Nutrient Recycling

Nutrient Utilization and Recycling

When algae biomass is grown and the water is removed, the wastewater from the algae is still rich in nutrients. To decrease operational costs and environmental impact, all available nutrients need to be assessed for possible recycling and also for reducing downstream eutrophication. We have constructed highly controlled growth systems (chemostats and turbidostats) that allow for reproducible physiological conditions. We use these to parameterize growth efficiencies (photons absorbed per unit carbon fixed). We have additionally used an algal growth chamber fitted with an integrating-sphere total-internal-reflection light metering system for recording in real time the total light energy absorbed during growth. This approach has been used to measure the solar to biomass conversion efficiency for algae from the combustion enthalpy of the dried biomass with exceptionally high precision.

Objectives

  1. Characterize the physiology of elite algae strains within the abiotic matrix that regulates growth and carbon partitioning
  2. Characterize carbon dioxide utilization in cyanobacteria at the molecular and cellular levels
  3. Examine biological nutrient supply and protection
  4. Develop and characterize a model pond
  5. Create a model and analysis of nutrient recycling loops

Accomplishments and Discoveries

Sapphire LCA

Many published LCA studies of algae-to-energy processing have modeled (a) lipid extraction and transesterification. CAB-Comm's work focused on (b) hydrothermal liquefaction of algae biomass. N, P are nitrogen and phosphorus fertilizer addition, En are the electricity flows, Qn are heat flows, primarily in the form of natural gas combustion. The fine dashed line distinguishes gas phase recycle. Coarse dashed line demarks the system boundaries.

Part of this research area investigated how algae species utilize nutrients and how that affects biomass growth. Researchers examined whether nitrogen-fixing cyanobacteria (Nodularia) can be viable as outdoor production strains and can provide nitrogen to other microalgae through co-culturing. They also examined interspecific tradeoffs among traits related to growth, biomass yield, and nutrient competitive abilities vs. lipid content and light competitive abilities.

Researchers also indentified combinations of species that greatly "over-yield" or produce far more biomass together than any one of the component species alone, and identified commercially relevant strains that utilize recycled nutrients after hydrothermal liquefaction and oil separation including Picochlorum and Haematococcus

In terms of algae biomass production systems research, a nutrient, water, and carbon mass balance model was created to assess best-practices and technologies for nutrient recycling. Two categories of nutrient and energy recovery technologies, anaerobic digestion and hydrothermal liquefaction, were examined to treat the algal biomass residue, and researchers identified that recycling residuals for energy and nutrient recovery can reduce the carbon intensity of algal biodiesel by as much as 40% under some conditions, compared to exporting these residuals as co-products.

Publications