Fate of Metals in Wastewater Discharge to Ocean

Trace metals with sewage and sludge particulates from the City of Los Angeles Hyperion Treatment Plant are found to mobilize to a great extent from solids to seawater in the ocean environment. The fate of these metals and the amount of annual transport to the ocean are evaluated, based on: (1) Concentrations of trace metals in the wastewater particulates; (2) sediment metal concentrations in the proximity of sewer outfalls; (3) the degree of metal release from wastewater particulates upon mixing and dilution with seawater under laboratory conditions; and (4) the settling velocity of sewage and sludge particulates. More than 90% of trace metals, such as cadmium, copper, lead, nickel, and zinc in the sludge particulates are solubilized through biochemical reactions. A higher degree of solubilization from the mixture of primary and secondary effluents is observed.