Globally, an overwhelming amount of plastic waste, approximately 400 million tons (Mt), is generated each year. The ocean plastic waste alone is expected to grow from 50 Mt in 2015 to 150 Mt by 2025, primarily due to poor waste management. Approximately 700 marine species interact with plastic debris, thriving in these threatened ecosystems. The challenge of plastic pollution, including microplastics and nanoplastics, is substantial. Plastics resist natural degradation due to their hydrophobic nature, stable covalent bonds, resistant functional groups, and large surface area that attracts other substances. Current efforts to tackle microplastics face significant challenges and require more mature and effective methods for widespread applications. Certain natural microorganisms can degrade plastics by 1) colonizing the surface, 2) producing exogenous enzymes to break-down polymers, and 3) metabolizing the resulting molecules. However, this process is still under research, with ongoing efforts to find the best natural and genetically modified microbes for more effective plastic degradation. Therefore, identifying the best microbe and efficient methods is crucial for reducing plastic pollution. This review summarizes the plastic problem, its types, accumulation, and natural degradation processes. It also examines current technologies and recently screened microorganisms for their potential to tackle plastics and microplastics for a cleaner future.

The majority of nutrients in municipal wastewater originate from urine. However, when flush water is used, the urine is diluted and mixed with other organic household waste, losing its high-value stream content. This study investigated the effect of source-separated human urine on the population dynamics, nutrient removal, growth, and biogas content of mixed microalgae grown in 250 L raceway ponds. Overall, a maximum biomass concentration of 1847 mg/L was reached, with up to 90% nitrogen and 80% phosphorus removal efficiencies, along with 254.96 L/kg vs. biogas production. The microbial community analysis identified Chlorella sorokiniana (Chlorophyta, Trebouxiophyceae) as the species with the highest abundance, after confirmation with four different markers (16S rRNA, 18S rRNA, 23S rRNA, and tufA). Moreover, principal component analysis was applied to capture the effect of environmental factors on culture diversity. The abundance of Chlorella sorokiniana increased almost sevenfold when the culture was exposed to open systems compared to the small-scale study carried out in 1 L Erlenmeyer bottles in laboratory conditions, both grown in urine and synthetic media (BBM). In conclusion, the present study contributes to the potential to valorize urine with microalgae by showing its high biogas content, and reveals that microalgae can adapt to adverse environmental conditions by fostering their diversity.

Economizing microalgal cultivation is a considerable milestone targeted by efforts put into microalgal biorefineries. In light of that, the present study was aimed to explore the potential of using anaerobic liquid digestate (ALD) as culture media to grow microalgae and compared it with three different synthetic media (i.e., N8, BBM, and M8) in terms of biomass yield, fatty acid composition, and nutrient utilization/recovery. Moreover, a mixed culture of wild-type microalgae was employed in this study owing to the ability of mixed cultures to survive extreme conditions, eliminating the risk of losing the culture easily, as it mostly happens with pure cultures. The highest nutrient yield coefficients were achieved when the mixed microalgae culture was cultivated in ALD, where the yield coefficient for nitrogen (YN) and yield coefficient for phosphorus (YP) were 10.7 mg biomass mg-1 N and 98 mg biomass mg-1 P, respectively. The highest lipid content (34%) and the highest concentrations of C16:0 (114 mg L-1) and C18:0 (60.9 mg L-1) were also recorded when the mixed microalgae culture was cultivated in ALD. Furthermore, the polyunsaturated fatty acids (PUFA) content also increased significantly in ALD, a beneficial phenomenon as PUFAs in microalgae allow them to adapt more effectively to extreme conditions. Based on the microbial community analysis performed using the multi-marker metabarcoding approach, Diphylleia rotans, Synechocystis PCC-6803, Cyanobium gracile PCC 6307, and Chlorella sorokiniana were identified as the most abundant species in the ALD growth. Overall, based on the findings of the present study, ALD could be used as a promising cultivation medium for microalgae, offering a process integration approach to combine anaerobic digestion and algae cultivation as an effective way to simultaneously treat the high-strength dark-colored ALD and valorize it into profitable byproducts.

Understanding how to address today’s global challenges is critical to improving corporate performance in terms of economic and environmental sustainability. In wastewater treatment systems, such an approach implies integrating efficient treatment technologies with aspects of the circular economy. In this business field, energy costs represent a large share of operating costs. This work discusses technological and management aspects leading to greater energy savings in Portuguese wastewater treatment companies. A mixed methodology, involving qualitative and quantitative aspects, for collecting and analysing data from wastewater treatment plants was used. The qualitative aspects consisted of a narrative analysis of the information available on reports and websites for 11 wastewater management companies in Portugal (e.g., technologies, treated wastewater volumes and operating costs) followed by a review of several international studies. The quantitative approach involved calculating the specific energy consumption (kWh/m3), energy operating costs (EUR/m3) and energy operating costs per population equivalent (EUR/inhabitants) using data from the literature and from Portuguese companies collected from the SABI database. The results suggested that the most environmentally and economically sustainable solution is algae-based technology which might allow a reduction in energy operating costs between 0.05–0.41 EUR/m3 and 15.4–180.8 EUR/inhabitants compared to activated sludge and other conventional methods. This technology, in addition to being financially advantageous, provides the ability to eliminate the carbon footprint and the valorisation of algae biomass, suggesting that this biotechnology is starting to position itself as a mandatory future solution in the wastewater treatment sector.

Harvesting microalgal biomass is a major challenge because of their small size, their density, and their low concentration in the culture medium. Thus, the energy inputs to the cultivation/harvesting processes are high, and often exceed the energy content of the microalgal biomass itself. In this study, the cross-flow membrane and submerged membrane systems were installed to raceway ponds, and the harvesting yields were compared. The highest algal concentration reached by submerged membrane system which was 10.44 g/L; and by cross-flow membrane system maximum biomass reached was 6.99 g/L, which corresponds to concentrate 6 and 4.2 fold, respectively.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Lutein is particularly known to help maintain normal visual function by absorbing and attenuating the blue light that strikes the retina in our eyes. The effect of overexposure to blue light on our eyes due to the excessive use of electronic devices is becoming an issue of modern society due to insufficient dietary lutein consumption through our normal diet. There has, therefore, been an increasing demand for lutein-containing dietary supplements and also in the food industry for lutein supplementation in bakery products, infant formulas, dairy products, carbonated drinks, energy drinks, and juice concentrates. Although synthetic carotenoid dominates the market, there is a need for environmentally sustainable carotenoids including lutein production pathways to match increasing consumer demand for natural alternatives. Currently, marigold flowers are the predominant natural source of lutein. Microalgae can be a competitive sustainable alternative, which have higher growth rates and do not require arable land and/or a growth season. Currently, there is no commercial production of lutein from microalgae, even though astaxanthin and β-carotene are commercially produced from specific microalgal strains. This review discusses the potential microalgae strains for commercial lutein production, appropriate cultivation strategies, and the challenges associated with realising a commercial market share.

In this study, mixed microalgal culture dominated by Chlorella vulgaris and Scenedesmus armatus was grown in Anaerobic Liquid Digestate (ALD) at different NaCl concentrations ranging between 0 and 100 mM. Highest lipid and carbohydrate amounts were observed as 38.4 and 36.2%, respectively, when the salinity was 50 mM NaCl. However, the protein content was drastically decreased to 12.8% with increased NaCl concentration. Furthermore, the algal biomass was subsequently decreased along with the total chlorophyll amount with increased NaCl concentration. Algal species showed diverse response to salinity stress and demonstrated a cost‐effective approach towards the cultivation of mixed microalgae within digestate and provided insight that ALD and/or other wastewaters can be diluted with seawater instead of tap water in the future studies. This study could be further converted into biofuels because of an increase in lipid content along with the digestate treatment, which will help to valorize ALD and bring into economy.

Anaerobic digestion is one of the most common methods used to generate energy from renewable sources. However, untreated anaerobic liquid digestate may cause eutrophication if directly discharged into the water bodies due to its high nutrient content. Microalgae can assimilate nutrients especially nitrogen and phosphorous from wastewater for their growth and produce valuable biomass. In this study, batch experiments were carried out to investigate the biokinetic coefficients for nutrient removal of mixed microalgae grown on anaerobic liquid digestate by Michaelis–Menten rate expression. The initial NH3-N concentration was varied between 18.6 and 87.1 mg L−1, while initial PO4-P concentration was between 1.85 and 6.88 mg L−1, which corresponds to 2%, 5%, 7%, and 10% dilution ratio of anaerobic digestate. According to the yield results (mg chl a mg−1 nutrient), mixed microalgae uptake 10 times more nitrogen than phosphorus. Biokinetic coefficients were determined as kN = 2.48 mg NH3-N mg−1 chl a day−1, KmN = 29.3 mg L−1, YN = 0.45 mg chl a mg−1 NH3-N for nitrogen; and kP = 0.21 mg PO4-P mg−1 chl a day−1, KmP = 2.94 mg L−1, YP = 5.03 mg chl a mg−1 PO4-P for phosphorus. The highest chlorophyll production (39 mg L−1 or 3.31 mg L−1 day−1) was observed at the highest dilution ratio of 10%. Moreover, the highest dilution resulted in highest biomass (1.25 g L−1) despite of dark, high ammonicial, and particulate rich wastewater.