## 4 Applications of Zeolites in Catalysis, Bioprocesses, and Environmental Remediation
### Microbial Immobilization  
The use of porous materials as supports for immobilization of distinct microorganisms (MOs) is increasingly used to solve industrial problems. There are some processes that use anaerobic routes for different functions, such as wastewater and solid waste treatment [288, 289], biodegradation of pollutants [290], alcohol fermentation [291], mineral self-healing concrete [292] and anaerobic treatment of agricultural wastes [293]. The physical properties and structure of zeolites, mostly the channel and pore cavities, minimum diameter pores, average surface area of 24.9 m\({}^{2}\)/g, low bulk density, high cation exchange capacity and adsorption make this material useful for biological processes. Moreover, the wastewater biological treatment has been a highlight, reducing inhibitory substances in feedstock such as ammonia [288]. In this context, anaerobic remediation has many good characteristics, such as the high degree of purification in loco even possessing high organic feeds, low nutrient requirements, small amount of excess sludge produced in the process, and the production of renewable biogas, enabling recovery of energy instead of just saving it and reducing costs in comparison with aerobic process [294]. When anaerobic digestion is achieved in the absence of a support for immobilization of a microorganism, there are some drawbacks: long processing, requiring a large reactor volume, and the possibility of washout of the microorganism due the high substrate loading rate, reducing the reactor performance. With porous solid materials as support for anaerobic microorganisms, there is an ideal environment, e.g., the bacterial growth that is increased by the porosity of material. Moreover, the chemical oxygen demand (COD) is reduced, preventing biomass loss at high loading rates [288]. The sorbent property for microbial immobilization is reported to be presented by clay rocks and has been used for oil-oxidizing microorganisms such as Pseudomonas yamamorum, Rhodotorula glutinis and the microalgae Chlorella vulgaris, acting as biogeorbents that increase the efficiency of cell immobilization, preserving viability and biochemical activity. The sorbents act as transport bases for Mos, allowing up to 10 years of anabiosis, i.e., reduction of metabolism. The zeolites analcime, clinoptiolite and glauconite have been found to be great biogeorbents in tests of hydrocarbon oxidation with the capacity of holding volatile low-molecular-weight alkanes [290]. Natural and modified zeolites have been also used for immobilization of the strain of Trichoderma viride SL-45 with success [295]. The immobilization of cells for ethanol fermentation is an important line of work using zeolites. Saccharomyces cerevisiae has been immobilized with a natural zeolite and the system presented 3-6-10\({}^{8}\) cells/mL in carrier capacity, reaching that required for immobilization and alcohol fermentation twofold higher than glass beads and being stable for 21 days without the loss of carrier. The immobilization of cells increases the reaction  
Figure 15: Proposed three-in-one continuous reaction of 2,5 dimethylfuran (DMF) and acrylic acid (AA) to produce p-xylene (pXL) and 2,5 dimethylbenzoic acid (DMBA). Reproduced from [285]. Copyright 2020 Royal Society of Chemistry. rates, enzyme productivities, and cell densities [291] (p. 34). A synthetic zeolite was used in the fermentation process of lactic acid production by immobilization of Lactobacillus rhamnus, where the simple cell separation from fermentation media and their reuse in repeated batch cycles were achieved with success [296]. In the process of ethanol fermentation, by-products are generated, such as in the corn ethanol industry, where thin stillage is generated. Thus, the nature of reactor used for this waste treatment has great importance, an anaerobic fluidized bed reactor generally being applied.