Wastewater based microalgal biorefinery for bioenergy production: Progress and challenges

Biological VFAs production from proteinaceous wastewater varied with protein type: The role of protein exposed enzyme cleavage sites and hydrolysates biotransformation capacity

Proteinaceous wastewater contains various proteins, which can be valorized to biobased volatile fatty acids (VFAs), important substrates for the synthesis of biodegradable plastics, biodiesel, bioelectricity, etc., but the influence of protein type on VFAs has never been documented. It was found that among the five proteinaceous wastewater proteins investigated, ovalbumin and casein produced the most and the least VFAs, respectively. The mechanism investigation shows that proteins with higher VFAs production had higher functional microorganism abundance and key enzyme activity in the reaction system due to their more enzyme cleavage sites and looser secondary structure, which made it easier for more hydrolase to bind, causing more protein hydrolysis. Also, metaproteomics and amino acid composition analyses revealed that the hydrolysates of proteins with higher VFAs had more isoleucine and proline, which were needed for the synthesis of recognizing and binding proteins (oligopeptide permease subunit A (OppA) and dipeptide permease (Dpp)) of acidogens and beneficial for transporters (Dpp subunit F/Opp subunit F), more hydrolysates (amino acids) were therefore transported into the cell. Further investigation indicates that more electron acceptor and electron donor paired amino acids were in the hydrolysates, facilitating the Stickland reaction and promoting intracellular amino acids bio-transformation to VFAs.

A novel deep learning-based floating garbage detection approach and its effectiveness evaluation in environmentally sustainable development

Floating garbage removal is an essential environmental strategy to reduce water pollution and achieve environmental sustainability, and it is a pressing issue for global ecological restoration. Under the interference of complex environments, floating garbage will gather, overlap, and change its shape due to water flow and wind. Efficient and automatic detection and collection of floating garbage gathered on the water surface is a challenging environmental management task. This study proposed an efficient and economical deep learning solution based on YOLOv8 (You Only Look Once v8). By improving the backbone, introducing the Wise-Powerful IoU loss, and adding the AuxHead detection head, the negative impact of complex environmental factors was effectively compressed, and the detection mean Average Precision(mAP) of the surface model aggregated floating garbage was improved to 89.4 %. The Precision(P) was improved to 95.8 %. The model size is only 18.8 MB, and the number of model parameters is reduced by 32.2 % compared with the original model. The proposed model addresses the challenging issue of detecting aggregated floating garbage on the water surface, and the lightweight model is also more conducive to promoting outdoor use. The research results can improve the aggregated floating garbage collection rate by up to 61.5 % compared with the mainstream model Faster R-CNN. It can save up to about 1730.3 kW·h of electricity per ton of recycled waste oil and reduce the emission of 452.7 kg of CO2 and 2328.8t of water pollution. The scheme is superior to the current technical level in terms of detection Precision and mean Average Precision and makes essential scientific contributions to the protection and restoration of water ecosystems, energy conservation, emission reduction, and carbon reduction.

Site-2 protease Sll0528 interacts with RbcR to regulate carbon/nitrogen homeostasis in the cyanobacterium Synechocystis sp. PCC 6803

Cyanobacteria play pivotal roles in global biogeochemical cycles through oxygenic photosynthesis. To maintain cellular homeostasis, these organisms utilize sophisticated acclimation mechanisms to adapt to environmental fluctuations, particularly concerning nitrogen availability. While nitrogen deprivation induces dormancy, excess ammonium can have toxic effects on cyanobacteria and other photosynthetic organisms-a phenomenon for which the acclimation mechanisms remain poorly understood. Through the physiological characterization of knockout and overexpression mutants in Synechocystis sp. PCC 6803, we identified the site-2 protease Sll0528 as a critical regulator of ammonium stress acclimation. TurboID-based proximity labeling, coupled with quantitative proteomics, revealed a robust set of putative Sll0528-interacting proteins, some of which were subsequently validated through bacterial two-hybrid assays and transcriptomic profiling. Notably, we confirmed the physical interaction between Sll0528 and RbcR, a low-carbon-responsive transcriptional regulator. Transcriptomic analysis showed that the knockout of sll0528 led to a significant downregulation of the RbcR regulon, including the ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) operon rbcLXS. Further analysis suggests that this downregulation might result from improper post-transcriptional regulation of RbcR, which depends on its interaction with Sll0528. Our findings reveal novel regulatory crosstalk between a cyanobacterial S2P protease and the carbon-responsive transcriptional machinery, providing new mechanistic insights into the control of cyanobacterial carbon-nitrogen homeostasis during nitrogen fluctuations. This study offers insights into the functional characterization of other S2P proteases in photosynthetic organisms and may facilitate the cyanobacteria-based bioremediation of ammonium-rich wastewater.

Microalgae and biogas: a boon to energy sector

The global energy generation market immensely depends on fossil fuels which balances our survival on this planet. Energy can be called as the "master element" for our daily needs, starting from household power supply, agricultural purpose, automobile and transportation, industrial workload to economic and research domains. Fuel switching initiatives are being adapted by environmentalist and scientists to bring a novel sustainable source of energy. An environment and renewable alternative to fossil fuels are a must. Over the years, the world has shifted toward generating green fuels immensely. One such potential alternative to fossil fuels are biogases. Being versatile and renewable in nature, it has drawn immense attention globally. Despite having such potentials there exist some major drawbacks which mainly deal with the starting material. One such source for biogases can be microalgae. Microalgae based biogas production can produce huge amount of energy and that has been implemented by many foreign countries and their companies. Despite being in use in many countries, there are issues which needs to be addressed which will overall improve the biogas potential from microalgae even more. This review mainly focuses on generation of biogas from microalgae as a feedstock which are very economical and sustainable in its nature, presenting improvement strategies which can be impended to boost the over biogas sector globally.

Synthetic biology approaches and bioseparations in syngas fermentation

Fossil fuel use drives greenhouse gas emissions and climate change, highlighting the need for alternatives like biomass-derived syngas. Syngas, mainly H2 and CO, is produced via biomass gasification and offers a solution to environmental challenges. Syngas fermentation through the Wood-Ljungdahl pathway yields valuable chemicals under mild conditions. However, challenges in scaling up persist due to issues like unpredictable syngas composition and microbial fermentation contamination. This review covers advancements in genetic tools and metabolic engineering to expand product range, highlighting crucial enabling technologies that expedite strain development for acetogens and other non-model organisms. This review paper provides an in-depth exploration of syngas fermentation, covering microorganisms, gas composition effects, separation techniques, techno economic analysis, and commercialization efforts.

Micro-nano bubbles enhanced immobilized Chlorella vulgaris to remove ofloxacin from groundwater

The phenomenon of antibiotic pollution has emerged as a significant global environmental concern. However, there is a lack of technical research on the effective removal of antibiotics based on the characteristics of the groundwater environment. This paper used micro-nano bubbles (MNBs) enhanced immobilized Chlorella technology to remove ofloxacin (OFLX) from groundwater. The study discussed the impact of initial antibiotic concentration (5-30 mg/mL), algae concentration (0.25-4 bead/mL), aeration time (5-30 min), and coexisting ions on the antibiotic removal rate and analyzed the removal mechanism by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The results showed that MNBs increased Chlorella vulgaris biomass by 2.48 times and significantly improved OFLX removal efficiency. The removal rate of OFLX exhibited a significant positive correlation with the algal concentration and coexisting ions and a significant negative correlation with the aeration time and the initial concentration of antibiotics. Enhanced immobilization of Chlorella vulgaris by MNBs for OFLX removal may involve -NH, -OH, -C=O, -CH2, and -C-O-C groups. Degradation (including biodegradation and non-biodegradation) is the primary mechanism of antibiotic removal. Overall, intensive immobilization of Chlorella by MNBs promises to be a technically feasible method for removing antibiotics from groundwater.

Marine cosmetics and the blue bioeconomy: From sourcing to success stories

As the global population continues to grow, so does the demand for longer, healthier lives and environmentally responsible choices. Consumers are increasingly drawn to naturally sourced products with proven health and wellbeing benefits. The marine environment presents a promising yet underexplored resource for the cosmetics industry, offering bioactive compounds with the potential for safe and biocompatible ingredients. This manuscript provides a comprehensive overview of the potential of marine organisms for cosmetics production, highlighting marine-derived compounds and their applications in skin/hair/oral-care products, cosmeceuticals and more. It also lays down critical safety considerations and addresses the methodologies for sourcing marine compounds, including harvesting, the biorefinery concept, use of systems biology for enhanced product development, and the relevant regulatory landscape. The review is enriched by three case studies: design of macroalgal skincare products in Iceland, establishment of a microalgal cosmetics spin-off in Italy, and the utilization of marine proteins for cosmeceutical applications.

Development and challenges of emerging biological technologies for algal-bacterial symbiosis systems: A review

The algal-bacterial symbiosis system (ABSS) is considered as a sustainable wastewater treatment process. This review provides a comprehensive overview of the mechanisms of ABSS for the removal of common pollutant, heavy metals, and especially for emerging pollutants. For the macroscopical level, this review not only describes in detail the reactor types, influencing factors, and the development of the algal-bacterial process, but also innovatively proposes an emerging process that combines an ABSS with other processes, which enhances the efficiency of removing difficult-to-biodegrade pollutants. Further for the microscopic level, interactions between algae and bacteria, including nutrient exchange, signaling transmission and gene transfer, have been deeply discussed the symbiotic relationship with nutrient removal and biomass production. Finally, recommendations are given for the future development of the ABSS. This review comprehensively examines ABSS principles, development, algal-bacterial interactions, and application in wastewater treatment, aiming to deepen theoretical and practical understanding and advance ABSS technology.

Optimal algae species inoculation strategy for algal-bacterial granular sludge: Sludge characteristics, performance and microbial community

The algal-bacterial granular sludge (ABGS) system is emerging as a promising technology for future wastewater treatment. This study assessed the impact of different algae species inoculation on granulation, performance, and microbial communities within ABGS systems. The experimental setup included single-species inoculations (Chlorella sp. (R1), Scenedesmus sp. (R2), and Desmodesmus sp. (R3)) and a mixed-species inoculation strategy (R4). Results revealed that R4 achieved the fastest completed granulation process (15 days) with the largest average granule diameter (772.93 μm) and highest physical strength (2.24 ± 0.26%) in the end of the experiment. The relative abundance of extracellular polymeric substances secreting bacteria of R4 maintained high level in whole operation time. Algae assimilation capacity and the abundance of functional bacteria can also influence removal performance. In mature stage, only the average effluent total nitrogen (3.15 ± 2.87 mg/L), total phosphorus (0.37 ± 0.27 mg/L), chemical oxygen demand (25.25 ± 2.98 mg/L) concentration in R4 was lower than that of Grade I discharge standard of municipal wastewater treatment plants in China. The best inorganic carbon utilization and lipid production ability were observed in R4 and R3, respectively. The choice of inoculated algae species was identified as a key factor for bacterial community dynamics. Overall, above results demonstrated that mixed algae species inoculation can be selected as the optimal algae inoculation strategy due to its excellent granulation, performance, and acceptable carbon utilization and lipid production.

Microalgae to bioenergy production: Recent advances, influencing parameters, utilization of wastewater - A critical review

Fossil fuel limitations and their influence on climate change through atmospheric greenhouse gas emissions have made the excessive use of fossil fuels widely recognized as unsustainable. The high lipid content, carbon-neutral nature and potential as a biofuel source have made microalgae a subject of global study. Microalgae are a promising supply of biomass for third-generation biofuels production since they are renewable. They have the potential to produce significant amounts of biofuel and are considered a sustainable alternative to non-renewable energy sources. Microalgae are currently incapable to synthesize algal biofuel on an extensive basis in a sustainable manner, despite their significance in the global production of biofuels. Wastewater contains nutrients (both organic and inorganic) which is essential for the development of microalgae. Microalgae and wastewater can be combined to remediate waste effectively. Wastewater of various kinds such as industrial, agricultural, domestic, and municipal can be used as a substrate for microalgal growth. This process helps reduce carbon dioxide emissions and makes the production of biofuels more cost-effective. This critical review provides a detailed analysis of the utilization of wastewater as a growth medium for microalgal - biofuel production. The review also highlights potential future strategies to improve the commercial production of biofuels from microalgae.

Environmental sustainable treatment and disposal technologies for reservoir wastes: a review

The process of dredging reservoirs serves the purpose of preserving water storage capacity and ensuring the functionality of navigational channels. Additionally, it has the potential to mitigate the presence of pollutants and chemicals that pose risks to both the environment and human well-being. This review article examines the many ways of disposal and treatment of dredged sediment, as well as the ecological and economic advantages associated with these approaches. Algae and reed-based treatment methods have the potential to effectively and economically remediate and sustainably manage dredged sediments. Landfills and ocean dumping are widely utilized methods for the disposal of excavated materials. However, other approaches such as land reclamation, the use of fill material, and the preservation of wetlands can offer cost-effective solutions while also contributing to environmental conservation. The implementation of sediment cleaning, stabilization, and solidification techniques has the potential to effectively mitigate waste and improve the quality of sediment, hence facilitating its reuse. Algae and reed-based treatment systems have been found to effectively mitigate disposal costs and contribute to environmental enhancement. Additionally, the practice of reusing dredged sediments has been recognized as a valuable strategy in promoting a circular economy.

Microalgae treatment of food processing wastewater for simultaneous biomass resource recycling and water reuse

Food processing wastewater presents a considerable challenge for treatment owing to its elevated nitrogen and phosphorus levels. Nonetheless, it possesses inherent value attributed to its abundant nutrients and organic content. This study presents an innovative approach for treating food processing wastewater and reusing biomass. Initially, the secondary-treated wastewater undergoes flocculation and sedimentation, followed by reverse osmosis to ensure that the effluent meets reuse standards. Subsequently, reverse osmosis concentrates, generated at varying water recovery rates, are utilized for microalgae cultivation to recover nitrogen and phosphorus. Furthermore, this study highlights the potential of reverse osmosis concentrates in reducing the water demand for microalgae cultivation and in producing commercial-grade nutrients. The findings reveal that reverse osmosis achieves removal rates exceeding 90 % for both nitrogen and phosphorus and effluent meets reuse standards. Following seven days of cultivation, microalgae cultured in reverse osmosis concentrated water with an 80 % water recovery rate demonstrate denitrification and phosphorus removal rates of 73.88 % and 80.92 % respectively, with a biomass concentration of 563 mg/L and a protein yield of 128 mg/L. Moreover, a total volumetric energy yield of 10.08 kJ/L is obtained, facilitating energy valorization. In conclusion, this study offers practical solutions for wastewater treatment and resource recovery, enabling the attainment of zero discharge of pollutants while generating valuable resources through microalgae cultivation.

Comprehensive assessment of microalgal-based treatment processes for dairy wastewater

The dairy industry is becoming one of the biggest sectors within the global food industry, and these industries use almost 34% of the water. The amount of water used is governed by the production process and the technologies employed in the plants. Consequently, the dairy industries generate almost 0.2-10 L of wastewater per liter of processed milk, which must be treated before being discharged into water bodies. The cultivation of microalgae in a mixotrophic regime using dairy wastewater enhances biomass growth, productivity, and the accumulation of value-added product. The generated biomass can be converted into biofuels, thus limiting the dependence on petroleum-based crude oil. To fulfill the algal biorefinery model, it is important to utilize every waste stream in a cascade loop. Additionally, the harvested water generated from algal biomass production can be recycled for further microalgal growth. Economic and sustainable wastewater management, along with proper reclamation of nutrients from dairy wastewater, is a promising approach to mitigate the problem of water scarcity. A bibliometric study revealing limited work on dairy wastewater treatment using microalgae for biofuel production. And, limited work is reported on the pretreatment of dairy wastewater via physicochemical methods before microalgal-based treatment. There are still significant gaps remains in large-scale cultivation processes. It is also crucial to discover robust strains that are highly compatible with the specific concentration of contaminants, as this will lead to increased yields and productivity for the targeted bio-product. Finally, research on reutilization of culture media in photobioreactor is necessary to augument the productivity of the entire process. Therefore, the incorporation of the microalgal biorefinery with the wastewater treatment concept has great potential for promoting ecological sustainability.

Applications of the Microalgae Chlamydomonas and Its Bacterial Consortia in Detoxification and Bioproduction

The wide metabolic diversity of microalgae, their fast growth rates, and low-cost production make these organisms highly promising resources for a variety of biotechnological applications, addressing critical needs in industry, agriculture, and medicine. The use of microalgae in consortia with bacteria is proving valuable in several areas of biotechnology, including the treatment of various types of wastewater, the production of biofertilizers, and the extraction of various products from their biomass. The monoculture of the microalga Chlamydomonas has been a prominent research model for many years and has been extensively used in the study of photosynthesis, sulphur and phosphorus metabolism, nitrogen metabolism, respiration, and flagellar synthesis, among others. Recent research has increasingly recognised the potential of Chlamydomonas-bacteria consortia as a biotechnological tool for various applications. The detoxification of wastewater using Chlamydomonas and its bacterial consortia offers significant potential for sustainable reduction of contaminants, while facilitating resource recovery and the valorisation of microalgal biomass. The use of Chlamydomonas and its bacterial consortia as biofertilizers can offer several benefits, such as increasing crop yields, protecting crops, maintaining soil fertility and stability, contributing to CO2 mitigation, and contributing to sustainable agricultural practises. Chlamydomonas-bacterial consortia play an important role in the production of high-value products, particularly in the production of biofuels and the enhancement of H2 production. This review aims to provide a comprehensive understanding of the potential of Chlamydomonas monoculture and its bacterial consortia to identify current applications and to propose new research and development directions to maximise their potential.

The Microalgae Chlamydomonas for Bioremediation and Bioproduct Production

The extensive metabolic diversity of microalgae, coupled with their rapid growth rates and cost-effective production, position these organisms as highly promising resources for a wide range of biotechnological applications. These characteristics allow microalgae to address crucial needs in the agricultural, medical, and industrial sectors. Microalgae are proving to be valuable in various fields, including the remediation of diverse wastewater types, the production of biofuels and biofertilizers, and the extraction of various products from their biomass. For decades, the microalga Chlamydomonas has been widely used as a fundamental research model organism in various areas such as photosynthesis, respiration, sulfur and phosphorus metabolism, nitrogen metabolism, and flagella synthesis, among others. However, in recent years, the potential of Chlamydomonas as a biotechnological tool for bioremediation, biofertilization, biomass, and bioproducts production has been increasingly recognized. Bioremediation of wastewater using Chlamydomonas presents significant potential for sustainable reduction in contaminants and facilitates resource recovery and valorization of microalgal biomass, offering important economic benefits. Chlamydomonas has also established itself as a platform for the production of a wide variety of biotechnologically interesting products, such as different types of biofuels, and high-value-added products. The aim of this review is to achieve a comprehensive understanding of the potential of Chlamydomonas in these aspects, and to explore their interrelationship, which would offer significant environmental and biotechnological advantages.

Strategies to enhance biohydrogen production from microalgae: A comprehensive review

Microalgae represent a promising renewable feedstock for the sustainable production of biohydrogen. Their high growth rates and ability to fix carbon utilizing just sunlight, water, and nutrients make them well-suited for this application. Recent advancements have focused on improving microalgal hydrogen yields and cultivation methods. This review aims to summarize recent developments in microalgal cultivation techniques and genetic engineering strategies for enhanced biohydrogen production. Specific areas of focus include novel microalgal species selection, immobilization methods, integrated hybrid systems, and metabolic engineering. Studies related to microalgal strain selection, cultivation methods, metabolic engineering, and genetic manipulations were compiled and analyzed. Promising microalgal species with high hydrogen production capabilities such as Synechocystis sp., Anabaena variabilis, and Chlamydomonas reinhardtii have been identified. Immobilization techniques like encapsulation in alginate and integration with dark fermentation have led to improved hydrogen yields. Metabolic engineering through modulation of hydrogenase activity and photosynthetic pathways shows potential for enhanced biohydrogen productivity. Considerable progress has been made in developing microalgal systems for biohydrogen. However, challenges around process optimization and scale-up remain. Future work involving metabolic modeling, photobioreactor design, and genetic engineering of electron transfer pathways could help realize the full potential of this renewable technology.

Technological solutions to landfill management: Towards recovery of biomethane and carbon neutrality

Inadequate landfill management poses risks to the environment and human health, necessitating action. Poorly designed and operated landfills release harmful gases, contaminate water, and deplete resources. Aligning landfill management with the Sustainable Development Goals (SDGs) reveals its crucial role in achieving various targets. Urgent transformation of landfill practices is necessary to address challenges like climate change, carbon neutrality, food security, and resource recovery. The scientific community recognizes landfill management's impact on climate change, evidenced by in over 191 published articles (1998-2023). This article presents emerging solutions for sustainable landfill management, including physico-chemical, oxidation, and biological treatments. Each technology is evaluated for practical applications. The article emphasizes landfill management's global significance in pursuing carbon neutrality, prioritizing resource recovery over end-of-pipe treatments. It is important to note that minimizing water, chemical, and energy inputs in nutrient recovery is crucial for achieving carbon neutrality by 2050. Water reuse, energy recovery, and material selection during manufacturing are vital. The potential of water technologies for recovering macro-nutrients from landfill leachate is explored, considering feasibility factors. Integrated waste management approaches, such as recycling and composting, reduce waste and minimize environmental impact. It is conclusively evident that the water technologies not only facilitate the purification of leachate but also enable the recovery of valuable substances such as ammonium, heavy metals, nutrients, and salts. This recovery process holds economic benefits, while the conversion of CH4 and hydrogen into bioenergy and power generation through microbial fuel cells further enhances its potential. Future research should focus on sustainable and cost-effective treatment technologies for landfill leachate. Improving landfill management can mitigate the adverse environmental and health effects of inadequate waste disposal.

Understanding microplastic pollution: Tracing the footprints and eco-friendly solutions

Microplastics (MPs) pollution has emerged as a critical environmental issue with far-reaching consequences for ecosystems and human health. These are plastic particles measuring <5 mm and are categorized as primary and secondary based on their origin. Primary MPs are used in various products like cosmetics, scrubs, body wash, and toothpaste, while secondary MPs are generated through the degradation of plastic products. These have been detected in seas, rivers, snow, indoor air, and seafood, posing potential risks to human health through the food chain. Detecting and quantifying MPs are essential to understand their distribution and abundance in the environment. Various microscopic (fluorescence microscopy, scanning electron microscopy) and spectroscopy techniques (FTIR, Raman spectroscopy, X-ray photoelectron spectroscopy) have been reported to analyse MPs. Despite the challenges in scalable removal methods, biological systems have emerged as promising options for eco-friendly MPs remediation. Algae, bacteria, and fungi have shown the potential to adsorb and degrade MPs in wastewater treatment plants (WWTPs) offering hope for mitigating this global crisis. This review examines the sources, impacts, detection, and biological removal of MPs, highlighting future directions in this crucial field of environmental conservation. By fostering global collaboration and innovative research a path towards a cleaner and healthier planet for future generations can be promised.

Introducing of high rich lysine, arginine, and unsaturated fatty acids microalga as a food supplement

Microalgae are powerful source for nutritionally valuable components as proteins, carbohydrates and especially unsaturated fatty acids. Microalgae may be employed in pharmaceutical, food, cosmetic, health industries, and biofuels. In this study for looking at high-level unsaturated fatty acids species, from 31 strains, by comparing growth curves, the best strain with a high growth rate and lipid content was selected by red Nile staining. It was determined by molecular identification that this strain belongs to the genus Chlorella sp. and is deposited into the Agricultural Biotechnology Research Institute of Iran Culture collection with culture collection number ABRIICC 30,041. Biomass analysis after growth optimization by response surface methodology showed that the selected strain had a specific growth rate of 0.216 ± 0.008 d-1, biomass productivity of 142.58 ± 4.41 mg/Ld, and lipid content of 13.9 ± 0.26% with a high level of unsaturated fatty acids of 53.15%. It also included 51.3 ± 0.53% protein with a very high quality essential amino acids of 40.36%, the most lysine (8.77%) and arginine (13.31%) has been reported until now, and 26.9 ± 0.23% carbohydrates in photoautotroph condition. By MTT assay, there is no effect of cytotoxicity. This research introduces a potent native strain comparable with commercial strains that can be a hopeful source for food supplements and valuable bioactive ingredients in functional foods.

Bioengineering strategies of microalgae biomass for biofuel production: recent advancement and insight

Algae-based biofuel developed over the past decade has become a viable substitute for petroleum-based energy sources. Due to their high lipid accumulation rates and low carbon dioxide emissions, microalgal species are considered highly valuable feedstock for biofuel generation. This review article presented the importance of biofuel and the flaws that need to be overcome to ensure algae-based biofuels are effective for future-ready bioenergy sources. Besides, several issues related to the optimization and engineering strategies to be implemented for microalgae-based biofuel derivatives and their production were evaluated. In addition, the fundamental studies on the microalgae technology, experimental cultivation, and engineering processes involved in the development are all measures that are commendably used in the pre-treatment processes. The review article also provides a comprehensive overview of the latest findings about various algae species cultivation and biomass production. It concludes with the most recent data on environmental consequences, their relevance to global efforts to create microalgae-based biomass as effective biofuels, and the most significant threats and future possibilities.

Nanotechnology based technological development in biofuel production: Current status and future prospects

Depleting fossil fuels and net carbon emissions associated with their burning have driven the need to find alternative energy sources. Biofuels are near-perfect candidates for alternative energy sources as they are renewable and account for no net CO2 emissions. However, biofuel production must overcome various challenges to compete with conventional fuels. Conventional methods for bioconversion of biomass to biofuel include chemical, thermochemical, and biological processes. Substrate selection and processing, low yield, and total cost of production are some of the main issues associated with biofuel generation. Recently, the uses of nanotechnology and nanoparticles have been explored to improve the biofuel production processes because of their high adsorption, high reactivity, and catalytic properties. The role of these nanoscale particles and nanocatalysts in biomass conversion and their effect on biofuel production processes and yield are discussed in the present article. The applicability of nanotechnology in production processes of biobutanol, bioethanol, biodiesel, biohydrogen, and biogas under biorefinery approach are presented. Different types of nanoparticles, and their function in the bioprocess, such as electron transfer, pretreatment, hydrolysis, microalgae cultivation, lipid extraction, dark and photo fermentation, immobilization, and suppression of inhibitory compounds, are also highlighted. Finally, the current and potential applications of nanotechnology in biorefineries are also discussed.

Microalgal-based bioremediation of emerging contaminants: Mechanisms and challenges

Emerging contaminants (ECs) in different ecosystems have consistently been acknowledged as a global issue due to toxicity, human health implications, and potential role in generating and disseminating antimicrobial resistance. The existing wastewater treatment system is incompetent at eliminating ECs since the effluent water contains significant concentrations of ECs, viz., antibiotics (0.03-13.0 μg L-1), paracetamol (50 μg L-1), and many others in varying concentrations. Microalgae are considered as a prospective and sustainable candidate for mitigating of ECs owing to some peculiar features. In addition, the microalgal-based processes also offer cost and energy-efficient solutions for the bioremediation of ECs than conventional treatment systems. It is pertinent that, microalgal-based processes also provides waste valorization benefits as microalgal biomass obtained after ECs treatment can be potentially applied to generate biofuels. Moreover, microalgae can effectively utilize alternative metabolic (cometabolism) routes for enhanced degradation of ECs. Additionally, the ECs removal via the microalgal biodegradation route is highly promising as it can transform the ECs into less toxic compounds. The present review comprehensively discusses different mechanisms involved in removing ECs and various factors that affect their removal. Also, the technoeconomic feasibility of microalgae than other conventional wastewater treatment methods is summarised. The review also highlighted the different molecular and genetic tools that can augment the activity and robustness of microalgae for better removal of organic contaminants. Finally, we have summarised the challenges and future research required towards microalgal-based bioremediation of emerging contaminants (ECs) as a holistic approach.

Cultivation of Chlorella sp. HS2 using wastewater from soy sauce factory

Incorporation of wastewater from industrial sectors into the design of microalgal biorefineries has significant potential for advancing the practical application of this emerging industry. This study tested various food industrial wastewaters to assess their suitability for microalgal cultivation. Among these wastewaters, defective soy sauce (DSS) and soy sauce wastewater (SWW) were chosen but DSS exhibited the highest nutrient content with 13,500 ppm total nitrogen and 3051 ppm total phosphorus. After diluting DSS by a factor of 50, small-scale cultivation of microalgae was conducted to optimize culture conditions. SWW exhibited optimal growth at 25-30 °C and 300-500 μE m-2 s-1, while DSS showed optimal growth at 30-35 °C. Based on a 100-mL lab-scale and 3-L outdoor cultivation with an extended cultivation period, DSS outperformed SWW, exhibiting higher final biomass productivity. Additionally, nutrient-concentrated nature of DSS is advantageous for transportation at an industrial scale, leading us to select it as the most promising feedstock for microalgal cultivation. With further optimization, DSS has the potential to serve as an effective microalgal cultivation feedstock for large-scale biomass production.

Genetic engineering for biohydrogen production from microalgae

The development of biohydrogen as an alternative energy source has had great economic and environmental benefits. Hydrogen production from microalgae is considered a clean and sustainable energy production method that can both alleviate fuel shortages and recycle waste. Although algal hydrogen production has low energy consumption and requires only simple pretreatment, it has not been commercialized because of low product yields. To increase microalgal biohydrogen production several technologies have been developed, although they struggle with the oxygen sensitivity of the hydrogenases responsible for hydrogen production and the complexity of the metabolic network. In this review, several genetic and metabolic engineering studies on enhancing microalgal biohydrogen production are discussed, and the economic feasibility and future direction of microalgal biohydrogen commercialization are also proposed.

Epitomizing biohydrogen production from microbes: Critical challenges vs opportunities

Hydrogen is a clean and green biofuel choice for the future because it is carbon-free, non-toxic, and has high energy conversion efficiency. In exploiting hydrogen as the main energy, guidelines for implementing the hydrogen economy and roadmaps for the developments of hydrogen technology have been released by several countries. Besides, this review also unveils various hydrogen storage methods and applications of hydrogen in transportation industry. Biohydrogen productions from microbes, namely, fermentative bacteria, photosynthetic bacteria, cyanobacteria, and green microalgae, via biological metabolisms have received significant interests off late due to its sustainability and environmentally friendly potentials. Accordingly, the review is as well outlining the biohydrogen production processes by various microbes. Furthermore, several factors such as light intensity, pH, temperature and addition of supplementary nutrients to enhance the microbial biohydrogen production are highlighted at their respective optimum conditions. Despite the advantages, the amounts of biohydrogen being produced by microbes are still insufficient to be a competitive energy source in the market. In addition, several major obstacles have also directly hampered the commercialization effors of biohydrogen. Thus, this review uncovers the constraints of biohydrogen production from microbes such as microalgae and offers solutions associated with recent strategies to overcome the setbacks via genetic engineering, pretreatments of biomass, and introduction of nanoparticles as well as oxygen scavengers. The opportunities of exploiting microalgae as a suastainable source of biohydrogen production and the plausibility to produce biohydrogen from biowastes are accentuated. Lastly, this review addresses the future perspectives of biological methods to ensure the sustainability and economy viability of biohydrogen production.

Toxic effects of long-term dual or single exposure to oxytetracycline and arsenic on Xenopus tropicalis living in duck wastewater

Direct discharge of aquaculture wastewater may have toxic effects, due to the presence of heavy metals, antibiotics, and even resistant pathogens, but little attention has been given. Here, tanks simulating a wild ecosystem were built to study the effects of long-term exposure to duck wastewater containing oxytetracycline (OTC) and/or arsenic (As) on the growth, physiological function, and gut microbiota evolution of Xenopus tropicalis. The results showed that duck wastewater had no apparent impact on X. tropicalis, but the impact increased significantly (P < 0.05) with exposure to OTC and/or As, especially the impact on body weight and growth rate. Biochemical indicators revealed varying degrees of oxidative stress damage, hepatotoxicity (inflammation, necrosis, and sinusoids), and collagen fibrosis of X. tropicalis in all treated groups after 72 days of exposure, which indirectly inhibited X. tropicalis growth. Moreover, 16S rDNA amplicon sequencing results showed that the gut microbiota structure and metabolic function were perturbed after chronic exposure, which might be the leading cause of growth inhibition. Interestingly, the abundance of intestinal resistance genes (RGs) increased with exposure time owing to the combined direct and indirect effects of stress factors in duck wastewater. Moreover, once the RGs were expressed, the resistance persisted for at least 24 days, especially that conferred by tetA. These results provide evidence of the toxic effects of DW containing OTC (0.1-4.0 mg/L) and/or As (0.3-3.5 µg/L) on amphibians and indicate that it is vital to limit the usage of heavy metals and antibiotics on farms to control the biotoxicity of wastewater.

Tunable sulphur doping on CuFe2O4 nanostructures for the selective elimination of organic dyes from water

In this work, sulphur doped copper ferrites (S-CuFe2O4) photocatalysts were successfully synthesized for the first time using the facile hydrothermal method. The as-synthesized photocatalysts were characterized through XRD, Raman, TGA, FT-IR, UV-Vis-DRS, SEM, EDX and PL techniques. The results revealed that doping with sulphur has been found to be a suitable alternative that causes strain in the lattices as anions replace the oxygen from the CuFe2O4 nanostructures. Due to sulphur dopants, photocatalysts are able to efficiently trap and transfer the photoinduced charges, which readily suppress charge recombination. A UV-Vis spectrophotometer was used to monitor the degradation of selective toxic organic dyes (RhB, CR, MO, and CV) in aqueous media. The dye degradation results provide evidence for the surprisingly superior performance of S-CuFe2O4 over pristine CuFe2O4. On the basis of its efficiencies, this work can be assigned as an excellent candidate for photocatalysis science.

Immobilized microalgal system: An achievable idea for upgrading current microalgal wastewater treatment

Efficient wastewater treatment accompanied by sustainable "nutrients/pollutants waste-wastewater-resources/energy nexus" management is acting as a prominent and urgent global issue since severe pollution has occurred increasingly. Diverting wastes from wastewater into the value-added microalgal-biomass stream is a promising goal using biological wastewater treatment technologies. This review proposed an idea of upgrading the current microalgal wastewater treatment by using immobilized microalgal system. Firstly, a systematic analysis of microalgal immobilization technology is displayed through an in-depth discussion on why using immobilized microalgae for wastewater treatment. Subsequently, the main technical approaches employed for microalgal immobilization and pollutant removal mechanisms by immobilized microalgae are summarized. Furthermore, from high-tech technologies to promote large-scale production and application potentials in diverse wastewater and bioreactors to downstream applications lead upgradation closer, the feasibility of upgrading existing microalgal wastewater treatment into immobilized microalgal systems is thoroughly discussed. Eventually, several research directions are proposed toward the future immobilized microalgal system for microalgal wastewater treatment upgrading. Together, it appears that using immobilization for further upgrading the microalgae-based wastewater treatment can be recognized as an achievable alternative to make microalgal wastewater treatment more realistic. The information and perspectives provided in this review also offer a feasible reference for upgrading conventional microalgae-based wastewater treatment.

Site-2 Protease Slr1821 Regulates Carbon/Nitrogen Homeostasis during Ammonium Stress Acclimation in Cyanobacterium Synechocystis sp. PCC 6803

Excess ammonium imposes toxicity and stress response in cyanobacteria. How cyanobacteria acclimate to NH4+ stress is so far poorly understood. Here, Synechocystis sp. PCC6803 S2P homolog Slr1821 was identified as the essential regulator through physiological characterization and transcriptomic analysis of its knockout mutant. The proper expression of 60% and 67% of the NH4+ activated and repressed genes, respectively, were actually Slr1821-dependent since they were abolished or reversed in ∆slr1821. Synechocystis 6803 suppressed nitrogen uptake and assimilation, ammonium integration and mobilization of other nitrogen sources upon NH4+ stress. Opposite regulation on genes for assimilation of nitrogen and carbon, such as repression of nitrogen regulatory protein PII, PII interactive protein PirC and activation of carbon acquisition regulator RcbR, demonstrated that Synechocystis 6803 coordinated regulation to maintain carbon/nitrogen homeostasis under increasing nitrogen, while functional Slr1821 was indispensable for most of this coordinated regulation. Additionally, slr1821 knockout disrupted the proper response of regulators and transporters in the ammonium-specific stimulon, and resulted in defective photosynthesis as well as compromised translational and transcriptional machinery. These results provide new insight into the coordinated regulation of nutritional fluctuation and the functional characterization of S2Ps. They also provide new targets for bioengineering cyanobacteria in bioremediation and improving ammonium tolerance in crop plants.

Microalgal Feedstock for Biofuel Production: Recent Advances, Challenges, and Future Perspective

Globally, nations are trying to address environmental issues such as global warming and climate change, along with the burden of declining fossil fuel reserves. Furthermore, countries aim to reach zero carbon emissions within the existing and rising global energy crisis. Therefore, bio-based alternative sustainable feedstocks are being explored for producing bioenergy. One such renewable energy resource is microalgae; these are photosynthetic microorganisms that grow on non-arable land, in extreme climatic conditions, and have the ability to thrive even in sea and wastewater. Microalgae have high photosynthetic efficiencies and biomass productivity compared to other terrestrial plants. Whole microalgae biomass or their extracted metabolites can be converted to various biofuels such as bioethanol, biodiesel, biocrude oil, pyrolytic bio-oil, biomethane, biohydrogen, and bio jet fuel. However, several challenges still exist before faster and broader commercial application of microalgae as a sustainable bioenergy feedstock for biofuel production. Selection of appropriate microalgal strains, development of biomass pre-concentrating techniques, and utilization of wet microalgal biomass for biofuel production, coupled with an integrated biorefinery approach for producing value-added products, could improve the environmental sustainability and economic viability of microalgal biofuel. This article will review the current status of research on microalgal biofuels and their future perspective.

Anaerobic digestion as a tool to manage eutrophication and associated greenhouse gas emission

Eutrophicated inland water bodies are noticed to be one of the contributing factors to greenhouse gas (GHGs) emissions. Direct discharge of untreated or partially treated water is a major concern. Microalgae-based technology and management are regarded as one of the potential nature-based approaches to combat eutrophication. In turn, the microalgae facilitate the recovery of GHGs contributing compounds in the form of organic biomass. The recovered algal biomass can be harnessed for the production of biofuels and other bio-products, like biofertilizer, using anaerobic digestion. By virtue, circular bio-economy can be achieved alongside mitigating GHGs emissions. Before implementing, it is vital to thoroughly explore the links between the process and potential alternatives for wastewater treatment, waste valorization, biofuel production, and land usage. Thus, the present review discusses the impact of eutrophication on ecology and environment, current technologies for mitigating eutrophication and GHGs, and energy recovery through the anaerobic digestion of algal biomass. Further, the processes at the intercept of wastewater treatment and biogas production were reviewed to leverage the potential of anaerobic digestion for making a circular bioeconomy framework.

A review on the sustainable procurement of microalgal biomass from wastewaters for the production of biofuels

The feasibility of microalgal biomass as one of the most promising and renewable sources for the production of biofuels is being studied extensively. Microalgal biomass can be cultivated under photoautotrophic, heterotrophic, photoheterotrophic, and mixotrophic cultivation conditions. Photoautotrophic cultivation is the most common way of microalgal biomass production. Under mixotrophic cultivation, microalgae can utilize both organic carbon and CO2 simultaneously. Mixotrophic cultivation depicts higher biomass productivity as compared to photoautotrophic cultivation. It is evident from the literature that mixotrophic cultivation yields higher quantities of polyunsaturated fatty acids as compared to that photoautotrophic cultivation. In this context, for economical biomass production, the organic carbon of industrial wastewaters can be valorized for the mixotrophic cultivation of microalgae. Following the way, contaminants' load of wastewaters can be reduced while concomitantly producing highly productive microalgal biomass. This review focuses on different aspects covering the sustainable cultivation of different microalgal species in different types of wastewaters.

Agro-Industrial Wastewaters for Algal Biomass Production, Bio-Based Products, and Biofuels in a Circular Bioeconomy

Recycling bioresources is the only way to sustainably meet a growing world population’s food and energy needs. One of the ways to do so is by using agro-industry wastewater to cultivate microalgae. While the industrial production of microalgae requires large volumes of water, existing agro-industry processes generate large volumes of wastewater with eutrophicating nutrients and organic carbon that must be removed before recycling the water back into the environment. Coupling these two processes can benefit the flourishing microalgal industry, which requires water, and the agro-industry, which could gain extra revenue by converting a waste stream into a bioproduct. Microalgal biomass can be used to produce energy, nutritional biomass, and specialty products. However, there are challenges to establishing stable and circular processes, from microalgae selection and adaptation to pretreating and reclaiming energy from residues. This review discusses the potential of agro-industry residues for microalgal production, with a particular interest in the composition and the use of important primary (raw) and secondary (digestate) effluents generated in large volumes: sugarcane vinasse, palm oil mill effluent, cassava processing waster, abattoir wastewater, dairy processing wastewater, and aquaculture wastewater. It also overviews recent examples of microalgae production in residues and aspects of process integration and possible products, avoiding xenobiotics and heavy metal recycling. As virtually all agro-industries have boilers emitting CO2 that microalgae can use, and many industries could benefit from anaerobic digestion to reclaim energy from the effluents before microalgal cultivation, the use of gaseous effluents is also discussed in the text.

Evaluation of visible-light wavelengths that reduce or oxidize the plastoquinone pool in green algae with the activated F0 rise method

We recently developed a chlorophyll a fluorescence method (activated F0 rise) for estimating if a light wavelength preferably excites PSI or PSII in plants. Here, the method was tested in green microalgae: Scenedesmus quadricauda, Scenedesmus ecornis, Scenedesmus fuscus, Chlamydomonas reinhardtii, Chlorella sorokiniana, and Ettlia oleoabundans. The Scenedesmus species displayed a plant-like action spectra of F0 rise, suggesting that PSII/PSI absorption ratio is conserved from higher plants to green algae. F0 rise was weak in a strain of C. reinhardtii, C. sorokiniana, and E. oleoabundans. Interestingly, another C. reinhardtii strain exhibited a strong F0 rise. The result indicates that the same illumination can lead to different redox states of the plastoquinone pool in different algae. Flavodiiron activity enhanced the F0 rise, presumably by oxidizing the plastoquinone pool during pre-illumination. The activity of plastid terminal oxidase, in turn, diminished the F0 rise, but to a small degree.

Employing algal biomass for fabrication of biofuels subsequent to phytoremediation

An alga belongs to the multi-pertinent group which can add to a significant sector of environment. They show a prevailing gathering of microorganisms for bioremediation due to their significant capacity to inactivate toxic heavy metals. It can easily absorb or neutralize the toxicity of heavy metals from water and soil through phytoremediation. Biosorption is a promising innovation that focuses on novel, modest, and exceptionally successful materials to apply in phytoremediation technology. Furthermore, algal biomass can be used for biofuel generation after phytoremediation using thermochemical or biological transformation processes. The algal components get affected by heavy metals during phytoremediation, but with the help of different techniques, these are yield efficient. The extreme lipid and mineral substances of microalgae have been proven helpful for biofuel manufacturing and worth extra products. Biofuels produced are bio-oil, biodiesel, bioethanol, biogas, etc. The reuse capability of algae can be utilized toward ecological manageability and economic facility. In this review article, the reuse and recycling of algal biomass for biofuel production have been represented. This novel technique has numerous benefits and produces eco-friendly and economically beneficial products.

Sustainable treatment of dye wastewater by recycling microalgal and diatom biogenic materials: Biorefinery perspectives

Discharge of untreated or partially treated toxic dyes containing wastewater from textile industries into water streams is hazardous for environment. The use of heavy metal(s) rich dyes, which are chemically active in azo and sulfur content(s) has been tremendously increasing in last two decades. Conventional physical and chemical treatment processes help to eliminate the dyes from textile wastewater but generates the secondary pollutants which create an additional environmental problem. Microalgae especially the diatoms are promising candidate for dye remediation from textile wastewater. Nanoporous diatoms frustules doped with nanocomposites increase the wastewater remediation efficiency due to their adsorption properties. On the other hand, microalgae with photosynthetic microbial fuel cell have shown significant results in being efficient, cost effective and suitable for large scale phycoremediation. This integrated system has also capability to enhance lipid and carotenoids biosynthesis in microalgae while simultaneously generating the bioelectricity. The present review highlights the textile industry wastewater treatment by live and dead diatoms as well as microalgae such as Chlorella, Scenedesmus, Desmodesmus sp. etc. This review engrosses applicability of diatoms and microalgae as an alternative way of conventional dye removal techniques with techno-economic aspects.

Biosynthesis of microalgal lipids, proteins, lutein, and carbohydrates using fish farming wastewater and forest biomass under photoautotrophic and heterotrophic cultivation

Biorefineries enable the circular, sustainable, and economic use of waste resources if value-added products can be recovered from all the generated fractions at a large-scale. In the present studies the comparison and assessment for the production of value-added compounds (e.g., proteins, lutein, and lipids) by the microalga Chlorella sorokiniana grown under photoautotrophic or heterotrophic conditions was performed. Photoautotrophic cultivation generated little biomass and lipids, but abundant proteins (416.66 mg/g_CDW) and lutein (6.40 mg/g_CDW). Heterotrophic conditions using spruce hydrolysate as a carbon source favored biomass (8.71 g/L at C/N 20 and 8.28 g/L at C/N 60) and lipid synthesis (2.79 g/L at C/N 20 and 3.61 g/L at C/N 60) after 72 h of cultivation. Therefore, heterotrophic cultivation of microalgae using spruce hydrolysate instead of glucose offers a suitable biorefinery concept at large-scale for biodiesel-grade lipids production, whereas photoautotrophic bioreactors are recommended for sustainable protein and lutein biosynthesis.

Current Progress in Natural Degradation and Enhanced Removal Techniques of Antibiotics in the Environment: A Review

Antibiotics are used extensively throughout the world and their presence in the environment has caused serious pollution. This review summarizes natural methods and enhanced technologies that have been developed for antibiotic degradation. In the natural environment, antibiotics can be degraded by photolysis, hydrolysis, and biodegradation, but the rate and extent of degradation are limited. Recently, developed enhanced techniques utilize biological, chemical, or physicochemical principles for antibiotic removal. These techniques include traditional biological methods, adsorption methods, membrane treatment, advanced oxidation processes (AOPs), constructed wetlands (CWs), microalgae treatment, and microbial electrochemical systems (such as microbial fuel cells, MFCs). These techniques have both advantages and disadvantages and, to overcome disadvantages associated with individual techniques, hybrid techniques have been developed and have shown significant potential for antibiotic removal. Hybrids include combinations of the electrochemical method with AOPs, CWs with MFCs, microalgal treatment with activated sludge, and AOPs with MFCs. Considering the complexity of antibiotic pollution and the characteristics of currently used removal technologies, it is apparent that hybrid methods are better choices for dealing with antibiotic contaminants.

Current perspective on wastewater treatment using photobioreactor for Tetraselmis sp.: an emerging and foreseeable sustainable approach

Urbanization is a revolutionary and necessary step for the development of nations. However, with development emanates its drawback i.e., generation of a huge amount of wastewater. The existence of diverse types of nutrient loads and toxic compounds in wastewater can reduce the pristine nature of the ecosystem and adversely affects human and animal health. The conventional treatment system reduces most of the chemical contaminants but their removal efficiency is low. Thus, microalgae-based biological wastewater treatment is a sustainable approach for the removal of nutrient loads from wastewater. Among various microalgae, Tetraselmis sp. is a robust strain that can remediate industrial, municipal, and animal-based wastewater and reduce significant amounts of nutrient loads and heavy metals. The produced biomass contains lipids, carbohydrates, and pigments. Among them, carbohydrates and lipids can be used as feedstock for the production of bioenergy products. Moreover, the usage of a photobioreactor (PBR) system improves biomass production and nutrient removal efficiency. Thus, the present review comprehensively discusses the latest studies on Tetraselmis sp. based wastewater treatment processes, focusing on the use of different bioreactor systems to improve pollutant removal efficiency. Moreover, the applications of Tetraselmis sp. biomass, advancement and research gap such as immobilized and co-cultivation have also been discussed. Furthermore, an insight into the harvesting of Tetraselmis biomass, effects of physiological, and nutritional parameters for their growth has also been provided. Thus, the present review will broaden the outlook and help to develop a sustainable and feasible approach for the restoration of the environment.

Screening of symbiotic Streptomyces spp. and optimization of microalgal growth in a microalgae-actinomycetes co-culture system

Microalgal biodiesel as a substitute for fossil energy has attracted extensive attention. However, the high cost of microalgae cultivation limits the industrial production of microalgal biodiesel. The co-culture system may offer a means to increase microalgae's biomass production. In this study, Streptomyces strains were selected to construct and optimize co-culture systems with Monoraphidium sp. HDMA-11 and the algal cell biomass, lipid content, phycocyanin content, starch content, and fatty acid composition were determined. The results showed that Streptomyces nojiriensis significantly promoted Monoraphidium sp. HDMA-11 growth and a co-culture system were established. Orthogonal experiments showed that the Monoraphidium sp. HDMA-11 biomass was further increased when the initial culture pH was 7.5, the inoculation time of Streptomyces strain supernatants was 36 h, the volume ratio of microalgal actinomycetes was 1:1, and no additional acetic acid was added. Under these conditions, compared with monocultured Monoraphidium sp. HDMA-11, the cell biomass and lipid productivity of the co-culture system increased by 525.8 and 155.1%, respectively. These results suggest that S. nojiriensis supernatant potentially enhances microalgae biomass and may represent a new method to improve microalgae growth.

Advances in algal biomass pretreatment and its valorisation into biochemical and bioenergy by the microbial processes

Urbanization and pollution are the major issues of the current time own to the exhaustive consumption of fossil fuels which have a detrimental effect on the nation's economies and air quality due to greenhouse gas (GHG) emissions and shortage of energy reserves. Algae, an autotrophic organism provides a green substitute for energy as well as commercial products. Algal extracts become an efficient source for bioactive compounds having anti-microbial, anti-oxidative, anti-inflammatory, and anti-cancerous potential. Besides the conventional approach, residual biomass from any algal-based process might act as a renewable substrate for fermentation. Likewise, lignocellulosic biomass, algal biomass can also be processed for sugar recovery by different pre-treatment strategies like acid and alkali hydrolysis, microwave, ionic liquid, and ammonia fiber explosion, etc. Residual algal biomass hydrolysate can be used as a feedstock to produce bioenergy (biohydrogen, biogas, methane) and biochemicals (organic acids, polyhydroxyalkanoates) via microbial fermentation.

Predictive Modeling of Bioenergy Production from Fountain Grass Using Gaussian Process Regression: Effect of Kernel Functions

Experimental studies have shown that bioethanol production from biomass sources has been reported to be influenced by several process parameters. It is not entirely known, however, how the interaction of these factors affects the concentration of bioethanol production. In this study, the use of Gaussian Process Regression (GPR) in predictive modeling of bioethanol production from fountain grass has been investigated. Parametric analysis showing the interaction effect of time, pH, temperature, and yeast extract on the bioethanol production was examined. The effect of kernel functions on the performance of the GPR in modeling the prediction of bioenergy output was also examined. The study shows that the kernel function, namely, rotational quadratic (RQGPR), squared exponential (SEGPR), Matern 5/2 (MGPR), exponential (EGPR), and the optimizable (Opt.GPR.), had varying effects on the performance of the GPR. Coefficients of determination (R2) of 0.648, 0.670, 0.667, 0.762, and 0.993 were obtained for the RQGPR, SEGPR, MGPR, EGPR, OptGPR, respectively. The OptGPR with R2 of 0.993 and RMSE of 45.13 displayed the best performance. The input parameters analysis revealed that the pH of the fermentation medium significantly influences bioethanol production. A proper understanding of how the various process variables affect bioethanol production will help in the real-time optimization of the process in the eventuality of scale-up.

Biodiesel production potential of microalgae, cultivated in acid mine drainage and livestock wastewater

The adaptability and biofuel production potential of two strains of microalgae isolated and cultivated in livestock wastewater effluent (LWE) with acid mine drainage (AMD) were investigated. The isolated strains of microalgae from samples obtained from LWE and AMD, two microalgal strains (Nephroselmis sp. KGE2 and Autodesmus obliquus KGE17) were selected based on their growth rate and lipid productivity. The dry cell weight of Nephroselmis sp. KGE2 and Autodesmus obliquus KGE17 after 20 days of cultivation in AMD increased from 0.05 to 0.59 g/L and from 0.05 to 0.55 g/L, respectively. These findings revealed a significant accumulation of fatty acids with increasing AMD content. Nephroselmis sp. KGE2 in LWE with 5% AMD demonstrated a higher growth rate (0.59 ± 0.03 g/L) and fatty acid production (401.5 ± 47.3 mg/L) than Autodesmus obliquus KGE17 with 5% AMD. Additionally, Nephroselmis sp. KGE2 had C16-C18 fatty acid content (92.4%) in LWE with AMD. Biodiesel produced from Nephroselmis sp. KGE2 had a higher cetane number (52.31) and iodine value (88.26 g I₂/100 g oil). Consequently, Nephroselmis sp. KGE2 can be considered a potential candidate for biodiesel production using AMD as an iron source.

Coupling Magnetic Field and Salinity Upshock To Improve Polyhydroxyalkanoate Productivity by Haloferax mediterranei Feeding on Molasses Wastewater

Low polyhydroxyalkanoate (PHA) volumetric productivity from wastewater limits low-cost PHA production. To resolve this problem, an external magnetic field (MF) coupled with upshock salinity was applied to PHA production by Haloferax mediterranei (family Halobacteriaceae). Elevating the fermentation salinity over the optimal growth salinity (200 g/L) increased the PHA cell content while inhibiting cell proliferation, decreasing volumetric productivity. When a MF of 50 mT in 300 g/L salinity was applied, H. mediterranei proliferation and PHA cell content were promoted, leading to a 7.95% increase in PHA volumetric productivity in synthetic molasses wastewater and a 13.82% increase in glucose feeding compared with those in 200 g/L salinity. Under the MF, osmotic pressure regulation was activated by accumulating K⁺ and increasing betaine synthesis. The maximum betaine content increased by 74.33% in 300 g/L salinity with a 50-mT MF compared with that in 200 g/L salinity. When a 50-mT MF in 300 g/L salinity was applied, the malondialdehyde (MDA) content decreased by 32.66% and the activity of superoxide dismutase (SOD) increased by 46.89%, which reduced the oxidative damage. This study provides a new solution to enhance PHA volumetric productivity by MF and an insight into the magnetic effects of H. mediterranei. IMPORTANCE The obstacle to replacing petroplastics with PHA is its high production cost. To increase the fermentation economy, a novel strategy of coupling a MF with salinity upshock was applied, which enhanced the PHA volumetric productivity of H. mediterranei in fermenting molasses wastewater. The magnetic effect of H. mediterranei was found at a MF of 50 mT, which improved the salt tolerance of H. mediterranei and reduced the oxidative damage induced by the elevated salinity, thereby promoting proliferation and PHA cell content. This is the first time a technical method for enhancing PHA volumetric productivity by means of a MF has been proposed. Such a strategy can advance the utilization of H. mediterranei for the industrial production of PHA using organic wastewater.

Progress in microalgal mediated bioremediation systems for the removal of antibiotics and pharmaceuticals from wastewater

Worldwide demand for antibiotics and pharmaceutical products is continuously increasing for the control of disease and improvement of human health. Poor management and partial metabolism of these compounds result in the pollution of aquatic systems, leading to hazardous effects on flora, fauna, and ecosystems. In the past decade, the importance of microalgae in micropollutant removal has been widely reported. Microalgal systems are advantageous as their cultivation does not require additional nutrients: they can recover resources from wastewater and degrade antibiotics and pharmaceutical pollutants simultaneously. Bioadsorption, degradation, and accumulation are the main mechanisms involved in pollutant removal by microalgae. Integration of microalgae-mediated pollutant removal with other technologies, such as biodiesel, biochemical, and bioelectricity production, can make this technology more economical and efficient. This article summarizes the current scenario of antibiotic and pharmaceutical removal from wastewater using microalgae-mediated technologies.

Organic wastes bioremediation and its changing prospects

Increasing inappropriate anthropogenic activities and industrialization have resulted in severe environmental pollution worldwide. Their effective treatment is vital for general health concerns. Depending on the characteristics of pollutants, the severity of pollution may differ. For sustainable treatment of polluted environments, bioremediation is accepted as the most efficient, economical, and environmentally friendly method hence largely preferred. However, every bioremediation technique has its own unique advantages and limitations due to its defined applications criteria. In bioremediation, microorganisms play a decisive role in detoxification by degrading, mineralizing and accumulating various forms of harmful and biodegradable pollutants from the surroundings and transforming them into less lethal forms. Bioremediation is performed ex-situ or in-situ, based on location of polluted site as well as characteristics, type and strength of the pollutants. Furthermore, the most popular methodologies for bioremediation include bioaugmentation, biostimulation, bioattenuation among others which depend on the prevailing environmental factors into the microbial system. Implementing them appropriately and effectively under ex-situ or in-situ method is extremely important not only for obtaining efficient treatment but also for the best economic, environmental, and social impacts. Therefore, this review aims to analyze various bioremediation methods for organic pollutants remediation from soil/sediments and wastewater, their strength, limitation, and insights for the selection of appropriate bioremediation techniques based on nature, types, degree, and location of the pollution. The novelty aspect of the article is to give updates on several key supporting technologies which have recently emerged and exhibited great potential to enhance the present bioremediation efficiency such as nanobubble, engineered biochar, mixotrophic microalgae, nanotechnology etc. Moreover, amalgamation of these technologies with existing bioremediation facilities are significantly changing the scenario and scope of environmental remediation towards sustainable bioremediation.