Microalgae for Combined Nutrient Recovery and Biofuel Production from Sewage

It is critical that we move towards a more sustainable society. Three of our largest challenges are the need for sustainable energy generation, currently dominated by fossil fuel combustion, sustainable food supply, reliant on energy intensive fertiliser production, and a sustainable supply of fresh water, the treatment of which is often unreliable or economically prohibitive. The use of microalgae for low-cost and effective nutrient removal in wastewater treatment works (WWTW) was established in the mid-20th century, but microalgae have gained renewed attention for their ability to accumulate lipids for biodiesel production. Furthermore, the ability of microalgae to accumulate high nutrient concentrations offers an opportunity to shift the focus of nutrient control in WWTW from removal to reuse (i.e. in agricultural fertilisers). This project addresses the hypothesis that microalgae may be cultivated within WWTW to simultaneously recover essential nutrients, produce biomass suitable for biodiesel production and contribute to the wastewater treatment process. A new method to measure algal biomass density using digital image analysis was developed. The method facilitates the use of small volume cultures for screening studies without compromising robust growth data. The effect of environmental conditions, present within WWTW, on the growth, nutrient uptake and lipid accumulation in the model microalga Chlamydomonas reinhardtii are presented. Results demonstrate that pH control to near-neutral is preferable for nutrient removal, nutrient recovery and biofuel potential, owing to the increase in biomass density. In ammonium-rich wastewaters, pH control is critical to prevent ammonia toxicity. The choice of nitrogen source (ammonium vs. nitrate) had no significant effect on microalgal growth or biomass composition, microalgal nutrient removal therefore facilitates removal of wastewater nitrification processes. Finally, the small molecule, diphenyl methylphosphonate is shown to cause oil retention in C.reinhardtii and offers a means to improve lipid quality for biodiesel production