The public defense of Anbarasan Anbalagan's doctoral thesis in Energy and Environmental Engineer

Doctoral thesis and Licentiate seminars

Datum: 2018-06-19
Tid: 09.00
Plats: MDH, room Delta, Västerås

The public defense of Anbarasan Anbalagan's doctoral thesis in Energy and Environmental Engineer will take place at Mälardalen University on June 19.

The title of the thesis is “A Passage to wastewater Nutrient Recovery Units – Microalgal Bacterial bioreactors”.

The faculty examiner is Professor Francisco Gabriel Acién Fernández, University of Almería, and the examining committee consists of Professor Jukka Rintala, Tampere University of Technology; Associate Professor Oskar Modin Chalmers University of Technology; Docent Sylvia Waara, Halmstad University.

Reserve: Professor Erik Dahlquist, Mälardalen University

The doctoral thesis has serial number 263

Summary

We, human beings, are leading our life as cool as cucumber at the expense of clean freshwater and energy from fossil fuels. The households generate wastewater rich in carbon, nitrogen and phosphorus (e.g. lipids, proteins and carbohydrates, faeces, detergents). Thus, the wastewater treatment plant has to reduce all the nutrients concentration to avoid water pollution. However, the crop nutrients are either lost as chemical sludge or greenhouse and dinitrogen gases during the wastewater treatment.

Have you ever thought the air that we breathe is a waste of naturally occurring tiny creatures called microalgae from lakes, rivers and oceans? They intake greenhouse gas together with crop nutrients and release O2 like plants. The conventional wastewater treatment plant aerates the wastewater mechanically to degrade organic compounds by bacteria. In this context, I aim to utilise microalgae-bacteria symbiosis in the same tank to reduce greenhouse gases and wastewater nutrients, to recycle and to recover crop nutrients from wastewater to the agricultural field.

Is it practical to utilise lab scale cultivation processes in the treatment facility conditions? Initially, I tried to cultivate the microalgae-bacteria combination in a wastewater tank at time intervals of 2, 4 and 6 days. The effective treatment time was determined to be 4 and 6 days using raw wastewater under laboratory conditions. However, the algal-bacterial nutrient removal process was effective only in the presence of external phosphorus in the case of treatment facility conditions.

Additionally, is it possible to utilise this process to remove CO2 from waste gas coming from industries? A cultivation tank connected to a vertical tubular column with waste gas supply was considered. The cultivated liquid was used to absorb the carbon dioxide in the column (similar to forcing pure CO2 in a soda stream) but with varying the liquid recirculation. As a result, almost complete nutrient removal was achieved at higher liquid recirculation under laboratory condition. Thus, the waste gas rich in CO2 can be utilised during the cultivation process.

Furthermore, is it possible to cultivate algae-bacteria under Swedish wastewater temperature (~13˚C) and limited lighting condition?  Longer (6 days) and shorter (1.5 days) treatment time showed that the cultivation was stable under this condition. However, the cultivated biomass showed higher aging of microalga-bacteria or sludge age (time of microalgae-bacteria in the tank before removal) due to rapid settling property in the tank. Thus, the sludge age influenced the removal of wastewater nutrient under limited lighting condition.                                                                                                    

Findings from this work suggest that identification of effective sludge age and treatment time can increase the nutrient removal capacity during wastewater treatment. In doing so, the treatment can be adjusted to higher nutrient removal and most importantly, the crop nutrients can be recovered along with greenhouse gas capture and without any emission of greenhouse gases during wastewater treatment.