simple past tense and past participle of activate
"The chemical reaction was activated when we mixed the two powders together."
In plain English: To activate something means to turn it on so that it works properly.
"The security system was activated when he pressed the button on his phone."
(of sewage) treated with aeration and bacteria to aid decomposition
"The city's wastewater treatment plant uses activated sludge to efficiently break down organic matter before releasing clean water into the river."
rendered active; e.g. rendered radioactive or luminescent or photosensitive or conductive
"The darkroom timer automatically activated the fluorescent lights when it detected that the film was fully exposed."