In this study, it is hypothesized that higher biomass productivity
and, hence, higher net energy could be attained with the nutrient-rich
AP recycled from HTL than with the standard growth medium. A
theoretical analysis is presented first to justify this hypothesis and
to simulate the effect of HTL temperature on net energy yield. The
hypothesis is then validated with experimental growth data on an
extremophile, Galdieria sulphuraria (hereafter G. sulphuraria), which is
the most versatile known alga with respect to organic carbon utilization
potential [15]. Furthermore, this strain grows at low pH where fewer
heterotrophs survive to compete for carbohydrate and organic nitrogen
sources. We have previously documented the utility of this strain for
direct, one-step, energy-efficient municipal wastewater treatment
defraying the cost of nutrients for algal feedstock production [16–19].
We and others have noted the synergy between algal WWT and
HTL energy extraction [14]. Here we address the energetics of
recycling low-temperature aqueous HTL extracts to boost biomass
productivity