Thesis Format
Monograph
Degree
Doctor of Philosophy
Program
Chemical and Biochemical Engineering
Supervisor
Berruti, Franco
2nd Supervisor
Moreira Valenzuela, Cesar M.
Affiliation
Escuela Superior Politécnica del Litoral, ESPOL
Co-Supervisor
Abstract
An ever-increasing population has directed an enormous growth in agricultural activities to ensure food security. This has led to higher agricultural residue production worldwide. The effective and resourceful management of these residues remains a challenge to this day. With the increasing population, there has also been a higher demand for textiles which are mostly fulfilled by fossil fuel derived synthetic fibers. This further results in the generation of toxic effluents, hence becoming an environmental liability. This project deals with the development of zero-waste methods for the management of agri-residues, by integrating the thermochemical treatment of the agri-residues with the biochemical process of fiber production.
In the first stage of the project, various agri-residues, such as wheat straw, hemp bast fibers, banana short fibers and agave straw, were pyrolyzed in batch and continuous processes. The products derived from the pyrolysis process - bio-oil, biochar and gas, were analyzed and compared. Wheat straw bio-oil had the maximum acetic acid concentration and was chosen for further application. In the second stage, the retting (biological degumming) process of decorticated pineapple leaf fibers (PALF) was investigated. The activities of cellulase, xylanase and pectinase enzymes were monitored, and process conditions were optimized to reduce retting time and improve efficiency. It was found that the addition of bio-oil, to adjust the initial pH of the system, along with bubbling (aeration) improved the efficiency of the process by reducing the time from 18 days to 4 days. In addition, the pectin and wax content of the fibers reduced by 55% and 36.5%, respectively, in comparison to the traditional retting where the wax content reduced only by 13.6%. The fibers were further processed to increase the alpha cellulose content, by steam explosion in the presence of an alkali. Biochar extracted water, with a pH of 12.8, was used to replace NaOH, which is traditionally used in the fiber treatment process. The fibers had a crude cellulose content of 87.21%, which was comparable to the NaOH treated fibers. Additionally, the crystallinity index and SEM images show that the biochar extracted water was a suitable alternative. Additionally, the effluent from the retting process was pH corrected using biochar, to be used for hydroponic growth of leafy greens. The results suggested that the treatment of the effluent did not have any negative effects on arugula growth when diluted 30:70 (v/v) with fertilizer solution. The biochar remaining from the effluent treatment was further utilized as a germination medium for the hydroponic system to replace rockwool. Finally, a qualitative life cycle assessment showed the benefits of the proposed scheme in comparison to the conventional treatment of agri-residues.
Overall, this project demonstrates the valorization and resourceful application of all waste streams generated during the process hence successfully demonstrating the implementation of a circular economy approach through a zero-waste process.
Summary for Lay Audience
Of the endless requirements of a constantly increasing population, food security and clothing are the two most important to fulfill. Whereas there has been a massive increase in agricultural activities to combat food security, clothing requirements are now taken over by the mass production of synthetic textiles. Both activities have led to the generation of a large amount of waste which turns out to be toxic for the natural environment. With the current environmental situation, it is becoming increasingly important to manage these residues in an eco-friendly way. One of the applications that addresses these concerns is the production of fibers using agricultural residues, such as pineapple leaves. However, these processes further result in the formation of wastewater and other toxic residues due to the application of synthetic chemicals. Following a circular economy approach, this project deals with the development of a zero-waste method by utilizing the agricultural residues for the generation of components that can be included in fiber processing thereby making the processes truly sustainable.
In the first stage, the agricultural residues are subjected to thermochemical conversion to produce bio-oil, biochar and gas, all of which can be utilized for energy generation or within the fiber processing cycle. Secondly, the biochemical process of fiber cleaning, known as retting, has been investigated to identify and optimize the process in an effort to reduce the time taken and improve efficiency. This was done with the addition of acidic bio-oil. Next, the fibers were further processed under high temperature and high-pressure conditions using biochar within the process to replace added chemicals, such as sodium hydroxide. Additionally, the acidity of the wastewater generated during the retting process was neutralized using the biochar developed from the thermochemical conversion of the agri-residues. This treated wastewater was then used as a fertilizer solution to hydroponically grow leafy greens. The biochar left from the treatment of the effluent was further utilized as a germination medium to replace the fossil fuel derived substrates that are currently used. In doing so, all waste streams generated as a result of all the processes in the system were successfully utilized therefore demonstrating a zero-waste system that is truly sustainable and conforms to the principles of circular economy.
Recommended Citation
Batta, Neha, "Circular Economy Approaches for Sustainable Agri-Residue Management: Integrating Pyrolysis and Biochemical Conversion for Developing Zero-Waste Fiber Production Processes" (2025). Electronic Thesis and Dissertation Repository. 10683.
https://ir.lib.uwo.ca/etd/10683
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This work is licensed under a Creative Commons Attribution 4.0 License.
