Optimum conditions of pH, temperature and preculture for biosorption of europium by microalgae Acutodesmus acuminatus

Microbial recovery of rare earth elements from various waste sources: a mini review with emphasis on microalgae

Rare Earth Elements (REEs) are indispensable in contemporary technologies, influencing various aspects of our daily lives and environmental solutions. The escalating demand for REEs has led to increased exploitation, resulting in the generation of diverse REE-bearing solid and liquid wastes. Recognizing the potential of these wastes as secondary sources of REEs, researchers are exploring microbial solutions for their recovery. This mini review provides insights into the utilization of microorganisms, with a particular focus on microalgae, for recovering REEs from sources such as ores, electronic waste, and industrial effluents. The review outlines the principles and distinctions of bioleaching, biosorption, and bioaccumulation, offering a comparative analysis of their potential and limitations. Specific examples of microorganisms demonstrating efficacy in REE recovery are highlighted, accompanied by successful methods, including advanced techniques for enhancing microbial strains to achieve higher REE recovery. Moreover, the review explores the environmental implications of bio-recovery, discussing the potential of these methods to mitigate REE pollution. By emphasizing microalgae as promising biotechnological candidates for REE recovery, this mini review not only presents current advances but also illuminates prospects in sustainable REE resource management and environmental remediation.

Cellular Response of Adapted and Non-Adapted Tetrahymena thermophila Strains to Europium Eu(III) Compounds

Europium is one of the most reactive lanthanides and humans use it in many different applications, but we still know little about its potential toxicity and cellular response to its exposure. Two strains of the eukaryotic microorganism model Tetrahymena thermophila were adapted to high concentrations of two Eu(III) compounds (EuCl3 or Eu2O3) and compared to a control strain and cultures treated with both compounds. In this ciliate, EuCl3 is more toxic than Eu2O3. LC50 values show that this microorganism is more resistant to these Eu(III) compounds than other microorganisms. Oxidative stress originated mainly by Eu2O3 is minimized by overexpression of genes encoding important antioxidant enzymes. The overexpression of metallothionein genes under treatment with Eu(III) compounds supports the possibility that this lanthanide may interact with the -SH groups of the cysteine residues from metallothioneins and/or displace essential cations of these proteins during their homeostatic function. Both lipid metabolism (lipid droplets fusing with europium-containing vacuoles) and autophagy are involved in the cellular response to europium stress. Bioaccumulation, together with a possible biomineralization to europium phosphate, seems to be the main mechanism of Eu(III) detoxification in these cells.

Harnessing the potential of microalgae-based systems for mitigating pesticide pollution and its impact on their metabolism

Due to increased pesticide usage in agriculture, a significant concentration of pesticides is reported in the environment that can directly impact humans, aquatic flora, and fauna. Utilizing microalgae-based systems for pesticide removal is becoming more popular because of their environmentally friendly nature, ability to degrade pesticide molecules into simpler, nontoxic molecules, and cost-effectiveness of the technology. Thus, this review focused on the efficiency, mechanisms, and factors governing pesticide removal using microalgae-based systems and their effect on microalgal metabolism. A wide range of pesticides, like atrazine, cypermethrin, malathion, trichlorfon, thiacloprid, etc., can be effectively removed by different microalgal strains. Some species of Chlorella, Chlamydomonas, Scenedesmus, Nostoc, etc., are documented for >90% removal of different pesticides, mainly through the biodegradation mechanism. The antioxidant enzymes such as ascorbate peroxidase, superoxide dismutase, and catalase, as well as the complex structure of microalgae cell walls, are mainly involved in eliminating pesticides and are also crucial for the defense mechanism of microalgae against reactive oxygen species. However, higher pesticide concentrations may alter the biochemical composition and gene expression associated with microalgal growth and metabolism, which may vary depending on the type of strain, the pesticide type, and the concentration. The final section of this review discussed the challenges and prospects of how microalgae can become a successful tool to remediate pesticides.

Microalgae: A potential bioagent for treatment of emerging contaminants from domestic wastewater

Water crisis around the world leads to a growing interest in emerging contaminants (ECs) that can affect human health and the environment. Research showed that thousands of compounds from domestic consumers, such as endocrine disrupting chemicals (EDCs), personal care products (PCPs), and pharmaceuticals active compounds (PhAcs), could be found in wastewater in concentration mostly from ng L-1 to μg L-1. However, generally, wastewater treatment plants (WWTPs) are not designed to remove these ECs from wastewater to their discharge levels. Scientists are looking for economically feasible biotreatment options enabling the complete removal of ECs before discharge. Microalgae cultivation in domestic wastewater is likely a feasible approach for removing emerging contaminants and simultaneously removing any residual organic nutrients. Microalgal growth rate and contaminants removal efficiency could be affected by various factors, including light intensity, CO2 addition, presence of different nutrients, etc., and these parameters could greatly help make microalgae treatment more efficient. Furthermore, the algal biomass harvests could be repurposed to produce various bulk chemicals such as sustainable aviation fuel, biofuel, bioplastic, and biochar; this could significantly enhance the economic viability. Therefore, this review summarizes the microalgae-based bioprocess and their mechanisms for removing different ECs from different wastewaters and highlights the different strategies to improve the ECs removal efficiency. Furthermore, this review shows the role of different ECs in biomass profile and the relevance of using ECs-treated microalgae biomass to produce green products, as well as highlights the challenges and future research recommendations.

Biomining for sustainable recovery of rare earth elements from mining waste: A comprehensive review

Rare earth elements (REEs) are essential for advanced manufacturing (e.g., renewable energy, military equipment, electric vehicles); hence, the recovery of REEs from low-grade resources has become increasingly important to address their growing demand. Depending on specific mining sites, its geological conditions, and sociodemographic backgrounds, mining waste has been identified as a source of REEs in various concentrations and abundance. Yttrium, cerium, and neodymium are the most common REEs in mining waste streams (50 to 300 μg/L). Biomining has emerged as a viable option for REEs recovery due to its reduced environmental impact, along with reduced capital investment compared to traditional recovery methods. This paper aims to review (i) the characteristics of mining waste as a low-grade REEs resource, (ii) the key operating principles of biomining technologies for REEs recovery, (iii) the effects of operating conditions and matrix on REEs recovery, and (iv) the sustainability of REEs recovery through biomining technologies. Six types of biomining will be examined in this review: bioleaching, bioweathering, biosorption, bioaccumulation, bioprecipitation and bioflotation. Based on a SWOT analyses and techno-economic assessments (TEA), biomining technologies have been found to be effective and efficient in recovering REEs from low-grade sources. Through TEA, coal ash has been shown to return the highest profit amongst mining waste streams.

An integration of algae-mediated wastewater treatment and resource recovery through anaerobic digestion

Eutrophication is one of the major emerging challenges in aquatic environment. Industrial facilities, including food, textile, leather, and paper, generate a significant amount of wastewater during their manufacturing process. Discharge of nutrient-rich industrial effluent into aquatic systems causes eutrophication, eventually disturbs the aquatic system. On the other hand, algae provide a sustainable approach to treat wastewater, while the resultant biomass may be used to produce biofuel and other valuable products such as biofertilizers. This review aims to provide new insight into the application of algal bloom biomass for biogas and biofertilizer production. The literature review suggests that algae can treat all types of wastewater (high strength, low strength, and industrial). However, algal growth and remediation potential mainly depend on growth media composition and operation conditions such as light intensity, wavelength, light/dark cycle, temperature, pH, and mixing. Further, the open pond raceways are cost-effective compared to closed photobioreactors, thus commercially applied for biomass generation. Additionally, converting wastewater-grown algal biomass into methane-rich biogas through anaerobic digestion seems appealing. Environmental factors such as substrate, inoculum-to-substrate ratio, pH, temperature, organic loading rate, hydraulic retention time, and carbon/nitrogen ratio significantly impact the anaerobic digestion process and biogas production. Overall, further pilot-scale studies are required to warrant the real-world applicability of the closed-loop phycoremediation coupled biofuel production technology.

Heavy metal tolerance in microalgae: Detoxification mechanisms and applications

The proficiency of microalgae to resist heavy metals has potential to be beneficial in resolving various environmental challenges. Global situations such as the need for cost-effective and ecological ways of remediation of contaminated water and for the development of bioenergy sources could employ microalgae. In a medium with the presence of heavy metals, microalgae utilize different mechanisms to uptake the metal and further detoxify it. Biosorption and the next process of bioaccumulation are two such major steps and they also include the assistance of different transporters at different stages of heavy metal tolerance. This capability has also proved to be efficient in eradicating many heavy metals like Chromium, Copper, Lead, Arsenic, Mercury, Nickel and Cadmium from the environment they are present in. This indicates the possibility of the application of microalgae as a biological way of remediating contaminated water. Heavy metal resistance quality also allows various microalgal species to contribute in the generation of biofuels like biodiesel and biohydrogen. Many research works have also explored the capacity of microalgae in nanotechnology for the formation of nanoparticles due to its relevant characteristics. Various studies have also revealed that biochar deduced from microalgae or a combination of biochar and microalgae can have wide applications specially in deprivation of heavy metals from an environment. This review focuses on the strategies adopted by microalgae, various transporters involved in the process of tolerating heavy metals and the applications where microalgae can participate owing to its ability to resist metals.

Bioimmobilization and transformation of chromium and cadmium in the fungi-microalgae symbiotic system

Microalgae and fungi in the fungi-microalgae symbiotic system(FMSS) can solve the problems of deep purification of heavy metals in wastewater and harvesting of microalgae cell by synergistic interaction. Therefore, it is of great significance to use the FMSS for remediation of heavy metal pollution. However, at present, the immobilization and transformation mechanism of heavy metals in the FMSS is not clear, which limits the development and industrial application of the FMSS with high adsorption performance, high selectivity, and high tolerance. In this study, the FMSS constructed using Aspergillus funigatus and Synechocystis sp. PCC6803, was used as the research object to explore heavy metal adsorption performance. Under optimal conditions, the adsorption efficiencies of Cd(II) and Cr(VI) were as high as 90.02% and 80.03%, respectively. The adsorption process was controlled by both internal and external diffusion. Extracellular absorption was dominant, and intracellular absorption was secondary. XRD, XPS, SEM-EDX and TEM-EDX results revealed that ionic crystals and precipitates (Cd(OH)₂, CdCO₃, calcium oxalate crystals, Cr(OH)₃, Cr₂O₃, and CrCl₃) were formed after adsorption. The adsorption of Cr(VI) involved the reduction of Cr(VI). Functional groups, such as amino, carboxyl, aldehyde, and ether groups, on the cell surface also interact with heavy metal ions. To summarize, by constructing the FMSS, optimizing the symbiosis conditions, exploring the adsorption and accumulation rules of Cd(II) and Cr(VI) inside and outside the cells in the system, and revealing the molecular response mechanism, we were able to establish a theoretical basis for further understanding the interaction between the FMSS and heavy metals.

Microalgae-based wastewater treatment: Mechanisms, challenges, recent advances, and future prospects

The rapid expansion of both the global economy and the human population has led to a shortage of water resources suitable for direct human consumption. As a result, water remediation will inexorably become the primary focus on a global scale. Microalgae can be grown in various types of wastewaters (WW). They have a high potential to remove contaminants from the effluents of industries and urban areas. This review focuses on recent advances on WW remediation through microalgae cultivation. Attention has already been paid to microalgae-based wastewater treatment (WWT) due to its low energy requirements, the strong ability of microalgae to thrive under diverse environmental conditions, and the potential to transform WW nutrients into high-value compounds. It turned out that microalgae-based WWT is an economical and sustainable solution. Moreover, different types of toxins are removed by microalgae through biosorption, bioaccumulation, and biodegradation processes. Examples are toxins from agricultural runoffs and textile and pharmaceutical industrial effluents. Microalgae have the potential to mitigate carbon dioxide and make use of the micronutrients that are present in the effluents. This review paper highlights the application of microalgae in WW remediation and the remediation of diverse types of pollutants commonly present in WW through different mechanisms, simultaneous resource recovery, and efficient microalgae-based co-culturing systems along with bottlenecks and prospects.

Biosorption and Bioaccumulation Capacity of Arthospiraplatensis toward Europium Ions

Europium recovery from wastewater is determined by its high significance for industry and toxicity for living organisms. The capacity of cyanobacteria Arthospira platensis (Spirulina) to remove Eu(III) through biosorption and bioaccumulation was evaluated. In biosorption experiments, the effects of four variables pH, metal concentration, time, and temperature on metal removal were studied. In bioaccumulation experiments, the effect of Eu(III) concentrations on biomass bioaccumulation capacity and biochemical composition was assessed. The efficiency of Eu(III) uptake in both experiments was determined using ICP-AES techniques. Maximum biosorption of Eu(III) was achieved at pH 3.0. Equilibrium data fitted well with the Langmuir and Freundlich models, with maximum adsorption capacity of 89.5 mg/g. The pseudo-first-, pseudo-second-order, and Elovich models were found to correlate well with the experimental data. According to thermodynamic studies the sorption was feasible, spontaneous, and endothermic in nature. At addition of Eu(III) ions in the cultivation medium in concentrations of 10–30 mg/L, its accumulation in biomass was 9.8–29.8 mg/g (removal efficiency constituting 98–99%). Eu(III) did not affect productivity and content of carbohydrates and pigments in biomass but led to the decrease of the content of protein and an increase in the amount of MDA. The high Eu(III) biosorption and bioaccumulation efficiency of Arthrospira platensis may constitute an effective and eco-friendly strategy to recover it from contaminated environment.

Pharmaceuticals in the Aquatic Environment: A Review on Eco-Toxicology and the Remediation Potential of Algae

The pollution of the aquatic environment has become a worldwide problem. The widespread use of pesticides, heavy metals and pharmaceuticals through anthropogenic activities has increased the emission of such contaminants into wastewater. Pharmaceuticals constitute a significant class of aquatic contaminants and can seriously threaten the health of non-target organisms. No strict legal regulations on the consumption and release of pharmaceuticals into water bodies have been implemented on a global scale. Different conventional wastewater treatments are not well-designed to remove emerging contaminants from wastewater with high efficiency. Therefore, particular attention has been paid to the phycoremediation technique, which seems to be a promising choice as a low-cost and environment-friendly wastewater treatment. This technique uses macro- or micro-algae for the removal or biotransformation of pollutants and is constantly being developed to cope with the issue of wastewater contamination. The aims of this review are: (i) to examine the occurrence of pharmaceuticals in water, and their toxicity on non-target organisms and to describe the inefficient conventional wastewater treatments; (ii) present cost-efficient algal-based techniques of contamination removal; (iii) to characterize types of algae cultivation systems; and (iv) to describe the challenges and advantages of phycoremediation.

Mitigation of tannery effluent with simultaneous generation of bioenergy using dual chambered microbial fuel cell

In this study, a dual chambered microbial fuel cell (MFC) was fabricated for the treatment of tannery wastewater with concurrent production of bio-energy. The tannery effluent acts as an anolyte and a synthetic electrolytic solution as the catholyte. Five electrochemically active bacteria from the biofilm were isolated that showed homology with Klebsiella quasipneumoniae, Klebsiella pneumoniae, Cloacibacterium normanese, Bacillus firmus and Pseudomonas reactans, using 16S rDNA analysis. The physiochemical studies of treated wastewater showcased the 88%, 74% and 94% reduction in COD, BOD and TDS level, respectively. The maximum voltage output and power density obtained using electroactive consortium in MFC was 940 mV and 7371 mW/cm³, respectively. The techno-economic feasibility of the bio-electrochemical system was studied for future bioprospecting. The present study reports a significant power generation with simultaneous effluent treatment up to a maximum of ∼85%, in a sustainable and eco-friendly manner.

E-waste mining and the transition toward a bio-based economy: The case of lamp phosphor powder

Abstract

Replacement of conventional hydrometallurgical and pyrometallurgical process used in E-waste recycling to recover metals can be possible.

The metallurgical industry has been considered biohydrometallurgical-based technologies for E-waste recycling.

Biorecovery of critical metals from phosphor powder from spent lamps is an example of transition to a bio-based circular economy.

E-waste contains economically significant levels of precious, critical metals and rare-earth elements (REE), apart from base metals and other toxic compounds. Recycling and recovery of critical elements from E-waste using a cost-effective technology are now among the top priorities in metallurgy due to the rapid depletion of their natural resources. This paper focuses on the perceptions of recovery of REE from phosphor powder from spent fluorescent lamps regarding a possible transition toward a bio-based economy. An overview of the worldwide E-waste and REE is also demonstrated to reinforce the arguments for the importance of E-waste as a secondary source of some critical metals. Based on the use of bioprocesses, we argue that the replacement of conventional steps used in E-waste recycling by bio-based technological processes can be possible. The bio-recycling of E-waste follows a typical sequence of industrial processes intensely used in classic pyro- and hydrometallurgy with the addition of bio-hydrometallurgical processes such as bioleaching and biosorption. We use the case study of REE biosorption as a new technology based on biological principles to exemplify the potential of urban biomining. The perspective of transition between conventional processes for the recovery of valuable metals for biohydrometallurgy defines which issues related to urban mining can influence the mineral bioeconomy. This assessment is necessary to outline future directions for sustainable recycling development to achieve United Nations Sustainable Development Goals.

Graphical Abstract

Bio-energy generation and treatment of tannery effluent using microbial fuel cell

In this study, Graphite Particle (GP) and Carbon Cloth (CC) are employed as anode electrodes to study both bio-energy generation, and decrease of Chemical Oxygen Demand (COD) simultaneously using tannery effluent. The influence of electrodes distance (10 cm and 20 cm) on electricity production was evaluated. COD removal level of GP (75%) and CC (60%), maximum power outputs for 10 cm distance (600 ± 5 mW m^-2) & (500 ± 10 mW m^-2) and for 20 cm distance (520 ± 5 mW m^-2) and also (430 ± 20 mW m^-2) GP and CC were noted correspondingly. The outcomes of different parameters of MFC namely pH, conductivity, COD concentration, membrane thickness and size of bio-energy generation from tannery effluent in the MFC were investigated. The experimental results reveal that electrode provides highest power output with 10 cm distance between anode and cathode chamber. As a result, GP electrode is gradually viable, biocompatible, effective and adaptable for field application in MFC. The GP electrode has high potential for more power output, when compared to the CC electrode. The MFC system performance was improved with increasing effluent COD concentration (2340-4720 ppm), anolyte conductivity (1.6-8.1 mS cm^-1) and membrane area (9-20 cm²). The system working with conductivity of 8.1 mS cm^-1 and its effluent COD concentration of 4720 ppm generated the maximum peak power density of 44.69 mW m^-2 with respective current density of 109 mA m^-2. The findings thus show that considerable power production and effluent treatment can be achieved by MFC.

Potential application of thermophilic bacterium Aeribacillus pallidus MRP280 for lead removal from aqueous solution

Bacteria used for application of lead (Pb) removal is usually kept under suboptimal growth conditions. Certain application of Pb removal may be carried out under different condition, such as under aqueous and high temperature conditions. It is, therefore, of interest to examine the Pb removal capacity of the bacteria under adverse environmental conditions. In the present study, Aeribacillus pallidus MRP280, a lead-tolerant thermophilic bacterium was used as an absorbent for the removal of Pb from aqueous solution. The Pb removal and uptake capacity of living and non-living bacterial cells of A. pallidus MRP280 was investigated in 100 mg/L Pb solution. The optimum condition was examined based on several analytical parameters, including temperature, pH, contact time, and cell density. Biosorbent analysis and characterization was carried out using Fourier Transform Infrared (FT-IR) spectroscopy, Scanning Electron Microscope (SEM)-Energy Dispersive X-ray (EDX), and Transmission Electron Microscope (TEM). The results showed that the maximum Pb removal of 96.78 ± 0.19% and 88.64 ± 0.60% were obtained using living and non-living biomass, respectively at 55 °C, pH 6, OD₆₀₀0.5 for 100 min. Meanwhile, the maximum uptake capacity of 86.47 ± 1.32 mg/g and 85.31 ± 1.37 mg/g by living and non-living cells was reached at 55 °C, pH 6, OD₆₀₀0.25 for 60 min. Moreover, Pb removing activity was facilitated by the biosorption and bioaccumulation process. Overall, it is shown that A. pallidus MRP280 is effective when applied as biosorbent in removing Pb from contaminated wastewater at high temperatures.

Kinetics and equilibrium study for the biosorption of lanthanum by Penicillium simplicissimum INCQS 40,211

Lanthanum (La) is a light rare-earth element that plays an essential role in manufacturing technological products, clean technologies, medical products, electron cathodes, scintillators, fluorescent lamps, and fertilizers. This study is the first investigation of La³⁺ biosorption using inactive lyophilized biomass from Penicillium simplicissimum INCQS 40,211. The maximum sorption capacity (q_max) for P. simplicissimum was 7.81 mg g^-1. La ³⁺ biosorption followed the Freundlich model, where the biosorption system possibly multilayer coverage of P. simplicissimum by lanthanum ions. The kinetic data for the adsorption process obeyed a pseudo-second-order (R ² > 0.92), indicating chemical sorption. The results indicated that inactive lyophilized biomass from Penicillium simplicissimum INCQS 40211are an excellent candidate for removing light rare-earth elements from aquatic environments.

Efficient removal of phenol compounds from water environment using Ziziphus leaves adsorbent

Industrial processes generate toxic organic molecules that pollute environment water. Phenol and its derivative are classified among the major pollutant compounds found in water. They are naturally found in some industrial wastewater effluents. The removal of phenol compounds is therefore essential because they are responsible for severe organ damage if they exist above certain limits. In this study, ground Ziziphus leaves were utilized as adsorbents for phenolic compounds from synthetic wastewater samples. Several experiments were performed to study the effect of several conditions on the capacity of the Ziziphus leaves adsorbent, namely: the initial phenol concentration, the adsorbent concentration, temperature, pH value, and the presence of foreign salts (NaCl and KCl). The experimental results indicated that the adsorption process reached equilibrium in about 4 h. A drop in the amount of phenol removal, especially at higher initial concentration, was noticed upon increasing the temperature from 25 to 45 °C. This reflects the exothermic nature of the adsorption process. This was also confirmed by the calculated negative enthalpy of adsorption (-64.8 kJ/mol). A pH of 6 was found to be the optimum value at which the highest phenol removal occurred with around 15 mg/g at 25 °C for an initial concentration of 200 ppm. The presence of foreign salts has negatively affected the phenol adsorption process. The fitting of the experimental data, using different adsorption isotherms, indicated that the Harkins-Jura isotherm model was the best fit, evident by the high square of the correlation coefficient (R²) values greater than 0.96. The kinetic study revealed that the adsorption was represented by a pseudo-second-order reaction. The results of this study offer a basis to use Ziziphus leaves as promising adsorbents for efficient phenol removal from wastewater.

Prospects of Microalgae for Biomaterial Production and Environmental Applications at Biorefineries

Microalgae are increasingly viewed as renewable biological resources for a wide range of chemical compounds that can be used as or transformed into biomaterials through biorefining to foster the bioeconomy of the future. Besides the well-established biofuel potential of microalgae, key microalgal bioactive compounds, such as lipids, proteins, polysaccharides, pigments, vitamins, and polyphenols, possess a wide range of biomedical and nutritional attributes. Hence, microalgae can find value-added applications in the nutraceutical, pharmaceutical, cosmetics, personal care, animal food, and agricultural industries. Microalgal biomass can be processed into biomaterials for use in dyes, paints, bioplastics, biopolymers, and nanoparticles, or as hydrochar and biochar in solid fuel cells and soil amendments. Equally important is the use of microalgae in environmental applications, where they can serve in heavy metal bioremediation, wastewater treatment, and carbon sequestration thanks to their nutrient uptake and adsorptive properties. The present article provides a comprehensive review of microalgae specifically focused on biomaterial production and environmental applications in an effort to assess their current status and spur further deployment into the commercial arena.

Tertiary treatment (Chlorella sp.) of a mixed effluent from two secondary treatments (immobilized recombinant P. pastori and rPOXA 1B concentrate) of coloured laboratory wastewater (CLWW)

Industrial development has increased wastewater (WW) volume; generating contamination and disturbing ecosystems, because of breeching disposal parameters. In this work, Coloured Laboratory Wastewater (CLWW), (1500.00 colour units, CU) was separately submitted to two secondary treatments. For the first one CLWW was treated for three cycles C1, C2 and C3 with P. pastoris X33/pGAPZαA-LaccPost-Stop producing rPOXA 1B laccase, immobilized in calcium alginate beads. For the second-one, rPOXA 1B enzyme concentrate was used (three processes: P1, P2, and P3). Both treatments were carried out in a 15 L reactor with 10 L effective work volume (EWV) with 72 h hydraulic retention time. C1, C2, and C3 effluents were flocculated and filtered through quartzite sand, while P1, P2, and P3 effluents were only filtered through quartzite sand. The mixture of secondary effluents was submitted to a tertiary treatment with Chlorella sp. For C1, C2, C3, P1, P2, and P3, CU removal was of 99.16, 99.58, 99.53, 96.72, 97.05 and 96.47%, respectively. Discharge parameters, total organic carbon (TOC), inorganic carbon (IC), chemical oxygen demand (COD) and biological oxygen demand (BOD₅) decreased, although they reached different final values. After the tertiary treatment (144 h) effluent discharge parameters were reduced to 34 ± 4 CU, TOC to 6.6 ± 0.9 mg L^-1 and COD to 155 ± 4 mg L^-1. It was demonstrated that secondary treatments (immobilized recombined cells or recombinant enzyme concentrate) combined with Chlorella sp., (tertiary treatment) attained a considerable removal of discharge parameters, demonstrating a promissory alternative for CLWW sequential treatment.

Sustainable Iron Recovery and Biodiesel Yield by Acid-Adapted Microalgae, Desmodesmus sp. MAS1 and Heterochlorella sp. MAS3, Grown in Synthetic Acid Mine Drainage

Sustainable resource recovery is the key to manage the overburden of various waste entities of mining practices. The present study demonstrates for the first time a novel approach for iron recovery and biodiesel yield from two acid-adapted microalgae, Desmodesmus sp. MAS1 and Heterochlorella sp. MAS3, grown in synthetic acid mine drainage (SAMD). Virtually, there was no difference in the growth of the strain MAS3 both in Bold's basal medium (control) and SAMD. Using the IC50 level (200 mg L-1) and a lower concentration (50 mg L-1) of iron in SAMD, the cell granularity, exopolysaccharide (EPS) secretion, iron recovery, and biodiesel were assessed in both the strains. Both cell granularity and accumulation of EPS were significantly altered under metal stress in SAMD, resulting in an increase in total accumulation of iron. Growth of the microalgal strains in SAMD yielded 12-20% biodiesel, with no traces of heavy metals, from the biomass. The entire amount of iron, accumulated intracellularly, was recovered in the residual biomass. Our results on the ability of the acid-adapted microalgal strains in iron recovery and yield of biodiesel when grown in SAMD indicate that they could be the potential candidates for use in bioremediation of extreme habitats like AMD.

Recent advances in the recovery of metals from waste through biological processes

Wastes containing critical metals are generated in various fields, such as energy and computer manufacturing. Metal-bearing wastes are considered as secondary sources of critical metals. The conventional physicochemical methods of metals recovery are energy-intensive and cause further pollution. Low-cost and eco-friendly technologies including biosorbents, bioelectrochemical systems (BESs), bioleaching, and biomineralization, have become alternatives in the recovery of critical metals. However, a relatively low recovery rate and selectivity severely hinder their large-scale applications. Researchers have expanded their focus to exploit novel strain resources and strategies to improve the biorecovery efficiency. The mechanisms and potential applicability of modified biological techniques for improving the recovery of critical metals need more attention. Hence, this review summarize and compare the strategies that have been developed for critical metals recovery, and provides useful insights for energy-efficient recovery of critical metals in future industrial applications.