Final Report: Flash Hydrolysis of Microalgae for On-site Nutrients Recovery and Biofuels Production

EPA Grant Number: SU835501
Title: Flash Hydrolysis of Microalgae for On-site Nutrients Recovery and Biofuels Production
Investigators: Kumar, Sandeep , Drake, Hannah , Garcia Moscoso, Jose Luis , Mfrase-Ewur, Kwamena , Popov, Sergiy , Ricci, Jonathan D , Talbot, Caleb , Teymouri, Ali , Wilson, Paul E
Institution: Old Dominion University
EPA Project Officer: Levinson, Barbara
Phase: I
Project Period: August 15, 2013 through August 14, 2014
Project Amount: $15,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2013) RFA Text |  Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Energy , P3 Challenge Area - Materials & Chemicals , P3 Awards , Sustainability

Objective:

Goal 1: Application of subcritical water as a green solvent to process microalgae.
Expected Outcomes:

  • Novel reactor design with tunable residence time for protein extraction;
  • Kinetics suitable for designing a pilot/demo-scale continuous reactor;

Goal 2: Analysis, separation, and characterization of protein, peptides, and amino acid in algae hydrolyzate for the subsequent application.
Expected Outcome:

  • Identification of intermediate compounds to understand the reaction pathways;

  • Knowledge of proteins/sugar derived compounds in the hydrolyzate of microalgae

Goal 3: Analysis and characterization of lipids-rich solids after Flash Hydrolysis.
Expected Outcomes:

  • Knowledge of the composition of lipid-rich residues that can guide its application in liquid fuels production

Summary/Accomplishments (Outputs/Outcomes):

Goal 1: Based on the yields of soluble peptide and arginine in aqueous phase and lipid-rich solids, Flash Hydrolysis at 280ºC and 9 s of residence time in a plug flow reactor was considered as optimum for processing Scenedesmus spp. From the experimental data of Flash Hydrolysis obtained of wet algae biomass (240 and 280ºC temperatures and 6, 9, and 12 s residence times), reaction kinetics parameter were determined. It was observed that protein solubilization followed a 2nd order reaction with activation energy of 40.71 kJ/mol and the arginine (the major free amino acid in algae hydrolyzate) solubilization was a 0thorder reaction with activation energy of 53.58 kJ/mol.

Goal 2: The algae hydrolyzate (aqueous product) contained up to 72% of the nitrogen that was measured in the algae biomass, and it’s now present in the form of soluble peptides, arginine and ammonia (as NH4+). Also in soluble forms were phosphorus (P), potassium (K) and sulfur (S) that were almost completely extracted from the biomass. All of these extracted elements are important nutrients for algae growth and they are present in the hydrolyzate in soluble forms that could be recycled and used to grow more algae significantly reducing the amount of fertilizers needed. It was observed that phenol fraction in hydrolyzate was much lower (less than 1/100th) when compared to conventional hydrothermal liquefaction (HTL). This helps in reducing phenol toxicity even if it is directly recycled without any dilution. The NMR and FT-IR spectra of algae hydrolyzate (freeze dried) indicated that the extracted protein is present mainly as water-soluble peptides and some as free amino acids. The NMR spectrum of the freeze dried product showed peaks that are characteristic of protein/peptide side chain carbons. The elemental analysis performed to the freeze-dried algae hydrolyzate showed 48.05 wt% C, 11.36 wt% N, and 7.12 wt% H. The high nitrogen content in the freeze-dried powder and IC results further supported the presence of high amount of peptides and amino acid.

Goal 3: The amount of solids reduced gradually with higher temperatures and residence times. The solids collected after Flash Hydrolysis was rich in carbon (>60%) and lipids content and depleted in nitrogen. These solids are sterilized, non-perishable, and hence can be stored for alonger period of time. The lipid-rich solids (62 wt%) were characterized as a suitable feedstock (energy-rich biofuels intermediate) for a biofuels production. On the material balance, 3.05 g of Scenedesmus spp. (dry basis) produced 1.75 g of algae hydrolyzate (freeze dried) and 0.87 g of lipid-rich residue after Flash Hydrolysis at 280°C and 9 s.

Conclusions:

Flash Hydrolysis can extract and solubilize up to 72% of the protein from algae biomass using only water under subcritical conditions in a plug flow reactor in seconds of residence time. Besides nitrogen (from algae protein) being extracted (as soluble peptides and amino acids) in substantial quantities, phosphorus, potassium, and sulfur are also extracted in aqueous phase. The direct use for these nutrients for cultivating more algae biomass will help in making algae cultivation a closed loop/sustainable system. Additionally, the soluble peptides and amino acids could be separated and purified separately as co-product to make algae to biofuels more cost- competitive. Further studies are required to validate the potential use as food and feed additive. The formation of phenols and other nitrogenous aromatic compounds as formed in conventional biomass hydrothermal liquefaction processes were minimized during Flash Hyrolysis process. The solid product was rich in lipids and carbohydrates while depleted in proteins, making it a much better feedstock for biofuels production.

Journal Articles:

No journal articles submitted with this report: View all 5 publications for this project

Supplemental Keywords:

Flash Hydrolysis, Scenedesmus spp., nutrients, amino acids, peptides, algae hydrolyzate

Progress and Final Reports:

Original Abstract