Abstract
The methods of separation of microalgae has a significant impact in the economic aspects of their cultivation. In this study, pine bark was used as a substrate for immobilization of microalgal biomass cultivated in raw municipal sewage. The experiment was conducted in cylindrical photobioreactors (PBRs) with circulation of wastewater. Biomass was cultivated for 42 days. After that time, abundant growth of the biofilm with microalgae on the surface of pine bark as well as improvement of the quality of treated sewage were observed. The efficiency of removal of nutrients from wastewater was 64–81% for total nitrogen and 97–99% for total phosphorus. Moreover, the concentration of suspended solids in sewage was reduced, which resulted in a decrease in turbidity by more than 90%. Colorimetric analysis and Volatile Matter (VM) content in the substrate showed a decrease in the Higher Heating Value (HHV) and concentration of VM due to the proliferation of biofilm.
Highlights
The methods of separation of microalgae has a significant impact in the economic aspects of their cultivation
The application of biofilm to microalgae cultivation causes their concentration, which reduces the costs of production of biomass, it makes it difficult to measure the amount of biomass[3,40]
Biofilm limits the availability of light due to the phenomenon of self-shading and the presence of bacteria, which affects the synthesis of bioproducts[3,7]
Summary
The methods of separation of microalgae has a significant impact in the economic aspects of their cultivation. Compared to the production of terrestrial plants biomass (€0.20 kg−1 for soybeans and €0.35 kg−1 for wheat and corn2), these are significant amounts Such large financial outlays in microalgae production in PBRs are generated mainly by the preparation of cultivation medium, irradiation, harvesting of biomass, CO2 supplementation and mixing[5,6,7]. One of the methods of separating the microalgae suspension is its immobilization in the form of a biofilm on a solid substrate[8,9] This system significantly reduces the costs of cultivation in comparison with conventional methods of separation (flocculation, membrane filtration, centrifugation etc.) and facilitates the harvesting of biomass[3,6,7]. The use of biofilm and sewage in algae cultivation contributes to a significant reduction of costs of biomass production, and to the removal of nutrients, heavy metals, suspended solids, as well as toxic organic compounds[10,17,22]
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