Wastewater potentially toxic elements

Repeated application of sludge from the algae pond could result in a progressive accumulation of some toxic elements originally present in the wastewaters fed to the pond. The rate of accumulation of the toxic elements will depend on various site-specific factors such as type of wastewater (municipal wastewater is much less likely than industrial wastewater to contain potentially toxic elements), soil type, texture and pH. It has been estimated that in many areas of the United States, it would require 50 to 80 years before the accumulation of toxic elements reached levels considered dangerous by the EPA for land devoted to food crop production (23). Exceeding these levels of toxic elements would eliminate the possibility of using the land for food crops at a later date. 

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