Toward a zero-waste model: Potential for microorganism growth on agricultural waste products in Hawaii

Microorganisms hold vast potential to address the growing demand for sustainable fuel, feed and other bioproducts. In Hawaii, over 85% of all goods (including food and petroleum) are imported, making the need for renewable products more pressing. The zero-waste model aims to use agricultural waste products from Hawaii, including those unmarketable due to post-harvest damage or pests, as the carbon substrate for the growth of heterotrophic microorganisms. The microbial end-product in turn can be used as a source of high protein or lipid (fat), depending on the species and substrate, for downstream production of biodiesel or other bioproducts. With the view to expand upon the model piloted on the microalgae Chlorella protothecoides grown on papaya culls, this study investigates the growth of four microorganisms on three different growth substrates and compares the composition of end-products. The substrates tested, all waste products, include off-grade culled papaya, off-grade Okinawan sweet potato and crude glycerol, a byproduct of biofuel synthesis from Pacific Biodiesel (Keaau, HI). In this study, we demonstrate the feasibility of microorganism growth on all three waste products and explore optimization of substrate/organism combinations for further investigation. In addition, this study measures proximate composition of the end-products to compare the relative percentage of key components of the dry material (i.e. protein, fat, fiber, ash, etc.) to identify to most viable bioproducts. The results of this study further support to feasibility of developing a zero-waste model for future scale-up at industrial scale of microorganism growth on waste substrate in Hawaii, and more broadly.