The Army bomb squad were called to West Kirby recycling centre after an unexploded mortar was found in a skip.
Merseyside Police evacuated the Greenbank Road site and sealed it off for several hours after they were called out at around 3.20pm on Saturday afternoon.
The device was taken to West Kirby beach and a controlled explosion was carried out.
A police spokesperson said: “Customers and staff at the centre were moved off site and a cordon established as a precaution. No residential properties were affected.
“The Army’s Explosive Ordnance Disposal Team attended and carried out the safe detonation of the device, a suspected World War II mortar, on West Kirby beach.
“We would like to thank the community for their patience while we dealt with this incident.”