Pollution
Humain
Environnement
Economique

For the purposes of a hydrostatic test, a plug was placed on the digestate discharge line of a digester of a cattle dung biogas plant that was going to be put into service. The plug was not removed before the plant was commissioned although the checks required during commissioning should have enabled it to be detected. This oversight was not noticed until later, when the digester was already loaded. Unloading the digester was impossible and the plug could only be removed from the outside. The operator contacted a specialist contractor to have the plug removed by a diver. The plug was successfully removed and the consequences were negligible. Biogas was burnt off by the flare stack for a dozen minutes to limit creating an explosive atmosphere (ATEX) while removing the vapour space in the digester.