Feasibility of microalgal treatment of abattoir anaerobic digestion effluent for the production of value- added products

Arsalan Alavianghavanini

The water consumption in Australian red meat processing facilities can reach up to 9 m³ per tonnes of hot standard carcase weight (tHSCW), and the industry in Australia handles approximately 2 million tHSCW on an annual basis. The combined organic waste streams from red meat facilities are normally introduced to an anaerobic digestion (AD) lagoon to produce biogas that can be used for generating electricity on site. However, the process results in release of carbon dioxide and AD effluents with high concentration of ammoniacal nitrogen (182 – 438 mg L⁻¹) and phosphorus (27 – 56 mg L⁻¹). Microalgae species grown on AD effluents using open raceway ponds have also shown promising potential to assimilate nutrients using carbon dioxide for the production of high value compounds such as protein, carbohydrate, and lipid which could be converted to value-added products. This PhD study aimed to investigate the techno economic and environmental impacts of both microalgae growth using anaerobic digested effluent in red meat industry as a culture medium (upstream) and conversion of microalgae to value added products (downstream). The methodology section of the research involved process flow diagram development, unit operation design modelling, cost estimation, feasibility analysis, lifecycle analysis, and case study model development in Western Australia (WA). The final comprehensive models derived from this research could provide an insight into the potential of establishing an environmentally friendly process to make a profit from abattoirs anaerobic digestion effluent in WA. The main outcomes of this research showed that it would be possible to produce 2.7 kg dry weight microalgae from 1 m³ anaerobic digested effluent with minimum production cost of 1.7 – 6.0 AUD kg⁻¹ in WA depending on scale of production. This method can produce a treated water stream with a quality of < 1 mg L⁻¹ ammoniacal nitrogen and 1 kg dry weight microalgae to avoid emitting 71 g nitrogen, 10 g phosphorus, and 499 g carbon from red meat processing facilities to the environment. The downstream techno economic results showed that small scale local abattoirs (< 1,000 m³ d⁻¹) can produce 5 L liquid biostimulant (amino acid concentrate) from 1 kg dry weight microalgae to make 4 AUD net profit from 1 m³ effluent. Larger scale local abattoirs in Western Australia (>1,600 m³ d⁻¹) would be able to produce more feasible products including 6 kg aquafeed, 73 g refined oil rich in poly unsaturated fatty acids, or 21 g high purity omega 3 oil from 1 kg dry weight microalgae grown in AD effluents. The production of these products in large scale abattoirs can lead to even 5 – 15 AUD net profit from 1 m³ AD effluent. Finally, the lifecycle analysis results of current wastewater treatment practice in red meat processing facilities showed that the green house gas emission is close to 7 kg CO₂ eq m⁻³, 305 g PO₄ eq m⁻³, and 323 g SO₂ eq m⁻³ of organic waste. However, the integration of microalgae production with anaerobic digestion operation locally in WA can result in more than 20 % reduction in carbon foot print from red meat processing industries. In case of producing feasible product such as aquafeed locally in WA from agricultural waste using microalgae biomass, the emissions of the entire upstream and downstream processing could reach the possible value of 32 kg CO₂ eq, -87 g PO₄ eq, and -272 g SO₂ eq from 1 m³ agricultural waste. As a result, it would be possible to make profit from agricultural effluent while protecting the environment using microalgae biomass, since they can recycle back detrimental nutrients from environment such as nitrogen, phosphorus, and carbon.

Feasibility of microalgal treatment of abattoir anaerobic digestion effluent for the production of value- added products

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