A Comprehensive Study on Chlorella pyrenoidosa for Phenol Degradation and its Potential Applicability as Biodiesel Feedstock and Animal Feed

Recent advances in remediation strategies for mitigating the impacts of emerging pollutants in water and ensuring environmental sustainability

The proliferation of emerging pollutants (EPs), encompassing a range of substances such as phthalates, phenolics, pharmaceuticals, pesticides, personal care products, surfactants, and disinfection agents, has become a significant global concern due to their potential risks to the environment and human well-being. Over the past two decades, numerous research studies have investigated the presence of EPs in wastewater and aquatic ecosystems, with the United States Environmental Protection Agency (USEPA) categorizing these newly introduced chemical compounds as emerging contaminants due to their poorly understood impact. EPs have been linked to adverse health effects in humans, including genotoxic and cytotoxic effects, as well as conditions such as obesity, diabetes, cardiovascular disease, and reproductive abnormalities, often associated with their estrogenic action. Microalgae have shown promise in the detoxification of both inorganic and organic contaminants, and several large-scale microalgal systems for wastewater treatment have been developed. However, the progress of algal bioremediation can be influenced by accidental contaminations and operational challenges encountered in pilot-scale research. Microalgae employ various processes, such as bioadsorption, biouptake, and biodegradation, to effectively remediate EPs. During microalgal biodegradation, complex chemical compounds are transformed into simpler substances through catalytic metabolic degradation. Integrating algal bioremediation with existing treatment methodologies offers a viable approach for efficiently eliminating EPs from wastewater. This review focuses on the use of algal-based biological remediation processes for wastewater treatment, the environmental impacts of EPs, and the challenges associated with implementing algal bioremediation systems to effectively remove emerging pollutants.

Efficiency, mechanism, influencing factors, and integrated technology of biodegradation for aromatic compounds by microalgae: A review

Aromatic compounds have received widespread attention because of their threat to ecosystem and human health. However, traditional physical and chemical methods are criticized due to secondary pollution and high cost. As a result of ecological security and the ability of carbon sequestration, biodegradation approach based on microalgae has emerged as a promising alternative treatment for aromatic pollutants. In light of the current researches, the degradation efficiency of BTEX (benzene, toluene, ethylbenzene, and xylene), polycyclic aromatic hydrocarbons (PAHs), and phenolic compounds by microalgae was reviewed in this study. We summarized the degradation pathways and metabolites of p-xylene, benzo [a]pyrene, fluorene, phenol, bisphenol A, and nonylphenol by microalgae. The influence factors on the degradation of aromatic compounds by microalgae were also discussed. The integrated technologies based on microalgae for degradation of aromatic compounds were reviewed. Finally, this study discussed the limitations and future research needs of the degradation of these compounds by microalgae.

Evaluation of the mechanisms underlying altered fatty acid biosynthesis in heterotrophic microalgal strain Chlorella sorokiniana during biodegradation of phenol and p-nitrophenol

Phenolic compounds have become a severe environmental concern due to water contamination, affecting the sustainability of the ecosystem. The microalgae enzymes have enticed for the efficient involvement in the biodegradation of phenolics compound in metabolic processes. In this investigation, the oleaginous microalgae Chlorella sorokiniana was cultured heterotrophically under the influence of phenol and p-nitrophenol. The enzymatic assays of algal cell extracts were used to decipher the underlying mechanisms for phenol and p-nitrophenol biodegradation. A reduction of 99.58% and 97.21% in phenol and p-nitrophenol values, respectively, was recorded after the 10th day of microalgae cultivation. Also, the biochemical components in phenol, p-nitrophenol, and control were found to be 39.6 ± 2.3%, 36.7 ± 1.3%, and 30.9 ± 1.8% (total lipids); 27.4 ± 1.4%, 28.3 ± 1.8%, and 19.7 ± 1.5% (total carbohydrates); and 26.7 ± 1.9%, 28.3 ± 1.9%, and 39.9 ± 1.2% (total proteins), respectively. The GC-MS and 1H-NMR spectroscopy attested the incidence of fatty acid methyl esters in the synthesized microalgal biodiesel. The activity of catechol 2,3-dioxygenase and hydroquinone 1,2-dioxygenase in microalgae under heterotrophic conditions has conferred the ortho- and hydroquinone pathways for phenol and p-nitrophenol biodegradation, respectively. Also, the acceleration of fatty acid profiles in microalgae is deliberated under the impact of the phenol and p-nitrophenol biodegradation process. Thus, microalgae enzymes in the metabolic degradation process of phenolic compounds encourage ecosystem sustainability and biodiesel prospects due to the increased lipid profiles of microalgae.

Phenol phycoremediation by Haematococcus pluvialis coupled with enhanced astaxanthin and lipid production under rac-GR24 supplementation for enhanced biodiesel production

The present study evaluated the impact of rac-GR24 on biomass and astaxanthin production under phenol stress coupled with biodiesel recovery from Haematococcus pluvialis. Phenol supplementation showed negative impact on growth, where the lowest biomass productivity of 0.027 g L^-1 day^-1 was recorded at 10 µM phenol, while 0.4 µM rac-GR24 supplementation showed the highest recorded biomass productivity of 0.063 g L^-1 day^-1. Coupling 0.4 µM rac-GR24 at different phenol concentrations confirmed the potential of rac-GR24 to mitigate the toxic effect of phenol by enhancing yield of PSII yield, RuBISCo activity, and antioxidant efficiency, which resulted in improved phenol phycoremediation efficiency. In addition, results suggested a synergistic action by rac-GR24 supplementation under phenol treatment where rac-GR24 enhanced lipid accumulation, while phenol enhanced astaxanthin production. Dual supplementation of rac-GR24 and phenol showed the highest recorded FAMEs content, which was 32.6% higher than the control, with improved biodiesel quality. The suggested approach could enhance the economic feasibility of triple-purpose application of microalgae in wastewater treatment, astaxanthin recovery, and biodiesel production.

Hormesis effects of phenol on growth and cellular metabolites of Chlorella sp. under different nutritional conditions using response surface methodology

The present study investigated the effects of different phenol concentrations (200 - 1000 mg L^-1) towards Chlorella sp. under different culture conditions (light vs. dark) and NaNO₃ concentrations (0 - 0.1 g L^-1) using central composite design. Phenol induced hormesis effects on the algal growth and cellular metabolites. Nitrate was identified as a crucial factor for promoting the uptake of phenol by Chlorella cells, while light was a limiting factor for growth, but the phyco-toxicity of phenol was decreased in the dark. The pigment contents were generally increased in the treated cells to protect against the oxidative phenol stress. The incorporation of 200 mg L^-1 phenol and 0.05 g L^-1 NaNO₃ to the illuminated cells markedly promoted biomass and lipid contents to 0.22 g L^-1 and 26.26% w/w, which was 44 and 112% higher than the phenol-less control, respectively. Under the same conditions, the increase of phenol concentration to 600 mg L^-1, the protein contents were increased to 18.59% w/w. Conversely, the algal cells were able to accumulate more than 60% w/w of soluble carbohydrates under dark conditions at 600 mg L^-1 of phenol. Nitrate replete conditions stimulated lipid accumulation at the expense of protein biosynthesis. Furthermore, most of the treatments showed an increase of H₂O₂ and malonaldehyde contents, especially for the illuminated cells. However, catalase activity tended to increase under dark conditions, especially at low phenol and nitrate concentrations. This study is valuable in indicating the effects of phenol on microalgae by exploiting response surface methodology, which can be applied as a powerful tool in growth monitoring and toxicity assessment.

Allelopathic effect of benzoic acid (hydroponics root exudate) on microalgae growth

Hydroponic effluent (HE) contains a reasonable amount of residual nutrients. Therefore, HE could be used as a low-cost growth media for microalgae mediated resource recovery and water recycling. However, the presence of root exudates (particularly, benzoic acid) may lead to toxicity in microalgae.In the present study, the allelopathic effects of benzoic acid on microalgal growth was tested. During 96 h batch growth, Chlorella pyrenoidosa showed the highest biomass concentration (0.064-0.037 g.L^-1) compared to Chlorella sorokiniana (0.09-0.26 g.L^-1) at the tested benzoic acid doses. Moreover, both the species showed growth stimulation and growth inhibition up to certain benzoic acid doses. Hence, both the microalgal species showed allelopathic behaviour at different doses of benzoic acid. Further, the observed half effective concentration (96 h EC₅₀) were 65.10 mg.L^-1 and 105.27 mg.L^-1, respectively, for Chlorella pyrenoidosa and C. sorokiniana with 95% confidence limits. Further, Haldane's model best fitted with experimental data of both the microalgae (r ∼ 0.99). Overall, the study reveals that the HE with low benzoic acid dose may serve as a suitable growth media for microalgae. However, further in-depth research interventions using real HE are desirable to determine its real-world applicability.

Capacity of Marine Microalga Tetraselmis suecica to Biodegrade Phenols in Aqueous Media

Phenolic compounds are toxic and dangerous to the environment and human health. Although the removal of phenols and their derivatives is very difficult, it has been achieved by applying some biological processes. The capacity of microalga to remove phenolic compounds has been demonstrated; however, few reports of the removal of these compounds in a mixture have been published. The removal of phenol, p-cresol and o-cresol was performed by batch kinetics at 50 and 100 mg L−1, and the simultaneous degradation of phenol, p-cresol and o-cresol was carried out in a mixture at 40 mg L−1 using the marine microalga Tetraselmis suecica. The kinetic study was carried out for 192 h. For concentrations of 50 mg L−1 and 100 mg L−1, phenolic compound consumption efficiencies greater than 100% and 85%, respectively, were obtained, and up to 73.6% removal in the mixture. The results obtained indicate that the marine microalga carries out a process of the oxidation of organic matter and phenolic compounds, mineralizing up to 31.4% to CO2 in the mixture. Biological treatments using the marine microalga T. suecica can be considered feasible to treat effluents with concentrations similar to those of the present study.

Phenol biodegradation by immobilized Rhodococcus qingshengii isolated from coking effluent on Na-alginate and magnetic chitosan-alginate nanocomposite

Phenol is a hazardous organic solvent to living organisms, even in its small amounts. In order to bioremediation of phenol from aqueous solution, a novel bacterial strain was isolated from coking wastewater, identified as Rhodococcus qingshengii based on 16S rRNA sequence analysis and named as strain Sahand110. The phenol-biodegrading capabilities of the free and immobilized cells of Sahand110 on the beads of Na-alginate (NA) and magnetic chitosan-alginate (MCA) nanocomposite were evaluated under different initial phenol concentrations (200, 400, 600, 800 and 1000 mg/L). Results illustrated that Sahand110 was able to grow and complete degrade phenol up to 600 mg/L, as the sole carbon and energy source. Immobilized cells of Sahand110 on NA and MCA were more competent than its free cells in degradation of high phenol concentrations, 100% of 1000 mg/L phenol within 96 h, indicating the improved tolerance and performance of the immobilized cells against phenol toxicity. Therefore, the immobilized Sahand110 on the studied beads, especially MCA bead regarding its suitable properties, has significant potential to enhanced bioremediation of phenol-rich wastewaters.

Potential Application of Algae in Biodegradation of Phenol: A Review and Bibliometric Study

One of the most severe environmental issues affecting the sustainable growth of human society is water pollution. Phenolic compounds are toxic, hazardous and carcinogenic to humans and animals even at low concentrations. Thus, it is compulsory to remove the compounds from polluted wastewater before being discharged into the ecosystem. Biotechnology has been coping with environmental problems using a broad spectrum of microorganisms and biocatalysts to establish innovative techniques for biodegradation. Biological treatment is preferable as it is cost-effective in removing organic pollutants, including phenol. The advantages and the enzymes involved in the metabolic degradation of phenol render the efficiency of microalgae in the degradation process. The focus of this review is to explore the trends in publication (within the year of 2000-2020) through bibliometric analysis and the mechanisms involved in algae phenol degradation. Current studies and publications on the use of algae in bioremediation have been observed to expand due to environmental problems and the versatility of microalgae. VOSviewer and SciMAT software were used in this review to further analyse the links and interaction of the selected keywords. It was noted that publication is advancing, with China, Spain and the United States dominating the studies with total publications of 36, 28 and 22, respectively. Hence, this review will provide an insight into the trends and potential use of algae in degradation.

Microalgae biofilm cultured in nutrient-rich water as a tool for the phycoremediation of petroleum-contaminated water

This study aimed at studying the phycoremediation of petroleum-contaminated water using microalgae biofilm cultured in nutrient-rich water. Microalgae biofilm was grown in a photobioreactor containing water rich in calcium nitrate, manganese chloride, sodium potassium tartrate, calcium phosphate, and ammonium sulfate. Petroleum contaminated water was poured into a photobioreactor, and the substrate containing microalgae biofilm was inserted into the photobioreactor and allowed for eight weeks for biofilm formation. Physicochemical parameters (pH, turbidity, conductivity, sulfate, alkalinity, chloride, TDS, TSS, nitrate, salinity, iron, potassium, phosphate, chlorine, chromium, magnesium, zinc, COD, BOD, and total petroleum hydrocarbon (TPH) of the petroleum contaminated water before and after treatment were determined. The microalgae biofilm used for the treatment was characterized before and after treatment using a Scanning Electron Microscope, X-Ray Fluorescence, and Fourier-transform infrared spectroscopy. The phytochemical constituent of the microalgae biofilm was also determined before and after treatment of the petroleum-contaminated water. The result obtained shows highest removal efficiency of physicochemical parameters (turbidity (81%), conductivity (51.2), sulfate (17.5%), alkalinity 28.4%), chloride (14.6%), TDS (7.9), TSS (26%), nitrate (33%), salinity (23.4), iron (16%), potassium (22%), phosphate (28.2%), chlorine (14%), chromium (13.6%), magnesium (30.3%), zinc (40.5%), COD (8%), BOD (16.7%) and total petroleum hydrocarbon (15%)). The microalgae's characterization shows microalgae biofilm's ability to adsorb pollutants in petroleum-contaminated water due to the presence of microspores and larger surface area of the cells of the microalgae forming the biofilm or due to the absorption efficiency of the extracellular polymeric substances (EPS). The analysis of the microalgae biofilm's phytochemical parameters shows the involvement of the chemicals components in pollutants degradation and antioxidant response of the microalgae to counteract the oxidative effect resulting from the exposure of the microalgae to the contaminated water. NOVELTY STATEMENT This is the first study that attempts the phycoremediation of petroleum contaminated water using microalgae biofilm. The reduction efficiency of the parameters treated in this study is very low compared to that reported in the literature but increases with the retention day. This low reduction efficiency is attributed to the slow assimilation of organic and inorganic pollutants due to the initial growth condition. This study is the first to re-affirm that microalgae biofilm can phycoremediate petroleum-contaminated water by adsorption and assimilation due to the presence of microspores and a larger surface area the cells of the microalgae forming the biofilm or the extracellular polymetric surface covering the biofilm. Several studies have reported that phytochemicals present in microalgae play an antioxidant response role to prevent the microalgae from oxidative damage resulting from water pollution. However, this study is the first to strongly link phytochemicals to the enhancement of pollutants degradation and adsorption by microalgae biofilm.

Phycoremediation of phenol-polluted petro-industrial effluents and its techno-economic values as a win-win process for a green environment, sustainable energy and bioproducts

The discharge of the toxic phenol-polluted petro-industrial effluents (PPPIE) has severe environmental negative impacts, thus it is mandatory to be treated before its discharge. The objective of this review was to discuss the sustainable application of microalgae in phenols degradation, with a special emphasis on the enzymes involved in this bioprocess and the factors affecting the success of PPPIE phycoremediation. Moreover, it confers the microalgae bioenergetic strategies to degrade different forms of phenols in PPPIE. It also points out the advantages of the latest application of bacteria, fungi and microalgae as microbial consortia in phenols biodegradation. Briefly, phycoremediation of PPPIE consumes carbon dioxide emitted from petro-industries for; valorization of the polluted water to be reused and production of algal biomass which can act as a source of energy for such integrated bioprocess. Besides, the harvested algal biomass can feasibly produce; third-generation biofuels, biorefineries, bioplastics, fish and animal feed, food supplements, natural dyes, antioxidants and many other valuable products. Consequently, this review precisely confirms that the phycoremediation of PPPIE is a win-win process for a green environment and a sustainable future. Thus, to achieve the three pillars of sustainability; social, environmental and economic; it is recommendable to integrate PPPIE treatment with algal cultivation. This integrated process would overcome the problem of greenhouse gas emissions, global warming and climate change, solve the problem of water-scarce, and protect the environment from the harmful negative impacts of PPPIE.

Using microalgae for remediation of crude petroleum oil-water emulsions

Crude petroleum oil spills are among the most important organic contaminations. While the separated oils accumulated on the surface water are relatively easily removed, the emulsified portions are more difficult to remove and pose significant threats to the environment. Bioremediation using bacteria has proven to be an effective method, but the biomass produced in this case does not have any significant remunerative value. In this work, microalgae were proposed to combine emulsified oil remediation process with the potential of microalgae as a biofuel feedstock, thus enhancing the economic and environmental benefits of the process. A freshwater strain of Chlorella vulgaris was grown in water containing different concentrations of emulsified crude oil at different temperatures. The specific growth rate (μ_max ) of the microalgae for each initial oil concentration was determined and was found to increase with the increase in initial oil concentration. For example, at 30°C, the specific growth rate, μ increased from 0.477 to 0.784 per day as the oil concentration increased from 57 to 222 mg/L. At 30°C, the effect of substrate concentration agreed with that of the microalgae growth, whereas at 40°C, the drop in oil concentration decreased with the increase in concentration. The results were fitted to a modified Monod kinetics model that used specific interfacial area as the influential substrate instead of the actual concentration. The results of this study clearly show the potential of using microalgae for emulsified oil remediation at relatively high concentrations.

Biodegradation of phenol by Chlamydomonas reinhardtii

The data presented in this particular study demonstrate that the biodegradation of phenol by Chlamydomonas reinhardtii is a dynamic bioenergetic process mainly affected by the production of catechol and the presence of a growth-promoting substrate in the culture medium. The study focused on the regulation of the bioenergetic equilibrium resulting from production of catechol after phenol oxidation. Catechol was identified by HPLC-UV and HPLC-ESI-MS/MS. Growth measurements revealed that phenol is a growth-limiting substrate for microalgal cultures. The Chlamydomonas cells proceed to phenol biodegradation because they require carbon reserves for maintenance of homeostasis. In the presence of acetic acid (a growth-promoting carbon source), the amount of catechol detected in the culture medium was negligible; apparently, acetic acid provides microalgae with sufficient energy reserves to further biodegrade catechol. It has been shown that when microalgae do not have sufficient energy reserves, a significant amount of catechol is released into the culture medium. Chlamydomonas reinhardtii acts as a versatile bioenergetic machine by regulating its metabolism under each particular set of growth conditions, in order to achieve an optimal balance between growth, homeostasis maintenance and biodegradation of phenol. The novel findings of this study reveal a paradigm showing how microalgal metabolic versatility can be used in the bioremediation of the environment and in potential large-scale applications.

Investigation on phenol degradation capability of Scenedesmus regularis: influence of process parameters

Phenol removal from environmental solutions has attracted much attention due to phenol's high toxicity, even at low concentrations. This study aims to reveal the phenol biodegradation capacity of Scenedesmus regularis. Batch system parameters (pH, amount of algal cell, phenol concentration) on biodegradation were examined. After 24 h of treatment, 92.16, 94.50, 96.20, 80.53, 65.32, 52 and 40% of phenol were removed by Scenedesmus regularis in aqueous solutions containing 5, 10, 15, 20, 30, 40 and 50 mg/L of phenol, respectively. To describe the correlation between degradation rate and phenol concentration, the Michaelis-Menten kinetic equation was used where V_max and K_m are 0.82 mg phenol g algea^-1 h^-1 and 24.97 ppm, respectively. Phenol remediation ability of S.regularis can enable the usage of the spent biomass as biofuel feedstock and animal feed makes it a 'green' environmental sustainable process.

Plant hormone induced enrichment of Chlorella sp. omega-3 fatty acids

BACKGROUND

Omega-3 fatty acids have various health benefits in combating against neurological problems, cancers, cardiac problems and hypertriglyceridemia. The main dietary omega-3 fatty acids are obtained from marine fish. Due to the pollution of marine environment, recently microalgae are considered as the promising source for the omega-3 fatty acid production. However, the demand and high production cost associated with microalgal biomass make it necessary to implement novel strategies in improving the biomass and omega-3 fatty acids from microalgae.

RESULTS

Four plant hormones zeatin, indole acetic acid (IAA), gibberellic acid (GBA) and abscisic acid (ABA) were investigated for their effect on the production of biomass and lipid in isolated Chlorella sp. The cells showed an increase of the biomass and lipid content after treatments with the plant hormones where the highest stimulatory effect was observed in ABA-treated cells. On the other hand, IAA showed the highest stimulatory effect on the omega-3 fatty acids content, eicosapentaenoic acid (EPA) (23.25%) and docosahexaenoic acid (DHA) (26.06%). On the other hand, cells treated with ABA had highest lipid content suitable for the biodiesel applications. The determination of ROS markers, antioxidant enzymes, and fatty acid biosynthesis genes after plant hormones treatment helped elucidate the mechanism underlying the improvement in biomass, lipid content and omega-3 fatty acids. All four plant hormones upregulated the fatty acid biosynthesis genes, whereas IAA particularly increased omega-3-fatty acids as a result of the upregulation of omega-3 fatty acid desaturase.

CONCLUSIONS

The contents of omega-3 fatty acids, the clinically important compounds, were considerably improved in IAA-treated cells. The highest lipid content obtained from ABA-treated biomass can be used for biodiesel application according to its biodiesel properties. The EPA and DHA enriched ethyl esters are an approved form of omega-3 fatty acids by US Food and Drug Administration (FDA) which can be utilized as the therapeutic treatment for the severe hypertriglyceridemia.

Potential application of chicken manure biochar towards toxic phenol and 2,4-dinitrophenol in wastewaters

In this study, chicken manure biochar (CBC) was prepared and applied as adsorbent for the removal of phenolic pollutants including phenol (Ph) and 2,4-Dinitrophenol (DNP) from wastewaters. The feasibility analysis was focused on the adsorption effects of various factors, such as initial concentration, adsorbent dosage and reaction time. The results showed that BC could efficiently remove the Ph and DNP within 90 min of reaction time. Increasing of CBC dosage up to 0.3 g results in the maximum removal efficiency of Ph and DNP and lowers initial concentration which is beneficial for the adsorption of phenolic compounds. The second-order kinetic model and the Langmuir isotherm provided the best correlation with the adsorption data. Based on the Langmuir isotherm, maximum adsorption capacities (q_max) of Ph and DNP were found at 106.2 and 148.1 mg g^-1, respectively. The obtained q_max values for CB were higher than those reported in literature on the adsorption of Ph and DNP using different biochar. Analyzing the regeneration characteristics, BC displayed high reusability with less than 20% loss in adsorption capacities of Ph and DNP, even after five repeated cycles. Investigation of the adsorption equilibrium under various conditions suggested several possible interaction mechanisms, including hydrogen bonding, electrostatic interaction and π- π bonding, which were attributed to the binding affinity of the adsorbent-adsorbate interaction. In the field application, the CBC showed an excellent removal efficiencies of Ph and DNP from industrial wastewaters (around 80% phenolic pollutants were removed). These findings support the potential use of CBC as effective adsorbent for treatment of wastewater containing Ph and DNP.

A cost-effective and environmentally sustainable process for phycoremediation of oil field formation water for its safe disposal and reuse

High volumes of formation water comprising of complex mixture of hydrocarbons is generated during crude oil exploration. Owing to ecotoxicological concerns, the discharge of the formation water without remediation of hydrocarbonaceous pollutants is not permitted. Keeping this into mind, we carried out phycoremediation of hydrocarbons in formation water so that it can be safely discharged or re-used. For this, a native algal species was isolated from formation water followed by its morphological and 18S ribosomal RNA based identification confirming the algal isolate to be Chlorella vulgaris BS1 (NCBI GenBank Accession No. MH732950). The algal isolate exhibited high biomass productivity of 1.76 gm L⁻¹ d⁻¹ (specific growth rate: 0.21 d⁻¹, initial inoculum: 1500 mg L⁻¹) along with remediation of 98.63% petroleum hydrocarbons present in formation water within 14 days of incubation indicating an efficient hydrocarbon remediation process. Concomitantly, the hydrocarbon remediation process resulted in reduction of 75% Chemical Oxygen Demand (COD) load and complete removal of sulfate from formation water making it suitable for safe disposal or reuse as oil well injection water respectively. The present process overcomes the bottlenecks of external growth nutrient addition or dilution associated with conventional biological treatment resulting in a practically applicable and cost-effective technology for remediation of oil field formation water.

Effects of Phenolic Pollution on Interspecific Competition between Microcystis aeruginosa and Chlorella pyrenoidosa and their Photosynthetic Responses

The demand for phenolic compounds has been increasing rapidly, which has intensified the production and usage of phenol at a commercial scale. In some polluted water bodies, phenol has become one of the typical aromatic contaminants. Such water bodies are inescapably influenced by nutrients from human activities, and also suffer from nuisance cyanobacterial blooms. While phenolic pollution threatens water safety and ecological balance, algal cells are ubiquitous and sensitive to pollutants. Therefore, effects of phenolic pollution on interspecific competition between a bloom-forming cyanobacterium and other common alga merit quantitative investigation. In this study, the effects of phenol on Microcystis aeruginosa (M. aeruginosa, a bloom-forming cyanobacterium) and Chlorella pyrenoidosa (C. pyrenoidosa, a ubiquitous green alga) were analyzed in mono- and co-cultures. The two species were exposed to a series of phenol treatments (0, 2, 20, and 200 μg mL⁻¹). Population dynamics were measured by a flow cytometer and analyzed by the Lotka-Volterra model. The results showed that M. aeruginosa was more sensitive to phenol (EC₅₀ = 80.8 ± 0.16 μg mL⁻¹) compared to C. pyrenoidosa (EC₅₀ = 631.4 ± 0.41 μg mL⁻¹) in mono-cultures. M. aeruginosa won in the co-cultures when phenol was below or equal to 20 μg mL⁻¹, while C. pyrenoidosa became the dominant species in the 200 μg mL⁻¹ treatment. Photosynthetic activity was measured by a fluometer. Results showed phenol significantly impacted the photosynthetic activity of M. aeruginosa by inhibiting the acceptor side of its photosystem II (PSII), while such inhibition in C. pyrenoidosa was only observed in the highest phenol treatment (200 μg mL⁻¹). This study provides a better understanding for predicting the succession of algal community structure in water bodies susceptible to phenolic contamination. Moreover, it reveals the mechanism on photosynthetic responses of these two species under phenolic stress.

Characterization of cometabolic degradation of p-cresol with phenol as growth substrate by Chlorella vulgaris

To investigate the potential application of Chlorella vulgaris in the treatment of coal gasification wastewater, the characteristics of phenol and p-cresol cometabolism by Chlorella vulgaris were studied, including phenol degradation, ammonia nitrogen removal, antioxidant enzyme activities, and phenol hydroxylase activity. The results showed that the highest tolerable concentrations of phenol and p-cresol for Chlorella vulgaris were 800 and 400 mg/L, respectively. During cometabolism, phenol at low concentrations (100 mg/L) significantly promoted the degradation of p-cresol. Meanwhile, the removal efficiency of ammonia nitrogen was approximately 60% and was not affected by variations in phenol concentration. Furthermore, the cometabolism of phenol and p-cresol was enhanced by improvement of phenol hydroxylase activity of Chlorella vulgaris after the addition of NaHCO₃ as an exogenous nutrient. Therefore, Chlorella vulgaris has a great potential for the biochemical treatment of coal gasification wastewater.

Microalgae cultivation for phenolic compounds removal

Microalgae are promising sustainable and renewable sources of oils that can be used for biodiesel production. In addition, they contain important compounds, such as proteins and pigments, which have large applications in the food and pharmaceutical industries. Combining the production of these valuable products with wastewater treatment renders the cultivation of microalgae very attractive and economically feasible. This review paper presents and discusses the current applications of microalgae cultivation for wastewater treatment, particularly for the removal of phenolic compounds. The effects of cultivation conditions on the rate of contaminants removal and biomass productivity, as well as the chemical composition of microalgae cells are also discussed.

Removal of dichlorophenol by Chlorella pyrenoidosa through self-regulating mechanism in air-tight test environment

Microalgae are surprisingly efficient to remove pollutants in a hermetically closed environment, though its growth is inhibited in the absence of pollutants. The final pH, algal density, Chl-a content, and the removal efficiency of 2,4-dichlorophenol (2,4-DCP) by Chlorellar pyrenoidosa in a closed system were observed under different initial pH, lighting regimes, and various carbon sources. The optimal condition for 2,4-DCP removal was obtained, and adopted to observe the evolution of above items by domesticated and origin strains. The results showed that both respiration and photosynthesis participated in the degradation of 2,4-DCP, and caused the changes of pH. The photosynthesis seemed to increase the solution pH, while the respiration and the biodegradation of 2,4-DCP to decrease the solution pH. The domesticated strain achieved nearly 100% removal when initial concentrations of 2,4-DCP lower than 200 μg L^-1, due to providing a appropriate but narrow pH evolution range, mostly falling between 6.5 and 7.9. The research helps to understand the mechanism of biodegradation of chlorophenol compounds by green algae.

Enhancement of lipid production in Synechocystis sp. PCC 6803 overexpressing glycerol kinase under oxidative stress with glycerol supplementation

In this study, the effect of glycerol kinase overexpression in Synechocystis sp. PCC 6803 on lipid content was investigated. The glycerol kinase overexpressing Synechocystis cells (OE) had a higher lipid content than the wild type. The OE treated with phenol up to 1 mM showed a slight increase in the cell biomass whereas the total lipid production increased considerably (0.39 ± 0.012 g/L) as compared to that of the wild type (0.26 ± 0.01 g/L). The supplementation of 12 g/L glycerol to BG11 medium increased the lipid content of phenol treated OE from 22 to 35% with the increase of lipid production from 0.39 ± 0.012 to 0.69 ± 0.035 g/L. The RT-PCR analysis revealed that the expression of glpK was upregulated from 1.3 to 2.4 and from 1.89 to 3.64-fold after phenol treatment and glycerol supplementation respectively.

Sustainable biodegradation of phenol by immobilized Bacillus sp. SAS19 with porous carbonaceous gels as carriers

In this study, high-efficient phenol-degrading bacterium Bacillus sp. SAS19 which was isolated from activated sludge by resuscitation-promoting factor (Rpf) addition, were immobilized on porous carbonaceous gels (CGs) for phenol degradation. The phenol-degrading capabilities of free and immobilized Bacillus sp. SAS19 were evaluated under various initial phenol concentrations. The obtained results showed that phenol could be removed effectively by both free and immobilized Bacillus sp. SAS19. Furthermore, for degradation of phenol at high concentrations, long-term utilization and recycling were more readily achieved for immobilized bacteria as compared to free bacteria. Immobilized bacteria exhibited significant increase in phenol-degrading capabilities in the third cycle of recycling and reuse, which demonstrated 87.2% and 100% of phenol (1600 mg/L) degradation efficiency at 12 and 24 h, respectively. The present study revealed that immobilized Bacillus sp. SAS19 can be potentially used for enhanced treatment of synthetic phenol-laden wastewater.

Multisubstrate specific flavin containing monooxygenase from Chlorella pyrenoidosa with potential application for phenolic wastewater remediation and biosensor application

Microbial degradation of phenolic pollutants in industrial wastewater is dependent on enzymatic pathway comprising a cascade of phenol metabolizing enzymes. Phenol hydroxylase is the first enzyme of the pathway catalysing the initial attack on phenol in green algae Chlorella pyrenoidosa. The present work reports cost-effective production of partially purified microalgal phenol hydroylase by single-step purification and characterization of its kinetic properties with the view of application for enzyme-based remediation of phenolic wastewater or in phenolic biosensor. The enzyme with a molecular weight of 25 kDa shows all characteristics of phenol hydroxylases, that is, hydroxylation of phenol to catechol (confirmed by HPLC), substrate-dependent NADPH oxidation, absorption spectrum typical of flavoproteins and peptide mass fingerprint corresponding to flavoprotein hydroxylase. The enzyme utilizes phenol with apparent Michealis constant (K_m) of 1.71 µM, maximal velocity (V_max) of 0.4 µM/min with optimal activity at pH 7 and 35°C. Fe²⁺chelators (Phenanthroline and sodium arsenate), heavy metals, denaturants and oxidizing agents showed inhibitory effect on phenol hydroxylation activity of the enzyme. The enzyme has broad substrate specificity against isomeric diphenols, isomeric methylphenols, halogen-substituted phenols, amino-substituted phenols, nitrophenols, hydroxybenzaldehyde and hydroxylbenzoic acid. The enzyme shows remarkable storage stability at room temperature and at 4°C. The multisubstrate specificity coupled to remarkable storage stability of the microalgal phenol hydroxylase opens up avenues for its application in remediation of a wide range of phenolics released in industrial wastewater or phenolic biosensor application.

Optimization of phenol degradation by the microalga Chlorella pyrenoidosa using Plackett-Burman Design and Response Surface Methodology

Statistical optimization designs were used to optimize the phenol degradation using Chlorella pyrenoidosa. The important factor influencing phenol degradation was identified by two-level Plackett-Burman Design (PBD) with five factors. PBD determined the following three factors as significant for phenol degradation viz. algal concentration, phenol concentration and reaction time. CCD and RSM were applied to optimize the significant factors identified from PBD. The results obtained from CCD indicated that the interaction between the concentration of algae and phenol, phenol concentration and reaction time and algal concentration and reaction time affect the phenol degradation (response) significantly. The predicted results showed that maximum phenol degradation of 97% could be achieved with algal concentration of 4g/L, phenol concentration of 0.8g/L and reaction time of 4days. The predicted values were in agreement with experimental values with coefficient of determination (R(2)) of 0.9973. The model was validated by subsequent experimentations at the optimized conditions.

Strain improvement of Chlorella sp. for phenol biodegradation by adaptive laboratory evolution

Microalgae are highly efficient photosynthesis cell factories for CO2 capture, biofuel productions and wastewater treatment. Phenol is a typical environmental contaminant. Microalgae normally have a low tolerance for, and a low degradation rate to, high concentration of phenol. Adaptive laboratory evolution was performed for phenolic wastewater treatment by Chlorella sp. The resulting strain was obtained after 31 cycles (about 95d) under 500mg/L phenol as environmental stress. It could grow under 500mg/L and 700mg/L phenol without significant inhibition. The maximal biomass concentrations of the resulting strain at day 8 were 3.40g/L under 500mg/L phenol and 2.70g/L under 700mg/L phenol, respectively. They were more than two times of those of the original strain. In addition, 500mg/L phenol was fully removed by the resulting strain in 7d when the initial cell density was 0.6g/L.