A canal responsible for carrying sewage away from the City of Oudenaarde to the Scheldt River was partially dammed in 1965 leaving an area of open water of approximately 1 hectare (600 meters by 17 meters). As the canal was only partially dammed, water from the canal continued to flow into the Scheldt River.
Two large municipal sewage collection discharge pipes feed the canal. The effluent discharged into this de facto lagoon is approximately half residential/domestic sewage (approximately 10,000 inhabitant equivalent) while the other half is industrial waste. The industrial waste generated is generally agricultural and small manufacturer based (see diagram page 5).
The situation is further compounded by the fact that residences and a school located in the vicinity of the canal discharge their effluent directly into the canal. As a result of these discharges the canal has become a virtual non-aerated lagoon that is far too small to accommodate the volume of waste it receives.
The fact that there still was a direct link between the canal and the Scheldt resulted in an increase in the COD of the Scheldt from approximately 100 ppm upstream of the canal to approximately 500 ppm downstream from the canal. In addition the effluent created significant odour problems that impacted residents in the area.
Treatment of the city of Oudenaarde (Belgium) sewage discharge canal case study