Biocompounds from wastewater-grown microalgae: a review of emerging cultivation and harvesting technologies.

Microalgae biomass has attracted attention as a feedstock to produce biofuels, biofertilizers, and pigments. However, the high production cost associated with cultivation and separation stages is a challenge for the microalgae biotechnology application on a large scale. A promising approach to overcome the technical-economic limitations of microalgae production is using wastewater as a nutrient and water source for cultivation. This strategy reduces cultivation costs and contributes to valorizing sanitation resources. Therefore, this article presents a comprehensive literature review on the status of microalgae biomass cultivation in wastewater, focusing on production strategies and the accumulation of valuable compounds such as lipids, carbohydrates, proteins, fatty acids, and pigments. This review also covers emerging techniques for harvesting microalgae biomass cultivated in wastewater, discussing the advantages and limitations of the process, as well as pointing out the main research opportunities. The novelty of the study lies in providing a detailed analysis of state-of-the-art and potential advances in the cultivation and harvesting of microalgae, with a special focus on the use of wastewater and implementing innovative strategies to enhance productivity and the accumulation of compounds. In this context, the work aims to guide future research concerning emerging technologies in the field, emphasizing the importance of innovative approaches in cultivating and harvesting microalgae for advancing knowledge and practical applications in this area.

Microalgae biomass as a renewable biostimulant: meat processing industry effluent treatment, soil health improvement, and plant growth.

Microalgae biomass contributes to effluent bioremediation. It is a concentrated source of nutrients and organic carbon, making it a potential alternative as a soil biostimulant. In this context, this study aimed to evaluate the soil application of microalgae biomass produced from the meat processing industry effluent treatment. The biomass was applied dry and as a mixture to demonstrate its potential to increase plant production and soil metabolic functions, analyzed short-term. Doses of 0.25%, 0.5%, 1%, and 2% biomass were applied in soils from (i) Horizon A: taken at a depth between 0 and 10 cm and; (ii) Horizon B: taken at a depth between 20 and 40 cm. Corn growth (Zea Mays L.), basal soil respiration, microbial biomass carbon, total organic carbon, ß-glucosidase, acid phosphatase, arylsulfatase, and urease enzymatic activity were evaluated in each sample. It is concluded that applying 2% microalgae biomass led to higher basal soil respiration, microbial biomass carbon, and ß-glucosidase, acid phosphatase, arylsulfatase enzymatic activity in both soils. On the other hand, boron may have contributed to urease activity reduction in Soil A. Although 2% biomass led to higher soils characteristics, that dose did not promote higher plant growth. Hence, considering that plant growth must be in line with changes in soil characteristics, the result that provided the higher plant shoot dry matter mass was by applying 0.55% biomass in both soils. Therefore, the application of microalgae biomass produced from a meat processing industry effluent treatment promoted a biologically active soil and boosted plant growth.

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.

Fires dynamics in the Pantanal: Impacts of anthropogenic activities and climate change.

Anthropogenic activities responsible for modifying climatic regimes and land use and land cover (LULC) have been altering fire behavior even in regions with natural occurrences, such as the Pantanal. This biome was highlighted in 2020 due to the record number of fire foci and burned areas registered. Thus, this study aimed to understand how changes in LULC and climate affect the spatial, temporal and magnitude dynamics of fire foci. The Earth Trends Modeler (ETM) was used to identify trends in spatiotemporal bases of environmental and climatic variables. No trend was identified in the historical series of precipitation data. However, an increasing trend was observed for evapotranspiration, normalized difference vegetation index (NDVI) and temperature. For soil moisture, a decreasing trend was observed. The comparison between the mean of the historical series and the year 2020 showed that the variables precipitation, temperature, soil moisture and evapotranspiration had atypical behavior. Such behavior may have contributed to creating a drier environment with available combustible material, leading to a record number of burned areas, about three million hectares (248%) higher than the historical average. The 2020 fire foci data were used in two types of spatial statistical analyses: Grouping, showing that 76% of the registered fire foci were at high risk of fire and; Hot and Cold Spots, indicating high concentrations of Hot Spots in the northern region of the Pantanal, close to Cerrado and Amazon biomes agricultural frontier. The results of the Land Change Modeler (LCM) tool evidenced a strong transition potential from the natural vegetation to agriculture and pasture in the eastern region of the Pantanal, indicating that this could be, in the future, a region of high concentration of fire foci and possibly high risk of fire. This tool also allowed the prediction of a scenario for 2030 that showed that if measures for environmental protection and combating fires are not adopted, in this year, 20% of the Pantanal areas will be for agricultural and pasture use. Finally, the results suggest that the advance of agriculture in the Pantanal and changes in climatic and environmental variables boosted the increase in fire foci and burned areas in the year 2020.

Innovative hybrid system for wastewater treatment: High-rate algal ponds for effluent treatment and biofilm reactor for biomass production and harvesting.

The use of algal biomass still faces challenges associated with the harvesting stages. To address this issue, we propose an innovative hybrid system, in which a biofilm reactor (BR) operates as an algal biomass production and harvesting unit connected to a high-rate algal pond (HRAP), a wastewater treatment unit. BR did not interfered with the biomass chemical composition (protein = 32%, carbohydrates = 11% and total lipids = 18%), with the wastewater treatment (removals efficiency: chemical oxygen demand = 59%, ammonia nitrogen = 78%, total phosphorus = 16% and Escherichia coli = 1 log unit), and did not alter the sedimentation characteristics of the biomass (sludge volume index = 29 mg/L and humidity content = 92%) in the secondary settling tank of the hybrid system. On the other hand, the results showed that this technology achieved a biomass production about 2.6x greater than the conventional system without a BR, and the efficiency of harvesting of the hybrid system was 61%, against 22% obtained with the conventional system. In addition, the BR promoted an increase in the density (~1011 org/m2) and diversity of microalgae in the hybrid system. Chlorella vulgaris was the most abundant species (>60%) from the 4th week of operation until the end of the experiment. Hence, results confirm that the integration of BR into a wastewater treatment plant optimised the production and harvesting of biomass of the hybrid system, making it a promising technology. The importance of economic and environmental analysis studies of BR is highlighted in order to enable its implementation on a large scale.