Doctoral dissertation

Dissertation: Microalgae can be used in wastewater treatment to extract nutrients and organic matter

Microalgae can efficiently remove nitrogen and phosphorus from wastewaters. Apart from enhancing wastewater treatment efficiency, the microalgae-based treatment systems were developed to promote microalgal growth as the produced microalgal biomass can be used in the production of e.g. biofuels and fertilizers.

Various kinds of wastewaters are produced in large quantities due to urbanization, industrialization and population growth. Efficient treatment of wastewaters is essential as wastewaters contain environmentally harmful substances, such as biodegradable organics, nutrients, metals and pathogens. However, many of the traditional wastewater treatment processes are energy- or resource-intensive.

Microalgae could enable more sustainable wastewater treatment systems and result in the recovery of nitrogen and phosphorus in a utilizable form. The generated microalgal biomass can be used as a feedstock for biofuel and fertilizer production, for example. Before its potential commercialization, further improvements are needed for efficient wastewater treatment with microalgae.

In her doctoral dissertation, MSc Ran Tao focused on nitrogen and phosphorus removal from wastewaters by the freshwater microalgae Chlorella vulgaris and Scenedesmus acuminatus. Her main objective was to enhance nutrient and organic matter removal efficiency using microalgal cultures in photobioreactors, while promoting microalgal biomass production.

Tao's results demonstrated that Scenedesmus acuminatus was able to remove nutrients efficiently from liquid digestates, in other words waste streams originating from the anaerobic digestion of sludge from pulp and paper industry. The growth of Scenedesmus acuminatus in the liquid digestates resulted in one of the highest biomass concentrations (7.8–10.8 g L-1 as dry weight) reported for microalgae in real wastewaters.

“To promote the algae-based biorefinery applications for wastewater treatment, we must be able to select the best suited microalgal species for each specific waste stream,” Tao notes.

Tao further demonstrated that zeolite in a microalgal membrane photobioreactor can work as an adsorbent for ammonium removal as well as a carrier for microalgal growth. In the membrane photobioreactor, the addition of a low concentration of zeolite to a mixed microalgal culture enhanced ammonium removal efficiency and microalgal biomass concentration.

The doctoral dissertation of MSc Ran Tao in the field of environmental engineering titled Nutrient and organic matter removal from wastewaters with microalgae will be publicly examined in the Faculty of Engineering and Natural Sciences at Tampere University at 2:00 pm on Wednesday, 22 May 2019 in the Festia building, room FA032 (Pieni sali 1), (address: Korkeakoulunkatu 8, Hervanta Campus, Tampere University, Finland). The Opponents will be Professor Martin Romantschuk from University of Helsinki (Finland), Dr. Bernhard Drosg from University of Natural Resources and Life Sciences (Austria), and Professor Monica Odlare from Mälardalen University (Sweden).

Ran Tao's doctoral research was conducted in the framework of the Advanced Biological Waste to Energy Technologies (ABWET) Innovative Training Network (ITN) European Joint Degree Programme. ABWET has four partner organizations: University of Cassino and Southern Lazio (Italy, coordinator), Université Paris-Est (France), IHE Delft (the Netherlands) and Tampere University (Finland). The Examination Committee of Ran Tao's doctoral dissertation includes one representative from each partner organization.

Ran Tao comes from China and currently works as a researcher in the Faculty of Engineering and Natural Sciences at Tampere University.

The dissertation is available in the Faculty of Engineering and Natural Sciences (Konetalo building K2222A) at Tampere University and by request from suvi.ikonen@tuni.fi

Further information: Ran Tao, tel. +358 40 3616527, ran.tao@tuni.fi

Watch the defence online here.