Table 5 Strategies for enhancing hydrogen production in microalgae: a Summary

Direct Photolysis

Sunlight-driven water molecule breakdown by microalgae’s PSII, producing hydrogen and oxygen, facilitated by chloroplast hydrogenases

- Achieves up to 98% purity hydrogen in certain strains.

- Direct conversion of solar energy to hydrogen.

[5, 164]

Indirect Photolysis (Two-Step Method)

(1) Sunlight converts CO₂ to organic compounds for energy storage; (2) Stored compounds generate hydrogen in an anaerobic, dark environment, avoiding oxygen inhibition of hydrogenase

- Circumvents oxygen inhibition of hydrogenase.

- Utilizes stored organic compounds for hydrogen production.

[5, 165]

Co-Cultivation with Specific Bacteria

Oxygen-consuming bacteria reduce oxygen levels in microalgal cultures, preventing hydrogenase inhibition and boosting hydrogen productivity

- Enhances hydrogen production by reducing oxygen levels.

- Leverages microbial interactions for bioenergy applications.

[5, 166]

Ca²⁺ Injection

Enhances microalgae’s photosynthesis and protects against ROS by adding Ca²⁺ to the medium, facilitating better hydrogen production

- Safeguards PSII activity.

- Promotes substrate assimilation and hydrogen production.

[5, 38, 167]

Genetic Engineering of Microalgae

Modifies microalgae genetically to improve hydrogenase activity and photosynthetic efficiency, increasing hydrogen production capabilities.

- Opens new avenues for optimizing biohydrogen production with higher productivities and efficiency.

[5, 168]