Hydrogen (H₂) is a highly efficient and clean energy source with the potential for renewable energy. The production of H₂ from biological routes such as biophotolysis, photofermentation, dark fermentation, and bioelectrochemical production is characterized as a renewable alternative to current production, which is mainly based on energy-intensive electrochemical and thermochemical processes and responsible for the emission of high amounts of environmentally harmful compounds. Dark fermentation is the most efficient and cost-effective method for producing biohydrogen, making it a key research focus. This article offers a comprehensive overview of the dark fermentation process with the aim of enhancing hydrogen productivity and yields. Aspects related to the main substrates used, the inoculum sources and their pretreatment, and physical-chemical parameters of the process are covered. Furthermore, this manuscript addresses topics such as process integration, genetic and metabolic engineering of fermentative microorganisms, and the main types of bioreactors aimed at greater yields and productivity of biohydrogen to enable its production through dark fermentation on a larger scale.

Agriculture is essential for nutrition and the global economy, becoming increasingly important due to population growth and higher food demand. This situation boosts interest in creating bioproducts that enhance productivity sustainably while reducing environmental issues and strain on natural resources. Bioinoculants are important innovations that use beneficial microorganisms to boost crop growth and resilience. They enhance the interaction between soil and plants by solubilizing essential nutrients and producing phytohormones. This not only boosts agricultural productivity but also promotes environmentally sustainable practices by decreasing reliance on chemical fertilizers. Considering the relevance of this subject to advances in agro-industrial biotechnology, this review analyzes recent studies and patent advances on the production and use of bioinoculants, as well as their integration into agricultural practices and plant development. It also explores the dynamics of production and downstream processes on an industrial scale, regulations in different countries, and growing market demands, which is an important feature of this review. Furthermore, future perspectives for the application of bioinoculants in agro-industrial biotechnology are discussed, emphasizing the critical role that these biological agents play in advancing agricultural sustainability.

Recycling bioresources is the only way to sustainably meet a growing world population’s food and energy needs. One of the ways to do so is by using agro-industry wastewater to cultivate microalgae. While the industrial production of microalgae requires large volumes of water, existing agro-industry processes generate large volumes of wastewater with eutrophicating nutrients and organic carbon that must be removed before recycling the water back into the environment. Coupling these two processes can benefit the flourishing microalgal industry, which requires water, and the agro-industry, which could gain extra revenue by converting a waste stream into a bioproduct. Microalgal biomass can be used to produce energy, nutritional biomass, and specialty products. However, there are challenges to establishing stable and circular processes, from microalgae selection and adaptation to pretreating and reclaiming energy from residues. This review discusses the potential of agro-industry residues for microalgal production, with a particular interest in the composition and the use of important primary (raw) and secondary (digestate) effluents generated in large volumes: sugarcane vinasse, palm oil mill effluent, cassava processing waster, abattoir wastewater, dairy processing wastewater, and aquaculture wastewater. It also overviews recent examples of microalgae production in residues and aspects of process integration and possible products, avoiding xenobiotics and heavy metal recycling. As virtually all agro-industries have boilers emitting CO₂ that microalgae can use, and many industries could benefit from anaerobic digestion to reclaim energy from the effluents before microalgal cultivation, the use of gaseous effluents is also discussed in the text.