Bioproducts from microalgae biomass: Technology, sustainability, challenges and opportunities.

Microalgae are a potential feedstock for several bioproducts, mainly from its primary and secondary metabolites. Lipids can be converted in high-value polyunsaturated fatty acids (PUFA) such as omega-3, carbohydrates are potential biohydrogen (bioH2) sources, proteins can be converted into biopolymers (such as bioplastics) and pigments can achieve high concentrations of valuable carotenoids. This work comprehends the current practices for the production of such products from microalgae biomass, with insights on technical performance, environmental and economical sustainability. For each bioproduct, discussion includes insights on bioprocesses, productivity, commercialization, environmental impacts and major challenges. Opportunities for future research, such as wastewater cultivation, arise as environmentally attractive alternatives for sustainable production with high potential for resource recovery and valorization. Still, microalgae biotechnology stands out as an attractive topic for it research and market potential.

Agro-industrial wastewater-grown microalgae: A techno-environmental assessment of open and closed systems.

Microalgae-based treatment can be applied to the bioremediation of agro-industrial wastewater, aiming at a circular economy approach. The present work compared the technical-environmental feasibility of operating a bubble column photobioreactor (PBR) and a high rate pond (HRP) for microalgae biomass production and wastewater treatment of a meat processing facility. The comparison was made regarding biomass productivity, phytoplankton composition, treatment efficiency, life cycle assessment, and energy balance. The daily yields of total biomass and the maximum specific growth rates were 483.33 mg L-1 d-1 and 0.23 d-1 for PBR and 95.00 mg L-1·d-1 and 0.193 d-1 for HRP, respectively, with a predominance of the species Scenedesmus acutus. The treatment efficiency of COD (~50%) and phosphorus (100%) were similar in the two reactors. However, the PBR showed greater assimilation of ammoniacal nitrogen (100% removal) due to the higher microalgal biomass productivity. Environmental impacts were assessed through the ReCiPe methodology for midpoint and endpoint levels. Results revealed that CO2 supply was the most impactful process for both systems (>60%), but HRP reached lower environmental burdens (-105.90 mPt) than PBR (60.74 mPt). Energy balance through the Net Energy Ratio also resulted in the HPR advantage over the PBR (NER = 14.23 and 1.09, respectively). Still, both reactors present advantages when applied to different valorization routes. At the same time, both present room for improvement in the light of bioeconomy and biorefineries, aiming at sustainable wastewater treatment plants.

Valorization of swine wastewater in a circular economy approach: Effects of hydraulic retention time on microalgae cultivation.

To optimize the swine wastewater (SWW) treatment, this study investigated different hydraulic retention times (HRTs) for microalgae cultivation. For this purpose, five pilot-scale reactors operated in semi-continuous flow, with HRTs equal to 9, 12, 15, 18, 21 days were evaluated in terms of SWW polishing and biomass production. The effluent treatment was discussed accompanied by principal component analysis, which allowed identification of causes of variance in the data set, ideal for studies with real effluent and influenced by environmental conditions. All reactors show satisfactory removals of N-NH4+ (91.6-95.3%), COD (15.8-39.9%), DO increment (in average 7.5 mg O2/L) and, only the longest HRT (21 days) was able to remove Ps (21%). The results obtained indicated that a consortium of microalgae and bacteria was developed for all the tested HRTs. On the other hand, HRT = 12 days provided a healthier culture of photosynthesizing organisms (chl-a/VSS = 3.04%). Carbohydrates (20.8-31.3%) and proteins (2.7-16.2%) were the compounds of commercial interest in the highest proportion in the biomass of all reactors, with contents comparable to that of terrestrial crops. Thus, it was suggested a valorization route of these compounds of high added value to return to pig farming, where the nutrients were intended to supplement the swine feed and clarified water for cleaning the pig stalls. Thus, in the circular economy context, this research contributes to water footprint reduction and the sustainability of the pig farming production chain. The economic and environmental analysis of the route is suggested to enable its implementation on a large scale, as well as further technical feasibility research (reactor types, exposure to external environment, evaluation of pathogen removal and animal feed supplementation from SWW microalgae biomass).