My corrections are shown below:
The city's sanitation company managed to reduce the theft of manhole covers and sewage grates by 50%. The vandals used to steal 10 items every week. Each one costs the city R$ 250,00, according to the sewage system manager.
This reduction was due to substituting iron covers for concrete ones.
According to the manager, the iron covers will remain only in the city center because it is more difficult to steal them as the *streets are generally busier.
*And in many cities there are surveillance systems (CCTV) downtown.