Nordkanal MBR, Technical Tour

The Nordkanal wastewater treatment plant, owned and operated by the Erftverband (Erft Association), treats wastewater from three nearby towns. Commissioned in January 2004 the plant was the world’s largest membrane bioreactor plant for municipal sewage at that time. It serves a population equivalent of 80,000 and has an installed maximum capacity of 48,000 m³/d.

The site has five buildings which respectively house the coarse screen, the fine screens, the membrane bioreactor and the process controls and the sludge mechanical dewatering process. (Fig.1) Additional installations include sludge and sludge liquor holding tanks, a grit chamber and the membrane bioreactors. Water is pumped from the site of the old decommissioned wastewater treatment plant 2.5 km east of the site to the 6 mm step screens. It is then fed via an aerated grit chamber to two rotary drum 1.5 mm mesh-grid fine screens. Screenings from the fine screens are discharged into the sludge dewatering process and subsequently disposed of by incineration off-site. The screened water is transferred to the MBR (Fig. 2).

The biological wastewater treatment consists of four parallel lines, with a nitrification tank fitted with two integrated membrane filtration trains and an upstream anoxic (denitrification) zone at a total 9,300 m³. The eight membrane trains are each fitted with 24 hollow fibre membrane cassettes of 440 m² membrane area, such that the total membrane area is 84,480 m2 (Fig. 3). There is also a simultaneous precipitation for phosphorous removal. Biosolids wasted from the tanks are stored in the mechanical thickeners and dewatered on-site by a centrifuge.

The installed membrane filters are now operative for seven years at a mean net flux of 23.7 LMH and a mean permeability of 150 to 200 LMH/bar at an average wastewater temperature of 13°C. Physical membrane cleaning comprises an intermittent coarse-bubble aeration and repeated back flushing of the membrane filters. Regular chemically enhanced backwashing and annual or biannual recovery cleaning are additional means of fouling control.

In the recent year, the process control system of the plant was retrofitted in order to facilitate savings in energy consumption of up to one third.

Figure 1. Exterior view of the Nordkanal site

Figure 2. Flow scheme of the Nordkanal MBR

Figure 3. Nordkanal MBR, a view of the nitrification basins and the integrated membrane filtration units