The efficiency of microalgae-based remediation as a green process for industrial wastewater treatment

Abstract

Wastewater treatment including microalgae is an economically promising and environmentally friendly alternative to conventional wastewater treatment due to the concurrent nutrient removal and production of high-value biomass. This work aimed to choose the most suitable type of wastewater and its appropriate dilution for sustaining microalgal growth by testing unialgal versus mixed microalgae cultures and raw versus autoclaved wastewater. Based on pilot experiments including microplate screening, unialgal cultures of Chlorella emersonii grown in 1:5 diluted, non-autoclaved wastewater were selected as the optimum scenario for further testing. In the main experiments, Chlorella emersonii was cultivated in Erlenmeyer flasks and bubble column reactors. Additionally, a photoautotrophic biofilm was grown in flumes. We studied three types of wastewater originating from a large municipal wastewater treatment plant, a brewery, and a dairy. Dairy wastewater performed best in all cultivation systems and resulted in a maximum biomass per irradiated area of around 145 μg cm−2 chlorophyll-a of Chlorella cultures in bubble columns, followed by 105 μg cm−2 in flumes run by a photoautotrophic biofilm. Furthermore, phosphorus reduction of 96 % for dairy, 40 % for the brewery, and 43 % for municipal wastewater were achieved in the flumes. Due to the easy harvest of algae biomass, low construction and operation costs, flumes represent a recommendable cultivation system for dairy wastewater treatment on a larger scale.