The villages of Oberzeuzheim and Niederzeuzheim, Germany are served by the Niederzeuzheim wastewater treatment plant. The plant was originally designed as a nitrification facility for a population of approximately 3,000.
Incoming wastewater is mechanically pretreated by a screen and grit chamber. The biological treatment stage consists of an STM-Aerotor™ tank and final clarifier. The STM-Aerotor tank, with a volume of 66,000 gallons (250 m3), is equipped with four (4) cell type STM-Aerotors, model ZR 8 x 2.5, with a total surface area of 104,400 ft2 (9,700 m2) for the fixed film biomass. Mixed Liquor Suspend Solids (MLSS) in the STMAerotor tank average 6,000 to 8,000 mg/l. Average daily power consumption is approximately 4.6 kW. A circular final clarifier with a diameter of 47.5 ft (14.5 m) and a side water depth of 6.95 ft (2.12 m) completes the biological treatment stage. A return sludge circuit operates between the final clarifier and the STM-Aerotor tank.
Dry weather flow to the plant varies between 105,000 and 132,000 gal/day (400 - 500 m3/day), with a diurnal peak up to 450 gpm (28 l/s). Stormwater flows of up to 1.2 mgd (55 l/s) are handled by an equalization basin and then treated in the biological treatment stage.