Microalgae-based wastewater remediation: Linking N:P ratio and nitrogen sources to treatment performance by Chlorella vulgaris and biomass valorisation
S.A. Sousa, Carlos Alberto Machado, Ana F. Esteves, Eva M. Salgado, Joana Maia Dias, João L. Vilaça, José C.M. Pires
Abstract
Microalgae-based systems are promising for wastewater bioremediation due to their ability to remove nutrients while producing valuable biomass for various applications. However, treatment efficiency is affected by fluctuations in wastewater characteristics, especially nitrogen and phosphorus sources and their concentrations and N:P ratio. This study aimed to assess the combined impact of varying N:P ratios and nitrogen sources on the growth of Chlorella vulgaris , wastewater treatment, and biomass composition. Four N:P ratios (9, 14, 20, and 27) were studied in combination with three sources of nitrogen (NO 3 − , NH 4 + , and both). Chlorella vulgaris grew successfully in all synthetic effluents, and the highest specific growth rate (0.74 ± 0.07 d −1 ) was obtained for the N:P ratio of 9 using NH 4 + as the only nitrogen source. Nitrogen was fully removed at an N:P ratio of 9, regardless of the nitrogen source. Phosphorus removal reached 99 % in all assays. The composition of Chlorella vulgaris biomass ranged from 18 ± 1 to 42.5 ± 0.7 % ( w /w) carbohydrates, 12.5 ± 0.6 to 22.3 ± 1 % (w/w) protein, and 9.9 ± 0.1 to 16.7 ± 0.5 % (w/w) lipids. Nitrogen limitations increased carbohydrate and lipid content while reducing protein content in the biomass. Combining NO 3 − and NH 4 + increased protein content compared to using NO 3 − alone, but a predominant NH 4 + source led to lower protein levels. These results demonstrate the microalgae's potential to treat diverse wastewaters with variable compositions, achieving optimal growth and nutrient removal at an N:P ratio of 9 when NH 4 + is the nitrogen source.