A total of 100 kg of chemicals was accidentally discharged into the industrial wastewater from an item of coating equipment at the coating unit of a pharmaceutical plant. The coating solution that was discharged contained isopropyl alcohol, acetone, and an active pharmaceutical ingredient not hazardous to the aquatic environment. The effluent was contained in the plant’s mixing tank. The operator tested the water exiting the facility and found that the chemical oxygen demand (COD) exceeded regulatory limits. The analysis also revealed the presence of isopropyl alcohol, acetone, and ethanol in the water. However, the pollution was deemed easily biodegradable (based on the value of the ratio between chemical oxygen demand and the biological oxygen demand).

The accidental release occurred during a degraded operating situation. A few hours earlier, the coating tank’s motherboard failed. As a result, the solution remaining in the tank (200 kg) at the end of the cycle could not be blanketed. Realising that there was an explosion risk (ATEX), the operator emptied the tank manually to bring the situation under control. While this was going on, a valve usually controlled by the PLC was not in the position required to contain the solution at the tank outlet. As the valve’s position was not visible, the operators were unaware of this. When they heard the flow in the pipe leading to the wastewater tank, they realised the problem and actuated the valve, thereby limiting the release to half the volume of the solution present in the tank.

Since the accident, the operator has replaced the PLC’s motherboard. It also improved its procedures for assessing risks during degraded operations. It is also working on a way to better identify the valves at its facilities.