Summer 2023 was busy at the Solbergstrand pilot facility. The two 1000-liter raceway ponds were operated for a cumulative 115 days and produced more than 1.5 kilos of freeze-dried biomass, which was delivered to our research partners. Cultivation was divided into three semicontinuous runs where, after the initial inoculation, the culture was maintained by exchanging 40% of the volume with fresh tertiary effluent twice weekly. In addition to the biomass produced, these experiments provided important data on the system's productivity. These experimental runs maintained a relatively stable biomass with an average density between 0.1 and 0.15 g/l cell dry weight for a period of 30 to 40 days without reinoculation.
ALGECO aims to both remediate the wastewater effluent and to produce algal biomass for downstream applications. In this context, system productivity can be considered as the amount of biomass produced given the volume of water remediated over a given amount of time (g/l/day). We have now demonstrated at the pilot scale that between 0.02 and 0.04 grams of dry algal biomass can be produced per liter per day.
Nutrient depletion rates have been investigated under batch operating conditions with smaller volumes during laboratory experiments. The results indicate the depletion of inorganic nitrogen from the wastewater effluent to be approximately 0.1 mg/l/hr. Therefore, effluent with an initial inorganic nitrogen concentration of 10 mg/l can be fully depleted with a retention time of 4 days.
These results will inform further pilot scale experiments scheduled for spring 2024. We expect to improve upon these results and demonstrate the full potential to apply this technology at the VEAS wastewater treatment plant.