Removal of Heavy Metal Contaminants from Wastewater by Using Chlorella vulgaris Beijerinck: A Review

Microalgal biorefineries: Advancement in machine learning tools for sustainable biofuel production and value-added products recovery

The microalgae can be converted into biofuels, biochemicals, and bioactive compounds in a biorefinery. Recently, designing and executing more viable and sustainable biofuel production from microalgal biomass is one of the vital challenges in the development of biorefinery. Scalable cultivation of microalgae is mandatory for commercializing and industrializing the biorefinery. The intrinsic complication in cultivation of microalgae is the physiological and operational factors that renders challenging impact to enable a smooth and profitable operation. However, this aim can only be successful via a simulation prospect. Machine learning tools provides advanced approaches for evaluating, predicting, and controlling uncertainties in microalgal biorefinery for sustainable biofuel production. The present review provides a critical evaluation of the most progressing machine learning tools that validate a potential to be employed in microalgal biorefinery. These tools are highly potential for their extensive evaluation on microalgal screening and classification. However, the application of these tools for optimization of microalgal biomass cultivation in industries in order to increase the biomass production, is still in its initial stages. Integrated hybrid machine learning tools can aid the industries to function efficiently with least resources. Some of the challenges, and perspectives of machine learning tools are discussed. Besides, future prospects are also emphasized. Though, most of the research reports on machine learning tools are not appropriate to gather generalized information, standard protocols and strategies must be developed to design generalized machine learning tools. On a whole, this review offers a perspective information about digitalized microalgal exploitation in a microalgal biorefinery.

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.

Utilization of microalgal-bacterial energy nexus improves CO2 sequestration and remediation of wastewater pollutants for beneficial environmental services

Carbon dioxide (CO2) emissions from the combustion of fossil fuels and coal are primary contributors of greenhouse gases leading to global climate change and warming. The toxicity of heavy metals and metalloids in the environment threatens ecological functionality, diversity and global human life. The ability of microalgae to thrive in harsh environments such as industrial wastewater, polluted lakes, and contaminated seawaters presents new, environmentally friendly, and less expensive CO2 remediation solutions. Numerous microalgal species grown in wastewater for industrial purposes may absorb and convert nitrogen, phosphorus, and organic matter into proteins, oil, and carbohydrates. In any multi-faceted micro-ecological system, the role of bacteria and their interactions with microalgae can be harnessed appropriately to enhance microalgae performance in either wastewater treatment or algal production systems. This algal-bacterial energy nexus review focuses on examining the processes used in the capture, storage, and biological fixation of CO2 by various microalgal species, as well as the optimized production of microalgae in open and closed cultivation systems. Microalgal production depends on different biotic and abiotic variables to ultimately deliver a high yield of microalgal biomass.

A pilot-scale study of the integrated phycoremediation-photolytic ozonation based municipal solid waste leachate treatment process

Municipal solid waste (MSW) leachate is a highly polluted liquid that accumulates in the landfill and contains a high concentration of toxic pollutants which can pollute the surrounding surface water and groundwater as well, if not treated properly. In this study, an integrated approach of phycoremediation with photolytic ozonation was employed for the leachate collected from the MSW dumpsite which has high Chemical Oxygen Demand (COD) and ammonium (NH₄⁺) levels. Photolytic ozonation treatment was employed as a pre-treatment step under operating parameters of pH: 9.0; Ozone dosage: 5 g/h; UV-C: λ = 254 nm; and contact time: 60 min, in which the COD and NH₄⁺ in the leachate was reduced up to 81% and 95%, respectively. The selected algae Chlorella vulgaris (C.vulgaris) was employed in a lab-scale study to optimize the inoculum conditions in the photolytic ozonated leachate (POL). The specific growth rate of C.vulgaris was observed as 0.14/d in the POL at the optimized condition (inoculum size of 25% (T25)) during the study period of 11 days. High-rate algal pond (HRAP) was employed for the pilot-scale study in controlled environmental conditions as in the T25 experimental run for the assessment of POL treatment and biomass production. C.vulgaris reduced the concentration of pollutants COD, NH₄⁺, and heavy metals (Cu, Fe) in the POL up to 93%, 94%, and 71%, respectively, with the dry biomass productivity of 0.727 g/L/d which is 3 times higher than the biomass productivity of C.vulgaris in freshwater conditions. The biochemical composition (carbohydrates, proteins, and lipids) of the harvested biomass has higher lipid production with lipid productivity of 120 mg/L/d which can be used as a feedstock for the production of value-a dded products.

Native Desmodesmus sp. and Chlorella sp. isolated from the Reconquista River display a different binding preference for Cu(II) and Zn(II)

The present work was developed to study the metal removal performance of unicellular algae isolated from the Reconquista River and to evaluate the effect of the presence of more than one metal in the removal process. Thus, native species of unicellular algae were isolated from the highly contaminated Reconquista River. All of the isolates were classified, at genus level, based on their morphological appearance. Nine isolates were screened for their Zn(II) removal capacities. Chlorella sp. RR5 and Desmodesmus sp. RR7 were selected based on their removal performance, and their potential in the remediation of multiple metals was analyzed. Therefore, zinc (Zn(II)), copper (Cu(II)), and chromium (Cr(VI)) removal was evaluated in mono- and multi-metallic solutions. Biosorption capacities were high (0.8-1.8 mmol g^-1) for Zn(II) and Cu(II) in mono-metallic solutions. Removal capacities decreased up to 48% in multi-metallic solutions. Interestingly, when multi-metallic systems were considered, each strain showed a metal preference. Chlorella sp. removed better Cu(II) meanwhile Desmodesmus sp. showed a preference for Zn(II). Thus, a metal-binding selectivity in each strain was determined. Chromium (VI) remediation was almost null in the conditions analyzed in this work. Fourier transformation infrared spectroscopy (FT-IR) analysis showed that polysaccharides were the main functional group involved in metal adsorption and, in some cases, also the carboxylates played an important role. Overall, we were able to analyze a new source of algal diversity and perform a metal removal characterization of them, leading to the identification of a metal selectivity based on the characteristics of the tested algal strains.