Microalgae-based Technologies Research Articles

A synthetic biology approach for the treatment of pollutants with microalgae.

The increase in global population and industrial development has led to a significant release of organic and inorganic pollutants into water streams, threatening human health and ecosystems. Microalgae, encompassing eukaryotic protists and prokaryotic cyanobacteria, have emerged as a sustainable and cost-effective solution for removing these pollutants and mitigating carbon emissions. Various microalgae species, such as C. vulgaris, P. tricornutum, N. oceanica, A. platensis, and C. reinhardtii, have demonstrated their ability to eliminate heavy metals, salinity, plastics, and pesticides. Synthetic biology holds the potential to enhance microalgae-based technologies by broadening the scope of treatment targets and improving pollutant removal rates. This review provides an overview of the recent advances in the synthetic biology of microalgae, focusing on genetic engineering tools to facilitate the removal of inorganic (heavy metals and salinity) and organic (pesticides and plastics) compounds. The development of these tools is crucial for enhancing pollutant removal mechanisms through gene expression manipulation, DNA introduction into cells, and the generation of mutants with altered phenotypes. Additionally, the review discusses the principles of synthetic biology tools, emphasizing the significance of genetic engineering in targeting specific metabolic pathways and creating phenotypic changes. It also explores the use of precise engineering tools, such as CRISPR/Cas9 and TALENs, to adapt genetic engineering to various microalgae species. The review concludes that there is much potential for synthetic biology based approaches for pollutant removal using microalgae, but there is a need for expansion of the tools involved, including the development of universal cloning toolkits for the efficient and rapid assembly of mutants and transgenic expression strains, and the need for adaptation of genetic engineering tools to a wider range of microalgae species.

Microalgae-based technologies for carbon neutralization and pollutant remediation: A comprehensive and systematic review

Microalgae, with their advantages of rapid growth, high lipid content, and high photosynthetic efficiency, are widely used for carbon neutralization and pollutant remediation. Moreover, microalgae biochars, derived from converting microalgae into biofuels, are also extensively utilized in these fields. This paper endeavors to provide a comprehensive review of the applications of microalgae and microalgae biochars in carbon neutralization and pollutant remediation. Given the growing utilization of wastewater and flue gas for cultivating microalgae, this review also delves into the toxic effects of different pollutants on microalgae. Furthermore, this review assesses the economic and environmental impacts of incorporating microalgae-based technologies into the microalgae biofuel industry, highlighting their substantial potential for bolstering the economic viability and sustainability of the industry. Finally, the challenges and future directions of these technologies are analyzed. This review may provide strategies for advancing carbon neutralization, pollutant remediation, and the development of the microalgae biofuel industry.

Partitioning and inactivation of enveloped and nonenveloped viruses in activated sludge, anaerobic and microalgae-based wastewater treatment systems

Anaerobic and microalgae-based technologies for municipal wastewater treatment have emerged as sustainable alternatives to activated sludge systems. However, viruses are a major sanitary concern for reuse applications of liquid and solid byproducts from these technologies. To assess their capacity to reduce viruses during secondary wastewater treatment, enveloped Phi6 and nonenveloped MS2 bacteriophages, typically used as surrogates of several types of wastewater viruses, were spiked into batch bioreactors treating synthetic municipal wastewater (SMWW). The decay of Phi6 and MS2 in anaerobic and microalgae-based reactors was compared with the decay in activated sludge batch reactors for 96 h (Phi6) and 144 h (MS2). In each reactor, bacteriophages in the soluble and solids fractions were titered, allowing the assessment of virus partitioning to biomass over time. Moreover, the influence of abiotic conditions such as agitation, oxygen absence and light excess in activated sludge, anaerobic and microalgae reactors, respectively, was assessed using dedicated SMWW control reactors. All technologies showed Phi6 and MS2 reductions. Phi6 was reduced in at least 4.7 to 6.5 log10 units, with 0 h concentrations ranging from 5.0 to 6.5 log10 PFU mL−1. Similarly, reductions achieved for MS2 were of at least 3.9 to 7.2 log10 units, from starting concentrations of 8.0 to 8.6 log10 PFU mL−1. Log-logistic models adjusted to bacteriophages’ decay indicated T90 values in activated sludge and microalgae reactors of 2.2 and 7.9 h for Phi6 and of 1.0 and 11.5 h for MS2, respectively, all within typical hydraulic retention times (HRT) of full-scale operation. In the case of the microalgae technology, T99 values for Phi6 and MS2 of 12.7 h and 13.6 h were also lower than typical operating HRTs (2–10 d), while activated sludge and anaerobic treatment achieved less than 99 % of Phi6 and 50 % of MS2 inactivation within 12 h of typical HRT, respectively. Thus, the microalgae-based treatment exhibited a higher potential to reduce the disinfection requirements of treated wastewater.

Exploring Exogenous Indole-3-acetic Acid's Effect on the Growth and Biochemical Profiles of Synechocystis sp. PAK13 and Chlorella variabilis.

Microalgae have garnered scientific interest for their potential to produce bioactive compounds. However, the large-scale industrial utilization of microalgae faces challenges related to production costs and achieving optimal growth conditions. Thus, this study aimed to investigate the potential role of exogenous indole-3-acetic acid (IAA) application in improving the growth and production of bioactive metabolites in microalgae. To this end, the study employed different concentrations of exogenously administered IAA ranging from 0.36 µM to 5.69 µM to assess its influence on the growth and biochemical composition of Synechocystis and Chlorella. IAA exposure significantly increased IAA levels in both strains. Consequentially, improved biomass accumulation in parallel with increased total pigment content by approximately eleven-fold in both strains was observed. Furthermore, the application of IAA stimulated the accumulation of primary metabolites. Sugar levels were augmented, providing a carbon source that facilitated amino acid and fatty acid biosynthesis. As a result, amino acid levels were enhanced as well, leading to a 1.55-fold increase in total amino acid content in Synechocystis and a 1.42-fold increase in Chlorella. Total fatty acids content increased by 1.92-fold in Synechocystis and by 2.16-fold in Chlorella. Overall, the study demonstrated the effectiveness of exogenously adding IAA as a strategy for enhancing the accumulation of microalgae biomass and biomolecules. These findings contribute to the advancement of microalgae-based technologies, opening new avenues to produce economically important compounds derived from microalgae.

Simultaneous purification of anaerobic digestion slurry and enhancement in produced biogas using different microalgae-based technologies under a variety of mixed light wavelengths and photoperiods

Simultaneous purification of anaerobic digestion slurry and enhancement in produced biogas using different microalgae-based technologies under a variety of mixed light wavelengths and photoperiods

Impact of wastewater characteristics on the removal of organic micropollutants by Chlorella sorokiniana

Microalgae-based technologies can be used for the removal of organic micropollutants (OMPs) from different types of wastewater. However, the effect of wastewater characteristics on the removal is still poorly understood. In this study, the removal of sixteen OMPs by Chlorella sorokiniana, cultivated in three types of wastewater (anaerobically digested black water (AnBW), municipal wastewater (MW), and secondary clarified effluent (SCE)), were assessed. During batch operational mode, eleven OMPs were removed from AnBW and MW. When switching from batch to continuous mode (0.8 d HRT), the removal of most OMPs from AnBW and MW decreased, suggesting that a longer retention time enhances the removal of some OMPs. Most OMPs were not removed from SCE since poor nutrient availability limited C. sorokiniana growth. Further correlation analyses between wastewater characteristics, biomass and OMPs removal indicated that the wastewater soluble COD and biomass concentration predominantly affected the removal of OMPs. Lastly, carbon uptake rate had a higher effect on the removal of OMPs than nitrogen and phosphate uptake rate. These data will give an insight on the implementation of microalgae-based technologies for the removal of OMPs in wastewater with varying strengths and nutrient availability.

Recent Progress in Microalgae-Based Technologies for Industrial Wastewater Treatment

The water resource crisis and concerns with environmental pollution prompt the necessity to upgrade conventional wastewater treatment processes. The microalgae-based wastewater treatment process has shown many advantages that can fulfill the stricter demands for improved wastewater treatment. Microalgae cultivation can be carried out in different photobioreactors and under different operational conditions. The cultivation of the microalgae biomass provides the bioremediation of some targeted pollutants through uptake/digestion or biosorption, resulting in treated effluent and the production of biomass. This paper reviews the progress in microalgae-biotechnology for industrial wastewater treatment. A brief overview of microalga types/classification, the cultivation photobioreactors type, and conditions was first provided. Next, a comprehensive review of the bioremediation of industrial wastewater, including distillery, heavy metals, textiles, and emerging contaminants, was provided. Finally, perspectives on the potential scale-up of the technology and some critical considerations were also discussed.

Microalgae-based constructed wetland system enhances nitrogen removal and reduce carbon emissions: Performance and mechanisms

Combination of constructed wetlands (CWs) and microalgae-based technologies has been proved as effective wastewater treatment option; however, little attention was paid to investigate the optimal combination ways. This study showed that the integrated system (IS) connecting microalgal pond with CWs exhibited improved pollutant-removal efficiencies and preferred carbon reduction effects compared to other alternatives such as coupled system or independent CWs. Microbial analysis demonstrated that core microorganisms (e.g., Acinetobacter and Thermomonas) of the IS were mostly associated with carbon, nitrogen, and energy metabolism. Based on co-occurrence networks, microbial quantity with denitrification function in the IS accounted for 71.01 % of the microorganism related to nitrogen metabolism, which was higher than that of 48.84 % in the independent CWs, indicating that the presence of microalgae in IS played important role in promoting biological denitrification. These findings provide insights into the microbial mechanism and highlights the complementary effects between microalgae and CWs.

Evaluation of Tolerant to CO2 Excess Microalgae for the Production of Multiple Biochemicals in a 3G Biorefinery

To date, the positive environmental impact of microalgae-based technologies has been demonstrated in numerous studies. However, there is still a number of major technical and economic obstacles to overcome. Therefore, further research and innovation are needed for the development and commercial exploitation of large-scale integrated and sustainable processes, based on robust ‘industrial’ microalgal strains and novel photobioreactors (PBRs). Note that the advancement of intensified microalgal cultivation processes can facilitate the economically feasible co-production of microalgal biomass and value-added biochemicals. In this context, the goal of the present investigation was to compare several microalgal strains based on a set of productivity criteria, including the maximum biomass growth and the maximum concentration of total biochemicals (i.e., carbohydrates, proteins, and lipids) under CO2 excess conditions (10% v/v). It was found that the wild type strain of Stichococcus sp. fully meets the above productivity criteria. In particular, a biomass concentration of 1.68 g·L−1 and a concentration of total biochemical products of 1.4 g·L−1 were measured in batch cultivation experiments in flasks using the selected strain. Further studies were performed in two different PBRs. Cultivation in a conventional stirred tank PBR showed successful scaling of the bioprocess, whereas cultivation in an innovative tubular recirculating PBR resulted in maximization of both biomass concentration (3.66 g·L−1) and total biochemical products concentration (3.33 g·L−1).

Assessment of the Tolerance of a Chlorophyte Desmodesmus to CuO-NP for Evaluation of the Nanopollution Bioremediation Potential of This Microalga

Broad application of CuO nanoparticles (CuO-NP) for industrial and household purposes leads to a continuous increase in their discharge to, and, hence, ever-increasing environmental hazards for aquatic ecosystems. Microalgae-based technologies hold promise for bioremediation of diverse hazardous micropollutants (HMP), including NP, from wastewater. In this study, we tested the ability of the green microalga Desmodesmus sp. to accumulate CuO-NP or their components. We also assessed the tolerance of this microalga to the environmentally relevant concentrations of CuO-NP. Using scanning electron microscopy, we demonstrated that the average size of CuO-NP was 50-100 nm, and their purity was confirmed with elemental composition analysis. Tests of the colloidal suspensions of CuO-NP showed that the hydrodynamic diameter of CuO-NP and their aggregates was below 100 nm. Flow cytometry analysis showed that CuO-NP at a concentration of 100 µg L-1 slightly inhibited the viability of microalgae cells and led to an increase in their oxidative stress. The assessment of the condition of photosystem II showed that CuO-NP exert a multifaceted effect on the photosynthetic apparatus of Desmodesmus sp., depending on the concentration of and the exposure to the CuO-NP. Desmodesmus sp. turned to be relatively tolerant to CuO-NP. In addition, the ICP-MS method revealed increased bioaccumulation of copper by microalgae cells in the experimental groups. The outcomes of this study indicate that the Desmodesmus sp. has a significant potential for bioremoval of the copper-based nanostructured HMP from an aquatic environment.

Large Scale Microalgae Biofuel Technology—Development Perspectives in Light of the Barriers and Limitations

Microalgal biomass can be used to derive many different types of biofuels. In order to widely commercialize this technology, its limitations and weaknesses must be eliminated. Many technical and economic issues also need to be clarified and unknowns answered. Microalgae-based technologies have been shown to be versatile, efficient and suitable for practical and commercial use. However, the current technological readiness level (TRL) of most microalgae-based bioenergy production systems precludes their quick and widespread implementation. Their development is limited by a combination of factors that must be precisely identified, after which their negative impact on scale-up prospects can be eliminated or minimized. The present study identifies the main barriers to the development of industrial microalgae-production and microalgae-to-biofuel systems. In addition, it proposes measures and efforts necessary to achieve a higher TRL, which will provide investors with sought-after performance and cost-efficiency data for the given project. The main barriers to the development of microalgae cultivation and processing systems have been identified to include: the complex nature of the cultivation process with multiple variables involved; lack of sufficient data from pilot-scale and near-full-scale plants, which often precludes reliable life cycle assessment (LCA); and insufficient legal assistance, advisory assistance, subsidies and funding for innovative projects. Potential ways of improving performance and competitiveness of microalgae-based systems include: process optimization techniques, genetic engineering, yield improvement through advanced process control and monitoring, use of waste as feedstock and dedicated support programs. The presented summary of the current stage of microalgal biofuel production technology development indicates the directions for further research and implementation work, which are necessary for the final verification of the application potential of these solutions.

The effects of influent chemical oxygen demand and strigolactone analog concentration on integral biogas upgrading and pollutants removal from piggery wastewater by different microalgae-based technologies

Microalgae-based technologies are promising strategies for efficient wastewater treatment and biogas upgrading. In this study, three types of microalga-fungi/bacteria symbiotic systems stimulated with the strigolactone analog (GR24) were used to simultaneously remove nutrients from treated piggery wastewater and CO2 from biogas. The effects of initial concentrations of chemical oxygen demand (COD) and GR24 on nutrient removal and biogas upgrading were investigated. When the initial COD concentration was 1200 mg/L, the Chlorella vulgaris–Ganoderma lucidum–endophytic bacteria co-cultivation systems achieved the best photosynthetic performance and microalgae growth. Moreover, under the appropriate COD concentration (1200 mg/L), the highest nutrient/CO2 removal efficiencies were obtained. In addition, 10−9 M GR24 significantly accelerated nutrient/CO2 removal efficiencies. These findings provide a theoretical basis for scale-up experiments using microalgae-based technologies

Effect of GR24 concentrations on tetracycline and nutrient removal from biogas slurry by different microalgae-based technologies

A biogas slurry composed of carbon, nitrogen, phosphorus, and antibiotics was generated. Investigations into the nutrient and tetracycline removal performance of four microalgae-based contaminant removal technologies, including Chlorella vulgaris, C. vulgaris co-cultured with endophytic bacteria, C. vulgaris co-cultured with Ganoderma lucidum, and C. vulgaris co-cultured with G. lucidum and endophytic bacteria, were conducted. The algal-bacterial-fungal consortium with 10−9 M strigolactone (GR24) yielded the maximum growth rate and average daily yield for algae at 0.325 ± 0.03 d−1 and 0.192 ± 0.02 g L−1 d−1, respectively. The highest nutrient/ tetracycline removal efficiencies were 83.28 ± 7.95 % for chemical oxygen demand (COD), 82.62 ± 7.97 % for total nitrogen (TN), 85.15 ± 8.26 % for total phosphorus (TP) and 83.92 ± 7.65 % for tetracycline. Adding an algal-bacterial-fungal consortium with an optimal synthetic analog GR24 concentration is seemingly an encouraging strategy for enhancing pollutant removal by algae, possibly overcoming the challenges of eutrophication and antibiotic pollution.

The Genome Sequence of an Algal Strain of Nannochloropsis QH25.

Species of Nannochloropsis are single-celled Stramenopiles commonly used in microalgae-based technologies for the manufacturing of bioproducts. Nannochloropsis oceanica QH25 was isolated from an algal cultivation pond located in Imperial, Texas (USA). We used PacBio continuous long read (CLR) sequencing to produce a highly contiguous 29.34 Mb genome.

Removal processes of individual and a mixture of organic micropollutants in the presence of Scenedesmus obliquus

Organic micropollutants (OMPs) need to be removed from wastewater as they can negatively affect aquatic organisms. It has been demonstrated that microalgae-based technologies are efficient in removing OMPs from wastewater. In this study, the removal processes and kinetics of six persistent OMPs (diclofenac, clarithromycin, benzotriazole, metoprolol, carbamazepine and mecoprop) were studied during cultivation of Scenedesmus obliquus in batch mode. These OMPs were added as individual compounds and in a mixture. Short experiments (8 days) were performed to avoid masking of OMP removal processes by light and nutrient limitation. The results show that diclofenac, clarithromycin, and benzotriazole were mainly removed by photodegradation (diclofenac), biodegradation (benzotriazole), or a combination of these two processes (clarithromycin). Peroxidase was involved in intracellular and extracellular biodegradation when benzotriazole was present as individual compound. Carbamazepine, metoprolol and mecoprop showed no biodegradation or photodegradation, and neglectable removal (<5%) by bioadsorption and bioaccumulation. Using an OMP mixture had an adverse effect on the photodegradation of clarithromycin and diclofenac, with reduced first-order kinetic constants compared to the individual compounds. Benzotriazole biodegradation was inhibited by the presence of the OMP mixture. This indicates that the presence of OMPs inhibits the photodegradation and biodegradation of some individual OMPs. These results will improve our understanding of removal processes of individual and mixtures of OMPs by microalgae-based technologies for wastewater treatment.

Outflow from a Biogas Plant as a Medium for Microalgae Biomass Cultivation—Pilot Scale Study and Technical Concept of a Large-Scale Installation

Microalgae-based technologies have huge potential for application in the environment sector and the bio-energy industry. However, their cost-efficiency has to be improved by drawing on design and operation data for large-scale installations. This paper presents a technical concept of an installation for large-scale microalgae culture on digestate liquor, and the results of a pilot-scale study to test its performance. The quality of non-treated digestate has been shown to be insufficient for direct use as a growth medium due to excess suspended solids, turbidity, and organic matter content, which need to be reduced. To that end, this paper proposes a system based on mechanical separation, flotation, and pre-treatment on a biofilter. The culture medium fed into photobioreactors had the following parameters after the processing: COD—340 mgO2/dm3, BOD5—100 mgO2/dm3, TN—900 mg/dm3, and TP—70 mg/dm3. The installation can produce approx. 720 kgVS/day of microalgal biomass. A membrane unit and a thickening centrifuge (thickener) were incorporated into the design to separate and dehydrate the microalgal biomass, respectively. The total energy consumption approximated 1870 kWh/day.

Antibiotic Resistance in the Drinking Water: Old and New Strategies to Remove Antibiotics, Resistant Bacteria, and Resistance Genes.

Bacterial resistance is a naturally occurring process. However, bacterial antibiotic resistance has emerged as a major public health problem in recent years. The accumulation of antibiotics in the environment, including in wastewaters and drinking water, has contributed to the development of antibiotic resistant bacteria and the dissemination of antibiotic resistance genes (ARGs). Such can be justified by the growing consumption of antibiotics and their inadequate elimination. The conventional water treatments are ineffective in promoting the complete elimination of antibiotics and bacteria, mainly in removing ARGs. Therefore, ARGs can be horizontally transferred to other microorganisms within the aquatic environment, thus promoting the dissemination of antibiotic resistance. In this review, we discuss the efficiency of conventional water treatment processes in removing agents that can spread/stimulate the development of antibiotic resistance and the promising strategies for water remediation, mainly those based on nanotechnology and microalgae. Despite the potential of some of these approaches, the elimination of ARGs remains a challenge that requires further research. Moreover, the development of new processes must avoid the release of new contaminants for the environment, such as the chemicals resulting from nanomaterials synthesis, and consider the utilization of green and eco-friendly alternatives such as biogenic nanomaterials and microalgae-based technologies.

Simultaneous biogas upgrading and biogas slurry treatment by different microalgae-based technologies under various strigolactone analog (GR24) concentrations

In this research, the effects of exogenous strigolactone analog (GR24) on the growth rate, daily productivity and photosynthesis of symbiotes of Chlorella vulgaris (C. vulgaris)–Ganoderma lucidum (G. lucidum)–endophytic bacteria, C. vulgaris–G. lucidum–activated sludge and C. vulgaris–G. lucidum–multi-walled carbon nanotube, and the simultaneous treatment of biogas slurry and biogas were examined. The C. vulgaris–G. lucidum–endophytic bacteria symbiote achieved the best treatment effectiveness for biogas slurry and biogas, with removal efficiencies of chemical oxygen demand, total nitrogen, total phosphorus and CO2 of 81.4 ± 7.6%, 79.6 ± 7.6%, 82.5 ± 8.2%, and 67.3 ± 6.3% under the optimal GR24 concentration of 10-9 M. Moreover, the treatment effects were positively correlated with growth performance and photosynthesis efficiency of the symbiote. These findings advance the development and application of symbiotic systems in the field of wastewater treatment and biogas upgrading.

Effect of Gr24 Concentrations on Tetracycline and Nutrients Removal by Different Microalgae-Based Technologies

Effect of Gr24 Concentrations on Tetracycline and Nutrients Removal by Different Microalgae-Based Technologies

Simultaneously Biogas Slurry Purifying and Biogas Upgrading Using Different Microalgae-Based Technologies Under a Variety of Mixed Light Wavelengths and Photoperiods by Induction with Strigolactone

Simultaneously Biogas Slurry Purifying and Biogas Upgrading Using Different Microalgae-Based Technologies Under a Variety of Mixed Light Wavelengths and Photoperiods by Induction with Strigolactone