@phdthesis{6941350,
  abstract     = {{In recent years, microalgae have received increasing attention in biotechnology research with regards to producing protein and polyunsaturated fatty acids (PUFAs) as human and animal nutrition and removing nutrient from wastewater. Because of their large cell/colony size and thick cell wall with high cellulose content, benthic filamentous algae and their communities have potentials of being more resistant to invertebrate grazers and easier and cheaper to harvest than the unicellular algae. Accordingly, benthic algae based bioreactors have been developed and are widely accepted in wastewater treatment. 
Algal biomass production, biochemical composition and nutrient removal capacity from wastewater are species-specific and highly depend on the wastewater composition (N/P type, concentration and ratio) and operation conditions (light, temperature, harvesting frequency, etc.). For an attached cultivation system, shear stress induced by water current is also crucial in biofilm formation on the substrate. Therefore, selection of the appropriate algal species and optimization of operational conditions will be vital in maintaining the dominance of benthic algae and improving biomass production and nutrient removal efficiency in a time and cost efficient way. Accordingly, four research chapters explore the performances of several benthic filamentous algae and their communities in nutrient removal from horticultural wastewater and the consequent biomass production and biochemical composition through indoor flasks and outdoor Algal Turf Scrubber (ATS).
In Chapter 1, the background information of algae-based technologies in nutrient removal from wastewater and relevant factors of the cultivation process was presented.
In Chapter 2, biomass of four benthic filamentous green algae Klebsormidium sp. LJ1, Klebsormidium sp. LJ2, Stigeoclonium sp. LJ1 and Uronema sp. was harvested from exponential growth phase, stationary phase, nitrogen deprivation and dark treatment. The four species had significantly different total protein content and fatty acid profiles. They had a protein content of 29-49% of dry weight in the exponential phase. The increasing culture age, nitrogen deprivation and dark treatment significantly increased their polyunsaturated fatty acids (PUFAs) percentage of total fatty acids (TFAs) from 21-58% to 55-87% of these four species. Klebsormidium spp. and Stigeoclonium sp. LJ1 can be good potential sources of C18:2ω6 and C18:3ω3 respectively.
In Chapter 3, three benthic filamentous green algae Klebsormidium sp. LJ2 and Stigeoclonium spp. and one cyanobacterium Pseudanabaena sp. were cultivated under varying N/P conditions in batch model. The four species could adapt to a wide range of N/P ratio and the proper N/P ratios for nitrogen and phosphorus removal were 7 to 10, 5 to 12, 5 to 15 and 7 to 20 for Klebsormidium sp. LJ2, Stigeoclonium sp. LJ1, Stigeoclonium sp. LJ2 and Pseudanabaena sp. respectively. The N/P ratio significantly influenced the algal growth and phosphorus uptake process, while nitrogen uptake process was less influenced by N/P ratio. The nitrogen and phosphorus content varied greatly following the increase of N/P ratio from 1:1 to 20:1 and the nitrogen and phosphorus recovery rates were 73-91% and 78-99% respectively. In addition, Stigeoclonium sp. LJ2 had a high capability of removing phosphorus from wastewaters of low N/P ratio, while Pseudanabaena sp. was highly suitable for removing nitrogen from wastewaters with high N/P ratio and high nitrogen concentration. A better understanding of the physiological diversity and stoichiometry of benthic algae and their habitat requirements can contribute significantly to selecting the appropriate algal strains or combinations for the large-scale application in nutrient removal from wastewater.
In Chapter 4, 1 m2 scale ATS was built to investigate the algal community, biomass production and nutrient removal performance of biofilms with different inoculums of benthic algal communities following the seasonal variations in Belgium. The biomass production in this study was relatively low, which was 0.1-1.9 g dry weight m-2 d-1 in spring, 0.7-4.9 g dry weight m-2 d-1 in summer and 0.2-1.6 g dry weight m-2 d-1 in autumn. Ash, carbon, nitrogen and phosphorus content was about 13-27%, 41-49%, 6-9% and 1.3-2.3% of dry weight respectively. At a low flow rate of 2 L min-1, the benthic filamentous algae Stigeoclonium had a longer-lasting dominance on the ATS than at high flow rate. In addition, it indicated that temperature and solar irradiance were the main limiting factors of biomass production and nutrient removal under the natural conditions of Belgium and flow rate was a potential factor influencing algal community, biomass production and nutrient removal of the ATS.
In Chapter 5, to assess the potential of the benthic filamentous algae in nutrient removal and reclaim from horticultural wastewater, three species Klebsormidium sp. LJ2 and Stigeoclonium spp. were cultivated in 250 ml laboratory flasks in monoculture and mixture as well as in 1 m2 scale outdoor ATS with different flow rates. Stigeoclonium spp. Competed well with the naturally occurring wastewater microalgae and contributed to most of the biomass production both in laboratory flasks and outdoor ATS with a relatively low flow rate of 2-6 L min-1 (3-9 cm s-1). The low flow rate facilitated the dominance of benthic filamentous algae, while the high flow rate enhanced the biomass production and nitrogen removal on the ATS. Additionally, phosphorus removal was less influenced by flow rate because of chemical precipitation and/or surface adsorption onto the periphyton or the plastic liner.
Chapter 6 finishes with a general discussion of this work and proposes further opportunities and challenges of benthic algal community in large scale applications. To conclude, the main strengths of the presented benthic algal community are the priority effects of certain species on the benthic algal community composition and the differences in biomass production and nutrient removal at various flow rates. Further optimizations regarding selecting the species with high light utilization efficiency and tolerance of low temperature and the appropriate substrates are needed to set the stage for the commercial applications.}},
  author       = {{Liu, Junzhuo}},
  keywords     = {{Waste water treatment,Nutrient removal,Benthic algae,Algal Turf Scrubber}},
  language     = {{eng}},
  pages        = {{170}},
  publisher    = {{Ghent University. Faculty of Sciences}},
  school       = {{Ghent University}},
  title        = {{Nutrient removal from horticultural waste water by natural and assembled communities of benthic algae}},
  year         = {{2015}},
}