# Cellulose Recovery from Agri-Food Residues by Effective Cavitational Treatments
## 3 Biomass Treatments for Cellulose Recovery
### Acoustic Cavitation (AC) as Effective Biomass Pretreatment
The recovered liquid fraction was further sonicated (100 W and 35 kHz for 10 min) in presence of NaCl to achieve a water phase rich in degraded sugars and a GVL phase rich in easily recoverable lignin. A cellulose conversion rate of about 90% was reported, 6.7-times higher than the reference sample. The sugars released in water phase were mainly represented by monosaccharides (70-160 g/kg) together with a considerable amount of oligo- and polysaccharides (45-180 g/kg). On the other hand, the lignin fraction recovered from GVL had a high purity degree (less sugar leftovers), a low molecular weight (1820-2970 g/mol) and low polydispersity (1.93-1.98), showing a typical \(p\)-hydroxyphenyl-guiaacyl-syringyl (HGS) type structure. GVL, as bioderived solvent ([PERSON] et al., 2016) [97,98], could be considered a promising medium for processing lignocellulosic materials, due to its safety and renewability and the above-mentioned study probably established the fundamentals for newly sustainable valorisation process for the conversion of residual Gramineaee biomass. In fact, a similar approach was investigated exploiting the ability of ILs to fractionate biomass, efficiently disrupting the complex network of noncovalent connections between biopolymers. It was described as the ILs imidazolium cations [HMIM]+ being able to particularly interact with the lignin aromatic rings by the \(\pi\) - \(\pi\) interactions to boost lignin solubilization, thus, [HMIM]+ as a small size of cation was efficient in fractionating lignocellulosic biomass. Moreover, lignin solubilization features of ILs could be improved by anions with strong hydrogen bond capability. At this regard, imidazolium based ILs with different anions (chloride, acetate, sulfate, phosphate, methane sulfonate, \(p\)-toluenesulfonate) were explored by [PERSON] et al. (2015) [99] for cellulose recovery by means of biomass fractionation. The Corn stover breakdown into cellulose and hemicellulose and lignin was successfully reported in ILs when combined with US irradiation (3 h, 400 W) at 70 \({}^{\circ}\)C. A 60% of original lignin (S-G-H type) was recovered in presence of [HMIM]Cl- and [HMIM]CH\({}_{3}\)COO-. Both the acidity and the hydrogen bond capability of utilized ILs contributed to the efficient fractionation. Moreover, smaller anions were desirable, due to their ability to diffuse more easily within the lignocellulosic matrix. Coupled with a small sized cation such as [HMIM]+ the chloride anion, being small-sized and a strong hydrogen-bond acceptor, makes [HMIM]Cl the solvent of choice for biomass splitting and cellulose recovery. EH of recovered cellulose was then accomplished with a 97.77% of reducing sugar yield. [PERSON] et al. (2019) [100] developed, for the first time, a pretreatment process based on ILs and US in association with surfactant PEG-8000 (polyethylene glycol) to enhance SCB (sugarcane bagasse) enzymatic saccharification. Firstly, five different ILs have been tested without US and PEG-800: [Emim][MeSO\({}_{3}\)] (1-ethyl-3-methylimidazolium methanesulfate), [Emim]Cl (1-ethyl-3-ethylimidazolium chloride), [Emim][CH\({}_{3}\)COO] (1-ethyl-3-methylimidazolium acetate), [Bmim]Cl (1-butyl-3-methylimidazolium chloride), and [Emim][Dmp] (1-ethyl-3-methylimidazolium dimethylphosphate). For this purpose, 0.25 g of SCB have been mixed with either of the IL at 0.25 g in an acetate buffer (50 mM, pH 5.0) at a biomass loading of 5%, (\(w/w\)) and then heated at 90 \({}^{\circ}\)C for 2 h. The efficiency of the ILs have been evaluated as resulting maximum sugar yield after pretreated SCB saccharification: [Bmim]Cl resulted the best IL for this biomass with a maximum sugar yield of 130 mg/g biomass.