Microalgae being treated with ammonia, resulting in hydrogen production.

From Waste to Wonder: How Free Ammonia Can Supercharge Microalgae Bio-hydrogen Production

Lena Kashyap in Climate & Environment August 2025 • 4 min read.

"Unlock the secrets of sustainable energy: A groundbreaking study reveals how free ammonia pretreatment can dramatically boost bio-hydrogen output from microalgae, turning wastewater into a valuable resource."

The quest for sustainable energy sources is more critical than ever. As traditional fossil fuels dwindle and environmental concerns escalate, the world is turning its attention to innovative, eco-friendly alternatives. Among these, bio-hydrogen production from microalgae has emerged as a promising contender, offering a low-carbon pathway to meet our growing energy demands.

Microalgae, tiny photosynthetic powerhouses, represent a third-generation feedstock with immense potential. They efficiently convert sunlight and carbon dioxide into valuable biomass, which can then be processed to produce bio-hydrogen. However, the natural biodegradability of microalgae is often limited, resulting in low bio-hydrogen yields. This bottleneck has spurred researchers to explore various pretreatment methods to enhance the breakdown of microalgae cells and boost hydrogen production.

Now, a groundbreaking study has unveiled a game-changing approach: free ammonia (FA) pretreatment. This innovative technology harnesses the power of ammonia, a readily available resource in wastewater treatment plants, to disrupt microalgae cell structure and significantly improve bio-hydrogen production. This method not only enhances energy output but also aligns with circular economy principles, transforming waste into a valuable resource.

The Science Behind the Breakthrough

Microalgae being treated with ammonia, resulting in hydrogen production.

The research, published in ACS Sustainable Chemistry & Engineering, details how FA pretreatment works at a microscopic level. Scientists discovered that exposing microalgae to controlled concentrations of free ammonia disrupts their cell walls, making them more susceptible to enzymatic breakdown during anaerobic dark fermentation.

Scanning electron microscopy (SEM) revealed that FA pretreatment caused the microalgae surface to become shrunken, with some cells collapsing. This structural change significantly increased the release of soluble chemical oxygen demand (SCOD), a measure of readily available organic matter, from 0.01 g SCOD/g VS microalgae to 0.05-0.07 g SCOD/g VS microalgae. This indicated enhanced solubilization, making it easier for microorganisms to access and convert the algal biomass into bio-hydrogen.

The benefits of the FA pretreatment method include:

Increased bio-hydrogen production potential.
Higher maximum bio-hydrogen production rate.
Enhanced microalgae solubilization.
Alignment with circular economy principles.

The study also examined the impact of different FA concentrations on bio-hydrogen production. The results showed that pretreating microalgae with 240-530 mg NH3-N/L of FA for one day substantially improved bio-hydrogen production. The bio-hydrogen production potential increased from 18.2 L H2/kg VS microalgae to 19.9-22.1 L H2/kg VS microalgae, while the maximum bio-hydrogen production rate rose from 2.5 L H2/kg VS microalgae/d to 3.1-3.8 L H2/kg VS microalgae/d.

A Greener Future Powered by Microalgae

The FA pretreatment technology offers a sustainable and economically viable approach to enhance bio-hydrogen production from microalgae. By harnessing a readily available resource from wastewater treatment plants, this method not only boosts energy output but also reduces waste and promotes a circular economy. As the world continues to seek cleaner, more sustainable energy solutions, innovations like FA pretreatment hold the key to unlocking the full potential of microalgae and paving the way for a greener future.

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This article is based on research published under:

DOI-LINK: 10.1021/acssuschemeng.8b05405, Alternate LINK

Title: Free Ammonia Pretreatment To Improve Bio-Hydrogen Production From Anaerobic Dark Fermentation Of Microalgae

Subject: Renewable Energy, Sustainability and the Environment

Journal: ACS Sustainable Chemistry & Engineering

Publisher: American Chemical Society (ACS)

Authors: Qilin Wang, Yanyan Gong, Sitong Liu, Dongbo Wang, Ranbin Liu, Xu Zhou, Long D. Nghiem, Yaqian Zhao

Published: 2018-12-03

Everything You Need To Know

What exactly is free ammonia pretreatment and how does it enhance bio-hydrogen production from microalgae?

Free ammonia pretreatment is a method that uses ammonia, found in wastewater, to break down the cell walls of microalgae. This process makes it easier for microorganisms to convert the algal biomass into bio-hydrogen during anaerobic dark fermentation. Exposing microalgae to controlled concentrations of free ammonia disrupts their cell structure, significantly improving bio-hydrogen production. This not only enhances energy output but also aligns with circular economy principles, transforming waste into a valuable resource.

What changes at the microscopic level occur in microalgae when subjected to free ammonia pretreatment, and how does this lead to increased bio-hydrogen production?

The study published in *ACS Sustainable Chemistry & Engineering* showed that free ammonia pretreatment causes the microalgae surface to shrink and some cells to collapse. This structural change increases the release of soluble chemical oxygen demand (SCOD). SCOD measures readily available organic matter. It increases from 0.01 g SCOD/g VS microalgae to 0.05-0.07 g SCOD/g VS microalgae after free ammonia pretreatment. This indicates enhanced solubilization, making it easier for microorganisms to access and convert the algal biomass into bio-hydrogen. This process uses scanning electron microscopy (SEM) to examine the changes.

What are the specific benefits observed when implementing free ammonia pretreatment for bio-hydrogen production, and how were these benefits quantified?

Using free ammonia pretreatment has several benefits: it increases the bio-hydrogen production potential and the maximum bio-hydrogen production rate. It enhances microalgae solubilization, making it easier to convert into bio-hydrogen, and it aligns with circular economy principles by using waste products to create energy. The study showed that pretreating microalgae with 240-530 mg NH3-N/L of free ammonia for one day improved bio-hydrogen production, increasing production potential from 18.2 L H2/kg VS microalgae to 19.9-22.1 L H2/kg VS microalgae, and the maximum production rate from 2.5 L H2/kg VS microalgae/d to 3.1-3.8 L H2/kg VS microalgae/d.

Why are microalgae considered a promising feedstock for bio-hydrogen production, and what challenges does free ammonia pretreatment address in unlocking their potential?

Microalgae's potential in bio-hydrogen production is substantial because they are efficient at converting sunlight and carbon dioxide into biomass. This biomass can then be processed to produce bio-hydrogen. The limitation of the natural biodegradability of microalgae, resulting in low bio-hydrogen yields, requires various pretreatment methods to enhance the breakdown of microalgae cells. Free ammonia pretreatment addresses this limitation by disrupting the cell walls of microalgae, making them more accessible for conversion into bio-hydrogen.

What are the broader environmental implications of utilizing free ammonia pretreatment to boost bio-hydrogen production from microalgae?

The environmental implications of using free ammonia pretreatment are significant. It allows for the transformation of wastewater, a waste product, into a valuable resource for bio-hydrogen production. This reduces waste and promotes a circular economy. By boosting bio-hydrogen production from microalgae, it provides a sustainable alternative to fossil fuels, reducing carbon emissions and dependence on non-renewable energy sources. The use of free ammonia pretreatment contributes to a greener future by maximizing the potential of microalgae as a renewable energy source.