Following a mains power failure at 5.30 p.m., 400m³ of screened and biologically treated water was released with sludge into the exit channel of the wastewater treatment plant of a malthouse. This discharge of waters coming from the soaking of brewery barley containing nitrogenous and phosphorous organic matter reached the Viranne via the existing clarifier overflows and gravity-flow drainage. At around 6 p.m., the production feed system was stopped. When they arrived at 7.30 p.m., the electricity department noted that the problem was due to the HV bridges of the high-voltage (HV) grid. Electricity was restored at around 11.20 p.m.

Wastewater treatment plant aeration was shut down for 6 hours. During the incident, discharge samples were taken regularly to quantify the pollutant flows. The COD (Chemical Oxygen Demand) and SS (total suspended solids) flow increased at the outlet. The COD was estimated at 250mg/l, i.e. 150mg/l above the authorised concentration (an extra 60kg). The cost of production stoppage during 13 hours was estimated at €5,600.

A failure of the main electric power supply on the grid line outside the plant was the cause of the incident.

The operator indicated that an electrical problem on the high-voltage line is impossible to anticipate on the malthouse side. The frequency of occurrence of this electrical incident is extremely low. An electric power failure can be remedied in 6 hours. The hire of generating sets was also proposed to the malthouse’s other industrial facilities.