Properties of the green microalga Monoraphidium sp. Dek19 for phycoremediation of wastewater and biofuel production
Kirchner, Nicholas James
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The focus of this thesis was to investigate the growth of Monoraphidium sp. Dek19 in post-primary filtration and final wastewater effluent for the purposes of phycoremediation and as a potential biofuel feedstock. The algae were inoculated in wastewater effluent collected from the local wastewater treatment facility in DeKalb, Illinois and grown in 1L flasks at 10°C and 22°C. It was determined that initial population density (IPD) played an important role in the successful growth of a culture. Cultures started at an E680 greater than 0.100 could grow, but at a suboptimal rate. However, it was found that when cultures were started at a higher E680 value of [almost equal to]0.60, cultures exhibited significantly shorter lag phases and therefore less time to the onset of stationary phase. Monoraphidium sp. Dek19 was shown to compete with other commonly occurring green microalgae when grown in a consortium of species. When cultures were inoculated with 20% Monoraphidium sp. Dek19 and an 80% mixture of Chlorella sp. and Ulothrix sp. in a culture grown at 10°C, Monoraphidium sp. Dek19 was able to maintain its population composition and made up [almost equal to]70% of the total algal biomass. Sucrose density gradients were developed as an efficient method to separate a desired microalga from a consortium of species. Photosynthetic oxygen evolution rates of Monoraphidium sp. Dek19 were observed at 10°C and an ambient lab temperature (22-25°C) in both post-primary filtration and final wastewater effluent. Equivalent rates of oxygen evolution were observed in both media. Photosynthetic rates were higher at ambient lab temperatures than at 10°C. Monoraphidium sp. Dek19 exhibited diminished rates of photosynthesis when tested at a higher or lower temperature than its growth condition, indicating a possible perturbation of photosynthesis when forced to quickly acclimate to a new temperature. Oxygen evolved during algae growth may supplement the activated sludge process during water treatment. A rise in the alga's chlorophyll a:b ratios may indicate an adaptation to cooler conditions. The algae were able to remediate polluting concentrations of nitrogen and phosphorous to minimal levels in both media. Monoraphidium sp. Dek19 cultures were able to rapidly accumulate lipids at the onset of stationary growth phase. This was determined through the use of Nile red dye and images taken with a confocal microscope. It was concluded that Monoraphidium sp. Dek19 could be used for phycoremediation of wastewater effluent either from primary filtration or from the final settling tanks prior to effluent discharge into local waterways. Monoraphidium sp. Dek19 could also be a potential feedstock for biofuel production as the cells can grow within the cooler range of temperatures observed at wastewater treatment facilities in the Midwest. This alga has lipids that can be successfully converted to biofuel.