Microalgae biomass production is recognized as a cost-effective and sustainable alternative to currently used approaches to tertiary wastewater treatment. However, such limitations, as algae biomass separation from water, process efficiency in cold climate and the algae biomass ability to reduce micropollutant content in wastewater hamper this method from full-scale use. This review discusses the identified drawbacks and offers possible improvements and modifications for wastewater phycobioremediation.

Four microalgal species, Chlorella vulgaris, Botryococcus braunii, Ankistrodesmus falcatus, and Tetradesmus obliquus were studied for enhanced phosphorus removal from municipal wastewater after their exposure to phosphorus starvation. Microalgae were exposed to phosphorus starvation conditions for three and five days and then used in a batch experiment to purify an effluent from a small WWTP. After 3-day P-starvation, C. vulgaris biomass growth rate increased by 50% and its PO₄ removal rate reached > 99% within 7 days. B. braunii maintained good biomass growth rate and nutrient removal regardless of the P-starvation. All species showed 2–5 times higher alkaline phosphatase activity increase for P-starved biomass than at the reference conditions, responding to the decline of PO₄ concentration in wastewater and biomass poly-P content. The overall efficiency of biomass P-starvation on enhanced phosphorus uptake was found to be dependent on the species, N/P molar ratio in the wastewater, as well as the biomass P content.

Eutrophication-promoting phosphorous loads originating from wastewater treatment plants are commonly controlled by chemical precipitation in the tertiary treatment phase. However, this approach is costly and generates additional waste. Therefore, inexpensive and sustainable methods for wastewater post-treatment are wanted. The artificial aquatic food-web that performs wastewater phycoremediation by algae and subsequent biomass harvest by filter-feeding organisms not only requires low energy consumption but also produces biomass for treatment process cost recovery. Still, the knowledge on its performance at different scales and under different climates are limited. In this review, the application possibilities of the artificial aquatic food-web for domestic wastewater post-treatment is discussed, focusing on its use in cold climate regions. Considering the reduced biological activity of aquatic organisms at low ambient temperature, possible solutions for its performance and prospect application at low temperatures are suggested. Finally, directions for future research regarding the practical use of artificial aquatic food-web are highlighted.

Promocijas darbā demonstrēta fosfora izdalīšana no komunālajiem notekūdeņiem palielinātā ātrumā, izmantojot fosfora deficītam pakļautu mikroaļģu biomasu.

The Thesis demonstrates the potential of enhanced phosphorus removal from municipal wastewater using microalgal biomass exposed to phosphorus deficiency conditions. The study focuses on identification of appropriate microalgal species for production in municipal wastewater after P-starvation, developing a reliable P-starvation technique and identifying indicators for phosphorus deficiency status quantification. Further, the optimum initial conditions for rapid phosphorus removal and valuable algal biomass production have been identified and verified during a continuous process in a sequencing batch photobioreactor. The author of this study shows that the results from batch experiments and optimization model validation in sequencing batch photobioreactor have provided knowledge that can be used for existing industrial scale microalgae cultivation systems as well as for microalgal based wastewater treatment system development.