# Bioreactors: Applications and Innovations for a Sustainable and Healthy Future--A Critical Review
## 2 Fundamental Concept Types of bioreactors
In addition to application in effluent treatment, these bioreactors can also be used in the intensification and consolidation of bioprocesses to obtain value-added products (polyols, biosurfactants, organic acids, and bacterial polyesters) in which the upstream and downstream steps can occur concomitantly. The membrane system acts to purify the biomolecules of interest. This strategy can reduce processing steps, directly affecting process time and costs, and can make the process economically viable [12]. Static or agitated bioreactors (occaional, continuous, or only with rotation) can also be used in SSF. The main types of bioreactors used for bench and industrial-scale SSF are (i) trays, (ii) fixed beds, and (iii) stirred drums. Despite their widespread use across various industries, there remains a continual need to evaluate and improve these systems due to several challenges [13]:  
Most SSF processes involve filamentous fungi as fermentation agents, and their delicate hyphae are prone to damage by mechanical agitation systems;  
The solid medium can agglomerate during fermentation, leading to uneven microbial biomass growth and complications with aeration and heat transfer;  
The large-scale inoculation, control, and sterilization of media volumes are often difficult. Improvements to bioreactors for SSF often require customizations based on the specificities of the bioprocess, as they depend on the microorganism used, the type of substrate, and the operational conditions [13]. On an industrial scale, key challenges include heat transfer and humidity control due to the larger volumes of substrate involved. As a result, research has focused on developing bioreactors with innovative designs and automation systems to mitigate these issues and boost productivity [22]. One promising area of development is the application of 3D printing technology, which has gained popularity in recent years. This technology enables the development of micro- and macrobioreactors for bench-scale cell or enzyme cultivation. Additionally, 3D printing can be employed to manufacture micromixers and matrices for the immobilization of cells and enzymes [15; 16; 23]. Three-dimensional printing offers a solution for optimizing both SmF and SSF processes by facilitating the design of bioreactors and accessories that enable easy performance optimization. This technology can be applied to various aspects of the process, including the bioreactor itself, support structures for biocatalyst confinement, and peripheral accessories, allowing for highly controlled bioprocess [16]. In pharmaceutical processes, micro bioreactors are primarily used for drug testing, cellular response optimization, and disease modeling, while macrobioreactors support the cultivation of functional tissues for implantation in tissue engineering studies [14; 15; 16; 23]. Operational safety includes preventing contamination and managing waste, with materials like PDMS (polydimethylsiloxane) playing a crucial role. PDMS is a versatile silicon-based organic polymer known for its flexibility, transparency, and gas permeability. These properties make it ideal for use in reaction microdevices, where it helps ensure the integrity and control of bioprocesses [24; 25]. In recent years, energy consumption and process productivity have been improved using artificial intelligence (AI), with machine learning algorithms adjusting parameters in real time, improving efficiency and reducing waste. These algorithms predict energy needs and implement predictive control strategies, which are particularly useful in continuous processes [24; 26]. Challenges in industrial-scale bioreactors involve engineering, safety and energy efficiency. Maintaining culture homogeneity and operational safety are essential. The choice of impellers and the integration of AI improve bioreactor efficiency. Automation, modeling, and the use of advanced materials ensure safer and more efficient operations, optimizing biotechnological processes. [PERSON] et al.