# Bio-Oil from Phototrophic Microorganisms: Innovative Technologies and Strategies

## TL;DR

This review explores how phototrophic microorganisms can be used to produce bio-oil through innovative technologies, offering a sustainable alternative to traditional biofuel sources.

## Contribution

The paper provides a comprehensive review of recent advancements in thermochemical and biotechnological strategies for algal bio-oil production.

## Key findings

- Hydrothermal liquefaction is effective for processing high-moisture algal biomass without drying.
- Fast pyrolysis yields high bio-oil from lipid-rich feedstocks.
- Catalytic upgrading improves bio-oil stability and fuel compatibility.

## Abstract

The transition to low-carbon energy systems requires scalable and energy-efficient routes for producing liquid biofuels that are compatible with existing fuel infrastructures. This review focuses on bio-oil production from phototrophic microorganisms, highlighting their high biomass productivity, rapid growth, and inherent capacity for carbon dioxide fixation as key advantages over conventional biofuel feedstocks. Recent progress in thermochemical conversion technologies, particularly hydrothermal liquefaction (HTL) and fast pyrolysis, is critically assessed with respect to their suitability for wet and dry algal biomass, respectively. HTL enables direct processing of high-moisture biomass while avoiding energy-intensive drying, whereas fast pyrolysis offers high bio-oil yields from lipid-rich feedstocks. In parallel, catalytic upgrading strategies, including hydrodeoxygenation and related hydroprocessing routes, are discussed as essential steps for improving bio-oil stability, heating value, and fuel compatibility. Beyond conversion technologies, innovative biological and biotechnological strategies, such as strain optimization, stress induction, co-cultivation, and synthetic biology approaches, are examined for their role in tailoring biomass composition and enhancing bio-oil precursors. The integration of microalgal cultivation with wastewater utilization is briefly considered as a supporting strategy to reduce production costs and improve overall sustainability. Overall, this review emphasizes that the effective coupling of advanced thermochemical conversion with targeted biological optimization represents the most promising pathway for scalable bio-oil production from phototrophic microorganisms, positioning algal bio-oil as a viable contributor to future low-carbon energy systems.