a solid; and a biofilm media that includes at least one media surface. The biofilm media may have a biofilm mass, biofilm volume, biofilm density, biofilm thickness, hydraulic retention time or solids residence time. The at least one media surface grows a biofilm that removes one or more constituents contained in the influent. The biofilm mass, biofilm volume, biofilm density, biofilm thickness, hydraulic retention time or solids residence time can be controlled by at least one of a physical process, a biological process or a chemical process.