Microalgae-assisted green bioremediation of food-processing wastewater: A sustainable approach toward a circular economy concept

Wastewater disposal is a major environmental issue that pollutes water, causing eutrophication, habitat destruction, and economic impact. In Mexico, food-processing effluents pose a huge environmental threat due to their excessive nutrient content and their large volume discharged every year. Some of the most harmful residues are tequila vinasses, nejayote, and cheese whey. Each liter of tequila generates 13-15 L of vinasses, each kilogram of cheese produces approximately 9 kg of cheese whey, and each kilogram of nixtamalized maize results in the production of 2.5-3.3 L of nejayote. A promising strategy to reduce the contamination derived from wastewater is through microalgae-based wastewater treatment. Microalgae have a high adaptability to hostile environments and they can feed on the nutrients in the effluents to grow. Moreover, to increase the viability, profitability, and value of wastewater treatments, a microalgae biorefinery could be proposed. This review will focus on the circular bioeconomy scheme focused on the simultaneous food-processing wastewater treatment and its use to grow microalgae biomass to produce added-value compounds. This strategy allows for the revalorization of wastewater, decreases contamination of water sources, and produces valuable compounds that promote human health such as phycobiliproteins, carotenoids, omega-3 fatty acids, exopolysaccharides, mycosporine-like amino acids, and as a source of clean energy: biodiesel, biogas, and bioethanol.

Valorization of Caribbean Sargassum biomass as a source of alginate and sugars for de novo biodiesel production

Since 2011, a massive influx of pelagic brown algae Sargassum has invaded coastlines causing environmental and economic disaster. Valorizing this plentiful macroalgae can present much needed economic relief to the areas affected. Here the production of biodiesel and a high-value alginate stream using Sargassum biomass collected from the coast of Quintana Roo, Mexico is reported. Biomass was pretreated via AEA (Alginate Extraction Autohydrolysis) and enzymatic saccharification via fungal Solid State Fermentation, releasing 7 g/L total sugars. The sugar mixture was fermented using engineered Yarrowia lipolytica resulting in 0.35 g/L total lipid titer at the lab tube scale. Additionally, the capability of extracting 0.3875 g/g DW of a high-value, purified alginate stream from this material is demonstrated. The findings presented here are promising and suggest an opportunity for the optimization and scale up of a biodiesel production biorefinery for utilization of Sargassum seaweeds during seasons of high invasion.

Microalgae-based livestock wastewater treatment (MbWT) as a circular bioeconomy approach: Enhancement of biomass productivity, pollutant removal and high-value compound production

The intensive livestock activities that are carried out worldwide to feed the growing human population have led to significant environmental problems, such as soil degradation, surface and groundwater pollution. Livestock wastewater (LW) contains high loads of organic matter, nitrogen (N) and phosphorus (P). These compounds can promote cultural eutrophication of water bodies and pose environmental and human hazards. Therefore, humanity faces an enormous challenge to adequately treat LW and avoid the overexploitation of natural resources. This can be accomplished through circular bioeconomy approaches, which aim to achieve sustainable production using biological resources, such as LW, as feedstock. Circular bioeconomy uses innovative processes to produce biomaterials and bioenergy, while lowering the consumption of virgin resources. Microalgae-based wastewater treatment (MbWT) has recently received special attention due to its low energy demand, the robust capacity of microalgae to grow under different environmental conditions and the possibility to recover and transform wastewater nutrients into highly valuable bioactive compounds. Some of the high-value products that may be obtained through MbWT are biomass and pigments for human food and animal feed, nutraceuticals, biofuels, polyunsaturated fatty acids, carotenoids, phycobiliproteins and fertilizers. This article reviews recent advances in MbWT of LW (including swine, cattle and poultry wastewater). Additionally, the most significant factors affecting nutrient removal and biomass productivity in MbWT are addressed, including: (1) microbiological aspects, such as the microalgae strain used for MbWT and the interactions between microbial populations; (2) physical parameters, such as temperature, light intensity and photoperiods; and (3) chemical parameters, such as the C/N ratio, pH and the presence of inhibitory compounds. Finally, different strategies to enhance nutrient removal and biomass productivity, such as acclimation, UV mutagenesis and multiple microalgae culture stages (including monocultures and multicultures) are discussed.

Seasonal characterization and quantification of biomolecules from sargassum collected from Mexican Caribbean coast - A preliminary study as a step forward to blue economy

Since 2014, Mexican Caribbean coasts have experienced an atypical massive arrival of pelagic Sargassum accumulated on the shores triggers economic losses, public health problems, and ecosystem damaging near the coastline. Mechanical harvesting has been implemented ending in landfills. Since Sargassum algae represent abundant biomass in tropical regions of the world, it has shown potential as a feedstock to supply bioprocesses focused on obtaining high-value compounds and bioproducts. Nevertheless, there is a lack of data on the biochemical composition of Sargassum biomass from Mexican Caribbean coasts to propose valorization pathways. This study conducted a biochemical and elemental characterization of Sargassum biomass and compared, through statistical analysis, the effect of the season (dry and wet), place of collection (from the beach and shallow water), and method of extraction (Microwave-Assisted Extraction and Enzyme Assisted Extraction) on biomass composition. The biomass composition, expressed in dry weight basis, revealed 5-7% moisture content, 24-31 % ash, 2.6-3.8 % lipids, 1.8-7.0 %, total carbohydrates, 3-11 % total proteins, 1.5-2.31 mgGAg-1 total phenolic compounds (TPC), 2.7-2.9 kcal g-1 calorific power, and metals such as As (30-146.3 ppm), Fe (16.5-45 ppm), P (197-472 ppm). The most influential factor on the compositional content of Sargassum biomass was the season of the year, followed by the extraction method and the place of collection of Sargassum. These results will elucidate information on the biotechnological potential of Sargassum biomass from the Mexican Caribbean, contributing to sustainability challenges of the region, minimizing waste, and making the most of resources.

Valorization of pelagic sargassum biomass into sustainable applications: Current trends and challenges

Since long ago, pelagic Sargassum mats have been known to be abundant in the Sargasso Sea, where they provide habitat to diverse organisms. However, over the last few years, massive amounts of pelagic Sargassum have reached the coast of several countries in the Caribbean and West Africa, causing economic and environmental problems. Aiming for lessening the impacts of the blooms, governments and private companies remove the seaweeds from the shore, but this process results expensive. The valorization of this abundant biomass can render Sargassum tides into an economic opportunity and concurrently solve their associated environmental problems. Despite the diverse fields where algae have found applications and the relevance of this recurrent situation, Sargassum biomass remains without large scale applications. Therefore, this review aims to present the potential uses of these algae, identifying the limitations that must be assessed to effectively valorize this bioresource. Due to the constraints identified for each of the presented applications, it is concluded that a biorefinery approach should be developed to effectively valorize this abundant biomass. However, there is an urgent need for investigations focusing on holopelagic Sargassum to be able to truly valorize this seaweed.

Phyco-remediation of swine wastewater as a sustainable model based on circular economy

Pork production has expanded in the world in recent years. This growth has caused a significant increase in waste from this industry, especially of wastewater. Although there has been an increase in wastewater treatment, there is a lack of useful technologies for the treatment of wastewater from the pork industry. Swine farms generate high amounts of organic pollution, with large amounts of nitrogen and phosphorus with final destination into water bodies. Sadly, little attention has been devoted to animal wastes, which are currently treated in simple systems, such as stabilization ponds or just discharged to the environment without previous treatment. This uncontrolled release of swine wastewater is a major cause of eutrophication processes. Among the possible treatments, phyco-remediation seems to be a sustainable and environmentally friendly option of removing compounds from wastewater such as nitrogen, phosphorus, and some metal ions. Several studies have demonstrated the feasibility of treating swine wastewater using different microalgae species. Nevertheless, the practicability of applying this procedure at pilot-scale has not been explored before as an integrated process. This work presents an overview of the technological applications of microalgae for the treatment of wastewater from swine farms and the by-products (pigments, polysaccharides, lipids, proteins) and services of commercial interest (biodiesel, biohydrogen, bioelectricity, biogas) generated during this process. Furthermore, the environmental benefits while applying microalgae technologies are discussed.

Robust natural ultraviolet filters from marine ecosystems for the formulation of environmental friendlier bio-sunscreens

Ultraviolet radiation (UVR) has detrimental effects on human health. It induces oxidative stress, deregulates signaling mechanisms, and produces DNA mutations, factors that ultimately can lead to the development of skin cancer. Therefore, reducing exposure to UVR is of major importance. Among available measures to diminish exposure is the use of sunscreens. However, recent studies indicate that several of the currently used filters have adverse effects on marine ecosystems and human health. This situation leads to the search for new photoprotective compounds that, apart from offering protection, are environmentally friendly. The answer may lie in the same marine ecosystems since molecules such as mycosporine-like amino acids (MAAs) and scytonemin can serve as the defense system of some marine organisms against UVR. This review will discuss the harmful effects of UVR and the mechanisms that microalgae have developed to cope with it. Then it will focus on the biological distribution, characteristics, extraction, and purification methods of MAAs and scytonemin molecules to finally assess its potential as new filters for sunscreen formulation.

Biotransformation of lignocellulosic biomass into industrially relevant products with the aid of fungi-derived lignocellulolytic enzymes

Lignocellulosic material has drawn significant attention among the scientific community due to its year-round availability as a renewable resource for industrial consumption. Being an economic substrate alternative, various industries are reevaluating processes to incorporate derived compounds from these materials. Varieties of fungi and bacteria have the ability to depolymerize lignocellulosic biomass by synthesizing degrading enzymes. Owing to catalytic activity stability and high yields of conversion, lignocellulolytic enzymes derived from fungi currently have a high spectrum of industrial applications. Moreover, these materials are cost effective, eco-friendly and nontoxic while having a low energy input. Techno-economic analysis for current enzyme production technologies indicates that synthetic production is not commercially viable. Instead, the economic projection of the use of naturally-produced ligninolytic enzymes is promising. This approach may improve the economic feasibility of the process by lowering substrate expenses and increasing lignocellulosic by-product's added value. The present review will discuss the classification and enzymatic degradation pathways of lignocellulolytic biomass as well as the potential and current industrial applications of the involved fungal enzymes.

Bioinspired biomolecules: Mycosporine-like amino acids and scytonemin from Lyngbya sp. with UV-protection potentialities

Since the beginning of life on Earth, cyanobacteria have been exposed to natural ultraviolet-A radiation (UV-A, 315-400 nm) and ultraviolet-B radiation (UV-B, 280-315 nm), affecting their cells' biomolecules. These photoautotrophic organisms have needed to evolve to survive and thus, have developed different mechanisms against ultraviolet radiation. These mechanisms include UVR avoidance, DNA repair, and cell protection by producing photoprotective compounds like Scytonemin, carotenoids, and Mycosporine-like amino acids (MAAs). Lyngbya marine species are commercially important due to their secondary metabolites that show a range of biological activities including antibacterial, insecticidal, anticancer, antifungal, and enzyme inhibitor. The main topic in this review covers the Lyngbya sp., a cyanobacteria genus that presents photoprotection provided by the UV-absorbing/screening compounds such as MAAs and Scytonemin. These compounds have considerable potentialities to be used in the cosmeceutical, pharmaceutical, biotechnological and biomedical sectors and other related manufacturing industries with an additional value of environment friendly in nature. Scytonemin has UV protectant, anti-inflammatory, anti-proliferative, and antioxidant activity. MAAs act as sunscreens, provide additional protection as antioxidants, can be used as UV protectors, activators of cell proliferation, skin-care products, and even as photo-stabilizing additives in paints, plastics, and varnishes. The five MAAs identified so far in Lyngbya sp. are Asterina-330, M-312, Palythine, Porphyra-334, and Shinorine are capable of dissipating absorbed radiation as harmless heat without producing reactive oxygen species.

Light Intensity and Nitrogen Concentration Impact on the Biomass and Phycoerythrin Production by Porphyridium purpureum

Several factors have the potential to influence microalgae growth. In the present study, nitrogen concentration and light intensity were evaluated in order to obtain high biomass production and high phycoerythrin accumulation from Porphyridium purpureum. The range of nitrogen concentrations evaluated in the culture medium was 0.075-0.450 g L^-1 and light intensities ranged between 30 and 100 μmol m^-2 s^-1. Surprisingly, low nitrogen concentration and high light intensity resulted in high biomass yield and phycoerythrin accumulation. Thus, the best biomass productivity (0.386 g L^-1 d^-1) and biomass yield (5.403 g L^-1) were achieved with NaNO₃ at 0.075 g L^-1 and 100 μmol m^-2 s^-1. In addition, phycoerythrin production was improved to obtain a concentration of 14.66 mg L^-1 (2.71 mg g^-1 of phycoerythrin over dry weight). The results of the present study indicate that it is possible to significantly improve biomass and pigment production in Porphyridium purpureum by limiting nitrogen concentration and light intensity.

Combination of nejayote and swine wastewater as a medium for Arthrospira maxima and Chlorella vulgaris production and wastewater treatment

Nejayote and swine wastewater are highly pollutant effluents and a source of organic matter load that sometimes released into water bodies (rivers or lakes), soils or public sewer system, with or without partial treatments. Nejayote is a wastewater product of alkaline cooking of maize, whereas, swine wastewater results from the primary production of pigs for the meat market. Owing to the presence of environmentally related pollutants, both sources are considered the major cause of pollution and thus require urgent action. Herein, we report a synergistic approach to effectively use and/or treat Nejayote and swine wastewater as a cost-effective culture medium for microalgae growth, which ultimately induces the removal of polluting agents. In this study, the strains Arthrospira maxima and Chlorella vulgaris were grown using different dilutions of Nejayote and swine wastewater. Both wastewaters were used as the only source of macronutrients and trace elements for growth. For A. maxima, the treatment of 10% nejayote and 90% of water (T3) resulted in a cell growth of 32 × 10⁴ cell/mL at 12 days (μ_max = 0.27/d). While, a mixture of 25% swine wastewater, 25% nejayote and 50% water (T2) produced 32 × 10⁴ cell/mL at 18 days (μ_max = 0.16/d). A significant reduction was also noted as 92% from 138 mg/L of TN, 75% from 77 mg/L of TP, and 96% from 8903 mg/L of COD, among different treatments. For C. vulgaris, the treatment of 10% swine wastewater and 90% water (T1) gave a cell growth of 128 × 10⁶ cell/mL (μ_max = 0.57/d) followed by T3 yielded 62 × 10⁶ cell/mL (μ_max = 0.70/d) and T2 yielded 48 × 10⁶ cell/mL (μ_max = 0.54/d). Up to 91% reduction from 138 mg/L of TN, 85% from 19 mg/L of TP and 96% from 4870 mg/L of COD was also recorded. These results show that microalgae can be used to treat these types of wastewater while at the same time using them as a culture media for microalgae. The resultant biomass can additionally be used for getting other sub-products of commercial interest.

Algal-based removal strategies for hazardous contaminants from the environment - A review

Owing to the controlled or uncontrolled industrial wastewater disposal, pharmaceutical-based hazardous emerging contaminants (ECs) can be found in the environment all over the world. With ever-increasing socioeconomic aspects and environmental awareness, people are now more concerns about the widespread occurrences of hazardous and persistent contaminants, around the globe. In this context, several studies have already shown that various types of emerging and/or re-emerging contaminants, regardless the source, type and concentration, are of supreme threat to the living system of flora and fauna. Recently, algae-based bioreactors have gained special research interest as a promising way to remove pharmaceuticals-based ECs from the wastewater either partially or completely. This paper covers the progress on the removal of selected pharmaceuticals using bioreactors. In laboratory scale studies, high removal percentages have been reached for most selected pharmaceuticals, but data on full-scale bioreactors is limited. In this paper, two types of bioreactors are discussed, i.e., (1) open pond and (2) bubble column photobioreactor, which are considered sustainable and an effective alternative to remove ECs. In these bioreactors, high removal percentages (>90%) have been found for metoprolol, triclosan, and salicylic acid, moderate (50-90%) for carbamazepine and tramadol and very low (<10%) for trimethoprim and ciprofloxacin by inoculating different microalgae. This technique may open new opportunities for the treatment of wastewater and reduce the environmental pollution that can have adverse effects on the ecosystem and human health. In summary, the present review focuses on the microalgae for wastewater remediation. An effort has also been made to describe the generalities of the photobioreactor.

Botryococcus braunii as a bioreactor for the production of nanoparticles with antimicrobial potentialities

BACKGROUND

Microalgae produce metabolites with notable potentialities to act as reducing and capping agents for the synthesis of silver nanoparticles (AgNPs) in a process widely recognized as an eco-friendly and cheaper alternative for the generation of nanoparticles (NPs).

METHODS

In the present work, AgNPs were synthesized using live Botryococcus braunii cultures. Two biosynthesis routes were explored: (1) intracellular and (2) extracellular at pH levels of 6-9 using 1-5 mM silver nitrate concentrations.

RESULTS

The generation of NPs was confirmed via ultraviolet-visible spectroscopy. The morphological characteristics were observed using scanning electron microscopy which revealed that the newly developed AgNPs were mostly spherical in sizes starting from 168 nm. The characteristic peaks in a typical Fourier transform infrared spectroscopy suggested that the exopolysaccharides were the possible reducing and capping agents. The antimicrobial spectrum of the newly developed AgNPs was tested against bacterial strains, both Gram-negative, Gram-positive, and yeast, ie, Escherichia coli (American Type Culture Collection [ATCC] 25922), Pseudomonas aeruginosa (ATCC 27853), Staphylococcus aureus (ATCC 25923), and the yeast Candida albicans (ATCC 10231), respectively. The antimicrobial activity tests showed a stronger inhibition against Gram-negative bacteria. Statistically, the NPs biosynthesized at pH values of 6 and 8 displayed a higher antimicrobial activity.

CONCLUSION

Our findings showed that B. braunii is capable of generating AgNPs with antimicrobial potential.

Process alternatives for bioethanol production from mango stem bark residues

Three alternatives for bioethanol production from pretreated mango stem bark after maceration (MSBAM) were evaluated as a biorefinery component for the mango agroindustry. These included separate hydrolysis and fermentation (SHF), simultaneous saccharification and fermentation (SSF), and pre-saccharification followed by simultaneous saccharification and fermentation (PSSF). The effects on ethanol concentration, yield and productivity of pretreated MSBAM solids loading, Tween 20 addition, and temperature were used for process comparisons. The highest yields for the SHF, SSF, and PSSF process alternatives were 58.8, 81.6, and 84.5%, respectively. Since saccharification and fermentation are carried out in the same vessel in the SSF alternative, and no significant SSF and PSSF differences in ethanol concentration were observed, SSF is recommended as the best process configuration.