Cultivation of algae on highly concentrated municipal wastewater as an energy crop for biodiesel production

There has been renewed interest in bio-fuel production over the past decade due to the sharp rise in fossil fuel prices and increasing concerns about the global climate change. This dissertation was inspired by the idea of coupling algae based biofuel generation and municipal wastewaster treatment. The objectives of this study are to employ potential algae strains for efficient simultaneous biodiesel production and wastewater nutrients removal, and to develop an operational strategy optimal for biomass and biodiesel production as well as nutrient removal from a highly concentrated municipal wastewater stream, centrate, which is generated during the sludge thickening process.;In the first stage, the feasibility of growing Chlorella sp. in the centrate for simultaneous wastewater treatment and energy production was tested. The characteristics of algal growth, biodiesel production, wastewater nutrient removal and the viability of scale-up and the stability of continuous operation were examined.;The second stage was targeted at screening one or several algae species/strains that can survive and grow well in centrate with high biomass and lipid productivity as well as superior nutrient removal efficiency, and investigating the significance of environmental factors including ligh intensity, light/dark cyle, and exogenous CO2 on biomass accumulation and biodiesel production using Plackett-Burman experiment design. In this stage the study was carried out in two sections, namely using aglae strains collected from local lake areas and those purchased from algae commercial bank.;In the third stage, the single effect of light intensity on biomass accumulation, wastewater nutrient removal through algae cultivation, and biodiesel productivity was investigated with algae species Chlorella kessleri and Chlorella protothecoide. Both species were capable of wastewater nutrients removal under all lighting conditions with high removal efficiencies. Since Chlorella kessleri showed superior capability of biomass accumulation and biodiesel production, it was used in the following sections.;The fourth stage was aimed at investigating the single effect of light/dark cycle at low light frequency on algae based biodiesel production using centrate wastewater stream with mixotrophic strain Chlorella kessleri. The data suggested that the length of lighting period during a day greatly affects the algal biomass accumulation, biodiesel production and wastewater nutrients removal. The biomass concentration, biodiesel content and the removal of ammonia, total nitrogen and total phosphorus all increased with increasing lighting period. However, the removal of COD showed different trend, with higher removal rate observed under shorter lighting period. The results showed that for maximum biomass accumulation, biodiesel production and wastewater nutrients removal in batch culture system, the optimum lighting period is 16 hours and the cultivation time should be controlled at three days.;In the fifth stage, the effect of supplying different concentrations of exogenous CO2 uder various light intensities at simulated light/dark cycle on biomass accumulation and wastewater nutrients removal was tested with aglae strain Chlorella kessleri. The results confirmed that there was an optimum CO2 level for algae growth, which is 2.5% for this investigation. When the light intensity reached a certain lower limit, the effect of CO2 supplementation became minimum because the photoautotrophic efficiency was significantly reduced. The objective of the last stage was to optimize the operational parameters, including light intensity, light-dark cycle, exogenous carbon dioxide concentration, and hydraulic retention time (HRT), for high algae biomass accumulation, biodiesel production and wastewater nutrients removal in designed fed-batch culture system. The results showed that response surface methodology with central composite design is effective in system optimization for algal-based biodiesel production using centrate wastewater in fed-batch culture. (Abstract shortened by UMI.).