(31e) Nutrients (N & P) Recovery from Algae Hydrolyzate By Hydrothermal Mineralization

Nutrients (N & P) Recovery from
Algae Hydrolyzate by Hydrothermal Mineralization

Ali
Teymouri and Sandeep Kumar

Department of Civil and Environmental Engineering,
Old Dominion University, Norfolk, VA 23529

Abstract

Microalgae are being considered a sustainable feedstock to produce advanced
biofuels and biocommodities. However, there is a considerable cost associated
with nutrients (N & P) use during algae cultivation particularly
phosphorous which is a finite natural resource. It
is important to note the need to seek comprehensive recovery systems for
biomass and all of its components in order to exploit the microalgae potential.
In this study, majority of algae nutrients were extracted in hydrolyzate
(aqueous phase) using Flash Hydrolysis (FH), a process which fractionates nutrients
and lipids under subcritical water conditions in a very short residence time. The
FH process was proved to be an environmentally benign method which extract more
than 60 wt% of the total nitrogen and more than 80 wt% of phosphorous content
(dry basis) from Scenedesmus sp.
within 9 s of residence time above 280ºC in the hydrolyzate while preserving the lipids in solids(biofuel intermediates).

Followed by the FH process, the algae hydrolyzate was subjected to
hydrothermal mineralization (HTM) in the temperature range of 100-280ºC in a batch
reactor. The HTM is a technique to recover and store nutrients as solids
(precipitates) that could be used as slow-released fertilizers. Solubilized N
and P precipitates as hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂)
and struvite (MgNH₄PO₄.6H₂O) by the addition
of Ca(OH)₂/Mg(OH)₂ mineralizer under hydrothermal
condition. Algae hydrolyzate and model compounds were studied for HTM to
measure the nitrogen and phosphorus recovery. More than 90% of the nutrients
were recovered in solid forms which could be stored and recycled as a nutrient
source.

A comprehensive characterization of effluent liquid and solids were
conducted using ion chromatography, XRD, SEM, FT-IR in order to determine the HTM
process parameters and mineralizers use. The integration of HTM with FH or
Hydrothermal Liquefaction (HTL) of algae is a novel concept considering that no
additional heating or pressurization will be required since the algae hydrolyzate
is a hot-compressed liquid which is directly suitable for HTM. The results of
this study suggested that it will provide an opportunity to produce biofuels and recover nutrients simultaneously.