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Title: Bioconversion of agricultural wastes from the livestock industry for biofuel and feed production

item MURRY, MARCIA - California Polytechnic State University
item MURINDA, SHELTON - California Polytechnic State University
item HUANG, SU TING - Heliae Corporation
item Ibekwe, Abasiofiok - Mark
item SCHWARTZ, GREGORY - California Polytechnic State University
item LUNDQUIST, TRYGVE - California Polytechnic State University

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 2/1/2019
Publication Date: 3/1/2019
Citation: Murry, M.A., Murinda, S.E., Huang, S., Ibekwe, A.M., Schwartz, G., Lundquist, T. 2019. Bioconversion of agricultural wastes from the livestock industry for biofuel and feed production. In: Hosseini, M., editor. Advanced Bioprocessing for Alternative Fuels, Biobased Chemicals, and Bioproducts. United Kingdom:Woodhead Publishing. p. 225-247.

Interpretive Summary: Large concentrated animal feeding operations (CAFOs) allow competitive animal production in a global market, but intensification of animal production requires intensification of manure recycling. Technologies and methods to recreate feed nutrients (crops) from waste nutrients, with minimal environmental impact, have not kept pace with CAFO development. Today, the rationale of wastewater treatment has shifted from simply reducing the biological oxygen demand (BOD) of organic wastes (primary and secondary aerobic treatment) and eliminating pathogens before discharge into receiving waters to include reclaiming nutrients and purifying water. The review points to knowledge gaps that have slowed the advancement of a leading candidate technology for accelerated manure recycling — algae-based animal feeds. This review provides the basic answers to a critical question: Can manure nutrients be recycled into microalgae-based animal feeds both safely and affordably? The basic conclusions show significant improvements in several key technologies, such as strain selection, species composition, best cultivation practices and harvesting are needed to advance the economics of algae-based waste treatment coupled to biofuel production and co-products derived from algae biomass. This information will be of interest to waste water treatment plant operators, government and non-government organizations, as well as livestock producers in both developed and developing countries.

Technical Abstract: The bioconversion of sunlight energy into biofuels can be coupled to nutrient recovery from organic wastes using systems that employ microalgae grown symbiotically with heterotrophic microorganisms. Microalgae are photosynthetic organisms with high productivity (many strains double in less than a day) that assimilate eutrophying nutrients from wastewaters. They have been used for over 50 years in municipal wastewater treatment and more recently for bioremediation of manure effluents. U.S. livestock industry produces an enormous quantity of manure, as much as 500 million tons of manure per year. Poor approaches to manure management, especially in concentrated feeding operations (CAFOs), have led to serious environmental problems including methane and CO2 emissions and eutrophication of our surface and ground waters by manure nutrients, primarily nitrogen (N) and phosphates (P). Microalgae have gained attention as agents for nutrient bioremediation due to annual yields 7-15 times greater than soy or corn and a low biomass C/N ratio which allows the potential to convert manure nutrients into biomass in smaller land areas than crop plants. Of interest for algae biofuel production is the high amounts of oil (lipid) produced, primarily as triglycerides. Algal neutral storage lipids are similar in structure and molecular weight (carbon chains ranging from 12 to 22) to the oils extracted from terrestrial plants. Microalgae can have oil contents that vary from 15 to 77% of the dry weight compared with 4% in corn. A major cost factor for algal biomass production is the provision of water and nutrients. Here we review progress made in microalgae-based systems using primary manure effluents with high biological oxygen demand (BOD) levels that aerobic microbes decompose into inorganic nutrients including CO2, ammonium and phosphate. Algae take up these products and convert into biomass and through photosynthesis produce O2 needed for bacterial growth. Anaerobic digesters offer an attractive alternative to direct treatment of agricultural wastes with several advantages from a fuel production perspective. During anaerobic digestion, organic matter is mineralized producing methane for fuel and inorganic C, N and P, nutrients needed for algal growth. In each case, a resource and economic synergy are possible as algae-based bioremediation generates revenue from the treatment service and improves the economics of biofuel production.