# Cellulose Recovery from Agri-Food Residues by Effective Cavitational Treatments
## 3 Biomass Treatments for Cellulose Recovery
### Acoustic Cavitation (AC) as Effective Biomass Pretreatment
US-assisted lignocellulosic fractionation proved to be effective also for a typical Mediterranean agri-food waste, _Olea europaea_, as reported by [PERSON] et al. (2011) [83] UAT (50 Hz, 420 W) enabled the achievement of a high delig  
Figure 4: SEM images of pretreated RapS pulps samples: UAT (T = 80 \({}^{\circ}\)C, time = 20 min, NaOH = 0.5 M) (**A**); UAT (T = 60 \({}^{\circ}\)C, time = 40 min, NaOH = 0 M) (**B**); UAT (T = 90 \({}^{\circ}\)C, time = 20 min, NaOH = 0 M) (**C**); HVED (T = 80 \({}^{\circ}\)C, time = 20 min, NaOH = 0.5 M) (**D**); HVED (T = 60 \({}^{\circ}\)C, time = 40 min, NaOH = 0 M) (**E**); HVED (T = 90 \({}^{\circ}\)C, time = 20 min, NaOH = 0 M) (**F**) and raw material (**G**) (magnification 100). Reprinted from _Biomass and Bioenergy_, 95, 92–98, Copyright (2016), with permission from Elsevier. Figure 5: Effect of combined treatment (NaOH sol. (control), Pulsed electric fields (PEF) + NaOH sol., HVED + NaOH sol., US + NaOH sol., MW + NaOH sol.) on sugar recovery after 24 h of enzyme hydrolysis (NaOH sol. conditions: 60 \({}^{\circ}\)C, 2 h, 0.3 molL\({}^{-1}\), physical treatment condition: 30 min of total solid/liquid contact time (150 kJ kg\({}^{-1}\) for PEF and HVED, 1500 kJ kg\({}^{-1}\) for US)). tained cellulose degradation. Moreover, the recovered lignin structure and its thermal properties were not affected by sonication process. [PERSON] and [PERSON] (2014) [84] examined the application of alkaline UAT on newspaper waste slurry, a substrate containing up to 23.07% of lignin. About 2-fold increase in delignification (around 80%) was achieved by cavitation (20 Hz, 100 W, 70 min) if compared to silent alkaline process (Table 2). The so obtained pretreated biomass could represent a suitable substrate for ethanol fermentation and EH due to its high cellulose content. The US pretreatment effect on fibres of oil palm empty fruit bunch (OPEFB) has been evaluated by [PERSON] et al. (2010) [85] for acid hydrolysis. It has been estimated that the amount of fermentable sugars from OPEFB, namely xylose (Xyl) and Glu account for ca. 70% of the overall composition. This feature makes this substrate extremely interesting for bioethanol production via fermentation. In detail, [PERSON] et al. applied a US probe operating at 20 kHz and 2 kW power, maintaining the working temperature of 25 \({}^{\circ}\)C. A maximum Xyl yield of 58% was achieved when the hydrolytic tests (100 \({}^{\circ}\)C, 2% H2 SO4, 1:25 solid/liquid (S/L) ratio) were performed on fibres treated with US for 45 min. On the contrary, only 22% of Xyl was obtained for raw biomass. A direct exposure of the OPEFB fibres to acoustic power at various amplitudes has a noticeable impact on the effectiveness of acid hydrolysis, estimated on the Xyl yield (Figure 6). This trend has been explained by the increasing removal of silica from the surface of the OPEFB fibres, prior to acid hydrolysis. \begin{table}
\begin{tabular}{c c c} \hline \hline
**US Parameters** & **Delignification** & **Rate Constant k** \\  & **(\%)** & **(min\({}^{-1}\))** \\ \hline Power (W) & & \\
60 & 42.77 & 0.0081 \\
70 & 50.21 & 0.0106 \\
80 & 60 & 0.0138 \\
90 & 73.26 & 0.0197 \\
100 & 80.16 & 0.0239 \\
110 & 82.01 & 0.0259 \\ Duty Cycle (\%) & & \\
40 & 63.15 & 0.0148 \\
50 & 69.97 & 0.0178 \\
60 & 75.59 & 0.0213 \\
70 & 79.94 & 0.0242 \\
80 & 80.92 & 0.0246 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Effect of US parameters on lignin removal rate. Figure 6: Influence of US amplitude on Xyl yields. [PERSON] et al. (2017) [86] recently investigated the recovery of cellulosic material from sugarcane bagasse (SCB), an agri-food waste prone to ethanol production without any hydrolytic protocol. The matrix was firstly pretreated under alkali (NaOH 22%-25%), acidic (H\({}_{2}\)SO\({}_{4}\) 2.5-3.5%) or US condition (20 kHz, 100 W), applied separately or in combination. In addition, SEM analysis showed that the combined acid/UAT was able to destroy the SBC complex structure. The pretreated biomass was then anaerobically fermented without EH.