# Influence of Light, Temperature, and Nutrient Availability on Growth and Biochemical Composition of Scenedesmus quadricauda Cultivated in Municipal Wastewater

## TL;DR

This study shows that Scenedesmus quadricauda algae can be successfully grown in municipal wastewater, effectively reducing nitrogen and phosphorus levels while adapting to environmental factors like light and temperature.

## Contribution

The study demonstrates the feasibility of using municipal wastewater for algae cultivation and identifies key environmental factors influencing algal growth and biochemical composition.

## Key findings

- Algae cultivation in wastewater reduced nitrogen and phosphorus concentrations by up to 89% and 86%, respectively.
- Optimal growth occurred at 25 °C with higher light levels increasing biomass yield.
- Wastewater-grown algae had higher carbohydrate content and lower protein and lipid content compared to BB medium.

## Abstract

Municipal wastewater contains high amounts of nitrogen (N) and phosphorus (P), as well as other compounds that are harmful to the environment; however, it can also be used as an algae growth medium. In this study locally (Lithuania) isolated algae Scenedesmus quadricauda were cultivated in local (Vilnius city) municipal wastewater. Data show that Scenedesmus algae can be grown in municipal wastewater as successfully as in Bold’s basal medium for 14 days. Algae cultivation significantly reduced the concentration of organic nitrogen forms and phosphate levels. The nitrogen concentration in wastewater after cultivation was reduced to 8 mg N L−1 (up to 89% reduction in total nitrogen concentration). Phosphorus concentration was reduced to 5.4 mg P L−1 (up to 86%). The analysis indicates that the optimal temperature for S. quadricauda cultivation is 25 °C; temperatures higher or lower than this result in a reduction in algal biomass. A higher amount of light leads to higher yields. No statistically significant differences were found comparing cultivation in BB medium and wastewater under different conditions. The analysis showed that the main factors influencing algae biochemical composition were final total nitrogen concentration and available total nitrogen amount per unit of algae biomass produced, as well as molar N:P ratios. Algae biomass cultivated in wastewater contained a consistent lipid concentration (on average 14.94 ± 2.38%), a lower final total nitrogen concentration, and overall lower total nitrogen availability, leading to higher carbohydrate concentrations (up to 51.10%) and a lower protein content (down to 15.52%). Algae biomass that was cultivated in the BB medium biochemical composition was not dependent on environmental factors and remained consistent (on average 22.89 ± 3.85% carbohydrate, 39.32 ± 3.89% protein, and 13.99 ± 2.21% lipid).