Work hard to process waste (5)
I believe the answer is:
sweat
'work hard' is the definition.
(thesaurus)
'process waste' is the wordplay.
'process' is an anagram indicator.
'waste' with letters rearranged gives 'SWEAT'.
'to' acts as a link.
(Other definitions for sweat that I've seen before include "It's hard work" , "Perspire" , "Salty fluid secreted by glands" , "Salty fluid secreted by the body" , "(Of argument) intense" .)