## 4 OMWW as a Source of Biopolymers and Bio-Energy Production
### Production of Bio-Energy and Biofuels  
The need to reduce dependence on conventional fossil fuels in favor of new alternative energy resources is a top global priority. Green energies could contribute to the reduction of greenhouse gas emissions and their consequent unfavorable impacts on global warming and climate change [90]. The high content of organic matter and the low content of nitrogen, volatile acid sugars, polyalcohols, and fats, make OMWW an attractive resource for the production of bioenergy and alternative biofuels, such as methane or ethanol [6; 51]. Several microorganisms are used for biohydrogen production, through single or combined catabolic pathways (e.g., _Rlhodobacter sphaeroides_, _Rlhodoseudomonas palustris_, and _Chlamydomonas reinhardtii_). The production of these substances takes place through a process of anaerobic digestion, which consists of two phases. During the first phase, macromolecules, such as carbohydrates, proteins, and lipids, are transformed by hydrolytic and acidogenic fermentative bacteria into simple or intermediate organic compounds, volatile organic acids (acetic, propionic, and butyric acids), alcohols (ethanol), ketones, CO\({}_{2}\), and hydrogen. In the second step, through interactions between methanogenic and acetogenic microorganisms, these metabolites are transformed into CH\({}_{4}\) and CO\({}_{2}\)[91]. However due to the presence of oils residues or phenols responsible for antimicrobial activity, OMWW must be first treated or diluted [92]. As already known, before implementing an anaerobic digestion process, the treatment of OMWW with some fungi, such as _A. niger_, _Aspergillus terreus_, and _Pleurrotus sajor-caju_ play a key role in order to increase the final production of the reference bioenergy compound. [PERSON] et al. [57] and [PERSON] and co-workers [93], through a comparative kinetic study, demonstrated that the pretreatment of OMWW with _A. niger_ and _A. terreus_ increased the methane yield. [PERSON] and [PERSON] [94] evaluated the ability of a _P. sajor-caju_ strain to degrade the phenols of OMWW producing ethanol. For this purpose, the authors examined the effects of dilution with water (in a 1:1 ratio), heat treatment (at 100 \({}^{\circ}\)C), and treatment with H\({}_{2}\)O\({}_{2}\). The results showed that the degradation of phenols by _P. sajor-caju_ reached a level of 50% in heat-treated OMWW, 53% in heat-treated OMWW pretreated with H\({}_{2}\)O\({}_{2}\), and 58% in undiluted heat-treated OMWW. The highest ethanol yield was obtained in samples pretreated with _P. sajor-caju_ and after 48 h of fermentation with 50% diluted and heat-treated OMWW. Further biological treatment was carried out with _Saccharomyces cerevisiae_. [PERSON] et al. [95] and [PERSON] et al. [96] confirmed the aptitude of _S. cerevisiae_ to produce ethanol and optimal fermentation parameters were detected using the 1:1 OMWW/water mixture ratio. The fermentation kinetics of molasses mixed with OMWW where _S. cerevisiae_ was immobilized affected the ethanol yield, reaching values up to 67.8 g/L per day. Moreover, [PERSON] et al. [97] proposed a multiphase treatment using _S. cerevisiae_ added to OMWW with glucose, to a final sugar concentration of 200 g/L, with _A. niger_ extract to hydrolyze the present polysaccharides. Although _S. cerevisiae_ showed low fermentative performance, indigenous strains belonging to _Pichia fermentants_ and _Candida_ spp. reduced phenolic content up to 15% and 18%, respectively, without any addition or pretreatment [98]. Furthermore, [PERSON] et al. [99] demonstrated the ability of _Y. lipolytica_ strain ACA-DC 5029 to grow on media containing a low concentration of crude glycerol and OMWW, producing a significant amount of citric acid and erythroid. In the presence of high glycerol concentration, a shift towards erythroid production was observed, simultaneously with high amounts of citric acid production.