Faculty of Applied Sciences
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Item Development of chitosan biopolymer films by fungal fermentation of waste substrates(2024-05) Naidoo, Krinolen Krishna Rajahrathanum; Permaul, Kugen; Govender, Algasan; Puri, Adarsh KumarZygomycetes are known for their relatively high chitosan content (approximately 10% m/m) in comparison with other fungal genera. In this study, Mucor circinelloides was grown on the following industrial waste substrates: corn steep liquor (CSL); soft drink overflow spillage waste (DBW); and sugarcane molasses (MOL). Biomass production on waste substrates was statistically optimized by Plackett-Burman design in conjunction with Response Surface Methodology, followed by validation of the model. DBW hindered fungal biomass growth and was found to be a statistically insignificant variable and therefore omitted from further optimizations. The validated model produced a biomass of 77.87 g/L, a 2.65-fold increase over the highest-yielding unoptimized medium. Fungal biomass obtained after batch fermentation was subjected to acid-alkaline treatment for chitin extraction from the cell wall and deacetylation of the chitin to chitosan. A yield of 8-9% chitosan was obtained from the fungal biomass. FTIR spectroscopic analysis was conducted on the extracted fungal chitosan to compare extracted chitosan against commercial chitosan and chitosan monomer. The waste-grown, fungal-derived chitosan profiles were similar to those of commercial crustacean chitosan. The extracted chitosan was used in conjunction with additives and solvent systems to create biopolymer variants with differing properties. A library of data from the chitosan biopolymer variants was generated with considerable differences in characteristics based on their composition. Improvements in sample #11 (the most modified formulation) in contrast to the most common chitosan biopolymer film composition used in literature (sample #9), included a 3.37-fold improvement in the static force required to break the film. There was a 3.39-fold increase in tensile strength and an 11-fold reduction in elongation (%) and elongation rates. The creation of these variants will allow the use of these chitosan biopolymers for specific industrial applications.Item Optimization of biomass and lipids production from microalgae using wastewater in a pilot scale raceway pond(2021) Rawat, Ismail; Bux, FaizalMicroalgae provide a sustainable renewable solution for the production of commodity products such as liquid biofuels. There are numerous benefits to using algae for the production of biofuels, however, the cost of production is a major hurdle to commercial-scale development. Major factors influencing the production of algae are the cost of nutrients, availability of water, contamination, and grazers. Research into algal biomass for biofuels production at laboratory scale does not translate directly to cultivation at large scale due to the change in cultivation conditions and the constant flux of environmental factors. This study focuses on the upstream processes of cultivation of biomass in a ~ 1146 m2 raceway pond. It demonstrates biomass productivity under different climatic conditions and utilisation of post-chlorinated wastewater as a water and nutrient source. The study further elucidates the population dynamics of the system and provides insight into the challenges faced during the cultivation of algae at large scale. An indigenous Scenedesmus sp. gave biomass productivity of 31.23 g/m2 /d with lipid production of 29.6 % lipid/g DCW in a 10 m2 raceway pond in a greenhouse using BG11. Biomass productivity was reduced to 13.09 g/m2 /d with a lipid content of 22.9 % lipid/g DCW under 3-fold higher irradiance. Biomass productivity of circular 3000L ponds at the large scale site resulted in the highest biomass and acceptable lipid content using 250mg/L NaNO3 although significantly lower than the 10 m2 raceway ponds. Wastewater has shown potential to replace conventional media. Post-chlorinated wastewater was found to have low levels of nitrogen and phosphorus but contained metals that act as micronutrients for algae. Supplemented wastewater proved to be an effective growth. Six individual runs of a covered 1146 m2 raceway pond driven by paddlewheel were conducted over 15 months. The average water temperature ranged from 20.61±0.68°C during mid-winter to 31.03±2.22°C in late summer. Daylight ranges from 10.25 to 14 hours in winter and summer respectively. The highest average light intensity was 359.00±212.71 µmol/m2 /s from Mid-winter to early spring and 645.44±330.58 µmol/m2 /s in late summer. Biomass productivities were low ranging from 2.7 to 7.34 g/m2 /d for most runs of the raceway pond, mainly due to the long periods of cultivation. Average productivity at day 7 for all raceway runs was 7.25 g/m2 /d. Adaptive Neuro-Fuzzy Inference System (ANFIS) modelling of the system elicited that the major factors affecting biomass productivity in the raceway pond were light intensity, pH, and depth for the raceway pond. The model showed that maximum biomass productivity is possible at a depth between 20 and 22 cm at light intensities between 200 and 400 µmol/m2 /s. pH in the range of 9 to 9.5 correlated positively with light intensity ranging from 200 to 1000 µmol/m2 /s with maximum biomass expected in the region of 400 to 500 µmol/m2 /s. The main algal constituents for the raceway ponds were Scenedesmus obliquus, Scenedesmus dimorphus, Chlorella, Keratococcus, and species of unidentified cyanobacteria. Either Scenedesmus or Chlorella was dominant for extended periods. Bacteria in open systems can have a positive or negative effect on the growth of microalgae but is dependent on the strains of microalgae and bacteria as well as prevailing conditions making these systems highly complex. Rhodobacteraceae, Plactomycetaceae, Xanthomonadaceae, Flavobacteriaceae, Phycisphaeraceae, Comamonadaceae, and Cyclobacteriaceae were found to be the major families of bacteria that proliferate at different levels during the cultivation period in the circular ponds and the raceway pond. These families of bacteria have several beneficial traits to algae cultivation however further investigation is required. Modelling the system revealed that pH, depth, and light intensity were factors having a substantial effect on biomass productivity. As the system was carbon limited addition of CO2 (preferably a waste stream) could significantly enhance the overall biomass productivity. A major factor negatively affecting biomass productivity was the size of the pond. Inadequate mixing impacts biomass productivity in terms of access to nutrients and gaseous exchange. Shorter periods of cultivation resulted in higher productivities. For the scale of the system, semi-continuous harvesting would be required to achieve shorter residence time. This must be balanced against the energy utilization and cost of harvesting potentially lower culture densitiesItem Valorisation of bambara and cowpea haulms for bioethanol production(2020) Okuofu, Somiame Itseme; Pillai, Santhosh Kumar KuttanBambara and cowpea are important pulses grown in semi-arid South Africa due to their balanced nutrient profile and drought resilient capacity. The haulm is the lignocellulosic residue obtained after grain harvest and are rich in carbohydrates. However, these haulms are underutilised and under researched. The aim of the study, therefore, was to investigate the potential to valorise bambara haulms (BGH) and cowpea haulms (CH) to bioethanol which is the most promising biofuel with commercial prospects currently. The structural and chemical composition of BGH and CH was elucidated using techniques such as compositional analysis, XRD, FTIR, ICP-AES, and SEM. Results indicated a volatile matter and fixed carbon mass fraction of 77.70% and 13.15% (w/w) in BGH and 76.16% and 16.26% (w/w) in CH respectively. The polysaccharides make up the largest fraction (51%), followed by extractives (> 20%), while the lignin in BGH (12%) and CH (10%) was low. X-ray diffraction pattern showed a higher percentage of amorphous regions in BGH (78%) than CH (56%). CH was then subjected to dilute acid pretreatment (DAP) to enhance biosugar production for bioethanol fermentation. The effects of operational factors for DAP including temperature, time, and acid concentration on sugar yield and inhibitor formation was investigated and optimised using response surface methodology (RSM). The solid recovered after DAP was subjected to prehydrolysis with simultaneous saccharification and fermentation (PSSF). In addition, the pretreatment hydrolysate was detoxified and fermented to ethanol using cocultures of Saccharomyces cerevisiae BY4743 and Scheffersomyces stipitis wild type (PsY633). A total ethanol titre of 15.67 g/L was obtained corresponding to 75% conversion efficiency. On the other hand, BGH was subjected to deep eutectic solvent (DES) pretreatment. Five deep eutectic solvents were prepared and screened for their effectiveness in improving enzymatic sugar yield. This was achieved by pretreating BGH with each DES followed by a 48 h enzymatic saccharification. Choline chloride – lactic acid (ChCl-LA) treatment provided the most promising result and was further optimised by investigating the effect of different temperatures and time on cellulose loss and enzymatic sugar yield. ChCl-LA pretreatment at 100°C for 1 h was observed to be the best condition for maximum sugar recovery. The hydrolysate thus obtained was concentrated and fermented for 72 h with S. cerevisiae BY4743. A maximum ethanol yield of 11.57 g/L was obtained. From the results, it is evident that bambara and cowpea haulm are promising substrates for bioethanol production. Dilute acid hydrolysis was shown to be effective in the pretreatment of CH with over 85% of the theoretical sugar recoverable for conversion to bioethanol. In addition, deep eutectic solvents are effective media for breaking the recalcitrance in BGH to achieve high sugar yield for conversion to bioethanol. However, further studies are required to reduce cellulose loss during pretreatment to improve bioethanol yield.