Microalgal-bacterial sludge offers sustainable solution for removing hormonal pollutants from wastewater

A team of researchers in China has developed a promising biotechnological approach that could help communities worldwide tackle the challenge of wastewater contamination by hormone-like pollutants. Their study reveals how microalgal-bacterial granular sludge (MBGS) can adapt and efficiently degrade estriol, a common endocrine-disrupting compound (EDC), under environmentally relevant conditions.

Estriol, a natural estrogen present in domestic sewage, hospital effluent, and pharmaceutical waste, is known for its persistence and biological activity, even at very low concentrations. Standard wastewater treatment plants are often unable to fully remove these compounds due to their low biodegradability and resistance to microbial breakdown. This can lead to environmental pollution and potential risks to human and ecological health.

To address these concerns, the research team, led by Yuting Shi at Wuhan University of Science and Technology and collaborators at Huazhong University of Science and Technology and Beijing Normal University, tested the performance of MBGS under a range of estriol concentrations that reflect both typical and worst-case scenarios found in wastewater streams.

MBGS is a self-aggregated system that combines the functions of photosynthetic microalgae and heterotrophic bacteria within a granular structure. This arrangement enhances the removal of both organic matter and nutrients, while also providing internal cycling of oxygen, which is crucial for breaking down difficult pollutants. The presence of certain bacteria known for their EDC-degrading potential further boosts the system’s capabilities.

In experiments, the team exposed MBGS to various concentrations of estriol—ranging from levels found in most municipal wastewater to those in heavily contaminated industrial sources. The results were striking: At a realistic low dose of 0.1 mg/L, MBGS achieved up to 98 percent removal of estriol during daylight hours, demonstrating both speed and efficiency. Even more impressively, the system adapted to repeated exposures, maintaining strong performance over time.

The researchers traced the removal mechanism to a two-step process. First, estriol is quickly adsorbed onto the granular sludge through interactions with microbial extracellular substances. Then, specialized bacteria take over, breaking the compound down into less toxic intermediates and finally into harmless end products. Genetic analysis revealed that families such as Sphingomonadaceae and Rhodanobacteraceae play a critical role in this process, activating a suite of enzymes that catalyze the stepwise breakdown of estriol’s molecular structure.

However, the study also found limits to this resilience. When exposed to higher doses (1 and 10 mg/L), which might occur in direct pharmaceutical or hospital waste, MBGS suffered structural damage, particularly to the supportive cyanobacteria forming the granule skeleton. This led to a decline in removal efficiency and destabilized the sludge structure. Key functional genes and microbial populations responsible for removing pollutants were also suppressed at these higher concentrations.

Despite this, the findings underscore the potential of MBGS for sustainable, cost-effective treatment of wastewater containing hormone pollutants. By harnessing the natural synergies between microalgae and bacteria, treatment plants could boost removal of dangerous estrogens and protect aquatic environments more effectively.

The research was supported by the National Natural Science Foundation of China and demonstrates the critical role that innovative microbiological solutions can play in advancing environmental protection and public health.

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Journal reference: Shi Y, Chen C, Ding B, Shu Y, Feng J, et al. 2025. Metabolic responses and biodegradation pathways of microalgal-bacterial granular sludge to estriol: structural remodeling, microbial shifts, and gene dynamics. Biocontaminant 1: e004

https://www.maxapress.com/article/doi/10.48130/biocontam-0025-0004

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About Biocontaminant:
Biocontaminant is a multidisciplinary platform dedicated to advancing fundamental and applied research on biological contaminants across diverse environments and systems. The journal serves as an innovative, efficient, and professional forum for global researchers to disseminate findings in this rapidly evolving field.

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