A preliminary study of processing seafood shells for eutrophication control

Shells from the seafood processing industry in New Zealand are currently an under-utilized waste resource. In this study we investigate the processing conditions required for the creation of calcium oxide (lime) from green-lipped mussel (Perna canaliculus) and pacific oyster (Crassostrea gigas) shells. Lime is commonly used in wastewater treatment for the removal of phosphorous compounds from water, thus providing a means of eutrophication control. Mussel and oyster shells were processed in a horizontal tube furnace at various temperatures (650-800 degrees C) in both air and nitrogen environments. From X-ray diffraction (XRD) and weight-loss measurements, the extent of limestone calcination was found to increase with increasing furnace temperature for both shell species and furnace atmospheres. Analysis showed that the lime was present as a layer on the surface of the shell particles. From scanning electron microscope (SEM) images, significant changes in the surface morphology of the raw shells were observed as a result of heat treatment in both air and nitrogen atmospheres. Preliminary testing of shells heat-treated in both air and nitrogen atmospheres indicated that both types of shell removed about 90% of phosphates in water within 30 min, whereas up to 40% of phosphates were removed with untreated shells. Our results for heat-treated oyster shell differ slightly with studies in the literature, which report an absence of compositional and structural changes in an air atmosphere. (c) 2007 Curtin University of Technology and John Wiley & Sons, Ltd.