Some 140 tonnes of recyclable waste had to be dumped after explosives were found in grey recycling bags, according to WasteServ.
Workers had to call in the army after they discovered the four explosives at the ECOHIVE complex at the Waste facility in Magħtab.
They included a Chinese flare and other flare pistol cartridges dating back to the second world war, the waste agency said.
It said the find meant 140 tonnes of recyclable material had to be quarantined and then disposed of in a landfill for safety reasons.
Members of the Explosive Ordnance Disposal Unit of the Armed Forces of Malta (AFM) detonated the explosives at a safe location.
Grey bags should be used to dispose of recyclable materials, like cardboard, plastic, and paper.
WasteServ condemned the "gross negligence" and appealed to the public to be more responsible.
“This incident could have had far more serious consequences, especially considering the presence of highly flammable materials such as paper, plastic, and cardboard,” WasteServ said.
“Situations such as these not only put our employees’ lives at risk but pose a serious threat to the operations and new infrastructure.”
Hazardous waste, such as used batteries, chemicals, and pesticides, can be safely disposed of at one of the six Civic Amenity sites found across Malta and Gozo.
According to the Waste Regulations, it is prohibited to mix and dispose of hazardous waste with other waste.
A spokesperson told Times of Malta that the explosives could have gone off in the trucks or at the facility, which could have led to a huge fire.
She said it is difficult to track down where the grey bag with the flares originated from and that the bag was likely to be part of last week's collection.
WasteServ said that any hazardous waste, including flares, batteries, electronic equipment, and other highly flammable or explosive materials are disposed of properly to prevent a similar incident in the future.
“As WasteServ, we are working tirelessly towards meeting the country’s recycling targets. However, we want to emphasise that our success is highly dependent on the cooperation of the public. Above all else, our company prioritises the safety of its employees and its infrastructure.”
Malta has issues with separating its waste correctly, and it is not the first time WasteServ has come across items in the wrong bag.
Back in 2020, WasteServ said that dead animals being dumped in grey recycling bags is a “daily” problem.
In 2021, WasteServ chief executive Richard Bilocca told Times of Malta that a third of the waste that reaches WasteServ's facilities is composed of non-recyclable materials and is rejected by the sorting machines.
As of last month, any individual or business caught depositing waste in the wrong bag can be liable to fines of up to €150.
Enforcement officers are authorised by law to check bags taken out for collection by households and businesses and to issue warnings and fines when waste items are found in the wrong bag.