Closed Systems

Open systems are currently still the preferable choice for microalgal production on a large scale, especially when they are designed to produce low-priced products, such as biofuels. However, due to the requirements of good manufacturing practice (GMP) guidelines, pro­duction of high-value products from microalgae for application in pharmaceuticals and cosmetics seems feasible only in well-controlled photobioreactors with closed system ope­rations. Therefore, several closed systems (photobioreactors) for microalgae cultivation are discussed here.

The term closed systems refers to photobioreactors that have no direct exchange of gases and contaminants between the cultivation systems and the outside environment. The necessary gas exchange is performed through a sterilized gas filter, to avoid contamination inside the culture system. Therefore, closed systems are characterized by the minimization of con­tamination over open systems. Besides the typical drawback of high equipment cost, closed- system photobioreactors do have several major advantages over open systems (Singh and Sharma, 2012): (1) Photobioreactors could minimize contamination and allow axenic algal cultivation of monocultures; (2) photobioreactors offer better control over conditions such as pH, temperature, light, CO2 concentration, and so on; (3) using photobioreactors leads to less CO2 loss and prevents water evaporation; (4) photobioreactors permit higher cell con­centrations; and (5) photobioreactors permit the production of complex biopharmaceuticals.

There are several types of closed systems designed and developed for the cultivation of microalgae, including vertical (tubular) columns, flat plate photobioreactors, and horizontal tubular photobioreactors. The detailed descriptions of those cultivation systems are provided here. In addition, their advantages and weaknesses are summarized and compared in Table 2.2.