Hydrothermal Liquefaction of Wastewater Algae

Concentrating dilute resources in waste streams into useful products while extracting energy and fuels along the way.

Wastewater Cultivated Algae:

Algae is cultivated by collaborators using effluent from after the second clarifier from the Lawrence, KS Municipal Wastewater Treatment Plant (WWTP).  We then determine the elemental content and energy density.  Cultivating algae with wastewater serves dual benefit by polishing wasterwater to reduce nutrient concentrations that pose environmental hazards while producing biomass for fuel conversion.  This wastewater algae is very different than typical controlled fertilized algae; comparatively having lower lipid and carbon content with higher inorganic and oxygen content.  This combination may seem to be a counter measure to producing fuels, however after thermochemical conversion with subcritical water the high level of inorganics seem to play catalytic roles in producing a biocrude of superior quality to those produced from controlled fertilized cultivated algae.

Hydothermal Liquefaction (HTL):

Roberts et al. Energy & Fuels, 2013.

We currently have the capacity to perform thermochemical conversion with variable reactor (batch) volumes from 10mL to 1.5gal and are working toward a continuous reactor design.  HTL of WW-algae give three main products; biocrude oil, solid biochar, and an aqueous co-product (ACP).  Our latest study calculates that the Lawrence WWTP can produce 6-9 barrells of crude oil and >1.5 metric tons of biochar perday.  The biocrude has similar properties to that of petrolem crude in terms or elemental and molecular composition, H/C and O/C ratios, and energy density.  The high level of biochar production is a direct result from the high level of inorganics present in the starting algae.  Where the majority of the inorganic material resides in the solid biochar.  The ACP contain some of the algal phosphorus and >50% of the algal nitrogen, therefore is suitable for studies for recycling to algal growth. 

Biochar:

Algal biochar has multiple uses.  The biochar still contains >20% organic material and can be burned as a coal supplement; burning much cleaner than coal because the low levels of sulfur and soot formation.  A more valuable use for biochar would be as either an absorbent material such as activated carbon or as a soil amendment/ solid fertilizer.  We are currently pursuing the efficacy of biochar for such applications.

ACP:

Current research is ongoing with collaborators to determine optimal recycle amounts of ACP that could be recycled for both heterotropic (bacteria) and autotrophic (algae) growth for more available biomass to be converted to crude oil. 


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