Microalgal-based biochar in wastewater remediation: Its synthesis, characterization and applications

The biochar derived from Spirulina platensis for the adsorption of Pb and Zn and enhancing the soil physicochemical properties

Microalgae can be collected in large quantities and hold significant potential for environmental remediation, offering a cost-effective solution. This study explores the use of Spirulina platensis (SP) as feedstock for biochar production. SP contains abundant nitrogen-rich components, such as proteins, which can serve as nitrogen sources. We prepared SP-derived biochar through pyrolysis for the adsorption of Pb and Zn from aqueous solutions and used it as an amending agent to remediate heavy metal-contaminated agricultural soil. Pyrolysis of proteins in SP introduces nitrogen-functional groups, resulting in nitrogen-doped biochar. We investigated the surface chemical behavior of thermally treated SP using X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy. Surface analysis revealed the presence of pyridine-N and pyrrole-N from protein pyrolysis products. The study also demonstrated that these functional groups affect interactions with heavy metals. Batch experiments examined the effects of pH and initial concentration on the adsorption of Pb and Zn using SP400 and SP600. Both types of biochar showed satisfactory performance in adsorbing Pb and Zn. The effect of SP400 and SP600 on the removal of Pb and Zn through the physicochemical properties and surface functional groups was investigated. Analysis of SP400 and SP600 highlighted that electrostatic interactions, cation exchange, complexation, and mineral precipitation contributed to Pb and Zn adsorption. The study concludes that SP-derived biochar, particularly SP600, is effective for immobilizing Pb and Zn in contaminated agricultural soil, with SP600 showing superior performance.

Treatment of agricultural wastewater using microalgae: A review

The rapid development of agriculture has led to a large amount of wastewater, which poses a great threat to environmental safety. Microalgae, with diverse species, nutritional modes and cellular status, can adapt well in agricultural wastewater and absorb nutrients and remove pollutants effectively. Besides, after treatment of agricultural wastewater, the accumulated biomass of microalgae has broad applications, such as fertilizer and animal feed. This paper reviewed the current progresses and further perspectives of microalgae-based agricultural wastewater treatment. The characteristics of agricultural wastewater have been firstly introduced; Then the microalgal strains, cultivation modes, cellular status, contaminant metabolism, cultivation systems and biomass applications of microalgae for wastewater treatment have been summarized; At last, the bottlenecks in the development of the microalgae treatment methods, as well as recommendations for optimizing the adaptability of microalgae to wastewater in terms of wastewater pretreatment, microalgae breeding, and microalgae-bacterial symbiosis systems were discussed. This review would provide references for the future developments of microalgae-based agricultural wastewater treatment.

Synthesis, delineation and technological advancements of algae biochar for sustainable remediation of the emerging pollutants from wastewater-a review

The use of algae for value-added product and biorefining applications is enchanting attention among researchers in recent years due to its remarkable photosynthetic ability, adaptability, and capacity to accumulate lipids and carbohydrates. Algae biomass, based on its low manufacturing costs, is relatively renewable, sustainable, environmentally friendly and economical in comparison with other species. High production rate of algae provides a unique opportunity for its conversion to biochar with excellent physicochemical properties, viz. high surface area and pore volume, high adsorption capacity, abundant functional groups over surface, etc. Despite several potential algal-biochar, a detailed study on its application for removal of emerging contaminants from wastewater is limited. Therefore, this technical review is being carried out to evaluate the specific elimination of inorganic and organic pollutants from wastewater, with a view to assessing adsorption performances of biochar obtained from various algae species. Species-specific adsorption of emerging pollutants from wastewater have been discussed in the present review. The promising methods like pyrolysis, gasification, dry and wet torrefaction for the production of algae biochar are highlighted. The strategies include chemical and structural modifications of algae biochar for the removal of toxic contaminants have also been considered in the current work. The overall aim of this review is to confer about the synthesis, technological advancements, delineation and application of algae biochar for the treatment of wastewater.

Ensuring carbon neutrality via algae-based wastewater treatment systems: Progress and future perspectives

The emergence of algal biorefineries has garnered considerable attention to researchers owing to their potential to ensure carbon neutrality via mitigation of atmospheric greenhouse gases. Algae-derived biofuels, characterized by their carbon-neutral nature, stand poised to play a pivotal role in advancing sustainable development initiatives aimed at enhancing environmental and societal well-being. In this context, algae-based wastewater treatment systems are greatly appreciated for their efficacy in nutrient removal and simultaneous bioenergy generation. These systems leverage the growth of algae species on wastewater nutrients-including carbon, nitrogen, and phosphorus-alongside carbon dioxide, thus facilitating a multifaceted approach to pollution remediation. This review seeks to delve into the realization of carbon neutrality through algae-mediated wastewater treatment approaches. Through a comprehensive analysis, this review scrutinizes the trajectory of algae-based wastewater treatment via bibliometric analysis. It subsequently examines the case studies and empirical insights pertaining to algae cultivation, treatment performance analysis, cost and life cycle analyses, and the implementation of optimization methodologies rooted in artificial intelligence and machine learning algorithms for algae-based wastewater treatment systems. By synthesizing these diverse perspectives, this study aims to offer valuable insights for the development of future engineering applications predicated on an in-depth understanding of carbon neutrality within the framework of circular economy paradigms.

Applications of engineered biochar in remediation of heavy metal(loid)s pollution from wastewater: Current perspectives toward sustainable development goals

Environmental pollution of heavy metal(loid)s (HMs) caused adverse impacts, has become one of the emerging concerns and challenges worldwide. Metal(loid)s can pose significant threats to living organisms even when present in trace levels within environmental matrices. Extended exposure to these substances can lead to adverse health consequences in humans. Removing HM-contaminated water and moving toward sustainable development goals (SDGs) is critical. In this mission, biochar has recently gained attention in the environmental sector as a green and alternative material for wastewater removal. This work provides a comprehensive analysis of the remediation of typical HMs by biochars, associated with an understanding of remediation mechanisms, and gives practical solutions for ecologically sustainable. Applying engineered biochar in various fields, especially with nanoscale biochar-aided wastewater treatment approaches, can eliminate hazardous metal(loid) contaminants, highlighting an environmentally friendly and low-cost method. Surface modification of engineered biochar with nanomaterials is a potential strategy that positively influences its sorption capacity to remove contaminants. The research findings highlighted the biochars' ability to adsorb HM ions based on increased specific surface area (SSA), heightened porosity, and forming inner-sphere complexes with oxygen-rich groups. Utilizing biochar modification emerged as a viable approach for addressing lead (Pb), cadmium (Cd), arsenic (As), mercury (Hg), and chromium (Cr) pollution in aqueous environments. Most biochars investigated demonstrated a removal efficiency >90 % (Cd, As, Hg) and can reach an impressive 99 % (Pb and Cr). Furthermore, biochar and advanced engineered applications are also considered alternative solutions based on the circular economy.

Facile fabrication of sulfonated porous yeast carbon microspheres through a hydrothermal method and their application for the removal of cationic dye

Water pollution containing dyes become increasingly serious environmental problem with the acceleration of urbanization and industrialization process. Renewable adsorbents for cationic dye wastewater treatment are becoming an obstacle because of the difficulty of desorbing the dye from the adsorbent surface after adsorption. To overcome this dilemma, herein, we report a hydrothermal method to fabricate sulfonic acid modified yeast carbon microspheres (SA/YCM). Different characterization techniques like scanning electron microscopy, FTIR spectroscopy, and X-ray diffraction have been used to test the SA/YCM. Decorated with sulfonic acid group, the modified yeast carbon microspheres possess excellent ability of adsorbing positively charged materials. The removal rate of Methyl blue (MB) by renewable adsorbent SA/YCM can reach 85.3% when the concentration is 500 mg/L. The SA/YCM regenerated by HCl showed excellent regeneration adsorption capacity (78.1%) after five cycles of adsorption-desorption regeneration experiment. Adsorption isotherm and kinetic behaviors of SA/YCM for methylene blue dyes removal were studied and fitted to different existing models. Owing to the numerous sulfonic acid groups on the surface, the SA/YCM showed prominent reusability after regeneration under acidic conditions, which could withstand repeated adsorption-desorption cycles as well as multiple practical applications.

Research advances on production and application of algal biochar in environmental remediation

Algae, comprising microalgae and macroalgae, have emerged as a promising feedstock for the production of functional biochar. Recently, the application of algal biochar in environmental remediation gains increasing attention. This review summarizes research advancements in the synthesis and application of algal biochar, a versatile and sustainable material for environmental remediation ranging from wastewater treatment to soil improvement. Algal biochar can be prepared by pyrolysis, microwave-assisted pyrolysis, and hydrothermal carbonization. Physical and chemical modifications have proven to be effective for improving biochar properties. Algal biochar is promising for removing diverse pollutants including heavy metals, organic pollutants, and microplastics. The role in soil improvement signifies a sustainable approach to enhancing soil structure, nutrient retention, and microbial activity. Research gaps are identified based on current understanding, necessitating further exploration into variations in biochar characteristics, the performance improvement, large-scale applications, and the long-term evaluation for environmental application. This review provides a better understanding of algal biochar as a sustainable and effective tool in environmental remediation.

Low-Cost Greywater Treatment Using Polyculture Microalgae-Microalgal Growth, Organics, and Nutrient Removal Subject to pH and Temperature Variations During the Treatment

Organics and nutrient removal studies are rarely done using polyculture microalgae, and that too in outdoor conditions, as they are often not deemed effective for wastewater treatment purposes. This study examined the organics and nutrient removal efficiency of polyculture microalgae cultivated in greywater. The reactor was operated in outdoor conditions. Hence, it was subjected to natural pH and temperature variations. A growth rate of 0.05 g L-1 day-1 was observed for temperatures up to 37 °C, beyond which the growth rate declined by 0.07 g L-1 day-1. During the treatment, the pH of the system was observed to be between 7.4 and 8.4. However, the growth rate would again pick up (0.05 g L-1 day-1) when the pH and temperature moved towards the optimum range, indicating that the polycultures adapt very quickly to their environment. The maximum biomass concentration reached 0.82 gL-1. The highest removal efficiency of organic carbon, ammonia, and phosphate was 80.7, 61.9, and 58.4%, respectively. Nitrate and nitrite concentrations remained ≤ 1.3 mgL-1 and ≤ 2 mgL-1, respectively, indicating the absence of nitrification/denitrification and ammonia volatilization. The mass balance of microalgae indicated that the primary removal mechanism of nitrogen and phosphorus removal was assimilation by the microalgae. The study proved polyculture microalgae to be as effective as some monoculture species in wastewater treatment, which require costlier controlled growth conditions. The high organics and nutrient removal by polycultures in outdoor conditions could pave the way to reducing wastewater treatment costs.

Coupling harmful algae derived nitrogen and sulfur co-doped carbon nanosheets with CeO2 to enhance the photocatalytic degradation of isothiazolinone biocide

Removing the algae from water bodies is an effective treatment toward the worldwide frequently occurred harmful algae blooms (HAB), but processing the salvaged algae waste without secondary pollution places another burden on the economy and environment. Herein, a green hydrothermal process without any chemical addition was developed to resource the HAB algae (Microcystis sp.) into autogenous nitrogen and sulfur co-doped carbon nanosheet materials C-CNS and W-CNS, whose alga precursors were collected from pure culture and a wild bloom pond, respectively. After coupling with CeO2, the obtained optimal C-CNS/CeO2 and W-CNS/CeO2 composites photocatalytically degraded 95.4% and 88.2% of the marine pollutant 4,5-Dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT) in 90 min, significantly higher than that of pure CeO2 (63.15%). DCOIT degradation on CNS/CeO2 was further conducted under different conditions, including pH value, coexisting cations and anions, and artificial seawater. Although different influences were observed, the removal efficiencies were all above 76%. Along with the ascertained good stability and reusability in five consecutive runs, the great potential of CNS/CeO2 for practical application was validated. UV-vis DRS showed the increased light absorption of CNS/CeO2 in comparison to pure CeO2. PL spectra and photoelectrochemical measurements suggested the lowered charge transfer resistance and thereby inhibited charge recombination of CNS/CeO2. Meanwhile, trapping experiments and electron paramagnetic resonance (EPR) detection verified the primary roles of hydroxyl radical (OH) and superoxide radical (O2-) in DCOIT degradation, as well as their notably augmented generation by CNS. Consequently, a mechanism of CNS enhanced photocatalytic degradation of DCOIT was proposed. The intermediates involved in the reaction were identified by LC-QTOF-MS, giving rise to a deduced degradation pathway for DCOIT. This study offers a new approach for resourceful utilization of the notorious HAB algae waste. Besides that, photocatalytic degradation has been explored as an effective measure to remove DCOIT from the ocean.

Immobilization of hydrochar in cellulose beads for eradicating paracetamol from synthetic and sewage water

Sodium carboxymethyl cellulose polymer was used as a support matrix in immobilizing activated hydrochar derived from bamboo using hydrothermal carbonization. The structural and textural morphology of the beads were studied using FTIR, XRD, SEM/EDS, BET and TGA. Activated hydrochar showed a rough surface with irregular spherical shaped structure. Various oxygenated functional groups in composite beads and activated hydrochar were identified that assist in interaction with PARA pollutant. TGA analysis showed weight loss at three stages 200 °C, 365 °C and 710 °C that leads to complete disintegration of composite beads. BET analysis showed a variation in the surface area between activated hydrochar and beads which could be due to air drying process. Batch adsorption test was conducted for investigating the efficiency of beads in removing PARA from water. Pseudo-second order and Langmuir isotherm fitted the best highlighting chemical mode of adsorption with homogenous interaction on the adsorbent surface. 48.12 mg g-1 was the maximum adsorption capacity estimated from sorption between beads and PARA. For practical applications beads were effectively used in reducing COD levels of PARA spiked sewage water with the defined experimental parameters. Ethanol would be effectively used as regenerating solvent in recycling the beads for the betterment of cost reduction. The activated hydrochar immobilized cellulose beads would be successfully applied as adsorbent in removing target pollutants from water thereby reducing the hurdles faced with respect to fine particles in water treatment.

Constructing mesoporous biochar derived from waste carton: Improving multi-site adsorption of dye wastewater and investigating mechanism

The development of cost-efficient biochar adsorbent with a simple preparation method is essential to constructing efficient wastewater treatment system. Here, a low-cost waste carton biochar (WCB) prepared by a simple two-step carbonization was applied in efficiently removing Rhodamine B (RhB) in aqueous environment. The maximum ability of WCB for RhB adsorption was 222 mg/g, 6 and 10 times higher than both of rice straw biochar (RSB) and broadbean shell biochar (BSB), respectively. It was mainly ascribed to the mesopore structure (3.0-20.4 nm) of WCB possessing more spatial sites compared to RSB (2.2 nm) and BSB (2.4 nm) for RhB (1.4 nm✕1.1 nm✕0.6 nm) adsorption. Furthermore, external mass transfer (EMT) controlled mass transfer resistance (MTR) of the RhB sorption process by WCB which was fitted with the Langmuir model well. Meanwhile, the adsorption process was dominated by physisorption through van der Waals forces and π-π interactions. A mixture of three dyes in river water was well removed by using WCB. This work provides a straightforward method of preparing mesoporous biochar derived from waste carton with high-adsorption capacity for dye wastewater treatment.

Comparison of microalgal hydrochar and pyrochar: production, physicochemical properties, and environmental application

Microalgal biomass has been considered the third-generation biofuel production feedstock, but microalgae-derived biochar still needs to be thoroughly understood. This study aims to evaluate the production and physicochemical properties of microalgae-derived hydrochar produced by hydrothermal carbonization (HTC) process by comparison with pyrochar produced by dry thermal carbonization (DTC) process for environmental applications. Microalgal biochar was produced with commercially available Chlorella vulgaris microalgae using HTC and DTC processes under various temperature conditions. Pyrochar presented higher pH, ash contents, porosity, and surface area than hydrochar. Hydrochar gave more oxygen-containing functional groups on the surface and higher lead adsorption than pyrochar, making the microalgal hydrochar applicable in soil amendment and various environmental remediations. HTC could be an economically feasible thermochemical process for microalgal biochar production. It can produce hydrochar with high production yield from wet microalgae at low temperatures without a drying process.

Removal of cadmium from aqueous solution by magnetic biochar: adsorption characteristics and mechanism

Experiments were conducted to investigate the potential of the efficient resource utilization of waste cow manure and corn straw in an agricultural ecosystem. In this study, a magnetic cow manure and straw biochar were synthesized by a co-precipitation method, and cadmium (Cd(II)) was removed by adsorption in aqueous solution. Several physicochemical characterization techniques were applied, including SEM, BET, Zeta, FTIR, Raman, XPS, and VSM. The effects of pH value, magnetic biochar content, adsorption kinetics, and isothermal adsorption on the adsorption of Cd(II) were investigated. The physicochemical characterizations revealed that the physical and chemical properties of the magnetic biochar were substantially changed compared to the unmodified biochar. The results showed that the surface of the biochar became rough, the number of oxygen (O)-containing functional groups increased, and the specific surface area increased. The results of the adsorption experiments showed that the adsorption capacity was affected by pH, magnetic biochar addition, Cd(II) concentration, and adsorption time. The adsorption kinetics and isothermal adsorption experiments showed that the Cd(II) adsorption processes of the cow manure and corn straw magnetic biochars were consistent with the Freundlich model and pseudo-second-order kinetic model. The results also showed that the Cd(II) adsorption effect of cow manure magnetic biochar was found to be more effective than that of corn straw magnetic biochar. The optimal conditions for Cd(II) adsorption were 800 ℃ for cow manure magnetic biochar, with a pH value of 5 and 0.14 g biochar addition, and 600 ℃ for straw magnetic biochar with a pH value of 8 and 0.12 g biochar addition. In conclusion, the cow manure magnetic biochar was an effective adsorbent for the absorption of Cd(II) in wastewater.

Microalgae-based biochar production and applications: A comprehensive review

Biochar, a solid carbonaceous substance synthesized from the thermochemical degradation of biomass, holds significant potential in addressing global challenges such as soil degradation, environmental pollution, and climate change. Its potential as a carbon sequestration agent, together with its versatile applications in soil amendments, pollutant adsorption, and biofuel production, has garnered attention. On the other hand, microalgae, with their outstanding photosynthetic efficiency, adaptability, and ability to accumulate carbohydrates and lipids, have demonstrated potential as emerging feedstock for biochar production. However, despite the significant potential of microalgal biochar, our current understanding of its various aspects, such as the influence of parameters, chemical modifications, and applications, remains limited. Therefore, this review aims to provide a comprehensive analysis of microalgae-based biochar, covering topics such as production techniques, pollutant removal, catalytic applications, soil amendments, and synthesis of carbon quantum dots to bridge the existing knowledge gap in this field.

The magic of algae-based biochar: advantages, preparation, and applications

Compared with other biomass sources, the use of algae as a raw material to prepare biochar (BC) has important advantages including safety, high yield and economy. The protein content of algae cells is as high as 3.2 mg DCW/L, and the graphitic-N and N-O functional groups generated by the pyrolysis of proteins could effectively activate free radicals. Combined with the generated pore structure, the electron transfer/exchange capability was enhanced, which is conducive to improving its catalytic performance. Algae as a natural N source, the manuscript analyzed the surface properties and physicochemical properties of algae-based BC, and investigated its degradation effect on organic/inorganic pollutants in wastewater. Subsequently, the effect of nitrogen-doped BC on the adsorption/catalysis capacity was discussed. Finally, the directed preparation of algae-based BC applied in different scenarios was summarized. Algae-based BC has the property of N doping, which broadens its application efficiency in the environmental field. Overall, this manuscript reviews how to achieve efficient utilization of algae-based BC in wastewater.

Net zero emission in circular bioeconomy from microalgae biochar production: A renewed possibility

The rapid expansion of industrialization and continuous population growth have caused a steady increase in energy consumption. Despite using renewable energy, such as bioethanol, to replace fossil fuels had been strongly promoted, however the outcomes were underwhelming, resulting in excessive greenhouse gases (GHG) emissions. Microalgal biochar, as a carbon-rich material produced from the pyrolysis of biomass, provides a promising solution for achieving net zero emission. By utilizing microalgal biochar, these GHG emissions can be captured and stored efficiently. It also enhances soil fertility, improves water retention, and conduct bioremediation in agriculture and environmental remediation field. Moreover, incorporating microalgal biochar into a zero-waste biorefinery could boost the employ of biomass feedstocks effectively to produce valuable bioproducts while minimizing waste. This contributes to sustainability and aligns with the concepts of a circular bioeconomy. In addition, some challenges like commercialization and standardization will be addressed in the future.

Recycling waste iron-rich algal flocs as cost-effective biochar activator for heterogeneous Fenton-like reaction towards tetracycline degradation: Important role of iron species and moderately defective structures

Harvesting aquatic harmful algal blooms (HABs) and reusing them is a promising way for antibiotic degradation. Herein, a novel iron-rich biochar (Fe-ABC), derived from algal biomass harvested by magnetic coagulation, was successfully designed and fabricated as activator for heterogeneous Fenton-like reaction. The modification methods and pyrolysis temperatures (400-800 °C) were optimized to enhance the formation of rich iron species and moderately defective structure, yielding Fe-ABC-600 with enhanced electron transfer and H2O2 activation capability. Thus, Fe-ABC-600 exhibited superior removal efficiency (95.33%) on tetracycline (TC), where the presence of multiple iron species (Fe3+, Fe2+ and Fe4+) and moderately defective structure accelerating the Fenton-like oxidation. The concentration of leaching Fe after each reaction was all below 0.74 mg/L in five cycles, ensuring the sustained degradation. And •OH was proved to be the major radical contributing to the degradation of TC, as well as the direct electron transfer mechanism together, in which the CO acted as electron regulator and electron donor. Fe-ABC as a cost-effective catalyst has notable application potentials in TC removal from wastewater owing to its remarkable advantages of high resource utilization, enhanced catalytic property, high ecological safe, notable TC degradation efficiency, low cost and environmental-friendliness.

Microalgae systems - environmental agents for wastewater treatment and further potential biomass valorisation

Water is the most valuable resource on the planet. However, massive anthropogenic activities generate threatening levels of biological, organic, and inorganic pollutants that are not efficiently removed in conventional wastewater treatment systems. High levels of conventional pollutants (carbon, nitrogen, and phosphorus), emerging chemical contaminants such as antibiotics, and pathogens (namely antibiotic-resistant ones and related genes) jeopardize ecosystems and human health. Conventional wastewater treatment systems entail several environmental issues: (i) high energy consumption; (ii) high CO₂ emissions; and (iii) the use of chemicals or the generation of harmful by-products. Hence, the use of microalgal systems (entailing one or several microalgae species, and in consortium with bacteria) as environmental agents towards wastewater treatment has been seen as an environmentally friendly solution to remove conventional pollutants, antibiotics, coliforms and antibiotic resistance genes. In recent years, several authors have evaluated the use of microalgal systems for the treatment of different types of wastewater, such as agricultural, municipal, and industrial. Generally, microalgal systems can provide high removal efficiencies of: (i) conventional pollutants, up to 99%, 99%, and 90% of total nitrogen, total phosphorus, and/or organic carbon, respectively, through uptake mechanisms, and (ii) antibiotics frequently found in wastewaters, such as sulfamethoxazole, ciprofloxacin, trimethoprim and azithromycin at 86%, 65%, 42% and 93%, respectively, through the most desirable microalgal mechanism, biodegradation. Although pathogens removal by microalgal species is complex and very strain-specific, it is also possible to attain total coliform and Escherichia coli removal of 99.4% and 98.6%, respectively. However, microalgal systems' effectiveness strongly relies on biotic and abiotic conditions, thus the selection of operational conditions is critical. While the combination of selected species (microalgae and bacteria), ratios and inoculum concentration allow the efficient removal of conventional pollutants and generation of high amounts of biomass (that can be further converted into valuable products such as biofuels and biofertilisers), abiotic factors such as pH, hydraulic retention time, light intensity and CO₂/O₂ supply also have a crucial role in conventional pollutants and antibiotics removal, and wastewater disinfection. However, some rationale must be considered according to the purpose. While alkaline pH induces the hydrolysis of some antibiotics and the removal of faecal coliforms, it also decreases phosphates solubility and induces the formation of ammonium from ammonia. Also, while CO₂ supply increases the removal of E. coli and Pseudomonas aeruginosa, as well as the microalgal growth (and thus the conventional pollutants uptake), it decreases Enterococcus faecalis removal. Therefore, this review aims to provide a critical review of recent studies towards the application of microalgal systems for the efficient removal of conventional pollutants, antibiotics, and pathogens; discussing the feasibility, highlighting the advantages and challenges of the implementation of such process, and presenting current case-studies of different applications of microalgal systems.

Integrating microalgae production into mine closure plans

Examples of successful mine closure and acceptable regional transitioning of mining areas are scarce. The recent changes to the environmental, social and governance (ESG) obligations of mining companies should help to ensure that water and land resources as well as post-mining employment opportunities are considered as a part of mine closure. Integrating microalgae production into mine closure plans is a potential opportunity for mining companies to improve many ESG outcomes. Mine sites with sufficient suitable land and water resources in high solar radiation geographies may be able to economically grow microalgae to capture atmospheric CO₂, re-purpose saline mine waters, treat acidic and near-neutral pH metalliferous waters as well as produce soil ameliorants (biofertiliser, biostimulants and/or biochar) to improve mine rehabilitation outcomes. Microalgae production facilities may also provide an alternative industry and employment opportunities to help transition regional mining towns that have become reliant on mining activities. The potential economic, environmental and social benefits of using mine-influenced water for microalgae production may offer an opportunity to successfully close and transition some mining landscapes.

Biochar production from microalgae: a new sustainable approach to wastewater treatment based on a circular economy

The generation of wastewater due to human activities are the main responsible for environmental problems. These problems are caused by the large amount of organic and inorganic pollutants related to the presence of pesticides, metals, pathogens, drugs and dyes. The photosynthetic treatment of effluents emerges as a sustainable and low-cost alternative for developing wastewater treatment systems based on a circular economy. Chemical compounds present in wastewater can be recovered and reused as a source of nutrients in microalgae cultivation to produce value-added bioproducts. The microalgal biomass produced in the cultivation with effluents has the potential to produce biochar. Biochar is carbon-rich charcoal that can be obtained by converting microalgae biomass through thermal decomposition of organic raw material under limited oxygen supply conditions. Pyrolysis, torrefaction, and hydrothermal carbonization are processes used for biochar synthesis. The application of microalgal biochar as an adsorbent material to remove several compounds present in effluents is an effective and fast treatment. This effectiveness is usually related to the unique physicochemical characteristics of the biochar, such as the presence of functional groups, ion exchange capacity, thermal stability, and high surface area, volume, and pore area. In addition, biochar can be reused in the adsorption process or applied in agriculture for soil correction. In this context, this review article describes the production, characterization, and use of microalgae biochar through a sustainable approach to wastewater treatment, emphasizing its potential in the circular economy. In addition, the article approaches the potential of microalgal biochar as an adsorbent material and its reuse after the adsorption of contaminants, as well as highlights the challenges and future perspectives on this topic.

Single/co-adsorption and mechanism of methylene blue and lead by β-cyclodextrin modified magnetic alginate/biochar

Due to the high biological toxicity, the concurrent elimination of lead (Pb (II)) and methylene blue (MB) has become a challenging problem. Therefore, a newly β-cyclodextrin (β-CD) modified magnetic alginate/biochar (β-CD@MBC_P) material was developed. Comprehensive characterizations proved the successful coating of β-CD onto MBC_P surface by microwave-aided fabrication. The β-CD@MBC_P achieved high-efficiency uptake for contaminants under a wide pH scope. In the dual system, Pb (II) elimination was facilitated with the presence of MB, due to the active sites provided by MB. In the presence of Pb (II), MB uptake was inhibited due to the electrostatic repulsion between positively charged MB and Pb (II). Electrostatic attraction and complexation contributed to capturing Pb (II), while π-π interactions, host-guest effect, and H-bonding were important in MB elimination. After four cycles, β-CD@MBC_P maintained comparatively good renewability. Findings demonstrated that β-CD@MBC_P could be an effective remediation material for Pb (II)/MB adsorption from aqueous environments.

Current application of seaweed waste for composting and biochar: A review

To address the origins of ocean acidification, seaweed aquaculture is emerging as a key biosequestration strategy. Nevertheless, seaweed biomass is involved in developing food and animal feed, whereas seaweed waste from commercial hydrocolloid extraction is dumped in landfills, which together limit the carbon cycle and carbon sequestration. This work sought to evaluate the production, properties, and applications of seaweed compost and biochar to strengthen the "carbon sink" implications of aquaculture sectors. Due to their unique characteristics, the production of seaweed-derived biochar and compost, as well as their existing applications, are distinct when compared to terrestrial biomass. This paper outlines the benefits of composting and biochar production as well as proposes ideas and perspectives to overcome technical shortcomings. If properly synchronized, progression in the aquaculture sector, composting, and biochar production, potentially promote various Sustainable Development Goals.

Recent developments in the production and utilization of photosynthetic microorganisms for food applications

The growing use of photosynthetic microorganisms for food and food-related applications is driving related biotechnology research forward. Increasing consumer acceptance, high sustainability, demand of eco-friendly sources for food, and considerable global economic concern are among the main factors to enhance the focus on the novel foods. In the cases of not toxic strains, photosynthetic microorganisms not only provide a source of sustainable nutrients but are also potentially healthy. Several published studies showed that microalgae are sources of accessible protein and fatty acids. More than 400 manuscripts were published per year in the last 4 years. Furthermore, industrial approaches utilizing these microorganisms are resulting in new jobs and services. This is in line with the global strategy for bioeconomy that aims to support sustainable development of bio-based sectors. Despite the recognized potential of the microalgal biomass value chain, significant knowledge gaps still exist especially regarding their optimized production and utilization. This review highlights the potential of microalgae and cyanobacteria for food and food-related applications as well as their market size. The chosen topics also include advanced production as mixed microbial communities, production of high-value biomolecules, photoproduction of terpenoid flavoring compounds, their utilization for sustainable agriculture, application as source of nutrients in space, and a comparison with heterotrophic microorganisms like yeast to better evaluate their advantages over existing nutrient sources. This comprehensive assessment should stimulate further interest in this highly relevant research topic.

Progress on microalgae cultivation in wastewater for bioremediation and circular bioeconomy

Water usage increased alongside its competitiveness due to its finite amount. Yet, many industries still rely on this finite resource thus recalling the need to recirculate their water for production. Circular bioeconomy is presently the new approach emphasizing on the 'end-of-life' concept with reusing, recycling, and recovering materials. Microalgae are the ideal source contributing to circular bioeconomy as it exhibits fast growth and adaptability supported by biological rigidity which in turn consumes nutrients, making it an ideal and capable bioremediating agent, therefore allowing water re-use as well as its biomass potential in biorefineries. Nevertheless, there are challenges that still need to be addressed with consideration of recent advances in cultivating microalgae in wastewater. This review aimed to investigate the potential of microalgae biomass cultivated in wastewater. More importantly, how it'll play a role in the circular bioeconomy. This includes an in-depth look at the production of goods coming from wastes tattered by emerging pollutants. These emerging pollutants include microplastics, antibiotics, ever-increasingly sewage water, and heavy metals which have not been comprehensively compared and explored. Therefore, this review is aiming to bring new insights to researchers and industrial stakeholders with interest in green alternatives to eventually contribute towards environmental sustainability.

Spirulina platensis Immobilized Alginate Beads for Removal of Pb(II) from Aqueous Solutions

Microalgae contain a diversity of functional groups that can be used as environmental adsorbents. Spirulina platensis is a blue-green microalga that comprises protein-N, which is advantageous for use in nitrogen-containing biomass as adsorbents. This study aimed to enhance the adsorption properties of alginate hydrogels by employing Spirulina platensis. Spirulina platensis was immobilized on sodium alginate (S.P@Ca-SA) via crosslinking. The results of field-emission scanning electron microscopy, Fourier-transform infrared, and X-ray photoelectron spectroscopy analyses of the N-containing functional groups indicated that Spirulina platensis was successfully immobilized on the alginate matrix. We evaluated the effects of pH, concentration, and contact time on Pb(II) adsorption by S.P@Ca-SA. The results demonstrated that S.P@Ca-SA could effectively eliminate Pb(II) at pH 5, reaching equilibrium within 6 h, and the maximum Pb(II) sorption capacity of S.P@Ca-SA was 87.9 mg/g. Our results indicated that S.P@Ca-SA fits well with the pseudo-second-order and Freundlich models. Compared with Spirulina platensis and blank alginate beads, S.P@Ca-SA exhibited an enhanced Pb(II) adsorption efficiency. The correlation implies that the amino groups act as adsorption sites facilitating the elimination of Pb(II).

Enhancement of nutrients removal and biomass accumulation of algal-bacterial symbiosis system by optimizing the concentration and type of carbon source in the treatment of swine digestion effluent

The algae-bacteria symbiosis system (ABS) is used to effectively solve the problems of low carbon/nitrogen (C/N) ratio, low biodegradability and high ammonia toxicity in swine digestion effluent. This study examined the effects of the concentration and type of carbon source on ABS in the pollutants removal especially ammonia. When C/N ratio was 30:1 and carbon source was sodium acetate, the ABS was most conducive to the removal of nitrogen, phosphorus and COD, and to the accumulation of biomass and lipids. To make the wastewater discharge meet the relevant standard, the ABS + mono-cultivation of algae reprocessing system (MAS), was applied to actual swine digestion effluent. Through adjusting the C/N ratio in ABS to 30:1, the biomass concentration was 2.06 times higher than that of raw wastewater, and the removal efficiencies of NH₄⁺-N, TN, TP and COD increased by 1.43, 1.46, 1.95 and 1.28 times, respectively. The final concentrations of NH₄⁺-N, TN, TP and COD after the treatment of ABS (C/N ratio of 30:1) + MAS, were 16.98 ± 1.07 mg L^-1, 18.72 ± 1.81 mg L^-1, 0.48 ± 0.01 mg L^-1 and 263.49 ± 11.89 mg L^-1, respectively, reached the Chinese discharge standards for livestock and poultry wastewater. Bacterial community analysis showed that the dominant species of the ABS (C/N ratio of 30:1) was Corynebacterium (genus level). This study revealed that adjusting the concentration and type of carbon source was helpful to the nutrient cycling and resource utilization of ABS, indicating a feasible technique for treating high ammonia nitrogen digestate.

Composition identification and UV-C irradiation growth inhibition effect of green shading on the greenhouse cover

Greenhouse cover pollution with green shading composed of dust, microalgae and bacteria is a severe problem in tropical areas. The shading results in lower greenhouse indoor light intensity reducing the yield and quality of protected horticulture crops. However, few studies have focused on environmentally efficient ways to remove green shading to increase greenhouse production. In this study, five purified microalgae were isolated from the green shading of three greenhouse roofs and were identified using morphological and molecular assessments. The effects of Ultraviolet-C irradiation (UV-C, 254 nm) at doses of 100, 200 and 300 mJ cm^-2 on the growth of GLY-1 microalgae were investigated. The results indicated that five purified microalgae all appeared to belong to the genus of Jaagichlorella. The purified microalgae cell density and chlorophyll content decreased respectively by 26.89-74.44 % and 42.02-77.31 % at 1-3 d after UV-C treatment with doses ranging from 100 to 300 mJ cm^-2. The inhibition of the growth rate of microalgae was significantly positively correlated with the UV-C irradiation dose and significantly negatively correlated with treatment time. In summary, UV-C irradiation treatment at 300 mJ cm^-2 and 3 d could substantially inhibit microalgae growth in green shading on greenhouse covers. UV-C irradiation could be an effective method for solving the problem of greenhouse cover pollution with microalgae.

Prosopis juliflora Seed Waste as Biochar for the Removal of Blue Methylene: A Thermodynamic and Kinetic Study

In this work, we studied the methylene blue (MB) dye adsorption capacity on biochar derived from residues of Prosopis juliflora seed waste, a species found in the region of the tropical dry forest of Piojó in the Department of Atlántico, Colombia. The materials were obtained by pyrolysis at temperatures of 300, 500, and 700 °C. Biochar was characterized using Fourier transform infrared (FTIR), scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDX), TGA, and Brunauer-Emmett-Teller (BET) techniques. The three biochar samples presented a macroporous, rough structure with pore size between 6 and 28 μm. The largest pore surface area observed was 1.28 m²/g for pyrolyzed biochar produced at 500 °C, larger than that of biochar produced at 700 °C, which was 0.83 m²/g. The adsorption results show that the maximum percentage of MB removal was 69%. According to SEM results, the material's pore sizes varied on average from 6 to 28 μm. We modeled MB adsorption on biomass through three different isotherm models. The Freundlich model was the best-fitting model for the removal of MB (K _F = 1.447; 1/n = 0.352). The kinetic results showed that the pseudo-second-order model was the best-fitting model for the sorption process (q _e = 2.94 mg/g; k ₂ = 0.087 g/(mg/min^-1)). Furthermore, the recycling test showed that the biochar did not change its adsorption capacity significantly. Finally, under the experimental conditions, the thermodynamic parameters indicated that the removal of MB using biochar was an endothermic and spontaneous process; all ΔG° values ranged from -2.14 to -0.95 kJ/mol; ΔH° was 23.54 kJ/mol and ΔS° was 79.5 J/mol.

Recent progress in microalgae-derived biochar for the treatment of textile industry wastewater

Textile industry utilize a massive amount of dyes for coloring. The dye-containing effluent is released into wastewater along with heavy metals that are part of dye structure. The treatment of textile industry wastewater using conventional techniques (coagulation, membrane technique, electrolysis ion exchange, etc.) is uneconomical and less efficient (for a low concentration of pollutants). Moreover, most of these techniques produce toxic sludge, making them less environmentally friendly. Algae base industry is growing for food, cosmetics and energy needs. Algae biomass in unique compared to lignocellulosic biomass due to presence of various functional group on its surface and presence of various cations. These two characteristics are unique for biochar as a tool for environmental decontamination. Algae biomass contain functional groups and cations that can be effective for removal of organic contaminants (dyes) and heavy metals. Algae can be micro and macro and both have entirely different biomass composition which will lead to a synthesis of different biochar even under same synthesis process. This study reviews the recent progress in the development of an economically viable and eco-friendly approach for textile industry wastewater using algae biomass-derived absorbents. The strategy employed microalgal biochar to remove organic pollutants (dyes) and heavy metals from textile effluents by biosorption. This article discusses different methods for preparing algal biochar (pyrolysis, hydrothermal carbonization and torrefaction), and the adsorption capacity of biochar for dyes and heavy metals. Work on hydrothermal carbonization and torrefaction of microalgal biomass for biochar is limited. Variation in structural and functional groups changes on biochar compared to original microalgal biomass are profound in contract with lignocellulosic biomass. Existing Challenges, future goals, and the development of these technologies at the pilot level are also discussed.

Valorization of agriculture waste biomass as biochar: As first-rate biosorbent for remediation of contaminated soil

Each year, Asia produces an estimated 350 million tonnes of agricultural residues. According to Ministry of Power projections, numerous tonnes of such waste are discarded each year, in addition to being used as green manure. The methodology used to convert agricultural waste into the most valuable biochar, as well as its critical physical and chemical properties, were described in this review. This review also investigates the beneficial effects of bio and phytoremediation on metal(lloid)-contaminated soil. Agriculture biomass-based biochar is an intriguing organic residue material with the potential to be used as a responsible solution for metal(lloid) polluted soil remediation and soil improvement. Plants with faster growth and higher biomass can meet massive remediation demands. Recent research shows significant progress in agricultural biomass-based biomass conversion as biochar, as well as understanding the frameworks of metal(lloid) accumulation and mobility in plants used for metal(lloid) polluted soil remediation. Biochar made from various agricultural biomass can promote native plant growth and improve phytoremediation efficiency in polluted soil with metal(lloid)s. This carbon-enriched biochar promotes native microbial activity by neutralising pH and providing adequate nutrition. Thus, this review critically examines the feasibility of converting agricultural waste biomass into biochar, as well as the impact on plant and microbe remediation potential in metal(lloid)s polluted soil.

Immobilization on anionic metal(loid)s in soil by biochar: A meta-analysis assisted by machine learning

Metal pollution in soil has become one of the most serious environmental problems in China. Biochar is one of the most widely used remediation agents for soil metal pollution. However, the literature does not provide a consistent picture of the performance of biochar on the immobilization of anionic metal(loid)s, especially arsenic, in soil. To obtain a baseline understanding on the interactions of metals and biochar, 597 data records on four metal(loid)s (As, Cr, Sb and V) were collected from 70 publications for this meta-analysis, and the results are highlighted below. Biochar has a significant immobilization effect on anionic metal(loid)s in soil and reduces the bioavailability of these metals to plants. Subgroup analysis found that biochar could decrease the potential mobility of Cr, Sb and V, but the immobilization effect on As was not always consistent. Meanwhile, biochar pH and soil pH are the most key factors affecting the immobilization effect. To summarize, biochar can effectively immobilize Cr, Sb and V in soil, but more attention should be given to As immobilization in future applications. By regulating the properties of biochar and appropriate modification, anionic metal(loid)s in soil can be immobilized more effectively. Hence, both of the soil quality and crop quality can be improved.

Hydroxyapatite tailored hierarchical porous biochar composite immobilized Cd(II) and Pb(II) and mitigated their hazardous effects in contaminated water and soil

A novel composite of hydroxyapatite tailored hierarchical porous biochar (HA-HPB) was synthesized and used for the adsorptive immobilization of Cd(II) and Pb(II) in water and soil. The hierarchical porous biochar (HPB) was prepared from rice husk through a molten-salt-assisted pyrolysis approach; then, a series of HA-HPB (with 0.5, 1, 2, 3, and 4 g of HPB) was prepared with co-precipitation procedure. All HA-HPBs, particularly HA-3HPB, revealed significantly higher removal efficiency of Cd(II) and Pb(II) (≥99.5%) in water than pristine biochar (5.79 - 24.12%). The immobilization efficiency of HA-3HPB for Cd(II) and Pb(II) was slightly inhibited by the ionic strength and co-existing cations. The Langmuir adsorption capacities of Cd(II) and Pb(II) were 88.1 and 110.2 mg/g, respectively. Ion exchange, complexation, cation-π interaction, and precipitation were the key mechanisms involved in the immobilization of Cd(II) and Pb(II) using HA-3HPB. The HA-3HPB reduced the availability of soil Cd (63.5 - 87.8%) and Pb (64.6 - 92.9%) compared to the unamended soil, and thus reduced their content in the Chinese cabbage shoots by 69.3 -95.4% for Cd and 66.5 -97.2% for Pb. These findings demonstrate the effectiveness of HA-HPB for remediation of Cd(II) and Pb(II) contaminated water and soil and mitigating the potential risks.

Assisting the carbonization of biowaste with potassium formate to fabricate oxygen-doped porous biochar sorbents for removing organic pollutant from aqueous solution

In contrast to the efforts dedicated to applying porous biochars in environmental remediation, the search for green synthesis methods, which are crucial for industrialized production, is often neglected. Herein, oxygen-doped porous biochars were prepared for the first time by the assisted carbonization of hydrochar with a novel noncorrosive activator, potassium formate, and these biochars displayed a porous structure with large amounts of micropores (surface area: 1242 ∼ 1386 m² g^-1). Interestingly, the biochars contained an abundance of oxygen element (20 ∼ 26%), which formed many functional groups. Through sorption experiments, it was demonstrated that the oxygen-doped porous biochars were excellent sorbents for diethyl phthalate, and maximum sorption quantity reached 453 mg g^-1. Monolayer sorption by pore filling, hydrogen bonding, electrostatic interaction and π-π stacking was the potential mechanism. This finding indicated that potassium formate was promising as an activator to greenly convert biowaste into advanced biochars for removing organic pollutants from aqueous solutions.

Degradation of 4-nonylphenol in marine sediments using calcium peroxide activated by water hyacinth (Eichhornia crassipes)-derived biochar

The contamination of marine sediments by 4-nonylphenol (4-NP) has become a global environmental problem, therefore there are necessaries searching appropriate and sustainable remediation methods for in-situ applications. Herein, water hyacinth [(WH) (Eichhornia crassipes)]-derived metal-free biochar (WHBC) prepared at 300-900 °C was used to promote the calcium peroxide (CP)-mediated remediation of 4-NP-contaminaed sediments. At [CP] = 4.37 × 10^-4 M, [WHBC] = 1.5 g L^-1, and pH = 6.0, the degradation of 4-NP was 77% in 12 h following the pseudo-first order rate law with rate constant (k_obs) of 4.2 × 10^-2 h^-1. The efficient 4-NP degradation performance and reaction mechanisms of the WHBC/CP system was ascribed to the synergy between the reactive species (HO• and ¹O₂) at the WHBC surface on which there were abundant electron-rich carbonyl groups and defects/vacancies in the catalyst structure provides active sites, and the ability of the graphitized carbon framework to act as a medium for electron shuttling. According to microbial community analysis based on amplicon sequence variants, bacteria of the genus Solirubrobacter (Actinobacteria phylum) were dominant in WHBC/CP-treated sediments and were responsible for the biodegradation of 4-NP. The results showed great promise and novelty of the hydroxyl radical-driven carbon advanced oxidation processes (HR-CAOPs) that relies on the value-added utilization of water hyacinth for contaminated sediment remediation in achieving circular bioeconomy.

Enhanced chlortetracycline removal by iron oxide modified spent coffee grounds biochar and persulfate system

Chlortetracycline (CTC) is a tetracycline derivative antibiotic that has been widely used in the livestock industry for prophylactic and therapeutic purposes. Effective measures should be taken to decrease the environmental risks associated with CTC-rich waste. Biochar produced by biomass waste showed great potential for organic contaminants removal by adsorption and catalytic degradation. This study prepared iron oxide-modified coffee grounds biochar (CGF) at different temperatures for enhanced CTC removal by adsorption and degradation. The main mechanism for CTC removal was found to be electrostatic interaction. In addition, pore diffusion, hydrogen bonds, and π-π bonds also contributed to CTC adsorption. Maximum CTC adsorption capacity was 223.63 mg/g for CGF800 (CGF prepared at 800 °C pyrolysis). The free radical content of CGF600 (CFG prepared at 600 °C pyrolysis) was higher than CGF800, and there were no significant advantages in using biochar prepared at a higher temperature for persulfate activation. The ion mass-to-charge ratio (M/z) is used to describe the ratio of mass to charge of an ion or peak, which can infer compound structure. The structure of CTC degradation products was analyzed by UPLC-MS, and the M/z values were determined as 444, 273, and 154. Thus, pyrolysis of coffee grounds at higher temperatures increased CTC adsorption capacity, and CGF can indirectly assist in CTC degradation by persulfate activation.

Trivalent antimony removal using carbonaceous nanomaterial loaded with zero-valent bimetal (iron/copper) and their effect on seed growth

As rapid industrial and social growth, antimony mines are the overexploited, leading to the accumulation of trivalent antimony in the aquatic environment near smelters, which harm human health. To eradicate trivalent antimony from water, an innovative nanomaterial in the form of sludge biochar loaded with zero-valent bimetal was synthesized using a liquid-phase reduction method. The adsorption performance of the nanomaterial for trivalent antimony was investigated based on a series of adsorption experiments using sludge biochar, nano zero-valent iron biochar, and nano zero-valent bimetal biochar. The results showed that the optimal adsorption performance of the three nanomaterials for trivalent antimony, considering the economic practicability, was highlighted at solution pH of 3 and 0.05 g of nanomaterial. Additionally, the maximum adsorption capacity of sludge biochar, nano zero-valent iron biochar, and nano zero-valent bimetal biochar is 3.89 mg g^-1 at 35 °C, 32.01 mg g^-1 at 25 °C, 50.96 mg g^-1 at 25 °C, respectively. The adsorption process of sludge biochar is endothermic, resulting in an increase in the adsorption capacity with increasing temperature, whereas the exothermic reaction contributes to decrease in the adsorption capacity at increasing temperature for the other two carbon nanomaterials. The inhibitory effect of coexisting ions was in the order: Al³⁺ > NH₄⁺ > Na⁺ > K⁺; CO₃^2- > CH₃COO^- > H₂PO₄^- > S^2-. Additionally, nanomaterials promoted seed germination and growth. Investigation of the adsorption mechanism using X-ray photoelectron spectroscopy showed that trivalent antimony was oxidised to pentavalent antimony, and Fe(III) was reduced to Fe(II). The formed primary battery formed by copper ions and iron acclerated electron transfer and improved the adsorption rate. This implied that trivalent antimony could be removed through the synergistic action of the adsorption behaviour and redox reaction. Therefore, the biochar loaded with the zero-valent bimetal serves as a pathway for eradicating trivalent antimony.

Exploring the Adsorption of Pb on Microalgae-Derived Biochar: A Versatile Material for Environmental Remediation and Electroanalytical Applications

Biochar, a carbon material obtained by pyrolysis of biomasses, is increasingly applied in environmental remediation and sensing thanks to its functional properties, cost-effectiveness and eco-friendliness. The adsorption capacity of biochar, strictly dependent on its specific surface area, heteroatom doping and surface functional groups, is crucial for these applications. Here, biochar produced at low temperature (350 °C) from a marine microalga (Nannochloropsis sp.) is proposed as an efficient adsorbent of lead (II) ions in aqueous solution; this production strategy promotes the natural self-doping of biochar without requiring harsh conditions. The kinetics and thermodynamics of the adsorption process, as well as the effect of pH, ionic strength and dissolved organic matter on the adsorption efficiency were systematically assessed. The microalgae-derived biochar shows superior adsorption performances compared to a nutshell-derived one (used as a reference of lignocellulosic feedstocks) under all the tested conditions. The microalgae-derived biochar was finally used to decorate screen-printed carbon electrodes to improve the electroanalytical performances towards the voltammetric detection of lead (II) ions. A two-fold increase in sensitivity was obtained compared to the unmodified electrode thanks to the enhanced electron transfer and adsorption properties provided by biochar. These results highlight the potentialities of microalgae-derived biochar for environmental and sensing applications.

Could termites be hiding a goldmine of obscure yet promising yeasts for energy crisis solutions based on aromatic wastes? A critical state-of-the-art review

Biodiesel is a renewable fuel that can be produced from a range of organic and renewable feedstock including fresh or vegetable oils, animal fats, and oilseed plants. In recent years, the lignin-based aromatic wastes, such as various aromatic waste polymers from agriculture, or organic dye wastewater from textile industry, have attracted much attention in academia, which can be uniquely selected as a potential renewable feedstock for biodiesel product converted by yeast cell factory technology. This current investigation indicated that the highest percentage of lipid accumulation can be achieved as high as 47.25% by an oleaginous yeast strain, Meyerozyma caribbica SSA1654, isolated from a wood-feeding termite gut system, where its synthetic oil conversion ability can reach up to 0.08 (g/l/h) and the fatty acid composition in yeast cells represents over 95% of total fatty acids that are similar to that of vegetable oils. Clearly, the use of oleaginous yeasts, isolated from wood-feeding termites, for synthesizing lipids from aromatics is a clean, efficient, and competitive path to achieve "a sustainable development" towards biodiesel production. However, the lacking of potent oleaginous yeasts to transform lipids from various aromatics, and an unknown metabolic regulation mechanism presented in the natural oleaginous yeast cells are the fundamental challenge we have to face for a potential cell factory development. Under this scope, this review has proposed a novel concept and approach strategy in utilization of oleaginous yeasts as the cell factory to convert aromatic wastes to lipids as the substrate for biodiesel transformation. Therefore, screening robust oleaginous yeast strain(s) from wood-feeding termite gut system with a set of the desirable specific tolerance characteristics is essential. In addition, to reconstruct a desirable metabolic pathway/network to maximize the lipid transformation and accumulation rate from the aromatic wastes with the applications of various "omics" technologies or a synthetic biology approach, where the work agenda will also include to analyze the genome characteristics, to develop a new base mutation gene editing technology, as well as to clarify the influence of the insertion position of aromatic compounds and other biosynthetic pathways in the industrial chassis genome on the expressional level and genome stability. With these unique designs running with a set of the advanced biotech approaches, a novel metabolic pathway using robust oleaginous yeast developed as a cell factory concept can be potentially constructed, integrated and optimized, suggesting that the hypothesis we proposed in utilizing aromatic wastes as a feedstock towards biodiesel product is technically promising and potentially applicable in the near future.

Insights into the highly efficient treatment of dyeing wastewater using algal bloom derived activated carbon with wide-range adaptability to solution pH and temperature

Here, a low-cost acid-base and temperature tolerant algal bloom derived activated carbon (ABAC) was successfully prepared to remove rhodamine B (RhB) from water. The ABAC exhibited maximum adsorption capacity of RhB (1101 ± 11 mg/g), higher than that of laboratory-prepared rape straw activated carbon (176 ± 5 mg/g) and commercial activated carbon (489 ± 5 mg/g). It is attributed to larger surface area and mesoporous structure of the ABAC. Furthermore, the effective adsorption of RhB by using ABAC was achieved at a wide range of solution pH (3.2-10.8) and temperature(25-50 °C). The mass transfer resistance of RhB adsorption process well depicted by Langmuir model was controlled by external mass transfer. The adsorption process involved both secondly chemisorption (H-bonds and π-π interaction) and dominated physisorption. Four dyes in river water were efficiently removed. This work provides a promising approach for developing high-absorption biomass materials for actual dye wastewater treatment.

Insights into the microalgae-bacteria consortia treating swine wastewater: Symbiotic mechanism and resistance genes analysis

This study investigated the effects of microalgae-bacteria consortia (MBC) (Chlorella pyrenoidosa-activated sludge (AS)) treating swine wastewater with low C/N ratios. After co-culture, the removal rates of NH₄⁺-N and PO₄^3--P increased by 53.84% and 43.52%. Furthermore, the sulfamethoxazole (SMX) degradation rates in MBC were slightly higher than in the activated sludge process. Interestingly, the absolute abundance of antibiotic resistance genes (ARGs) in effluent from MBC is relatively less than in the AS process. C. pyrenoidosa has a negative zeta potential that allows bacteria to adhere to its surface. The concentrations of carbohydrates and proteins in extracellular polymeric substance (EPS) of MBC dramatically increased compared with the AS process. At the phylum level, Proteobacteria, Bacteroidota, and Cyanobacteria were the main bacteria, while Ascomycota and Basidiomycota were the primary fungi in MBC. Overall, those findings lead to a better understanding of the swine wastewater containing antibiotic treatment by MBC.

Recent Developments in the Application of Bio-Waste-Derived Adsorbents for the Removal of Methylene Blue from Wastewater: A Review

Over the last few years, various industries have released wastewater containing high concentrations of dyes straight into the ecological system, which has become a major environmental problem (i.e., soil, groundwater, surface water pollution, etc.). The rapid growth of textile industries has created an alarming situation in which further deterioration to the environment has been caused due to substances being left in treated wastewater, including dyes. The application of activated carbon has recently been demonstrated to be a highly efficient technology in terms of removing methylene blue (MB) from wastewater. Agricultural waste, as well as animal-based and wood products, are excellent sources of bio-waste for MB remediation since they are extremely efficient, have high sorption capacities, and are renewable sources. Despite the fact that commercial activated carbon is a favored adsorbent for dye elimination, its extensive application is restricted because of its comparatively high cost, which has prompted researchers to investigate alternative sources of adsorbents that are non-conventional and more economical. The goal of this review article was to critically evaluate the accessible information on the characteristics of bio-waste-derived adsorbents for MB's removal, as well as related parameters influencing the performance of this process. The review also highlighted the processing methods developed in previous studies. Regeneration processes, economic challenges, and the valorization of post-sorption materials were also discussed. This review is beneficial in terms of understanding recent advances in the status of biowaste-derived adsorbents, highlighting the accelerating need for the development of low-cost adsorbents and functioning as a precursor for large-scale system optimization.

Cultivation and Biorefinery of Microalgae (Chlorella sp.) for Producing Biofuels and Other Byproducts: A Review

Microalgae-based carbon dioxide (CO2) biofixation and biorefinery are the most efficient methods of biological CO2 reduction and reutilization. The diversification and high-value byproducts of microalgal biomass, known as microalgae-based biorefinery, are considered the most promising platforms for the sustainable development of energy and the environment, in addition to the improvement and integration of microalgal cultivation, scale-up, harvest, and extraction technologies. In this review, the factors influencing CO2 biofixation by microalgae, including microalgal strains, flue gas, wastewater, light, pH, temperature, and microalgae cultivation systems are summarized. Moreover, the biorefinery of Chlorella biomass for producing biofuels and its byproducts, such as fine chemicals, feed additives, and high-value products, are also discussed. The technical and economic assessments (TEAs) and life cycle assessments (LCAs) are introduced to evaluate the sustainability of microalgae CO2 fixation technology. This review provides detailed insights on the adjusted factors of microalgal cultivation to establish sustainable biological CO2 fixation technology, and the diversified applications of microalgal biomass in biorefinery. The economic and environmental sustainability, and the limitations and needs of microalgal CO2 fixation, are discussed. Finally, future research directions are provided for CO2 reduction by microalgae.