A bomb scare closed a Fenland recycling centre last week.
Staff at the Wisbech Recycling Centre discovered a suspicious object in one of the skips at the Boleness Road site on Thursday.
Police had cordoned off the site, after the object was discovered at 10am.
Army bomb squad officers were called out and found a railway signalling detonator in the skip.
A spokesman for Cambridgeshire County Council has put out an appeal to people visiting the tip.
He said: “It may be that the person who brought the object had not realised what it was but we would ask people to always check if they are not sure if something should be recycled.
“They can ask on site or telephone us to get advice.
“The object was discovered while staff were searching the skip to ensure the right items were within it.”
The centre re-opened as normal at 2pm after the detonator had been removed by the army.
Bomb disposal officers are often being called to waste recycling centres.
On Friday last week, RAF Cranwell officers were called to the Skegness Recycling centre after an ammunition shell had been discovered.