Enhancing Wastewater Treatment with Algae and Yeast

By Muhammad OsamaReviewed by Laura ThomsonNov 13 2024

A research paper recently published in the journal Applied Microbiology and Biotechnology, explored the potential of using microalgae (specifically green algae) and heterotrophic microorganisms (mainly yeast) to improve wastewater treatment efficiency.

The study addresses the growing concern of eutrophication caused by nutrient-rich wastewater from industrial and domestic sources, which harms aquatic ecosystems. The researchers aimed to identify the best combinations of microorganisms to enhance carbon, nitrogen, and phosphorus removal rates, offering a sustainable approach to environmental degradation.

Challenge of Eutrophication and Wastewater Treatment

Daily human activities generate large amounts of wastewater containing carbon and nutrients, primarily nitrogen and phosphorus. These pollutants are the main contributors to eutrophication and the excessive nutrient enrichment of aquatic ecosystems. Eutrophication disrupts system balance and leads to harmful algal blooms, oxygen depletion, and environmental damage. Therefore, efficiently removing these nutrients reduces eutrophication and protects water quality.

Advancement in Wastewater Treatment

Wastewater treatment technologies have evolved significantly since the early 20^th century, with biological, chemical, and physical methods to reduce pollution. Traditional methods, such as the activated sludge process, are energy-intensive and often struggle to remove nitrogen and phosphorus efficiently. Due to the high energy demand for aeration, this process accounts for 60-80% of total operational costs, highlighting the need for more efficient, cost-effective alternatives. These methods often require additional treatment stages for nitrogen and phosphorus removal.

Recent advancements have shown promise in integrating green algae into wastewater treatment systems. Green algae use sunlight for photosynthesis, reducing the need for aeration while absorbing nutrients like nitrogen and phosphorus. This method improves nutrient removal and enables biomass recovery, which can be used for biofuels and other purposes.

Using Microalgae and Heterotrophic Microorganisms

This paper aimed to identify the best combinations of microalgae and heterotrophic microorganisms for improved wastewater treatment. The authors tested three species of microalgae: Chlamydomonas reinhardtii, Chlorella vulgaris, and Arthrospira platensis, and five types of heterotrophic microorganisms, including various strains of Saccharomyces cerevisiae and Bacillus species.

The study used artificial wastewater to simulate different nutrient concentrations. Microalgae and yeast were pre-cultured under controlled conditions to ensure they were in the mid-exponential growth phase before being added to the wastewater. The treatment was carried out under controlled light intensity and temperature, allowing a systematic evaluation of nutrient removal efficiency for each microbial combination.

The researchers used transcriptome analysis to examine gene expression changes linked to different treatment combinations to understand the molecular mechanisms behind the observed improvements. Ribonucleic acid (RNA) was extracted from the microorganisms after treatment, and next-generation sequencing identified differentially expressed genes (DEGs) that could contribute to improved nutrient uptake and treatment efficiency. Treatment efficiency was measured by tracking the removal rates of total organic carbon (TOC), ammonium (NH₄⁺), and phosphate (PO₄³⁻) over 18 hours.

Key Findings and Insights

The authors showed that combining C. reinhardtiiand S. cerevisiae achieved the highest removal rates for TOC, phosphate, and NH₄⁺. Specifically, TOC removal reached 82%, while PO₄³⁻ and NH₄⁺ removal rates were 93% and 71%, respectively. These outcomes suggest that co-cultivation significantly enhanced the nutrient uptake capabilities of green algae, likely due to synergistic interactions with the yeast. The findings also indicated that co-cultivation improved nutrient removal while maintaining high TOC removal, demonstrating the effectiveness of this approach for treating wastewater with varying nutrient concentrations.

Transcriptome analysis provided insights into the molecular mechanisms behind the enhanced performance of the microbial combinations. During the combined treatment, 1,371 genes in C. reinhardtii and 692 genes in S. cerevisiae showed expression changes.

Notably, genes related to nutrient transport were upregulated in C. reinhardtii, suggesting that co-cultivation improved nitrogen and phosphorus uptake. In contrast, downregulated genes were mostly linked to photosynthesis, indicating that yeast may have reduced the algae's photosynthetic activity without affecting their nutrient removal efficiency. This study highlights the complex interactions between autotrophic green algae and heterotrophic yeast in co-cultivation systems, paving the way for more efficient wastewater treatment strategies.

Potential Applications

This research has significant implications for developing sustainable wastewater treatment technologies. By harnessing the natural capabilities of green algae and yeast, this approach offers an effective alternative to traditional methods, which are often energy-intensive and less efficient in nutrient removal. The high nutrient removal efficiencies demonstrated suggest that similar co-cultivation strategies could be applied to different types of wastewater, including agricultural runoff and industrial effluents.

The potential for biomass recovery from these systems opens up opportunities for resource recovery, supporting a circular economy. The biomass produced could be used for bioenergy production, animal feed, or fertilizer.

Conclusion and Future Directions

In summary, combining green algae and yeast effectively enhanced wastewater treatment efficiency. The optimal combination of C. reinhardtii and S. cerevisiae improved nutrient removal rates and provided insights into the genetic mechanisms that support this process. As wastewater treatment techniques evolve, further research is needed to explore the scalability of these systems and their potential in real-world applications.

Future research should focus on optimizing growth conditions, understanding the ecological dynamics between co-cultured species, and exploring the metabolic pathways involved in nutrient uptake. Integrating omics technologies could provide deeper insights into microbial community interactions, leading to the development of robust and efficient wastewater treatment strategies that support sustainability goals.

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