Phycoremediation of wastewater for pollutant removal: A green approach to environmental protection and long-term remediation

A comparative study on the treatment of kitchen grey water using microalgae consortia and microalgae-synthesized silver nanoparticles

Comparative study on the potential of microalgae consortia and green-synthesized silver nanoparticles using microalgae (M-AgNP) consortia for the treatment of kitchen grey water was investigated in this study. The microalgae consortia consisting of four species, viz., Chlorella sp., Scenedesmus sp., Coelastrum sp., and Pediastrum sp. were isolated from a local fish pond and the silver nanoparticles were synthesized with the same. Thus, synthesized silver nanoparticles exhibited a distinctive yellowish-brown colour and spherical morphology. Extensive qualitative and quantitative characterization techniques were employed to determine their size and morphology. Both microalgae consortia and M-AgNP were used separately for the treatment of kitchen grey water under experimental conditions. The synthesized silver nanoparticles demonstrated promising potential for domestic wastewater treatment, leading to substantial reductions in various parameters: total dissolved solids (29.6%), conductivity (49.4%), chemical oxygen demand (64.6%), and heavy metals (arsenic-63.5%, zinc-45.6%, cadmium-88%, copper-60.52%, and lead-80.82%). Notably, microalgae exhibited superior removal efficiency for nitrate (83.1%), sulphate (70.3%), and phosphate (96.5%) compared to microalgae-synthesized silver nanoparticles. This study underscores the effective utilization of both microalgae and microalgae-synthesized silver nanoparticles for wastewater treatment applications.

Is Cladophora fracta an efficient tool of accumulating critical raw materials from wastewater and there a potential health risk of use of algae as organic fertilizer?

 In this study investigation of accumulations of critical raw materials (cobalt (Co), antimony (Sb), vanadium (V), lanthanum (La) and tungsten (W)) from wastewater by using C. fracta were aimed. Besides, assessment of the potential health risks in terms of the use of organic fertilizer obtained from the macroalga to be harvested from the treatment were also aimed. Highest Co, Sb, V, La and W accumulations by algae in reactor were 125±6.2%, 201.25±10%, 318.18±15%, 357.97±18%, and 500±25%, respectively. When compared with control, Co, Sb, V, La and W in algae increased 2.25, 3.01, 4.18, 4.58, and 6 times, respectively. The algae was very high bioaccumulative for Co and La. Highest MPI was calculated as 3.94. Non-carcinogenic risk of CRMs according to different exposure types (ingestion, inhalation, and dermal) were calculated for man, woman and child. There is not any non-carcinogenic risk from the investigated exposure ways of algae as organic fertilizer.

Proteomics reveals toxin tolerance and polysaccharide accumulation in Chlorococcum humicola under high CO2 concentration

Algae have great application prospects in excess sludge reclamation and recovery of high-value biomass. Chlorococcum humicola was cultivated in this research, using sludge extract (mixed with SE medium) with additions of 10%, 20%, and 30% CO2 (v/v). Results showed that under 20% CO2, the dry weight and polysaccharide yield reached 1.389 ± 0.070 g/L and 313.49 ± 10.77 mg/L, respectively. 10% and 20% CO2 promoted the production of cellular antioxidant molecules to resist the toxic stress and the toxicity of 20% CO2 group decreased from 62.16 ± 3.11% to 33.02 ± 3.76%. 10% and 20% CO2 accelerated the electron transfer, enhanced carbon assimilation, and promoted the photosynthetic efficiency, while 30% CO2 led to photosystem damage and disorder of antioxidant system. Proteomic analysis showed that 20% CO2 mainly affected energy metabolism and the oxidative stress level on the early stage (10 d), while affected photosynthesis and organic substance metabolism on the stable stage (30 d). The up-regulation of PSII photosynthetic protein subunit 8 (PsbA, PsbO), A0A383W1S5 and A0A383VRI4 promoted the efficiency of PSII and chlorophyll synthesis, and the up-regulation of A0A383WH74 and A0A2Z4THB7 led to the accumulation of polysaccharides. The up-regulation of A0A383VDH1, A0A383VX37 and A0A383VA86 promoted respiration. Collectively, this work discloses the regulatory mechanism of high-concentration CO2 on Chlorococcum humicola to overcome toxicity and accumulate polysaccharides.

Synthesis of iron oxide nanoparticles using orange fruit peel extract for efficient remediation of dye pollutant in wastewater

The removal of color-causing compounds from wastewater is a significant challenge that industries encounter due to their toxic, carcinogenic, and harmful properties. Despite the extensive research and development of various techniques with the objective of effectively degrading color pollutants, the challenge still persists. This paper introduces a simple technique for producing iron oxide nanoparticles (Fe2O3 NPs) using orange fruit peel for sustainable dye degradation in aqueous environment. The observation of color change and the measurement of UV-visible absorbance at 240 nm provided a confirmation for the development of Fe2O3 NPs. Transmission electron microscopy examination demonstrated that the Fe2O3 NPs have an agglomerated distribution and forming spherical structures with size ranging from 25-80 nm. Energy-dispersive X-ray spectroscopy analysis supported the existence of Fe and O. Fourier transform infrared spectroscopy conducted to investigate the involvement of orange peel extract in the reduction, capping, and synthesis of Fe2O3 NPs from the precursor salt. Fe2O3 NPs showed a photocatalytic remediation of 97%, for methylene blue under visible light irradiation. Additionally, prepared NPs exhibited concentration depended biofilm inhibition action against E. coli and S. aureus. In conclusion, Fe2O3 NPs can efficiently purify water and suppress pathogens due to their strong degrading activity, reusability, and biofilm inhibition property.

Microplastics as vectors of other contaminants: Analytical determination techniques and remediation methods

The ubiquitous and persistent presence of microplastics (MPs) in aquatic and terrestrial ecosystems has raised global concerns due to their detrimental effects on human health and the natural environment. These minuscule plastic fragments not only threaten biodiversity but also serve as vectors for contaminants, absorbing organic and inorganic pollutants, thereby causing a range of health and environmental issues. This review provides an overview of microplastics and their effects. This work highlights available analytical techniques for detecting and characterizing microplastics in different environmental matrices, assessing their advantages and limitations. Additionally, this review explores innovative remediation approaches, such as microbial degradation and other advanced methods, offering promising prospects for combatting microplastic accumulation in contaminated environments. The focus on environmentally-friendly technologies, such as the use of microorganisms and enzymes for microplastic degradation, underscores the importance of sustainable solutions in plastic pollution management. In conclusion, this article not only deepens our understanding of the microplastic issue and its impact but also advocates for the urgent need to develop and implement effective strategies to mitigate this critical environmental challenge. In this context, the crucial role of advanced technologies, like quantitative Nuclear Magnetic Resonance spectroscopy (qNMR), as promising tools for rapid and efficient microplastic detection, is emphasized. Furthermore, the potential of the enzyme PETase (polyethylene terephthalate esterase) in microplastic degradation is examined, aiming to address the growing plastic pollution, particularly in saline environments like oceanic ecosystems. These innovations offer hope for effectively addressing microplastic accumulation in contaminated environments and minimizing its adverse impacts.

Environmental fate of aquatic pollutants and their mitigation by phycoremediation for the clean and sustainable environment: A review

Emerging pollutants such as natural and manufactured chemicals, insecticides, pesticides, surfactants, and other biological agents such as personal care products, cosmetics, pharmaceuticals, and many industrial discharges hamper the aquatic environment. Nanomaterials and microplastics, among the categories of pollutants, can directly interfere with the marine ecosystem and translate into deleterious effects for humans and animals. They are either uncontrolled or poorly governed. Due to their known or suspected effects on human and environmental health, some chemicals are currently causing concern. The aquatic ecology is at risk from these toxins, which have spread worldwide. This review assesses the prevalence of emerging and hazardous pollutants that have effects on aquatic ecosystems and contaminated water bodies and their toxicity to non-target organisms. Microalgae are found to be a suitable source to remediate the above-mentioned risks. Microalgae based mitigation techniques are currently emerging approaches for all such contaminants, including the other categories that are discussed above. These studies describe the mechanism of phycoremediation, provide outrage factors that may significantly affect the efficiency of contaminants removal, and discuss the future directions and challenges of microalgal mediated remediations.

Resource recovery and valorization of food wastewater for sustainable development: An overview of current approaches

The food processing industry is one of the world's largest consumers of potable water. Agri-food wastewater systems consume about 70% of the world's fresh water and cause at least 80% of deforestation. Food wastewater is characterized by complex composition, a wide range of pollutants, and fluctuating water quality, which can cause huge environmental pollution problems if discharged directly. In recent years, food wastewater has attracted considerable attention as it is considered to have great prospects for resource recovery and reuse due to its rich residues of nutrients and low levels of harmful substances. This review explored and compared the sources and characteristics of different types of food wastewater and methods of wastewater treatment. Particular attention was paid to the different methods of resource recovery and reuse of food wastewater. The diversity of raw materials in the food industry leads to different compositional characteristics of wastewater, which determine the choice and efficiency of wastewater treatment methods. Physicochemical methods, and biological methods alone or in combination have been used for the efficient treatment of food wastewater. Current approaches for recycling and reuse of food wastewater include culture substrates, agricultural irrigation, and bio-organic fertilizers, recovery of high-value products such as proteins, lipids, biopolymers, and bioenergy to alleviate the energy crisis. Food wastewater is a promising substrate for resource recovery and reuse, and its valorization meets the current international policy requirements regarding food waste and environment protection, follows the development trend of the food industry, and is also conducive to energy conservation, emission reduction, and economic development. However, more innovative biotechnologies are necessary to advance the effectiveness of food wastewater treatment and the extent of resource recovery and valorization.

An insight on pollutant removal mechanisms in phycoremediation of textile wastewater

Pollutants, including dyes and heavy metals from textile industrial discharge, adversely affect the surface and groundwater resources, and pose a severe risk to the living organisms in the ecosystem. Phycoremediation of wastewater is now an emerging trend, as it is colossally available, inexpensive, eco-friendly, and has many other benefits, with high removal efficiency for undesirable substances, when compared to conventional treatment methods. Algae have a good binding affinity toward nutrients and toxic compounds because of various functional groups on its cell surface by following the mechanisms such as biosorption, bioaccumulation, or alternate biodegradation pathway. Algae-based treatments generate bioenergy feedstock as sludge, mitigate CO2, synthesize high-value-added products, and release oxygenated effluent. Algae when converted into activated carbon also show good potential against contaminants, because of its higher binding efficiency and surface area. This review provides an extensive analysis of different mechanisms involved in removal of undesirable and hazardous substances from textile wastewater using algae as green technology. It could be founded that both biosorption and biodegradation mechanisms were responsible for the removal of dye, organic, and inorganic pollutants. But for the heavy metals removal, biosorption results in higher removal efficiency. Overall, phycoremediation is a convenient technique for substantial conserving of energy demand, reducing greenhouse gas emissions, and removing pollutants.

Factors driving PPCPs uptake by crops after wastewater irrigation and human health implications

Currently, water scarcity affects more than three billion people. Nevertheless, the volume of treated wastewater discharged into the environment is estimated to exceed 100 m3 per inhabitant/year. These water resources are regularly used in agriculture worldwide to overcome water shortages. Such a practice, however, entails the uptake of waterborne pollutants, such as pharmaceuticals and personal care products (PPCPs), by crops and their further access to the food web, constituting an additional route of human exposure to PPCPs, with potential health outcomes. In this study, the occurrence of 56 PPCPs in tomatoes, lettuce, and carrot, together with soil and irrigation water, was evaluated using a QuEChERS-based methodology for extraction and LC-MS/MS for analysis. The influence of the selected cultivation conditions on the plant uptake levels of PPCPs was assessed. Two irrigation water qualities (secondary and tertiary treatment effluents), two soil compositions (sandy and clayey), two irrigation systems (dripping and sprinkling), and three crop types (lettuce, tomato, and carrot) were tested. Carrots showed the highest load of PPCPs (7787 ng/g dw), followed by tomatoes (1692 ng/g dw) and lettuces (1248 ng/g dw). The most translocated PPCPs were norfluoxetine (fluoxetine antidepressant main metabolite) (521 ng/g dw), and the anti-inflammatory diclofenac (360 ng/g dw). Nine PPCPs, are reported to be accumulated in crops for the first time. Water quality was the most important factor for reducing PPCPs' plant uptake. Overall, the best conditions for reducing PPCP uptake by crops were irrigation with reclaimed water by sprinkling in soils with higher clay content. The risk assessment performed revealed that the crops' consumption posed no risk to human health. This study serves as the first comprehensive assessment of the relevance of diverse cultivation factors on PPCPs' plant uptake under field agricultural practices.

A critical review on phycoremediation of pollutants from wastewater-a novel algae-based secondary treatment with the opportunities of production of value-added products

Though the biological treatment employing bacterial strains has wide application in effluent treatment plant, it has got several limitations. Researches hence while looking for alternative biological organisms that can be used for secondary treatment came up with the idea of using microalgae. Since then, a large number of microalgal/cyanobacterial strains have been identified that can efficiently remove pollutants from wastewater. Some researchers also found out that the algal biomass not only acts as a carbon sink by taking up carbon dioxide from the atmosphere and giving oxygen but also is a renewable source of several value-added products that can be extracted from it for the commercial use. In this work, the cleaning effect of different species of microalgae/cyanobacteria on wastewater from varied sources along with the value-added products obtained from the algal biomass as observed by researchers during the past few years are reviewed. While a number of review works in the field of phycoremediation technology was reported in literature, a comprehensive study on phycoremediation of wastewater from different industries and household individually is limited. In the present review work, the efficiency of diverse microalgal/cyanobacterial strains in treatment of wide range of industrial effluents along with municipal wastewater having multi-pollutants has been critically reviewed.

Removal of organic and inorganic contaminants from the air, soil, and water by algae

Rapid increases in human populations and development has led to a significant exploitation of natural resources around the world. On the other hand, humans have come to terms with the consequences of their past mistakes and started to address current and future resource utilization challenges. Today's primary challenge is figuring out and implementing eco-friendly, inexpensive, and innovative solutions for conservation issues such as environmental pollution, carbon neutrality, and manufacturing effluent/wastewater treatment, along with xenobiotic contamination of the natural ecosystem. One of the most promising approaches to reduce the environmental contamination load is the utilization of algae for bioremediation. Owing to their significant biosorption capacity to deactivate hazardous chemicals, macro-/microalgae are among the primary microorganisms that can be utilized for phytoremediation as a safe method for curtailing environmental pollution. In recent years, the use of algae to overcome environmental problems has advanced technologically, such as through synthetic biology and high-throughput phenomics, which is increasing the likelihood of attaining sustainability. As the research progresses, there is a promise for a greener future and the preservation of healthy ecosystems by using algae. They might act as a valuable tool in creating new products.

Sustainable fabrication of hybrid silver-copper nanocomposites (Ag-CuO NCs) using Ocimum americanum L. as an effective regime against antibacterial, anticancer, photocatalytic dye degradation and microalgae toxicity

In this study, a sustainable fabrication of hybrid silver-copper oxide nanocomposites (Ag-CuO NCs) was accomplished utilizing Ocimum americanum L. by one pot green chemistry method. The multifarious biological and environmental applications of the green fabricated Ag-CuO NCs were evaluated through their antibacterial, anticancer, dye degradation, and microalgae growth inhibition activities. The morphological features of the surface functionalized hybrid Ag-CuO NCs were confirmed by FE-SEM and HR-TEM techniques. The surface plasmon resonance λ_max peak appeared at 441.56 nm. The average hydrodynamic size distribution of synthesized nanocomposite was 69.80 nm. Zeta potential analysis of Ag-CuO NCs confirmed its remarkable stability at -21.5 mV. XRD and XPS techniques validated the crystalline structure and electron binding affinity of NCs, respectively. The Ag-CuO NCs demonstrated excellent inhibitory activity against Vibrio cholerae (19.93 ± 0.29 mm) at 100 μg/mL. Anticancer efficacy of Ag-CuO NCs was investigated against the A549 lung cancer cell line, and Ag-CuO NCs exhibited outstanding antiproliferative activity with a low IC₅₀ of 2.8 ± 0.05 μg/mL. Furthermore, staining and comet assays substantiated that the Ag-CuO NCs hindered the progression of the A549 cells and induced apoptosis as a result of cell cycle arrest at the G₀/G₁ phase. Concerning the environmental applications, the Ag-CuO NCs displayed efficient photocatalytic activity against eosin yellow degradation up to 80.94% under sunlight irradiation. Microalgae can be used as an early bio-indicator/prediction of environmental contaminants and toxic substances. The treatment of the Ag-CuO NCs on the growth of marine microalgae Tetraselmis suecica demonstrated the dose and time-dependent growth reduction and variations in the chlorophyll content. Therefore, the efficient multifunctional properties of hybrid Ag-CuO NCs could be exploited as a regime against infective diseases and cancer. Further, the findings of our investigation witness the remarkable scope and potency of Ag-CuO NCs for environmental applications.

Understanding the risk of using herbicides for tree root removal into wastewater treatment plant performance

Adding herbicides to sewer lines, a common practice for controlling root intrusion in sewer pipes, may adversely impact downstream wastewater treatment by inhibiting nitrification and denitrification performance. This study investigated the effects of herbicides, namely diquat, triclopyr, and 2-methyl-4-chlorophenoxyacetic acid (MCPA)-dicamba, on these processes. Various parameters were monitored, including oxygen uptake rate (OUR), nutrients (NH₃-N, TP, NO₃-N, and NO₂-N), chemical oxygen demand (COD), and herbicide concentrations. It was found that nitrification was not affected by OUR in the presence of each herbicide at various concentrations (1, 10, and 100 mg L^-1). Additionally, MCPA-dicamba at various concentrations demonstrated minimal inhibition in the nitrification process compared to diquat and triclopyr. COD consumption was not affected by the presence of these herbicides. However, triclopyr significantly inhibited NO₃-N formation in the denitrification process at various concentrations. Similar to nitrification process, both COD consumption and herbicide reduction concentration were not affected by the presence of herbicides during the denitrification process. Adenosine triphosphate measurements showed minimal impact on nitrification and denitrification processes when herbicides were present in the solution up to a concentration of 10 mg L^-1. Tree root kill efficiency experiments were performed on Acacia melanoxylon. Considering the performance on nitrification and denitrification process, diquat emerged as the best herbicide option (concentration of 10 mg L^-1), with a 91.24% root kill efficiency.

Designing the heterostructured FeWO4/FeS2 nanocomposites for an enhanced photocatalytic organic dye degradation

The present study, reports a facile approach for the synthesis of FeWO₄/FeS₂ nanocomposites were demonstrated through hydrothermal method. The surface morphology, crystalline structure, chemical composition, optical properties of the prepared samples was analysed by different various technique. The result observed analysis indicates that, the formation of heterojunction by 2:1 wt.% of FeWO₄/FeS₂ nanohybrid has the lowest recombination rate of electron-hole pairs and the least electron transfer resistance. Due to its the broad absorption spectral range and preferable energy band gap, the (2:1) FeWO₄/FeS₂ nanohybrid photocatalyst exhibits an excellent ability to remove MB dye when exposed to UV-Vis. Light irradiation. Its photocatalytic activity of (2:1) FeWO₄/FeS₂ nanohybrid is higher than other as prepared samples due to its synergistic effects, enhanced light absorption and high charge carrier separation. Radical trapping experimental result implies that the photo-generated free electrons and hydroxyl radials are essential to degrade the MB dye. Furthermore, a possible future mechanism for FeWO₄/FeS₂ nanocomposites photocatalytic activity was discussed. Moreover, the recyclability analysis demonstrated that the FeWO₄/FeS₂ nanocomposites can be recycled multiple times. The enhanced photocatalytic activity of 2:1 FeWO₄/FeS₂ nanocomposites is promising for the further application of visible light driven photocatalyst in wastewater treatment.

Comparative Evaluation of Chlorella vulgaris and Anabaena variabilis for Phycoremediation of Polluted River Water: Spotlighting Heavy Metals Detoxification

This study investigated the phycoremediation abilities of Chlorella vulgaris (microalga) and Anabaena variabilis (cyanobacterium) for the detoxification of polluted river water. Lab-scale phycoremediation experiments were conducted for 20 days at 30 °C using the microalgal and cyanobacterial strains and water samples collected from the Dhaleswari river in Bangladesh. The physicochemical properties such as electrical conductivity (EC), total dissolved solids (TDS), biological oxygen demand (BOD), hardness ions, and heavy metals of the collected water samples indicated that the river water is highly polluted. The results of the phycoremediation experiments demonstrated that both microalgal and cyanobacterial species significantly reduced the pollutant load and heavy metal concentrations of the river water. The pH of the river water was significantly raised from 6.97 to 8.07 and 8.28 by C. vulgaris and A. variabilis, respectively. A. variabilis demonstrated higher efficacy than C. vulgaris in reducing the EC, TDS, and BOD of the polluted river water and was more effective at reducing the pollutant load of SO₄^2- and Zn. In regard to hardness ions and heavy metal detoxification, C. vulgaris performed better at removing Ca²⁺, Mg²⁺, Cr, and Mn. These findings indicate that both microalgae and cyanobacteria have great potential to remove various pollutants, especially heavy metals, from the polluted river water as part of a low-cost, easily controllable, environmentally friendly remediation strategy. Nevertheless, the composition of polluted water should be assessed prior to the designing of microalgae- or cyanobacteria-based remediation technology, since the pollutant removal efficiency is found to be species dependent.

New trajectories of technologies for the removal of pollutants and emerging contaminants in the environment

Modern society has increasingly a diffusion of pollutants and emerging contaminants (e.g., different types of chemicals and endocrine disruptors in pharmaceuticals, pesticides, household cleaning, and personal care products, etc.) that have detrimental effects on the environment (atmosphere, hydrosphere, biosphere and anthroposphere) and also generate diseases and disorders on the people health. Environmental science requires efforts in the detection and elimination of manifold pollutants and emerging pollutants with appropriate product and process technologies. This study aims to analyze different paths of treatment technologies to investigate their evolution and predict new directions of promising technological trajectories to support the removal of contaminants directed to reach, whenever possible, sustainable development objectives. The work is mainly devoted to wastewater treatment technologies. A proposed model analyzes the evolution of patents (proxy of innovation and new technology) on publications (proxy of science and knowledge advances) to quantify the relative growth rate of new trajectories of technologies to remove pollutants and emerging contaminants. Results reveal that new directions of treatment technologies having an accelerated rate of growth are (in decreasing order): biochar and reverse osmosis in physical-based technologies, coagulation, and disinfection water treatments in chemical-based technologies and anaerobic processes in biological-based technologies. Other main technologies, such as carbon nanotubes and advanced oxidation processes, seem to be in the initial phase of development and need learning by using processes and further science and technology advances to be implemented as effective treatments and cost-effective. The results here are in accord with global water and wastewater equipment treatment market revenues by technology, showing a similar trend. These findings bring us to the main information to extend the knowledge about new directions of technologies for the treatment and/or elimination of pollutants and microorganisms that can support decisions of policymakers towards goals of sustainable development by reducing environmental degradation and people health disorders.

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

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

Sewage Water Treatment Using Chlorella Vulgaris Microalgae for Simultaneous Nutrient Separation and Biomass Production

Recovery of wastewater is essential for better management of water resources and can aid in reducing regional or seasonal water shortages. When algae were used to clean wastewater, amazing benefits were guaranteed, such as a decrease in the formation of dangerous solid sludge and the creation of valuable algal biomass through recycling of the nutrients in the wastewater. The trace elements nitrogen, phosphorus, and others that microalgae need for cell development are frequently present in contaminated wastewater. Hence, microalgal bioremediation is used in this study as an effective technique for the simultaneous treatment of COD, NH3-N, and orthophosphate from domestic wastewater and biomass production. Different concentrations of wastewaters were used. The maximum removals attained were: 84% of COD on the fifth day using the lowest mixing ratio of 50%, 95% of ammoniacal nitrogen, and 97% of phosphorus. The highest biomass production was achieved at day 12, except for the mixing ratio of 80% where the growth rate increased until day 14 at 400 mg/L.

A review on multi-synergistic transition metal oxide systems towards arsenic treatment: Near molecular analysis of surface-complexation (synchrotron studies/modeling tools)

The science and interface chemistry between the arsenic (As) anions and the different adsorbent systems have been gaining interest in recent years in environmental remediation applications. Metal-oxides and the corresponding hybrid systems have shown promising performance as novel adsorbents in various treatment technologies. The abundance, surface chemistry, high surface area (active-centres), various synthesis and functionalization methodologies, and good recyclability make these metal oxide-based nanomaterials as potential remediating agents for As oxyanions. This work critically reviews eight different platforms focused on the arsenic contamination issue, where the first classification describes the origin of arsenic contamination and presents geographical and demo-graphical considerations. The following section briefs the state-of-the-art remediation techniques for arsenic treatment with a comparative evaluation. An emphasized discussion has been provided regarding the adsorption and classification of various metal oxide adsorbents. In the next classification, various multi-synergism abilities like Redox activity, Surface functional groups, Surface area/morphology, Heterogeneous catalysis, Reactive oxygen species, Photo-catalytic/electro-catalytic reactions, and Electrosorption are detailed. The classification of various characterization tools for accessing the arsenic remediation qualitatively and quantitatively are given in the fifth chapter. The first-of-its-kind dedicated analysis has been given on the surface complexation aspects of the arsenic speciation onto various metal adsorbent systems using synchrotron results, surface-complexation modeling, and molecular simulation (e.g., DFT) in the sixth chapter. The current sensing applications of these novel nano-material systems for arsenic determination using colorimetric and electrochemical-based analytical tools and a note about the economic parameters, i.e., regeneration aspects of various adsorbent systems/the sustainable applications of the treated sludge materials, are provided in the final sections. This work makes a critical analysis of 'Environmental Nanotechnology' towards 'Arsenic Treatment'.

Recent advances in carbon-based nanomaterials for the treatment of toxic inorganic pollutants in wastewater

Wastewater contains inorganic pollutants, generated by industrial and domestic sources, such as heavy metals, antibiotics, and chemical pesticides, and these pollutants cause many environmental problems.

Bioremediations analysis using multifactorial porous materials derived from tea residue

Titanium dioxide nanoparticles (TiO₂ NPs) are becoming more and more renowned as biocompatible nanomaterials with diverse biological functions. In the present study, the aqueous extract of tea residue (tea filtered waste powder) was used to synthesize the TiO₂ NPs and treated for effluent bioremediations. Maximum absorption in the UV-Vis spectrum of the TiO₂ NPs was seen at 358 nm, and the XRD pattern reveals peaks at 2 h values of 25.78, 38.24, 47.98, 54.76, 55.32, 62.64, 69.05, 70.15, 75.24, and 83.59 that may be indexed to the (101), (004), (200), (105), (211), (204), (116), (220), (215) and (303). The FT-IR spectra of TiO₂ NPs showed a peak at 3420, 2925, 1621, 1382, 1098, and 687 cm-1. The spherical form and size were disclosed by FE-SEM analyses, and the EDAX pattern verified the purity of the TiO₂ NPs. The average particles size of the TiO₂ NPs was 32 nm. The photodegradation of paper mill waste water is significantly deteriorated up to 99.08% for 600 min, but textile waste water is degraded up to 98.06% for the same duration. Furthermore, we reported that TiO₂ NPs may rapidly breakdown industrially hazardous effluents when exposed to sunshine. Overall, this new, straightforward, and environmentally beneficial strategy may be of interest to the management of efficient degradation of dye solutions in the polluted regions.

Biodegradation of the pyrethroid cypermethrin by bacterial consortia collected from orange crops

Pyrethroids, such as cypermethrin (CYP), are widely employed in agriculture, promoting environmental pollution and the need for efficient decontamination methods. In this study, bacteria from orange crops were explored for CYP biodegradation. Among 40 tested bacterial strains, 20 grew in the presence of CYP and 19 performed statistically significant CYP biodegradation in 5 days (20.5%-97.8%). In addition, 3-phenoxybenzoic acid, the main metabolite from CYP, was quantified ranging from 1.1 mg.L^-1 to 32.1 mg.L^-1. The five most efficient strains, and consortia composed of 5, 10 and 20 bacteria biodegraded the CYP formulation as sole carbon source in phosphate buffer and in minimum mineral medium. Under optimized conditions determined employing Response Surface Methodology, Bacillus sp. CSA-1 and the consortium composed of 10 strains biodegraded 71.0% and 71.6% CYP in 24 h, respectively. Moreover, metabolite identification enabled the proposal of an extended biodegradation pathway with 29 identified compounds, including different new amide and amine derivatives that expanded the knowledge about the fate of this compound in the environment. Experiments of bioaugmentation in soil using Bacillus sp. CSA-1 and the consortium of 10 bacterial strains resulted in faster CYP biodegradation than natural attenuation, showing that the selection of efficient strains for composing a consortium is an interesting approach for bioremediation of pyrethroids.

Polyol-assisted hydrothermal synthesis of Mn-doped α - Fe2O3(MFO) nanostructures: Spin disorder-induced magnetism and photocatalytic properties

Hierarchical nanostructures play an important role in environmental clean-up and sustainability applications. The magnetic and photocatalytic characteristics of flower-like Mn-doped α-Fe₂O₃ nanostructures were prepared by using a polyol-assisted hydrothermal method. Crystallite sizes are in the range of 35-42 nm, and the existence of 3D hierarchical nanostructures was observed in FESEM pictures. The optical band gap energy varies between 2.08 and 2.16 eV, while XPS examination exposes the ions' charge states and validates Mn³⁺ inclusion in the Fe³⁺ lattice. At room temperature, the addition of Mn to α-Fe₂O₃ results in a spin disorder ferromagnetism and coercivity of about 600 Oe was achieved. Methylene blue (MB) dye solution degraded by 92% when 2.5% Mn doped with α-Fe₂O₃ under visible conditions for 120 min irradiation time.

Sustainability and carbon neutralization trends in microalgae bioenergy production from wastewater treatment: A review

Reducing CO2 emissions using biomass is gaining popularity as an environmentally friendly strategy. Due to high growth rates, low production costs, and ability to withstand harsh conditions, microalgae have become quite popular. Microalgae may also undertake photosynthesis, converting CO2 and solar energy into sugar before becoming biomass, making them an excellent source of renewable and promising biofuels. CO2 sequestration and biofixation was utilized to compare the synthesis of biodiesel as a third-generation biofuel from various types of wastewater was also used as a source for the algal cultivation. This review article focuses on recent developments, research discoveries in the field of microalgal CO2 capture modification and the optimization of conversion efficiency. This review is intended to serve as a helpful and reference for the use of wastewater treatment with microalgae to collect CO2. The overarching objective of this study is to assist wastewater treatment systems in achieving carbon neutrality.

Green synthesis, characterization, and application of metal oxide nanoparticles for mercury removal from aqueous solution

In this work, a novel surface-modified, green-based wheat straw-supported magnetite nanoparticles (Fe₃O₄-NPs) were synthesized via the green synthesis method, and the adsorption of mercury (Hg(II)) ion from aqueous solutions was methodically investigated. The synthesized wheat straw-supported magnetite (Fe₃O₄-WSS) NPs were characterized using X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and scanning electron microscopic (SEM) methods. FT-IR and TGA confirmed that the surface of Fe₃O₄-NPs was functionalized well. The XRD analysis revealed the existence of magnetite in the synthesized wheat straw-supported Fe₃O₄-NPs of 19.83 nm average crystalline size. SEM analysis showed Fe₃O₄-NPs were almost spherical, with an average particle size of 22.48 nm. Adsorption studies were carried out to investigate the adsorption of Hg(II) ions onto Fe₃O₄-WSS NPs and the effect of various adsorption parameters such as pH, time, adsorbent dosage, and Hg(II) ion concentration. The optimum adsorption conditions were obtained: pH of 6, contact time of 45 min, adsorbate of 40 mg/L, and adsorbent of 1 g. A maximum of 98.04% Hg(II) ion removal efficiency was obtained at these optimum conditions. FT-IR analysis also indicated that surface functional groups such as C = C,-OH, and C-C of the newly produced Fe₃O₄-NPs led to the more efficient removal of Hg(II) from aqueous solution. The synthesized nano-adsorbent showed an excellent adsorption capability of 101.01 mg/g. Hg(II) ions adsorption onto Fe₃O₄-WSS NPs fitted well with the Langmuir adsorption isotherm model. Therefore, these reasonable findings reveal that Fe₃O₄-WSS NPs are an efficient and promising adsorbent for Hg(II) removal from aqueous water environments.

Carbon-based adsorbents as proficient tools for the removal of heavy metals from aqueous solution: A state of art-review emphasizing recent progress and prospects

Carbon-centric adsorbents (CCA) are diverse forms, from simple biochar (BC) to graphene derivatives, carbon nanotubes (CNTs), and activated carbon (AC), which have been vastly explored for their removal of a plethora of pollutants, including heavy metals (HM). The prominent features of CCA are their operational attributes like extensive surface area, the occurrence of flexible surface functional groups, etc. This work offers a comprehensive examination of contemporary research on CCA for their superior metal removal aptitude and performances in simulated solutions and wastewater flows; via portraying the recent research advances as an outlook on the appliances of CACs for heavy metal adsorption for removal via distinct forms like AC, BC, Graphene oxide (GO), and CNTs. The bibliometric analysis tool was employed to highlight the number of documents, country-wise contribution, and co-occurrence mapping based on the Scopus database. The coverage of research works in this review is limited to the last 5 years (2017-2021) to highlight recent progress and prospects in using CCAs such as AC, BC, GO, and CNTs to remove HM from aqueous media, which makes the review unique. Besides an overview of the common mechanisms of CACs, the future scope of CAC, especially towards HM mitigation, is also discussed in this review. This review endorses that further efforts should be commenced to enhance the repertory of CCAs that effectively eliminate multiple targeted metals in both simulated and real wastewater.

Adsorption of brilliant green dye onto activated carbon prepared from cashew nut shell by KOH activation: Studies on equilibrium isotherm

Activated carbon from cashew nut shell via a potassium hydroxide (KOH) at 600 °C in an N₂ atmosphere and their characteristics using FT-IR, XRD, SEM with EDS, and BET analysis was investigated. The cashew nut shell activated carbon obtained by KOH activation with a CNS/KOH ratio of 1:1 at 600 °C (N₂ atmosphere) for 2 h had the highest surface area (407.80 m²/g) as compared to other ratio samples. Amongst, CNS/KOH ratios of 1:1 sample are used for the adsorbent, they are effects of contact time, pH, adsorbent dose, and initial dye concentration on brilliant green (BG) removal efficiency were studied. Moreover, the Langmuir and Freundlich adsorption models consisted utilized to affirm the adsorption isotherms. They are, best fitting for BG experimental equilibrium data was achieved with the Langmuir isotherm, giving a maximum BG adsorption capacity of 243.90 mg/g.

Diclofenac removal by the microalgae species Chlorella vulgaris, Nannochloropsis oculata, Scenedesmus acutus, and Scenedesmus obliquus

In this work, we evaluated the removal efficiency of diclofenac by Chlorella vulgaris OW-01, Nannochloropsis oculata CCAP 849/7, Scenedesmus acutus UTEX 72, and Scenedesmus obliquus CCAP 276/2. Each microalga was grown in media with different concentrations (50 and 100% of the original formulation) of carbon, nitrogen, and phosphorus, to evaluate their effect on the removal of diclofenac. We also evaluated the photodegradation of diclofenac under the same conditions. The diclofenac removed from the media ranged from 59 to 92%, obtaining the highest removal with S. obliquus. The diclofenac adsorbed on the cell walls ranged from 12.2 to 26.5%, obtaining the highest adsorption with S. obliquus. The diclofenac degraded by light ranged from 15 to 28%. The nutrient deficit showed no influence on the removal of diclofenac in any of the microalgae under study. These results indicate that S. obliquus is the best alternative for the bioremediation of diclofenac.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03268-2.

A techno-economic approach for eliminating dye pollutants from industrial effluent employing microalgae through microbial fuel cells: Barriers and perspectives

Microbial fuel cells are biochemical factories which besides recycling wastewater are electricity generators, if their low power density can be scaled up. This also adds up to work on many factors responsible to increase the cost of running a microbial fuel cell. As a result, the first step is to use environment friendly dead organic algae biomass or even living algae cells in a microbial fuel cell, also referred to as microalgal microbial fuel cells. This can be a techno-economic aspect not only for treating textile wastewater but also an economical way of obtaining value added products and bioelectricity from microalgae. Besides treating wastewater, microalgae in its either form plays an essential role in treating dyes present in wastewater which essentially include azo dyes rich in synthetic ions and heavy metals. Microalgae require these metals as part of their metabolism and hence consume them throughout the integration process in a microbial fuel cell. In this review a detail plan is laid to discuss the treatment of industrial effluents (rich in toxic dyes) employing microbial fuel cells. Efforts have been made by researchers to treat dyes using microbial fuel cell alone or in combination with catalysts, nanomaterials and microalgae have also been included. This review therefore discusses impact of microbial fuel cells in treating wastewater rich in textile dyes its limitations and future aspects.

Mycodegradation of diazinon pesticide utilizing fungal strains isolated from polluted soil

The current study aimed to isolate biodegradable soil fungi capable of metabolizing diazinon. The collected soil samples were investigated for diazinon pollution to detect the pesticide level in the polluted soil samples. Food poisoning techniques were utilized to preliminary investigate the biodegradation efficiency of the isolated fungal strains to diazinon pesticide using solid and liquid medium and also to detect their tolerance to different concentrations. GC-MS analysis of control and treated flasks were achieved to determine the diazinon residues for confirmation of the biodegradation efficiency. The total diazinon residues in the collected soil samples was found to be 0.106 mg/kg. Out of thirteen fungal strains isolated form diazinon polluted soils, six strains were potentially active in diazinon biodegradation. Food poisoning technique showed that A. niger, B. antennata, F. graminearum, P. digitatum, R. stolonifer and T. viride strains recorded fungal growth diameters of 65.2 ± 0.18, 57.5 ± 0.41, 47.2 ± 0.36, 56.5 ± 0.27, 85.0 ± 0.01, 85.0 ± 0.06 mm respectively in the treated group which were non significantly different compared to that of control (P > 0.05), indicating the high efficiency of these strains in diazinon degradation compared to the other isolated strains. GC-MS analysis revealed that B. antennata was the most efficient strain in diazinon degradation recording 32.24 ± 0.15 ppm concentration after 10 days incubation. Linear regression analysis confirmed that B. antennata was the most effective biodegradable strain recording the highest diazinon dissipation (83.88%) with the lowest T_1/2 value of 5.96 days while T. viride, A. niger, R. stolonifer and F. graminearum exhibited a high biodegradable activities reducing diazinon to 80.26%, 78.22%, 77.36% and 75.43% respectively after 10 days incubation. In conclusion, these tolerant fungi could be considered as promising, eco-friendly and biodegradable fungi for the efficient and potential removal of hazardous diazinon from polluted soil.

Process optimization of struvite recovered from slaughterhouse wastewater and its fertilizing efficacy in amendment of biofertilizer

The intensive discharge of slaughterhouse waste into water bodies increases Nitrogen (N), Phosphorus (P) in the wastewater and leads to various environmental problems. On the other hand, the increasing treatment effort after the extraction of these valuable nutrients in the commercial fertilizer reduces the dependence on scarce phosphate resources. The viable solution is to recover N, P as struvite (magnesium ammonium phosphate) from nutrient rich waste water as a small scale treatment unit application. The main parameters that have a significant impact on the process, including pH, Mg: P ratio, and precipitation time, were investigated from slaughterhouse wastewater using a central composite design and the experimental data's were statistically analysed. The results indicated that pH and Mg/P ratio level had a significant impact and thus 85% struvite precipitation efficiency was achieved at 9.6 pH and 1.5 dose mol ratio (mol Mg per mol P), in an inexpensive, stirred tank batch reactor with a retention time of 70 min. The fertilization efficiency was tested on the growth of Solanum melongena L with the obtained struvite and the integration of struvite with the Azospirullum rhizobium and Bacillus megaterium. Treatment of struvite, struvite with Azospirillum rhizobium and Bacillus megaterium increased growth parameters by 10%, 20%, and 25%, respectively, over control. The assessment of growth factors showed the most amazing number of fruits, shoots, and root length in a standard ratio of 60:40 of struvite to bio-inoculants compared to sole struvite fertilizer. Findings of this study would be beneficial to determine the feasibility of slaughterhouse waste as a phosphorus source for struvite recovery.

Effect of doping and loading Parameters on photocatalytic degradation of brilliant green using Sn doped ZnO loaded CSAC

Sn doped ZnO loaded cotton stalk activated carbon (Sn-ZnO/CSAC) was prepared by chemical precipitation method, and the products were characterized. The XRD resultants confirm that the presence of hexagonal wurtzite phase of the bare ZnO. Furthermore, particular particle size gradually decreases (21.49 nm) due to doping and loading. UV-Vis absorption intensity of doped/loaded sample was red-shifted and then PL intensity is reduced. The photocatalytic performances of bare, Sn-doped ZnO and Sn-ZnO/CSAC was estimated by photodegradation of brilliant green (BG) under sunlight. The photodegradation of BG dye in 120 min over Sn-doped ZnO/CSAC is nearly 96.52%, which is considerably improved than bare ZnO (72.60%), respectively.

Microwave-assisted thermochemical conversion of Zr-FeOOH nanorods to Zr-ZnFe2O4 nanorods for bacterial disinfection and photo-Fenton catalytic degradation of organic pollutants

Herein, we report a CoO_x-loaded Zr-doped ZnFe₂O₄ (CoO_x/Zr-ZFO) NR photocatalyst synthesized by successive microwave and wet impregnation methods for bacterial inactivation and degradation of organic pollutants. For the first time, microwave treatment was used for Zn attachment on hydrothermally synthesized self-assembled Zr-FeOOH NRs to produce Zr-doped ZnFe₂O₄ (Zr-ZFO) NRs. The lowest bandgap energy (1.96 eV) enables for significant absorption in the visible light region, which helps to improve bacteria degradation inactivation efficiency. Further, various metal oxides (Cu, Ag and Co) were loaded onto the surface of photocatalysts (Zr-ZFO NRs) by a wet impregnation method. As-synthesized CoO_x/Zr-ZFO-3 NRs were systematically characterized and used as photocatalysts for inactivation of E. coli and S. aureus and degradation of organic pollutants. The CoO_x/Zr-ZFO-3 NR photocatalyst exhibited better inactivation efficiency (99.4 %) than other metal oxide-loaded Zr-ZFO NRs (Ag₂O_x-loaded Zr-ZFO NRs (33.6 %), CuO_x-loaded Zr-ZFO NRs (77.6 %)). Additionally, the optimum CoO_x/Zr-ZFO-3 NR photocatalyst showed 98.3 % and 98.1 % degradation efficiencies for BPA and orange II dye, respectively, under visible light irradiation (λ ≥ 420 nm). Therefore, this work affords a novel, simple and rapid approach for the development of photocatalysts which active in visible light for bacterial disinfection and organic degradation.

Adsorptive removal of AB113 dye using green synthesized hydroxyapatite/magnetite nanocomposite

In the present study, magnetite nanoparticles (Fe₃O₄NPs) synthesized using Thunbergia grandiflora leaf extract as a reducing agent were doped with hydroxyapatite sourced from waste bivalve clamshells to produce hydroxyapatite/magnetite nanocomposite (HA/Fe₃O₄NPs). The magnetic nanocomposite was examined using several characterization techniques. The results of XRD and FESEM, analysis showed HA/Fe₃O₄NPs have a crystalline phase and irregular spherical particles respectively. EDAX and FTIR confirmed the presence of specific elements and functional groups of both iron oxide and hydroxyapatite nanoparticles respectively. The surface area and superparamagnetic property of the composite were determined by BET and VSM analysis. Central Composite Design (CCD) was used to optimize the adsorption process to remove of AB113 from aqueous solutions. The optimal adsorption efficiency was found out to be 94.38% at pH 8, AB113 dye concentration 54 ppm, HA/Fe₃O₄NPs dose 84 mg, and an agitation speed of 174 rpm. The monolayer Langmuir isotherm was the best model with a sorption capacity of 109.98 mg/g which was higher than the reported values. The pseudo-second-order kinetic model displayed a good fit with an R² = 0.99. Thermodynamic parameters were assessed which confirmed the exothermic adsorption process. Therefore, the synthesized magnetic nanocomposite can be employed as a novel nanoadsorbent for the removal of anionic dyes from waste effluents.

Assessment, characterization, and quantification of microplastics from river sediments

Microplastic (MP), as a pollutant, is currently posing a biological hazard to the aquatic environment. The study aims to isolate, quantify, and characterize the MP pollutants in sediment samples from 14 study sites at Kaveri River, Killa Chinthamani, Tiruchirappalli, South India. With Sediment-MP Isolation (SMI) unit, density separation was done with a hydrogen peroxide solution. Four forms of MPs namely, fragments, films, foams, and fibers with orange, white, green, and saffron red were observed. The plenitude and distribution of four forms of MPs and natural substrates were geometrically independent, with large amounts of microfragments within the research region accounting for 79.72% variation by Principal Component Analysis. FT-IR analyses of MPs showed the presence of polyamide, polyethylene, polyethylene glycol, polyethylene terephthalate, polypropylene, and polystyrene. Additionally, the scanning electron microscopic analysis revealed that the MPs have differential surface morphology with rough surfaces, porous structures, fissures, and severe damage. Most MPs comprised Si, Mg, Cu, and Al, according to energy dispersive X-ray analyses. The combined SMI, instrumental analyses and evaluation (heat map) of MPs in river sediments help assess contamination levels and types of MPs. The findings might provide an insight into the status of MPs in Kavery River sediments that could help in formulating regulations for MPs reduction and contamination in rivers eventually to protect the environment.

Trace phenolic acids simultaneously enhance degradation of chlorophenol and biofuel production by Chlorella regularis

Coupling the cultivation of microalgae with wastewater treatment is a promising technology to recover bioresources from wastewater. However, toxic pollutants in wastewater seriously inhibit the growth of microalgae and the removal of pollutants. Phenolic acids are similar to phytohormones, could potentially relieve the toxicity to microalgae and simultaneously promote pollutant degradation and lipid accumulation. Chlorella and 4-chlorophenol (4-CP) were utilized to simulate the toxic wastewater treatment, and the roles of two typical phenolic acids, such as p-hydroxybenzoic acid (p-HBA) and caffeic acid (CA), were explored. The 0.2 μM concentration of p-HBA or CA improved the specific growth rate by 7.6% by enhancing photosynthesis and DNA replication. The oxidative damage caused by 4-CP was reduced by 30.3-49.7% via the synthesis of more antioxidant enzymes and the direct scavenging of free radicals by phenolic acids. Furthermore, the 4-CP removal rate increased by 27.0%, and toxic 4-CP was degraded into non-toxic compounds. The phenolic acids did not change the 4-CP degradation pathway but accelerated its removal and detoxification by enhancing the expression of 4-CP degradation enzymes. Simultaneously, lipid production increased by 20.5-23.1% due to the upregulation of enzymes related to fatty acid and triacylglycerol synthesis. Trace phenolic acids stimulated the mitogen-activated protein kinase signaling cascade and the calcium signaling pathway to regulate the physiology of the microalgae and protect cells from toxic stress. This study provides a promising new strategy for toxic wastewater treatment and bioresource recovery.

The Biological Performance of a Novel Electrokinetic-Assisted Membrane Photobioreactor (EK-MPBR) for Wastewater Treatment

Developing an effective phycoremediation system, especially by utilizing microalgae, could provide a valuable approach in wastewater treatment for simultaneous nutrient removal and biomass generation, which would help control environmental pollution. This research aims to study the impact of low-voltage direct current (DC) application on Chlorella vulgaris properties and the removal efficiency of nutrients (N and P) in a novel electrokinetic-assisted membrane photobioreactor (EK-MPBR) in treating synthetic municipal wastewater. Two membrane photobioreactors ran in parallel for 49 days with and without an applied electric field (current density: 0.261 A/m2). Mixed liquid suspended soils (MLSS) concentration, chemical oxygen demand (COD), floc morphology, total phosphorus (TP), and total nitrogen (TN) removals were measured during the experiments. The results showed that EK-MPBR achieved biomass production comparable to the control MPBR. In EK-MPBR, an over 97% reduction in phosphate concentration was achieved compared to 41% removal in the control MPBR. The control MPBR outperformed the nitrogen removal of EK-MPBR (68% compared to 43% removal). Induced DC electric field led to lower pH, lower zeta potential, and smaller particle sizes in the EK-MPBR as compared with MPBR. The results of this novel study investigating the incorporation of Chlorella vulgar is in an electrokinetic-assisted membrane photobioreactor indicate that this is a promising technology for wastewater treatment.

Phytoremediation of pollutants from wastewater: A concise review

As there is a global water crisis facing the whole world, it is important to find alternative solutions to treat wastewater for reuse. Hence, plants have an effective role in removing pollutants from wastewater, which has been emphasized in this review article. Biological treatment of wastewater can be considered an eco-friendly and cost-effective process that depends on in the future. Living organisms, including plants, can remediate pollutants in wastewater, especially in agricultural fields, such as dyes, heavy metals, hydrocarbons, pharmaceuticals, and pesticides. This review discusses the different activities of plants in pollutant elimination from wastewater and sheds light on the utilization of plants in this scope. This review focuses on the remediation of the most common contaminants present in wastewater, which are difficult to the removal with microorganisms, such as bacteria, fungi, and algae. Moreover, it covers the major role of plants in wastewater treatment and the potential of phytoremediation as a possible solution for the global water crisis.

A new technique for reducing accumulation, transport, and toxicity of heavy metals in wheat (Triticum aestivum L.) by bio-filtration of river wastewater

The occurrence of contaminants such as heavy metals in an aqueous environment has become a global concern. In the present study, a bio-filter was designed to eliminate heavy metals from river wastewater contaminated with industrial effluents. Moreover, we analyzed simple tap water, bio-filtered water, and unfiltered river wastewater and measured the concentrations of different heavy metals in the samples, such as cadmium (Cd), nickel (Ni), lead (Pb), and copper (Cu). The current experiment explored irrigation effects of three water regimes (tap water, bio-filtered water, and wastewater) on two wheat (Triticum aestivum L.) varieties (NARC-2009 and NARC-2011). Results of the present study indicated that wastewater negatively influenced the growth parameters and photosynthetic contents along with a significant increase in oxidative damage in terms of electrolyte leakage (EL) (50 and 61%), hydrogen peroxide (H₂O₂) (52 and 61 μmol/g), and malondialdehyde (MDA) (16 and 17.7 μmol/g) contents in NARC-2009 and NARC-2011 respectively. However, bio-filtered water positively regulated the growth profile, activities of antioxidants such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), total soluble sugars, amino acids, total protein, and proline contents in wheat as compared with untreated wastewater. In addition, bio-filtered water had significant impacts on the reduction of Cd, Ni, Pb, and Cu concentrations in roots, shoots, and grains of both wheat varieties as compared to wastewater. The concentrations (mg/kg) of Cd (15 and 18), Ni (35 and 57), Pb (5 and 7), and Cu (69 and 72) in roots, Cd (5 and 6), Ni (24 and 43), Pb (3 and 4), and Cu (16 and 19) in shoots, and Cd (0.7 and 1.0), Ni (11 and 26), Pb (2 and 3), and Cu (1.6 and 1.5) in grains of NARC-2009 and NARC-2011 were found under river wastewater treatment. Overall, wastewater treatment through bio-filtration process is an effective strategy for the reduction of toxic elements in bio-filtered water and their accumulation by plants.

Biomass production and phycoremediation of microalgae cultivated in polluted river water

The present study evaluated polluted river water as a medium for the growth of oleaginous microalgae under mixotrophic conditions. Microalgae grow in the medium and produce biomass, pigments, and lipids with the removal of pollution loads from wastewater. Selenastrum sp. SL7 produced maximum biomass and lipids of 660 mg L^-1 and 194.5 mg L^-1, respectively. Fatty acid profiling data showed that elevated saturated fatty acid production and major fatty acids found in lipid from these algae were palmitic acids, oleic acid, stearic acid, linolenic acid, and linoleic acid. The low percentage of polyunsaturated fatty acids of EPA was also detected. Water quality in terms of pH, DO, TDS, COD, and BOD was significantly improved. The use of this medium for microalgae cultivation not only improves the biomass and lipid yields but also serves as an excellent means of phycoremediation of pollutants in waste streams with value addition and environmental benefits.

Physiological and Biochemical Responses of Bicarbonate Supplementation on Biomass and Lipid Content of Green Algae Scenedesmus sp. BHU1 Isolated From Wastewater for Renewable Biofuel Feedstock

In the present study, different microalgae were isolated from wastewater environment and evaluated for higher growth and lipid accumulation. The growth adaptability of all the isolated microalgae were tested for carbon source with supplementation of sodium bicarbonate in BG-11 N⁺ medium. Further based on the uptake rate of sodium bicarbonate and growth behavior, microalgal strains were selected for biofuel feedstock. During the study, growth parameters of all the isolates were screened after supplementation with various carbon sources, in which strain Scenedesmus sp. BHU1 was found highly effective among all. The efficacy of Scenedesmus sp. BHU1 strain under different sodium bicarbonate (4–20 mM) concentration, in which higher growth 1.4 times greater than control was observed at the concentration 12 mM sodium bicarbonate. In addition, total chlorophyll content (Chl-a + Chl-b), chlorophyll fluorescence (Fv/Fm, Y(II), ETR max, and NPQmax), and biomass productivity were found to be 11.514 μg/ml, 0.673, 0.675, and 31.167 μmol electrons m⁻² s⁻¹, 1.399, 59.167 mg/L/day, respectively, at the 12 mM sodium bicarbonate. However, under optimum sodium bicarbonate supplementation, 56.920% carbohydrate and 34.693% lipid content were accumulated, which showed potential of sodium bicarbonate supplementation in renewable biofuel feedstock by using Scenedesmus sp. BHU1 strain.

Mixed Contaminants: Occurrence, Interactions, Toxicity, Detection, and Remediation

The ever-increasing rate of pollution has attracted considerable interest in research. Several anthropogenic activities have diminished soil, air, and water quality and have led to complex chemical pollutants. This review aims to provide a clear idea about the latest and most prevalent pollutants such as heavy metals, PAHs, pesticides, hydrocarbons, and pharmaceuticals—their occurrence in various complex mixtures and how several environmental factors influence their interaction. The mechanism adopted by these contaminants to form the complex mixtures leading to the rise of a new class of contaminants, and thus resulting in severe threats to human health and the environment, has also been exhibited. Additionally, this review provides an in-depth idea of various in vivo, in vitro, and trending biomarkers used for risk assessment and identifies the occurrence of mixed contaminants even at very minute concentrations. Much importance has been given to remediation technologies to understand our current position in handling these contaminants and how the technologies can be improved. This paper aims to create awareness among readers about the most ubiquitous contaminants and how simple ways can be adopted to tackle the same.

Biodetoxification mercury by using a marine bacterium Marinomonas sp. RS3 and its merA gene expression under mercury stress

Mercury (Hg) pollution in water has been a problem for the ecosystem and human health, thus eco-friendly remediation methods are gaining traction around the world. In this study, a bacterial strain designated as RS3 isolated from the Red Sea (Saudi Arabia) has shown tolerance to more than 250 mg/L of Hg²⁺ on minimum inhibitory studies. The isolate RS3 was identified as Marinomonas sp., (Accession No: OK271312) using 16s rRNA sequencing. Tracing the growth curve for the RS3 showed that maximum growth attained at 72 h and only 10% reduction than the control medium for 50 mg/L HgCl₂ supplemented seawater medium, which continued to reduce as 21% to 60 with the increment of HgCl₂ from 100 to 350 mg/L. The Hg²⁺ removal potential of RS3 is observed to be 78% at 50 mg/L HgCl₂/72 h, which is significantly altered with the addition of carbon source such as glucose (84.5%) > fructose (79.8%) > control (78%) > citrate (73.4%) > acetate (60.2%) > maltose (54.7%). Box-Behnken design (BBD) well proposed a model with R² value of 0.8922, which predict a utmost Hg²⁺ removal of 89.5% by RS2 at favorable conditions (pH-7; NaC 1% and glucose 5%) at 72 h. Mercuric reductase enzyme encoded merA gene expression was found to be high in RS3 isolates cultivated in 100 mg/L of HgCl₂ in comparison with other variables. Thus the seawater isolate Marinomonas sp. RS3 expressed a significant tolerance and removal potential towards the Hg²⁺, which would make it is a noteworthy applicant for effective mercury remediation practices.

Advanced HRT-Controller Aimed at Optimising Nitrogen Recovery by Microalgae: Application in an Outdoor Flat-Panel Membrane Photobioreactor

A fuzzy knowledge-based controller of hydraulic retention time (HRT) was designed and tested in an outdoor membrane photobioreactor (MPBR) to improve nitrogen recovery from a microalgae cultivation system, maintaining the algae as photosynthetically active as possible and limiting their competition with other microorganisms. The hourly flow of the MPBR system was optimised by adjusting the influent flow rate to the outdoor environmental conditions which microalgae were exposed to at any moment and to the nitrogen uptake capacity of the culture. A semi-empirical photosynthetically active radiation (PAR) prediction model was calibrated using total cloud cover (TCC) forecast. Dissolved oxygen, standardised to 25 °C (DO25), was used as an on-line indicator of microalgae photosynthetic activity. Different indexes, based on suspended solids (SS), DO25, and predicted and real PAR, were used as input variables, while the initial HRT of each operating day (HRT0) and the variation of HRT (ΔHRT) served as output variables. The nitrogen recovery efficiency, measured as nitrogen recovery rate (NRR) per nitrogen loading rate (NLR) in pseudo-steady state conditions, was improved by 45% when the HRT-controller was set in comparison to fixed 1.25-d HRT. Consequently, the average effluent total soluble nitrogen (TSN) concentration in the MPBR was reduced by 47%, accomplishing the discharge requirements of the EU Directive 91/271/EEC.

Outdoor phycoremediation and biomass harvesting optimization of microalgae Botryococcus sp. cultivated in food processing wastewater using an enclosed photobioreactor

Microalgae cultivation is well known as a sustainable method for eco-friendly wastewater phycoremediation and valuable biomass production. This study investigates the feasibility and kinetic removal of organic compounds and nutrients from food processing wastewater (FPW) using Botryococcus sp. in an enclosed photobioreactor. Simultaneously, response surface methodology (RSM) via face-centered central composite design (FCCCD) was applied to optimize the effects of alum and chitosan dosage and pH sensitivity on flocculation efficiency. The maximum growth rate of Botryococcus sp. cultivated in FPW was 1.83 mg day^-1with the highest removal of chemical oxygen demand (COD), total organic carbon (TOC), and total phosphorus (TP) after 12 days of phycoremediation of 96.1%, 87.2%, and 35.4%, respectively. A second-order polynomial function fits well with the experimental results. Both coagulant dosage and pH significantly (p < 0.05) affect the flocculation efficiency of Botryococcus sp. biomass cultivated in FPW. The highest flocculation efficiency (92.4%) was obtained at a dosage of 166 mg L^-1and pH 12 for alum coagulant, while 94.9% flocculation efficiency was achieved with optimum chitosan dosage and pH of 30 mg L^-1and 5.54, respectively. In general, Botryococcus sp. shows a great removal efficiency of FPW contamination, whereas RSM provides excellent analysis for biomass harvesting optimization using a flocculation technique.

Waste Ox bone based heterogeneous catalyst synthesis, characterization, utilization and reaction kinetics of biodiesel generation from Jatropha curcas oil

The present investigation has been carried out to utilize waste animal (Ox) bone for the progress of an innovative, low-budget, pollution free, and extremely resourceful heterogeneous catalyst synthesis for Jatropha curcas oil (JCO) conversion into biodiesel. The heterogeneous catalyst synthesized was characterized by its basic strength and subjected to spectroscopic (Fourier TransformInfrared and X-Ray Diffraction) and thermogravimetric analyses. Also, the physical properties of produced biodiesel were studied. The calcined Ox bone catalyst characterization distinctly showed that there was a tremendous catalytic activity for biodiesel synthesis. The kinetic study was accomplished employing a tri-necked RB flask furnished with a condenser and agitator. At the agitation speed of 500 rpm, 5% catalyst loading rate (w/w) of oil and 12:1 methanol-oil ratio (molar), biodiesel yields were tracked based on reaction time (1-4 h) and temperature (313-338 K). The temperature at 338 K was found to be optimal to obtain maximum (96.82%) biodiesel yield. Pseudo-first order kinetics was followed in the reaction. The energy required for the activation (E_a) was 38.55 kJ mol^-1 with a frequency factor (k_o) of 7.03 × 10⁶ h^-1. The reusability studies demonstrated that the calcined animal bone catalyst was much stable up to three cycles with >90% FAME yield, which was reduced significantly (P < 0.05) to 61% in the fourth cycle. The outcome of this investigation brought to light the possibilities of utilizing calcined Ox bone catalyst and JCO as low-cost and frequently obtainable discarded waste materials that can be used as feedstock for the commercial-scale generation of biodiesel to fulfill the prospective community demands.

The Effect of Trophic Modes on Biomass and Lipid Production of Five Microalgal Strains

Five microalgae strains, namely Isochrysis galbana, Microchloropsis gaditana, Scenedesmus obliquus, Nannochloropsis oculata and Tetraselmis suecica, were selected as potential candidates for polyunsaturated fatty acids’ production, evaluating biomass productivity and their capacity to accumulate high lipid contents under different trophic modes. Microalgae strains were cultivated in the presence of 1% glucose using mixotrophic and heterotrophic conditions, while autotrophic cultures served as control experiments. The results demonstrate that S. obliquus performed the highest biomass productivity that reached 0.13 and 0.14 g L−1 d−1 under mixotrophic and heterotrophic conditions, respectively. I. galbana and S. obliquus utilized elevated contents of glucose in mixotrophy, removing 55.9% and 95.6% of the initial concentration of the carbohydrate, respectively, while glucose consumption by the aforementioned strains also remained high under heterotrophic cultivation. The production of lipids was maximal for I. galbana in mixotrophy and S. obliquus in heterotrophy, performing lipid productivities of 24.85 and 22.77 mg L−1 d−1, respectively. The most abundant saturated acid detected for all microalgae strains evaluated was palmitic acid (C16:0), while oleic and linolenic acids (C18:1n9c/C18:3n3) comprised the most abundant unsaturated fatty acids. I. galbana performed the highest linoleic acid (C18:2n6c) content under heterotrophic nutrition, which reached 87.9 mg g−1 of ash-free dry weight. Among the microalgae strains compared, the biomass and lipid production monitored for I. galbana and S. obliquus confirm that both strains could serve as efficient bioproducers for application in algal biorefineries.