# Combination of Exhaust Gas Fermentation Effluent and Dairy Wastewater for Microalgae Production: Effect on Growth and FAME Composition of Chlorella sorokiniana

## TL;DR

This study explores using a mix of dairy wastewater and gas fermentation effluent to grow microalgae, achieving high biomass and nutrient removal while improving fatty acid content for potential feed use.

## Contribution

The first use of gas fermentation effluent for microalgae cultivation and its combination with dairy wastewater to enhance biomass and nutrient removal.

## Key findings

- A 50:50 dilution of effluent and dairy wastewater achieved highest biomass accumulation (1.96 g L−1) and productivity (0.5 g L−1 d−1).
- The strategy removed 100% of nitrogen and phosphate, 68% of sulfate, and 61% of carbon, showing strong bioremediation potential.
- The fatty acid profile showed increased polyunsaturated fatty acids, improving the biomass's value as a feed supplement.

## Abstract

Microalgae cultivation in wastewater is a promising strategy for reducing nutrient loads and generating biomass that can be further exploited. Although microalgae grown under such conditions are not suitable for high-value applications, the resulting biomass can still be valuable for uses such as biofuels, biofertilizers, or animal feed. In this study, Chlorella sorokiniana was cultivated in dairy wastewater and, to the best of our knowledge, for the first time in a spent effluent from gas fermentation, to assess its potential as a sustainable growth medium. Growth kinetics and biomass productivity were evaluated at different dilution ratios, and it was found that high concentrations of ammonium and hexanol in undiluted effluents were inhibitory, while an optimized 50:50 dilution led to the highest biomass accumulation (1.96 g L−1) and productivity (0.5 g L−1 d−1) of C. sorokiniana. This strategy significantly reduced the nitrogen (100%), phosphate (100%), sulfate (68%), and carbon (61%) contents, demonstrating effective bioremediation activity. Furthermore, the fatty acid profile revealed an increased polyunsaturated fatty acid fraction, enhancing the potential of C. sorokiniana biomass as a feed supplement. Overall, contributing to the circular bioeconomy, this approach is scalable and cost-effective, reducing freshwater and chemical dependency in microalgae biomass production.