Abstract
Wastewater solids could be an attractive source of secondary raw cellulose, mainly originating from toilet paper. Cellulose can be recovered through sieving of raw wastewater, return sludge, or excess sludge. In particular, a large fraction of cellulose (13–15%) can be found in the excess sludge of the aerobic granular sludge produced by the Nereda® wastewater technology. A cellulose extraction method was developed during this study, allowing the recovery of a pulp with over 86 wt% purity. The wastewater derived cellulose fibres could be an excellent source for production of recovered cellulose nanocrystals (rCNC). Several pre-treatment steps needed in cellulose nanocrystals (CNC) production from wood pulp are already performed in the production of toilet paper. Here, the technical feasibility of such rCNC is studied. As reference materials, microcrystalline cellulose and toilet paper were also used. The rCNC were obtained by acid hydrolysis, with yields of ∼30 wt% (pulp basis). The wastewater-based material was rod-like, with high aspect ratio (10–14), crystallinity (62–68%), and chemical structure similar to commercial CNC. The yield of rCNC per gram of cellulose recovered from the influent was 22%, while for excess sludge cellulose it was less (4%). Bio-nanocomposites of rCNC and alginate were also investigated. At 50 vol% loading of rCNC, there was a 50% relative increase in stiffness (18 GPa) compared to matrix (12 GPa). The characterization of rCNC and positive impact in composite materials confirms a suitable quality of wastewater derived CNC. Ultimately, the nanocellulose is a tangible example that recovery of high-end products from wastewater is possible, in line with a circular economy.
Highlights
For thousands of years, mankind process cellulose derived from plants in the production of pulp, paper, and derivatives
For Nereda® excess sludge, after first alkaline treatment (2 wt% NaOH), the samples were still viscous, and fibres presented a dark-brownish appearance. This was solved with more successive alkaline treatments - two times or more depending on wastewater solids characteristics - or even treatments with increased NaOH concentration (4e8 wt%)
The procedure is similar to what is applied in the delignification and pulping used by the paper industry to remove as much as possible the non-cellulosic components, i.e., hemicellulose and lignin-like compounds (García et al, 2016)
Summary
Mankind process cellulose derived from plants in the production of pulp, paper, and derivatives. With the adoption of toilet paper in modern societies, cellulose fibres became, in many countries, a primary insoluble substrate entering sewage treatment plants (STP). They compose 30e50% of the total solids in the sewage of western countries (Ghasimi et al, 2015a). A large fraction of this cellulosic matter is recalcitrant to current physicochemical and biological treatment technologies, resulting in extra surplus sludge production. Limited research has been conducted on the Abbreviations: CNC, Cellulose NanoCrystals; rCNC, recovered Cellulose NanoCrystals; STP, Sewage Treatment Plant; TP, recycled pulp Toilet Paper
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
