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Microalgae have been reported to exhibit mutualistic interactions with other microorganisms like bacteria, filamentous fungi, and yeast and help each other co-exist. The potential of microalgae to perform photosynthesis and accumulate lipids make them suitable candidates for lipid production. Biofuel production from various single oleaginous microorganisms is already in practice. However, the high cost of biomass harvesting, extraction of lipids, and contamination issues are significant challenges of biofuel bioprocess commercialization. Recent microalgal co-culture studies showed considerable potential for easy biomass harvesting and reduction in overall energy consumption cost. Therefore, microalgal co-culture could be an alternative to overcome these constraints and enhance biomass and lipid production. Additionally, the integration of the nutrient sequestration process from potential agro-industrial wastewater using microalgal co-culture can reduce the cost of the substrate requirement for cultivation as well as ecological load. The co-culture in wastewater has shown excellent total phosphate removal efficiencies by microalgae Chlorella sorokiniana and yeast Rhodotorula glutinis, nitrogen removal by microalgae C. sorokiniana with activated sludge, and ammonium-nitrogen removal by C. vulgaris and fungi Aspergillus sp. co-culture. This review summarized the current advances towards biofuel and its value-added production from various microalgae co-culture and compared it with monoculture fermentation. It also includes some critical challenges of co-culturing for the economically viable bioprocess development for biofuel production. Furthermore, techno-economic analysis and life-cycle assessment of co-culture technology were also discussed for biofuel production feasibility from microalgal co-culture.

Hydrogen gas, along with conventional fossil fuels, has been used as a green fuel with enormous potential. Due to the rapid depletion of fossil fuels, a new dimension of hydrogen production technology has arrived to reduce reliance on nonrenewable energy sources. Microwave-based hydrogen production is a more promising and cost-effective technology than other existing green hydrogen production methods such as fermentation and gasification. Microwave heating may be superior to traditional heating due to several advantages such as less power consumption compared to other methods, higher yield, and a higher rate of conversion. Compared to another process for hydrogen production, the microwave-driven process worked efficiently at lower temperatures by providing more than 70% yield. The process of production can be optimized by using properly sized biomass, types of biomass, water flow, temperature, pressure, and reactor size. This method is the most suitable, attractive, and efficient technique for hydrogen production in the presence of a suitable catalyst. Hot spots formed by microwave irradiation would have a substantial impact on the yield and properties of microwave-processed goods. The current techno-economic situation of various technologies for hydrogen production is discussed here, with cost, efficiency, and durability being the most important factors to consider. The present review shows that a cost-competitive hydrogen economy will necessitate continual efforts to increase performance, scale-up, technical prospects, and political backing.