Arsalan Alavianghavanini

The possibility of using microalgae to assimilate nitrogen from agricultural anaerobic digestion effluents (ADE) not only has environmental benefits but also can result in making profit from ADE by converting microalgae to value added products. Here, a techno economic model was developed to study the possibility of producing oil and amino acid concentrate products from microalgae grown on ADE. The results show that it would be possible to produce 14 L biostimulant (amino acid concentrate), 198 g refined oil, and 57 g omega 3 isolate from 1 m3 ADE using microalgae with possible production cost of 0.9 – 2.1 AUD L−1, 86 – 120 AUD kg−1, and 700 – 730 AUD kg−1 respectively depending on the scale. The profitability results at the scale of 500 to 3,000 m3 d−1 ADE capacity indicate that the production of biostimulant, refined oil, and omega 3 isolate products from wastewater grown microalgae can lead to 4 – 15, 6 – 9, and 5 AUD m−3 net profit respectively.

A model based framework was established for large scale assessment of microalgae production using anaerobically digested effluent considering varied climatic parameters such as solar irradiance and air temperature. The aim of this research was to identify the optimum monthly average culture depth operation to minimize the cost of producing microalgae grown on anaerobic digestion effluents rich in ammoniacal nitrogen with concentration of 248 mg L−1. First, a productivity model combined with a thermal model was developed to simulate microalgae productivity in open raceway ponds as a function of climatic variables. Second, by combining the comprehensive open pond model with other harvesting equipment, the final techno economic model was developed to produce a microalgae product with 20 wt% biomass content and treated water with <1 mg L−1 ammoniacal nitrogen. The optimization approach on culture depth for outdoor open raceway ponds managed to reduce the cost of microalgae production grown in anaerobic digested wastewater up to 16 %, being a suitable solution for the production of low cost microalgae (1.7 AUD kg−1 dry weight) at possible scale of 1300 t dry weight microalgae yr−1.

The integration of microalgae production with anaerobically digested effluents might result in development of sustainable processes not only to remove nitrogen but also to produce value-added products rich in protein. This work analyses the feasibility of producing protein-based products derived from microalgae grown on anaerobically digested wastewater by performing techno-economic evaluation. The results show that it would be possible to propose an upstream process flow diagram producing 2.7 kg microalgae from 1 m−3 wastewater with possible production cost of 1.8–8.1 USD kg−1 depending on the scale of anaerobic digested effluent. It would be possible to produce protein isolate, concentrate, and animal feed from anaerobically digested effluents with possible production cost of 33 USD kg−1, 28 USD kg−1, and 6 USD kg−1 respectively at the scale of 1600 m3 d−1 effluent. Although currently the production of protein-based products might not be feasible, increasing the scale of production might result in some feasible outcomes. However, the associated costs regarding collecting more AD wastewater from different sources should be evaluated to increase the scale of production.
[Display omitted]