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.

At Bantaeng in South Sulawesi and Kwinana in Western Australia new industrial scale ports will be built to serve the industrial precincts at these locations. At both these sites a 12Mtpa Geopolymer Concrete/cement? (GPC) plant is proposed for precast production of some 1,600 port modules as well as other infrastructure requiring some 750,000 cubic metre of (cum) of concrete and thereafter the plant can be repurposed for other products for local markets such as reef modules and wall panels. Geopolymer concrete can be the replacement for conventional concrete and be made from waste ceases to be waste based on specif conditions (waste-derived materials) while having a lower carbon footprint. The plant is designed to be operated by renewable energy and an energy audit estimated that a 1metric tonne per annum (Mtpa) geopolymer production plant needs up to 200 Gigawhatt hour (GWh) per annum (pa) to operate. This could be served by 6-10 onland wind turbines combined with solar PV farm at a total cost 4555 million USD. The electricity generated around 100/MWh was worth 12-20M pa that could result in a payback of 2-5 years. In Kwinana, planning is already underway for a large wind farm as part of the overall decarbonisation strategy for this industrial precinct. Feedstock materials can be harnessed for use in the geopolymer production plant by means of Circularity Hubs. These hubs can be established through the KIC4 and 6-Capitals models of Industrial Symbiosis to optimise the proposed geopolymer plant within the industrial precincts at Bantaeng and Kwinana. Such an approach can contribute to Regenerative Development when both ports are built.

Wastewater generated within agricultural sectors such as dairies, piggeries, poultry farms, and cattle meat processing plants is expected to reach 600 million m3 yr−1 globally. Currently, the wastewater produced by these industries are primarily treated by aerobic and anaerobic methods. However, the treated effluent maintains a significant concentration of nutrients, particularly nitrogen and phosphorus. On the other hand, the valorisation of conventional microalgae biomass into bioproducts with high market value still requires expensive processing pathways such as dewatering and extraction. Consequently, cultivating microalgae using agricultural effluents shows the potential as a future technology for producing value-added products and treated water with low nutrient content. This review explores the feasibility of growing microalgae on agricultural effluents and their ability to remove nutrients, specifically nitrogen and phosphorus. In addition to evaluating the market size and value of products from wastewater-grown microalgae, we also analysed their biochemical characteristics including protein, carbohydrate, lipid, and pigment content. Furthermore, we assessed the costs of both upstream and downstream processing of biomass to gain a comprehensive understanding of the economic potential of the process. The findings from this study are expected to facilitate further techno-economic and feasibility assessments by providing insights into optimized processing pathways and ultimately leading to the reduction of costs.

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.
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