Using wastewater as a cultivation alternative for microalga Dunaliella salina: potentials and challenges

Untreated or poorly treated wastewater still represents environmental issues world-widely. Wastewater, especially saline wastewater treatment, is still primarily associated with high costs from physical and chemical processes, as high salinity hinders biological treatment. One favourable way is to find the suitable biological pathways and organisms to improve the biological treatment efficiency. In this context, halophilic microorganisms could be strong candidates to address the economics and effectiveness of the saline wastewater treatment process. Dunaliella salina is a photoautotrophic microalga that grows in saline environments. It is known for producing marketable bio-compounds such as carotenoids, lipids, and proteins. A biological treatment based on D. salina cultivation offers the opportunity to treat saline wastewater, reducing the threat of possible eutrophication from inappropriate discharge. At the same time, D. salina cultivation could yield compounds of industrial relevance to turn saline wastewater treatment into a profitable and sustainable process. Most research on D. salina has primarily focused on bioproduct generation, leaving thorough reviews of its application in wastewater treatment inadequate. This paper discusses the future challenges and opportunities of using D. salina to treat wastewater from different sources. The main conclusions are (1) D. salina effectively recovers some heavy metals (driven by metal binding capacity and exposure time) and nutrients (driven by pH, their bioavailability, and functional groups in the cell); (2) salinity plays a significant role in bioproducts generation, and (3) wastewater can be combined with the generation of bioproducts

Organic Carbon is ineffective in enhancing the growth of Dunaliella

(1) Background: Mixotrophic growth is commonly associated with higher biomass productivity and lower energy consumption. This paper evaluates the impact of using different carbon sources on growth, protein profile, and nutrient uptake for Dunaliella tertiolecta CCAP 19/30 to assess the potential for mixotrophic growth. (2) Methods: Two experimental sets were conducted. The first assessed the contribution of atmospheric carbon to D. tertiolecta growth and the microalgae capacity to grow heterotrophically with an organic carbon source to provide both carbon and energy. The second set evaluated the impact of using different carbon sources on its growth, protein yield and quality. (3) Results: D. tertiolecta could not grow heterotrophically. Cell and optical density, ash-free dry weight, and essential amino acids index were inferior for all treatments using organic carbon compared to NaHCO3. Neither cell nor optical density presented significant differences among the treatments containing organic carbon, demonstrating that organic carbon does not boost D. tertiolecta growth. All the treatments presented similar nitrogen, phosphorus, sulfur recovery, and relative carbohydrate content. (4) Conclusions: Based on the results of this paper, D. tertiolecta CCAP 19/30 is an obligated autotroph that cannot grow mixotrophically using organic carbon

Life cycle assessment of microalgal cultivation medium: biomass, glycerol, and beta-carotene production by Dunaliella salina and Dunaliella tertiolecta

Purpose Dunaliella is a halophilic genus of microalgae with high potential in the global food market. The microalgal cultivation process contributes to not only economic impact but also environmental impact, especially regarding the artificial medium composition. In this context, a life cycle assessment was carried out to analyze the impacts associated with the components of the modified Johnson medium (MJM) and to predict the best scenarios to cultivate Dunaliella tertiolecta and Dunaliella salina for biomass, glycerol, and beta-carotene production. Method Two chains were analyzed separately: (1) Dunaliella salina (strain DF 15) cultivated in 8 scenarios combining different nitrogen (0.1 and 1.0 g L−1 KNO3) and magnesium (1.1–2.3 g L−1 MgCl2.6H2O) concentrations to produce biomass, glycerol, and beta-carotene and (2) Dunaliella tertiolecta (strain CCAP 19/30) cultivated in 5 scenarios combining different nitrogen (0.1 and 1.0 g L−1 KNO3) and salt (116.9–175.4 g L−1 sea salt) concentrations to produce biomass and glycerol. In addition, we evaluated the potential of cultivating these species to reduce the carbon footprint of the proposed scenarios. Results and discussion For D. salina, S5 (1 g L−1 KNO3, 1.1 g L−1 MgCl2.6H2O) had the lowest environmental damage for biomass (74.2 mPt) and glycerol production (0.95 Pt) and S3 (0.1 g L−1 KNO3, 1.9 g L−1 MgCl2.6H2O) for beta-carotene (3.88 Pt). T4 (1 g L−1 KNO3, 116.9 g L−1 sea salt) was the best for D. tertiolecta for biomass (74 mPt) and glycerol (0.49 Pt). “Respiratory inorganics,” “Non-renewable energy,” and “Global warming” were the most impacted categories. “Human health,” “Climate change,” and “Resources” had the highest share of all damage categories. All the scenarios presented negative carbon emission after proposing using brine as alternative salt source: S5 was the best scenario (− 157.5 kg CO2-eq) for D. salina and T4 for D. tertiolecta (− 213.6 kg CO2-eq). Conclusion The LCA proved its importance in accurately predicting the optimal scenarios for MJM composition in the analyzed bioproducts, as confirmed by the Monte Carlo simulation. Although the absolute values of impacts and productivity cannot be directly compared to large-scale cultivation, the validity of the LCA results at this scale remains intact. Productivity gains could outweigh the impacts of “surplus” MJM components. Our study showcased the potential of combining D. salina and D. tertiolecta cultivation with CO2 capture, leading to a more environmentally friendly cultivation system with a reduced carbon footprint

Concepts and Trends for Extraction and Application of Microalgae Carbohydrates

The proposed chapter aims to provide a more in-depth explanation of the composition of carbohydrates in microalgae biomass, focusing on separation methods, chemistry, molecular characterization, as well as their application in several areas. The purpose of this review chapter is to show that biological products from microalgae have potential in health, food, and industry applications (materials and biofuel production). Steps for extraction and purification will be discussed, as well as the relationship between the type of microalgae and its composition, as a way of optimizing protocol selection and product making, without breaking down the cell to begin with (total carbohydrate extraction present in the cell). An overall overview of the current and prospective trends and methodologies for the use of microalgae carbohydrate will be included as starting points to shed light on some of the possible issues that currently do not allow the development and feasibility of microalgae biorefineries

AVALIAÇÃO DA EXTRAÇÃO DE PIGMENTOS NATURAIS DA BIOMASSA REMANESCENTE DE UM SISTEMA ALGAL TURF SCRUBBER (ATS)

A biomassa proveniente de microrganismos contém recursos potencialmente renováveis e com a utilização correta pode-se gerar produtos de alto valor agregado, proporcionando um ganho ambiental e econômico. Um dos bioprodutos que apresenta grande potencial são os pigmentos naturais, os quais apresentam atividades biológicas benéficas. Assim, o foco desta pesquisa foi avaliar os pigmentos presentes na biomassa de um sistema Algal Turf Scrubber (ATS) em água de superfície local. A análise e identificação dos pigmentos foram realizadas através das técnicas de cromatografia em camada delgada (CCD) e de alta eficiência com detector por arranjo de diodos (CLAE-DAD). A espectroscopia de absorção no ultravioleta visível (UV-vis) e fluorescência com varredura foram também utilizadas para fornecer informações complementares dos extratos. A partir da análise por CLAE-DAD e com base na comparação dos tempos de retenção e dos espectros encontrados para cada pico cromatográfico foi possível estimar os possíveis pigmentos na biomassa. Assim, os pigmentos possíveis identificados foram: clorofila a, epímero da clorofila a, feoftina a1 e feoftina a2, diadinocromo, violaxantina e dois carotenoides desconhecidos

AVALIAÇÃO DE FORMAÇÃO DE BIOFILME PERIFÍTICO E IDENTIFICAÇÃO DE MICROALGAS EM UM SISTEMA PILOTO ALGAL TURF SCRUBBER

Os corpos d'água costumam sofrer eutrofização como resultado do excesso de nutrientes, e isso impulsionou a necessidade de desenvolvimento de tecnologias para auxiliar e manter a qualidade da água. Os sistemas Algal Turf Scrubber (ATS) são alternativas para a preservação e monitoramento das condições da água, bem como proporcionar sustentabilidade ambiental e financeira ao longo do tempo. Com base nisso, objetivamos estudar o potencial de desenvolvimento de um biofilme em um sistema piloto de ATS instalado em um lago durante o período de outono/inverno. Para isso, monitoramos alguns parâmetros da água, avaliamos o rendimento de biomassa e identificamos as microalgas no perifíton. As estações selecionadas e as condições ambientais complicaram o desenvolvimento do biofilme. Apesar disso, obtivemos um rendimento de biomassa de 4,67 g m-2 d-1 e sua composição de lipídios foram de 10%, em que os ácidos graxos em maior abundância foram o ácido palmítico e oleico. Através de estudos morfológicos e taxonômicos, quatro gêneros de microalgas foram identificados: Chlorella; Desmodesmus; Pedriastrum e Spirogyra. Acreditamos que analisando em outras estações e variações das condições ambientais poderia levar a um maior desenvolvimento do perifíton e, consequentemente, a melhores tratamentos para massas de água eutrofizadas

MONITORING OF 2-METHYLISOBORNEOL AND GEOSMINE IN A CONSTRUCTED LAKE TO PUBLIC SUPPLY IN SOUTHERN BRAZIL

People that consumed treated water from Dourado Lake, Santa Cruz do Sul, RS, Brazil perceived alterations in its taste and odor. Based on this, we focused our study on the monitoring of 2-MIB and GSM in samples collected from Dourado Lake, using solid-phase microextraction (SPME) coupled to gas chromatography/mass spectrometry (GC/MS). The monitoring was done by performing exploratory evaluations at several points on the lake during the summers of 2017 and 2018 and in all seasons of 2019, considering points of water in an inlet and an outlet of the lake. At the inlet point, the average concentration of GSM was 7.56 ± 1.94 ng L-1 and that of 2-MIB was 33.09 ± 6.89 ng L-1. However, for the outlet point, the average concentrations of GSM and 2-MIB were 10.62 ± 2.51 ng L-1 and 28.72 ± 10.47 ng L-1, respectively. In all cases, the presence of GSM and 2-MIB was perceptible by the people consuming the water (during all seasons), showing the need for correct management of water resources.People that consumed treated water from Dourado Lake, Santa Cruz do Sul, RS, Brazil, perceived alterations in its taste and odor. Based on this, it was studied the monitoring of 2-mthylisoborneol (2-MIB) and geosmin (GSM) in samples collected from Dourado Lake, using solid-phase microextraction (SPME) coupled to gas chromatography/mass spectrometry (GC/MS). The monitoring was done by performing exploratory evaluations at several points on the lake during the summers of 2017 and 2018 and in all seasons of 2019, considering points of water in an inflow and an outflow of the lake. At the inlet point, the average concentration of GSM was 7.56 ± 1.94 ng L-1 and that of 2-MIB was 33.09 ± 6.89 ng L-1. However, for the outlet point, the average concentrations of GSM and 2-MIB were 10.62 ± 2.51 ng L-1 and 28.72 ± 10.47 ng L-1, respectively. In all cases, the presence of GSM and 2-MIB was perceptible by the people consuming the water(during all seasons), showing the need for correct management of water resources

Potential use of microalga Dunaliella salina for bioproducts with industrial relevance

Using microalgal technology has been getting attention over the last decades, mainly for primary use but also for generating high-value compounds. Dunaliella salina is one of the most important microalgae, and its biomass can be used to yield carotenoids, lipids, glycerol, carbohydrates, and proteins for biofuel, pharmaceuticals, and food generation. Many factors affect bioproduct yields, such as light regime and intensity, salinity, harvesting period, and media composition, which directly impact the feasibility of biorefineries. Although it has been addressed over the past decades, there is still a lack of consensus regarding an effective method for biomass and bioproduct generation and recovery on an industrial scale. In this study, a bibliometric analysis over the five years is used to identify (I) the global distribution of research; (II) the bioproducts yielded by D. salina, and (III) the future perspective for the valorization of its biomass. China is the major contributor to research on D. salina, followed by India and the United States of America. Carotenoid production has been the major focus of the research, followed by protein, lipid, carbohydrate, and glycerol. The genetic engineering approach seems to carry out the future of D. salina to improve the generation of bioproducts, especially pigments and protein