Novel materials for intensified bioenergetic biomass production and aquaculture wastewater treatment

The growing energy and water demand over the last centuries has resulted on an increase in greenhouse gases, wastewater effluents and a depletion on fossil fuels. Wastewater must be treated before returning to the environment. Therefore, the quest for sustainable and environmentally friendly wastewater treatment and energy provision has become imperative. Environmental policy strategies (e.g. Sustainable Development Goals, SDG from the UN or The Knowledge Centre for Bioeconomy of the European Comission) have been set up in Europe and across the world for the next half century in order to boost the growth of bio-based products to address energy challenges. In particular, the production of biofuels generated from microalgal biomass has received an increasing interest due to its greater energy security, reduced environmental impact and higher biomass productivities than land crops.

Microalgae are unicellular or multicellular photosynthetic organisms whose biochemical properties make them a useful tool to transform the energy sector into a more environmentally friendly based industry. These diverse light-driven microorganisms can thrive in a wide spectrum of environmental conditions due to their flexible metabolism which enables them to produce a vast range of metabolites that can be biotechnologically processed to biofuels, feed, drugs or wastewater treatment agents. However, large-scale cultivation still remains economically challenging due to high operational cost, water and down-streaming energy use. Using fertilizers to supply nutrients such as nitrogen or phosphorus and other micronutrients as microalgal growth medium can imply up to half of the cultivation cost. In order to cut costs, one strategy is to replace these commercially available nutrients with wastewater nutrients. Following this approach, the present project aims to address this operational drawback by using wastewater from intensive fish farming effluents which has high loads of nitrogen and phosphorous. Due to the increasing amount of wastewater produced by aquaculture this could represent an alternative source of macronutrients to cultivate microalgal biomass whereas removing the excess of nutrients from wastewater. Current treatment systems used to remove high nutrient wastewater loads, such as biological nitrification/denitrification, chemical stripping and absorption or chemical precipitation, are efficient but produce carbon dioxide emissions and/or toxic sludge. This PhD project will look into increasing the amount of microalgal biomass produced from aquaculture wastewater treatment by assessing several novel shapes of 3D-printed translucid plastic materials in the form of beads, large spheres, rings or saddles. Materials 3D-printed have been shown to improve denitrification process in bacteria by promoting and controlling biofilms generation. Successful systems have already been commercialised for nitrifying microorganisms, however, the use of 3D-printed materials in microalgal cultivation to improve biomass generation remains to be explored. Microalgal cultivation provides the conversion of both, carbon dioxide to oxygen, and contaminant nutrients to algal biomass which can be converted to energetic products such as biodiesel. By cultivating microalgae along with novel materials, it is expected to increase biomass loads, and nutrient removals. Microalgae produced using this approach will be harvested by flotation, characterised and assessed for product conversion. The first phase of the experiments will be developed on a bench-scale in order to determine and characterise optimal conditions. This initial proof of concept phase will work towards setting-up and studying a system that can be transferred to large scale cultivation at the industrial partner premises.