Sustainability assessment of open and closed systems in microalgae cultivation: A review

Abstract

Microalgae are attracting interest in many sectors, particularly agriculture, energy, environment, food, medicine, and cosmetics, due to their high biomass production capacity and ability to grow in various environments. The environmental, economic, and social sustainability of products derived from microalgae is one of the most discussed topics today. The cultivation system for microalgae is the most important factor influencing their long-term viability. Microalgae are typically grown in two systems: open ponds and closed systems, also known as photobioreactors. Open systems, like open raceway ponds, natural lakes, and lagoons, have direct contact with the atmosphere and are generally simpler. In contrast, photobioreactors are closed systems that produce microalgae under controlled conditions. In this study, these two fundamental systems commonly used in microalgae cultivation were compared in terms of sustainability. Open-system microalgae production offers greater economic benefits; it is less environmentally sustainable. The primary causes of this are the high risk of contamination and evaporation resulting from these systems' contact with the environment. Although product yield is low in these systems, more resilient species can typically be cultivated. Because closed systems produce microalgae under more controlled conditions and have a higher biomass yield, they have been found to be more beneficial for environmental sustainability. However, because of setup capital and operating costs, microalgae production in these systems is more costly. To summarize, both open and closed systems for microalgae cultivation have benefits and drawbacks in terms of environmental and economic sustainability. As a result, rather than selecting a single system, working with hybrid systems and focusing on operational conditions to local needs and resources should be viewed as the key to microalgae sustainability.