Nitrogen rich wastewaters (10-400 mg N L-1) are usually produced by municipal, industrial and agricultural wastes, such as effluents from anaerobic treatments. These represent a risk to the environment due to the high nutrient concentrations (nitrogen and phosphorous), which can cause eutrophication of water bodies, deteriorating the quality of the ecosystems. As a solution, the potential nitrogen removal capacity of a novel bio-treatment system, namely the Photo-Activated Sludge (PAS), which is composed of microalgae and bacteria consortia, is presented in this thesis. This novel bio-treatment is based on the symbiosis between microalgae, nitrifiers and heterotrophic bacteria (microalgal-bacterial consortia). Experimental work using photobioreactors for the cultivation of microalgae and bacteria under sequencing batch conditions showed that microalgal-bacterial consortia can remove ammonium 50% faster than solely microalgal consortia. The increase in ammonium removal rates was due to the action of nitrifying bacteria, supplied with oxygen produced by algae. Nitrification was the main ammonium removal mechanism within the microalgal-bacterial biomass, followed by algal uptake and nutrient requirements for bacterial growth. Carbon oxidation and denitrification were the main removal mechanisms for organic carbon. Hence, the role of algae within the microalgal-bacterial system is to provide oxygen to support the aerobic processes. The microalgal-bacterial system offers the possibility of reducing the hydraulic retention time, which can decrease the large area requirements often demanded by algal systems.
1 General introduction
1.2 Problem statement
1.3 Outline of thesis
2 Microalgal-bacterial consortia for wastewater treatment: a review
2.1 Microalgal-bacterial consortia
2.2 Microalgal-bacterial modelling
2.3 Aims of this PhD research
3 Nitrification by microalgal-bacterial consortia for ammonium removal in a flat panel sequencing photobioreactor
3.2 Materials and methods
3.3 Results and discussion
4 Ammonium removal mechanisms in a microalgal-bacterial sequencing-batch photobioreactor at different SRT
4.2 Materials and methods
4.3 Results and Discussion
5 Modelling of nitrogen removal using a microalgal-bacterial consortium
5.2 Materials and Methods
5.3 Results and Discussion
6 Modelling of nitrogen removal using a microalgal-bacterial consortium under different SRTs
6.2 Materials and Methods
6.3 Results and discussion
7 Respirometric tests for microalgal-bacterial biomass: modelling of nitrogen storage by microalgae
7.2 Materials and Methods
7.3 Results and discussion
8 Conclusions and recommendations
8.2 Advantages of microalgal-bacterial consortia for ammonium removal
8.3 Influence of the SRT on the operation of a microalgal-bacterial photobioreactor
8.4 Evaluation of the microalgal-bacterial consortia using mathematical models
8.5 Outlook and concluding remarks
IHE Delft PhD programme leads to a deepening of a field of specialisation. PhD fellows do scientific research, often with conclusions that directly influence their region. At IHE Delft, PhD researchers from around the world participate in problem-focused and solution-oriented research on development issues, resulting in an inspiring research environment. PhD fellows work together with other researchers from many countries dealing with topics related to water and the environment.
PhD research is often carried out in the ‘sandwich’ model. Preparation and final reporting – the first and last portion of the programme – are carried out in Delft, while actual research is done in the fellow’s home country, under co-supervision of a local institute. Regular contacts with the promotor are maintained through visits and long-distance communication. This enables researchers to employ solutions directly to problems in their geographical region.
IHE Delft PhD degrees are awarded jointly with a university. The degrees are highly valued and fully recognised in all parts of the world.