Improving circularity of bio-based side streams with pretreatments
Nguyen, Anh (2022)
Nguyen, Anh
2022
Master's Programme in Environmental Engineering
Tekniikan ja luonnontieteiden tiedekunta - Faculty of Engineering and Natural Sciences
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Hyväksymispäivämäärä
2022-11-30
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-202211148379
https://urn.fi/URN:NBN:fi:tuni-202211148379
Tiivistelmä
Agriculture plays a leading role in the African economy, yet its impacts on the environment as well as human living conditions are preventing sustainable development in this continent. A large amount of side stream from agricultural crops ends up in landfills or incinerators without proper management, which is wasteful as biomass residues are known as rich resources of lignocellulose which can be retrieved and recycled for several applications. Lignocellulose, mainly including cellulose, hemicellulose, and lignin, is especially potential in the manufacturing of innovative bio-based materials called biocomposite, which can be further utilized in biopackaging production.
However, the utilization of biomass residues for biocomposite and biopackaging in Africa is limited at present due to the contamination caused by microorganisms, molds in particular. To resolve the issue and enhance the recyclability of crop side streams, appropriate elimination methods for mold must be applied. Thus, the thesis aims at studying and assessing current pretreatment methods of agricultural biomass waste in terms of their mold removal efficiency which is determined via antifungal efficacy/fungicidal effect. The most suitable method will be selected based on applicability, affordability and sustainability concerning the African context besides its removal efficiency. From the literature review, pretreatment with chemicals such as hydrogen peroxide (H2O2), organic acids or ethanol (EtOH) was considered the most simple, practical, and eco-friendly among all available methods. Apart from chemical pretreatment, a basic physicochemical technology i.e. autoclave was also contemplated in this case thanks to its widespread application in medical and food disinfection.
During the experiment, the mold concentration was determined by the plating and culturing method before and after pretreatment. The fungi were also characterized through microscopic examination. The pretreatment testing was implemented with two stages, screening and repetition. The side stream was dipped into H2O2 alone at 3-5% for different durations from 10 to 120 minutes, and into H2O2 added organic acids (formic and acetic). The vapor form of H2O2 was also examined on the residues. With ethanol, the samples were immersed in 35 and 50% EtOH at room temperature and 50 °C for 10 minutes. For autoclave examination, the samples were sterilized in one standard cycle i.e. at 121 °C for 20 minutes.
The processes with H2O2 alone and H2O2 in addition to acids along with autoclave were selected for further replication. Most of the methods obtained the satisfactory removal efficiency of mold i.e. 4-log or higher. There was no presence of mold growth after the incubation in the cases of autoclave, 5% H2O2 in 10 minutes and H2O2 in combination with acetic acid, suggesting that the removal efficiency might go up to 99.9999% or above. Yet, due to the uneven distribution of fungi on the side stream, such a high estimated value can be unreliable. The residue portion used in these experiments may contain little to none of molds.
On the other hand, pretreatment with 5% H2O2 in 20 minutes showed the most consistent results with an average removal efficiency of ca. 5-log concerning pretest and repetition outcomes. Additionally, the use of H2O2 fits all selection criteria as the chemical is affordable and accessible worldwide. The operation of dipping pretreatment is simple. The method is also sustainable as H2O2 decomposition is eco-friendly and no residue is left on the side stream, while its wastewater can be either directly released or managed with current wastewater treatment technology. Hence, this process is expected to be further applied in reality.
However, the utilization of biomass residues for biocomposite and biopackaging in Africa is limited at present due to the contamination caused by microorganisms, molds in particular. To resolve the issue and enhance the recyclability of crop side streams, appropriate elimination methods for mold must be applied. Thus, the thesis aims at studying and assessing current pretreatment methods of agricultural biomass waste in terms of their mold removal efficiency which is determined via antifungal efficacy/fungicidal effect. The most suitable method will be selected based on applicability, affordability and sustainability concerning the African context besides its removal efficiency. From the literature review, pretreatment with chemicals such as hydrogen peroxide (H2O2), organic acids or ethanol (EtOH) was considered the most simple, practical, and eco-friendly among all available methods. Apart from chemical pretreatment, a basic physicochemical technology i.e. autoclave was also contemplated in this case thanks to its widespread application in medical and food disinfection.
During the experiment, the mold concentration was determined by the plating and culturing method before and after pretreatment. The fungi were also characterized through microscopic examination. The pretreatment testing was implemented with two stages, screening and repetition. The side stream was dipped into H2O2 alone at 3-5% for different durations from 10 to 120 minutes, and into H2O2 added organic acids (formic and acetic). The vapor form of H2O2 was also examined on the residues. With ethanol, the samples were immersed in 35 and 50% EtOH at room temperature and 50 °C for 10 minutes. For autoclave examination, the samples were sterilized in one standard cycle i.e. at 121 °C for 20 minutes.
The processes with H2O2 alone and H2O2 in addition to acids along with autoclave were selected for further replication. Most of the methods obtained the satisfactory removal efficiency of mold i.e. 4-log or higher. There was no presence of mold growth after the incubation in the cases of autoclave, 5% H2O2 in 10 minutes and H2O2 in combination with acetic acid, suggesting that the removal efficiency might go up to 99.9999% or above. Yet, due to the uneven distribution of fungi on the side stream, such a high estimated value can be unreliable. The residue portion used in these experiments may contain little to none of molds.
On the other hand, pretreatment with 5% H2O2 in 20 minutes showed the most consistent results with an average removal efficiency of ca. 5-log concerning pretest and repetition outcomes. Additionally, the use of H2O2 fits all selection criteria as the chemical is affordable and accessible worldwide. The operation of dipping pretreatment is simple. The method is also sustainable as H2O2 decomposition is eco-friendly and no residue is left on the side stream, while its wastewater can be either directly released or managed with current wastewater treatment technology. Hence, this process is expected to be further applied in reality.