Despite the extensive literature on microalgal production, most studies focus on controlled laboratory-scale systems, resulting in a critical lack of confidence at industrial scale. This is further compounded by the frequently observed inconsistencies, with only modest increases achieved in operational scale. This work demonstrates the design, construction, and operation of a commercial-scale tubular photobioreactor and associated equipment for the production of algae using CO₂ derived from an industrial nickel refinery. The reactor was demonstrated by growing the species Nannochloropsis gaditana. Biomass concentrations of 1.0 to 1.3 g L⁻¹ were achieved with a productivity of 0.11 g L⁻¹ d⁻¹. Extrapolation to a 300-day production year showed that the reactor was capable of producing 541.2 kg algae and sequestering around 1 tonne of CO₂. A technoeconomic assessment showed that the total plant CAPEX was £583,905 and the OPEX was £98,196. Sales of algae alone showed poor economic performance. However, economic favourability is observed for species that contain phycocyanin pigment and yield a positive net present value within 4 to 7 years based on recovery yield. This work effectively provides reliable process data developed at scale that can be used to formulate business cases for further scale-up and expansion of algal production systems. This moves the technology a step closer to full-scale realisation and the potential for a net-zero, sustainable future.

Cultivating microalgae requires a nitrogen and phosphorous feed source. Anaerobic digestion waste (digestate) provides a cheap sustainable feedstock for these materials. Previous studies have successfully demonstrated the feasibility of nutrient recovery and subsequent algae growth. There is now a need to fully characterise digestate filtration to improve our understanding of this process prior to its commercialisation. In this work, digestate filtration is characterised at bench scale using frontal (dead-end) filtration and a 100 kDa MWCO ultrafiltration membrane. Our experiments demonstrated rapid cake formation causing significant flux decline. The steady-state permeate flux for digestate was 2.4 to 4.8 L m⁻² h⁻¹, a reduction of ~90% compared to clean water flux. The specific cake resistance was ~1015 m kg⁻¹ and the compressibility index 1.07. A series of four filtration and cleaning cycles showed 90% flux recovery following a clean water wash. Digestate filtration was then evaluated at a commercial scale using crossflow and the KOCH ABCOR^® tubular membrane (100 kDa MWCO). The results were similar to those at the bench scale, i.e., rapid initial fouling leading to a period of steady-state flux (approximately 7 L m⁻² h⁻¹). The commercial membrane was flushed with water and diluted bleach after each use, and a digestate permeate flux decline of only 4.8% over a 12-month active use period was observed. The present research provides bench scale characterisation and demonstrates the commercial scale operation of anaerobic digestate filtration using ultrafiltration. The overall filtration performance was excellent, and the process can now be scaled to any operational capacity.