# Bioreactors: Applications and Innovations for a Sustainable and Healthy Future--A Critical Review
## 2 Fundamental Concept Types of bioreactors
With the intensification of studies and the use of microalgae in various industrial sectors, vertical tubular airlift and bubble column photobioreactors have been used on laboratory scales of up to 20 L [19]. An alternative to the STR bioreactor in submerged cultivation of animal and plant cells, especially those most sensitive to shear, are wave bioreactors [7]. This type of bioreactor was developed in the late 1990s for crops with low oxygen demand, which do not require submerged gasification, and for cells with anchorage-dependent growth [20]. The equipment has a simple configuration, as it consists of a Cellbag (plastic bag of varyingvolume and sterile) with a hydrophobic filter for gas exchange coupled to a rocking table responsible for oscillatory movements and temperature control. Despite advantages such as no need for sterilization, as the Cellbag is sterile and disposable, this type of bioreactor has the disadvantage of limited scale expansion up to a capacity of 500 L of effective volume. This type of bioreactor is currently used in the pharmaceutical industry for the production of vaccines and other biopharmaceuticals, as it is suitable for cultivating animal cells and also unstable products, such as bioconjugates [8]. Another recent innovation is disposable or single-use bioreactors, also widely used in the pharmaceutical industry for the growth of animal cells in SmF. They are equipment manufactured with high-quality plastic materials, such as low-density polyethylene, polypropylene, or polycarbonate, which eliminates the need for cleaning and sterilization between cultivation batches. This reduces the risk of cross-contamination and simplifies validation and regulatory compliance processes. When compared to glass or stainless-steel bioreactors, they are flexible and efficient. These bioreactors can come in various sizes and configurations, from bench to industrial scale with a volume of 2000 L. This type of equipment is adaptable to different types of crops, allowing parallel experiments to be carried out or production to be scaled as necessary [9]. Although made of plastic, many disposable bioreactors are designed for energy-efficient recycling or incineration after use. Furthermore, its energy efficiency during use can offset the environmental impact associated with manufacturing and disposal. This represents an advantage in terms of sustainability compared to conventional stainless steel or glass bioreactors, which consume more resources and energy throughout their life cycle [10]. Among the main advances in the development of disposable bioreactors, the possibility of customizing the design according to the application stands out, offering different types of vessel and impeller geometry for mixing and mass transfer, as well as the development of non-invasive sensors and the integration of process analytical technologies (PAT) with the principles of quality by design (QbD). These advances will allow the development of more versatile bioreactors, for the cultivation of a variety of cells under physiologically favorable conditions and in the development of robust and repeatable processes [21]. Membrane bioreactors (MB) have also gained prominence in recent years, especially when they are applied in the industrial treatment of effluents. MB is equipment designed with semi-permeable membranes that allow the selective passage of substances of varying sizes while retaining larger cells or particles inside the reactor. These membranes can be microfiltering, ultrafiltering, or nanofiltering, depending on the size of the particles that you want to separate from the cultivation medium. The main advantages of this equipment are (i) efficient separation, (ii) the possibility of continuous operation, (iii) contamination control, and (iv) space savings. However, their disadvantages are (i) cost, (ii) complex maintenance, and (iii) flow limitations [11].