Treated water may be discharged to sewers, or passed through secondary treatment systems such as activated carbon units.

In some cases, this water is contaminated and needs some form of treatment before being discharged to sewers or to receiving waters.

However, when dental amalgam is discharged to sewers, it can be transformed under certain conditions and become harmful to the environment.

Some of the MISA documents (e.g., the 1988 report entitled Controlling Industrial Discharges to Sewers) provided evidence of harmful substances in STP effluent from industrial discharges.

The changes were helped by the introduction of more stringent pollution control legislation, which required industrial waste to be discharged to sewers, and the formation of the Trent River Authority, which had new duties relating to managing water quality issues.

Standards are set for the levels of dust, noise, odour, emissions to air and groundwater, and discharge to sewers or waterways of all chemicals of concern or chemicals likely to be produced during the remediation by processing of the contaminants.

Discharges to sewers or tailings dams, deposits of substances to landfills and the removal of substances from a facility for destruction, treatment, recycling reprocessing, recovery or purification are considered transfers and therefore exempt from being reported under NPI.

Cello has invested considerably in its air and water emissions where 100% of all air emissions are captured in one of three bag houses or a wet scrubber, and all cooling water is now economically recycled rather than being discharged to sewers.