Zebra mussel shells as an alternative mineral resource for lime production as a phosphorus precipitant

Zebra mussels are an invasive species to North America and are presently found in many rivers and lakes in prolific numbers. Along with many other issues, zebra mussels present a problem when their shells are deposited on shore, carpeting beaches and reducing beach usability. A possible solution presented in this study is to use the zebra mussel shells as an alternative mineral resource to mined calcium carbonate for the production of lime to remove phosphorus in wastewater. Heat-treated coarse (500-1000 μm) and fine (<75 μm) zebra mussel shell dosed to 10 mg L^-1 phosphate solution at 0.50 g L^-1 and 0.25 g L^-1, removed over 99% phosphorus while maintaining pH levels significantly lower than pure calcium hydroxide dosed under the same conditions. It was found that ground zebra mussel shells (<75 μm) heated for 1 h at temperatures of 600°C, 700°C, 800°C, 900°C, and 1000°C were capable of removing varying levels of phosphorus in water. Shells heated at 800°C and dosed at 1.00 g L^-1 reduced phosphorus in collected real wastewater effluent by 99.48%. It was also shown that shells heat treated at 1000°C achieved 98.7% phosphorus removal when dosed at 0.25 g L^-1, while maintaining a final effluent pH of 9.13, demonstrating the lowest overall energy costs of any of the effective shell treatments. The results indicate that zebra mussel shells show promise as an alternative resource for phosphorus precipitation in wastewater.