# Cellulose Recovery from Agri-Food Residues by Effective Cavitational Treatments
## 3 Biomass Treatments for Cellulose Recovery
### Acoustic Cavitation (AC) as Effective Biomass Pretreatment
They proved that the alkaline UAT (NaOH) enabled 3.5 times higher concentration of reducing sugar than untreated one, after 48 h of EH (2.91 vs. 0.85 g L\({}^{-1}\)). These results can be attributed to the US pretreated samples' higher cellulose content as well as their lower hemicellulose and lignin content and to their higher porosity and surface area compared to untreated ones. Nevertheless, it should be stated that the cellulose content of processed straw, together with its surface area and porosity rose with the increasing concentration of used NaOH (0.4%, 0.6%, 0.8% and 1.0%, \(w/v\)). A UAT in presence of tetra-butylammonium hydroxide (TBAOH) was recently launched by [PERSON] et al. (2017) [90] to boost the biodegradability of a largely diffuse agri-food residue: the wheat straw (WS). The synergistic mechanical and chemical effects induced by the combined UAT-TBAOH pretreatment were responsible for both WS surface destruction and internal structure disruption of pretreated samples (Figure 9). High-efficient lignin removal combined with structural transformation (crystallinity reduction) was accomplished after the process. Experimental screening indicated that sonication time, temperature and US power intensity were pivotal for the pretreatment success of WS in presence of tetra-butylammonium hydroxide. A 4-fold increased saccharification yield (_ca._ 92.4%) was obtained from residual cellulosic fraction if compared to untreated matrix. In detail, the WS were submitted at 50 \({}^{\circ}\)C to 30 min of sonication at 344 W/cm2. Figure 8: Reducing sugars recovered from pretreated and raw RS samples. U/F-RS = combined US 6 Fenton process); F-RS = (conventional Fenton’s process); U-RS = (UAT-RS at 400 W); (R-RS = (raw RS). Moreover, the author pointed out that a certain extent of lignin removal (60-70%) is enough to attain high saccharification efficiency. Meanwhile, an excessive lignin removal achievable under harsher pretreatment conditions may cause cellulose degradation that is not desirable from a biomass valorisation prospective based on cellulose recovery (Figure 10). In addition, it was reported that TBAH could be recycled several times without considerable loss of activity. Figure 10: Influence of lignin removal on saccharification yield. Figure 9: Mechanism of UAT with TBAH. US technology under different power input (60-540 W) and duration (10-30 min) was successfully applied by [PERSON] et al. (2017) [91] as suitable cellulose isolation process for sugar beet shreds biomass (2-4% of solids loading). In fact, under the tested conditions, US (22-25 kHz), caused up to 28% material solubilization while the recovery of cellulose was approximately 90%. In addition, US provided sugar beet shreds extremely prone to enzymes adsorption (allowing an adsorption capacity of 1.4 to 15 times higher), thus enhancing the EH. The best yield of cellulose EH (approximately 780 mg/g cellulose) was 3.7 times higher than that recorded for the raw substrate, indicating that US could be a good choice to recover from this agri-food waste a cellulosic fraction prone to enzymes conversion. Coffee silver skin (CSS) is an agri-food processing waste largely produced at almost constant rate in roasting factories over all the year. The CSS could be employed as a fermentable sugars source within a biorefinery approach for its exploitation. [PERSON] et al. (2017) [92] investigated the effect of the US-assisted dilute acid pretreatment on the effective recovery of cellulose from CSS biomass. The effects of two mainly operating parameters--biomass loading (ranging between 3 and 10% \(w/v\)) and H\({}_{2}\)SO\({}_{4}\) (96% w) concentration (ranging between 0.5 and 2% \(v/v\))--were evaluated over sugar yields after EH. A probe type ultrasonic device (20 kHz) was used for the US pretreatment at specific sonication power (energy for dry biomass unit) of 300 W/gDM for 8 min.