## 3 Reuse of OMWW  
### OMWW Management and Bioremediation  
The implementation of any treatment based on the circular economy approach and \"waste\" reuse concept represents a competitive and innovative choice for agro-food companies for achieving a reduction in cost management and environmental impact. According to [PERSON] and co-workers [39], 1 m\({}^{3}\) of OMWW corresponds to 100-200 m\({}^{3}\) of domestic wastewater. The COD and BOD\({}_{5}\) values of OMWW are very consistent and even higher when obtained by conventional systems (150 g O\({}_{2}\)/L COD and 90 g O\({}_{2}\)/L BOD\({}_{5}\) vs. 90 g O\({}_{2}\)/L COD and 30 g O\({}_{2}\)/L BOD\({}_{5}\) for conventional and two-phase extraction systems, respectively). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Values** & **Reference** \\ \hline Organic matter (\%) & 57–62 & \\ Total carbon (\%) & 2.0–3.3 & [26; 30; 31] \\ Total nitrogen (g/L) & 2.0–2.4 & [21] \\ Total sugar (g/L) & 5.0–12.0 & [16; 22; 32; 33; 34] \\ Total fat (\%) & 1.0–23 & [35] \\ Total suspended solids (g/L) & 25–30 & [36; 37] \\ Polyalcohol (\%) & 9.0–15 & [21; 35; 38] \\ Total phenols (g/L) & 0.5–6.1 & [6; 26; 29; 33; 39; 40; 41] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Cont. According to the European Directive 2000/60/CE [49], the OMWW requires specific treatment prior to direct discharge to ensure environmental protection and for regenerated wastewater. Indeed, the disposal of untreated OMWW on agricultural soil causes severe environmental damages, such as altering the color of natural water sources and exercising toxic effects on aquatic life and soil quality. OMWW is characterized by a high content of components with low biodegradability (e.g., long-chain fatty acids, lipids, and simple and complex sugars). Therefore, the most common applied systems for OMWW reuse are concerned with lowering the pollutant load and/or extracting bioactive compounds for different applications [25]. A plethora of physicochemical treatments has been developed in order to remove the phenolic compounds. However, in the majority of the studies no ecotoxicological evaluation has been reported and the success of treatment is mainly based on the reduction of color, COD, phenol content, etc. The most relevant parameter used to evaluate compost phytotoxicity is the germination index (GI). Low GI values could be attributed to the fact that at the starting stage, substrates have high concentrations of water-soluble organic substances, toxic constituents such as alcohols, organic fatty acids and phenolic compounds, high C/N ratios due to the presence of ammonia and other toxic nitrogen-based products, as well as high heavy metal and mineral salt contents [50; 51]. In addition to traditional settling (conducted in tanks called \"hell\"), various treatments have been proposed: physicochemical, biological, or a combination. Physicochemical systems include different methods based on the use of flocculants, coagulants, membrane filtration and reverse osmosis [52], or applying oxidation cryogenesis, electrocoagulation [53; 54], or a photochemical system [55]. Generally, after these treatments, the resulting products can be spread on agricultural soil as an organic fertilizer or simply subjected to evaporation in open tanks [56]. However, these practices are expensive as they produce matrices, such as sludge, that must either undergo further treatments or be disposed of. Several reports confirm that microorganisms can be proposed as a promising alternative for bioremediation of OMWW [51]. Biological methods, involving anaerobic or aerobic digestion and composting, have been applied to break complex organic compounds into simpler molecules and may lead to the production of proteins, exopolysaccharides, or energy [57; 58]. The main interest in anaerobic digestion is the production of energy and reuse of the effluent for irrigation purposes [59]. However, the leading limitation is the inhibition of methangenic bacteria by both phenolic and organic acids compounds [60].