Production of biosurfactants using industrial waste streams as substrates

Moshtagh, Bahareh (2019) Production of biosurfactants using industrial waste streams as substrates. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Surfactants have a widespread household and industrial applications such as pharmaceutical, cosmetic, petroleum, agriculture, environmental, health care, and food industries. Chemical surfactants can be toxic and non-biodegradable. Biosurfactants which are produced with microorganisms are biodegradable and potential substitute to chemically synthesized surfactants. Large-scale production of biosurfactants is limited due to high costs associated with production. These costs could be decreased by using industrial wastes and by-products as substrates in the growth medium and additionally reduce the environmental impacts of the wastes. Another useful method for achieving economic viability for biosurfactant production is optimization of the cultural conditions such as temperature, pH, agitation, aeration, and medium compositions. The effectiveness of different local industrial waste streams for biosurfactant production was assessed using some indigenous Bacillus subtilis, Rhodococcus erythropolis and Acinetobacter calcoaceticus strains. The potentiated waste streams regarding appropriateness for microbial growth and biosurfactant production were obtained including brewery waste, glycerol from the conversion of fish oil to biodiesel, fish wastes, waste cooking oil and produced water. The waste streams were treated, centrifuged and filtered through membrane filters. According to the appropriate medium composition for each strain, which was derived from other studies, different mineral salts and trace elements were added to the waste streams. The cultivations were performed in flasks containing 50 mL medium and stirred in a rotary shaker at 30°C and 200 rpm for several days. Biosurfactant productivity was evaluated by surface tension and emulsification index measurement. After running numerous tests for biosurfactant production, low production rate sources of carbon were omitted from further studies, and suitable levels or concentrations of effective waste streams for each strain, as well as some other cultivation conditions, were identified. Also, the appropriate composition for the medium was derived through these pre-tests. Eventually, indigenous Bacillus subtilis N3-1P strain with the brewery waste and Acinetobacter calcoaceticus P1-1A strain with the refined waste cooking oil as the sole carbon sources yielded the best results and were chosen for further studies. Appendix I demonstrates a comprehensive explanation of the initial tests. The medium and cultivation conditions optimizations were conducted in a series of experiments. Different factors have been chosen to facilitate a higher production rate of the biosurfactant such as carbon source concentration, nitrogen source concentration, NaCl concentration, agitation speed, temperature, and initial pH. Finally, response surface methodologies employing the Design Expert software were used to optimize different parameters. The optimizations were performed separately on the two selected strains with their appropriate waste streams as carbon sources. The predicted responses were validated experimentally under the optimum conditions. The indigenous Bacillus subtilis N3-1P and the brewery waste as carbon source were used to model the biomass growth, biosurfactant production, and substrate utilization by fitting the experimental data to the Logistic, Contois and Luedeking-Piret models using the MATLAB software and regression analysis. The achieved models can be used for simulating the large-scale production of biosurfactants. The results of these studies confirm that the local brewery waste and the refined waste cooking oil can be used as the sole carbon sources for biosurfactant production by indigenous Bacillus subtilis N3-1P and Acinetobacter calcoaceticus P1-1A, respectively. Using these sustainable and inexpensive carbon sources reduces costs associated with biosurfactant production and helps to generate an environmentally friendly way for waste treatment and disposal. Also, finding the optimum conditions for different parameters and using the simulated models can decrease the production costs and be useful tools for understanding the cultivation process and scaling up the biosurfactant production. The economically produced biosurfactants would have the ability to be used as an effective method to minimize the impacts of spilled oil in offshore Newfoundland and Labrador.

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