## 4 OMWW as a Source of Biopolymers and Bio-Energy Production  
### Enzyme and Exopolysaccharides_  
OMWW represents a suitable substrate for the production of enzymes by fungi. Fungi are microorganisms known for their ability to synthesize different biological catalysts that can be used in different areas. In particular, [PERSON] and co-workers [46] demonstrated that ligninolytic fungi are a useful source of phenoloxidase, polyphenoxidase, and peroxidase useful for removing recalcitrant compounds in OMWW.  
Several yeast strains have been characterized as highly pectolytic, xylanolytic, provided with cellulase, \(\beta\)-glucanase, \(\beta\)-glucosidase, peroxidase, and polygalacturonase activities, which could effectively degrade the complex compounds responsible for OMWW toxicity [65,72].  
Several yeasts have been described as able to reduce phenolics and sugars present in OMWW, although white-rot fungi appear to contribute more to discoloration [73]. Moreover, [PERSON] and co-workers [74] isolated six phenotypically distinct groups of yeasts and three selected isolates were identified through biochemical tests and partial 18S rDNA gene sequence analysis as most closely related to _Saccharomyces_ spp., _Candida boidini_, and _G. candidum_. These fungal genera have been reported as able to degrade the phenolic content present in OMWW [75,76].  
Several reports also propose strains belonging to different species, such as _Panus trigirinus_, _Hericium erinaceus_, and _Pleutrotus citrinopileatus_ for lacase (Lac) and manganese peroxidase (Mnp) production [77,78,79]. Filamentous fungi, such as _Aspergillus oryzae_, _A. niger_, _Aspergillus biericus_, _Aspergillus wavam_, _G. candidum_, _Rizlopus oryzae_, _Rhizopus arrhizus_, and _Penicillium citrinum_, have been described as lipolytic reservoirs due to their ability to produce lipase [80]. These enzymes have been used in different industries, such as dairy and pharmaceutical [81]. Moreover, OMWW has been confirmed as a suitable substrate for production of pectinase, with _Cryptococcus albidus_ var. _albidus_ IMAT 473 showing the best biotechnological aptitude. This enzyme, compared with other products on the market, showed a broad spectrum endopolygalacturonase activity [82; 83; 84].  
Besides enzyme production, OMWWs have also been evaluated as a source of polysaccharides, especially exopolysaccharides (ESP) [85] with glucose as the main monosaccharide, followed by galactose, arabinose, rhamnose, and galacturonic acid. Xanthan, a glucose-mannose and glucuronic acid repeating unit compound, is the main ESP used in different products, such as in cosmetic formulations or as a supplement and thickening compound [86]. However, the EPS production through a fermentation process depends on the type of microorganism. The first production of EPS in OMWW (used at 30% _v/v_) was obtained through a strain of _Xanthomonas campestris_ that showed a productive capacity of 4 g/L [87]. Similarly, _Paeinobacillus jamilae_ sp. highlighted, on OMWW, the production of an EPS consisting of fucose, xylose, rhamnose, arabinose, mannose, galactose, and glucose. [PERSON] et al. [88] reported that _P. jamiae_ CECT 5266 strain (in a 80% _v/v_ of OMWW) produced an EPS consisting of glucose, galactose, mannose, arabinose, rhamnose, hexosamine, and uronic acid, in agreement with results previously reported by [PERSON] et al. [89] using the strain _P. jamiae_ CP-7.