Biodegradation of wastewater from the milk industry by GRAS microorganisms
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The dairy industry, revolving around milk processing, generates large volumes of industrial effluents. These effluents can be nutritious and high in organic matter, with the main component being lactose, and thus problematic to handle for municipal wastewater treatment plants. Consequently around 50% of dairy wastes are discharged to receiving water-bodies, with potential environmental consequences. This project aimed at developing a microbial degradation process that could be implemented by the dairy industry to reduce the chemical oxygen demand (COD) content of their waste before its discharge. The project involved the screening of potentially suitable organisms (bacteria, yeast and fungi), followed by investigations of their ability to degrade the waste components and the selection of the most promising candidate for optimizing and upscaling the process. For this purpose 10 different GRAS organisms (Cryptococcus laurentii, Cryptococcus flavus, Kluyveromyces lactis var. Lactis, Kluyveromyces marxianus, Lactococcus Lactis subsp. Cremoris, Lactobacillus Plantarum subsp. Plantarum, Lactobacillus plantarum, Lactobacillus acidophilus, Saccharomyces cerevisiae and Pichia pastoris) were first screened for their ability to degrade lactose and use it as a carbon source. Following this, the strains ability to grow in media containing wastewater was investigated, as well as their ability to degrade the lactose and reduce the overall COD. Based on the results, the most promising strains, K. lactis, C. laurentii and L. plantarum were selected for further study. Their growth characteristics, lactose biodegradation rates and efficiency in removing COD were studied in wasterwater supplemented with minimal amounts of nutrients. The fungus strain of C. laurentii degraded lactose mainly during stationary growth phase, and removed in excess of 30% COD in shake flask cultivation. The yeast strain K. lactis, in contrast degraded all the lactose during exponential cell growth phase and removed in excess of 30% COD in shake flask cultivation. Finally, based on the above results, a batch and continuous flow fermentation was performed with K. lactis as a first step into the otpimisation and upscaling of the biodegradation process. The batch fermentation proved to lead to the best lactose degradation rates and a removal of 67% of COD within the first 24 h.
Master's thesis in Environmental technology *KAR OK IKKE PUBLISER*