Phosphorus and iron loading to Lake Ontario from waste water treatment plants in Hamilton and Toronto (Ontario)

Resurgences in blue-green algal blooms in the lower Great Lakes led to an examination of the role of phosphorus and iron loading from wastewater treatment plants (WWTP). While phosphorus has been successfully linked to algal blooms in the past, there have been significant reductions in phosphorus concentrations in wastewater effluent with the increased use of iron chloride flocculation. This expansion of iron chloride flocculation use has led to increased iron loading to receiving waters from WWTPs without large-scale tertiary clarification. Data obtained from the Provincial Water Quality Monitoring Network also show that iron concentrations downstream of some wastewater treatment plants are higher than those upstream. Based on recent ecological research on the role of phosphorus and iron in stimulating cyanobacterial productivity, it is concluded that expanded iron chloride use to reduce phosphorus concentrations in wastewater effluent may be stimulating toxic blue-green algal blooms. As blue-green algae are toxic to the environment, it is necessary for an exploration of alternative means of phosphorus removal from wastewater without causing secondary iron pollution.