An efficient Chlorella sp.-Cupriavidus necator microcosm for phenol degradation and its cooperation mechanism

Bioremediation for the recovery of oil polluted marine environment, opportunities and challenges approaching the Blue Growth

The Blue Growth strategy promises a sustainable use of marine resources for the benefit of the society. However, oil pollution in the marine environment is still a serious issue for human, animal, and environmental health; in addition, it deprives citizens of the potential economic and recreational advantages in the affected areas. Bioremediation, that is the use of bio-resources for the degradation of pollutants, is one of the focal themes on which the Blue Growth aims to. A repertoire of marine-derived bio-products, biomaterials, processes, and services useful for efficient, economic, low impact, treatments for the recovery of oil-polluted areas has been demonstrated in many years of research around the world. Nonetheless, although bioremediation technology is routinely applied in soil, this is not still standardized in the marine environment and the potential market is almost underexploited. This review provides a summary of opportunities for the exploiting and addition of value to research products already validated. Moreover, the review discusses challenges that limit bioremediation in marine environment and actions that can facilitate the conveying of valuable products/processes towards the market.

Cultivation of microalgae-bacteria consortium by waste gas-waste water to achieve CO2 fixation, wastewater purification and bioproducts production

The cultivation of microalgae and microalgae-bacteria consortia provide a potential efficient strategy to fix CO2 from waste gas, treat wastewater and produce value-added products subsequently. This paper reviews recent developments in CO2 fixation and wastewater treatment by single microalgae, mixed microalgae and microalgae-bacteria consortia, as well as compares and summarizes the differences in utilizing different microorganisms from different aspects. Compared to monoculture of microalgae, a mixed microalgae and microalgae-bacteria consortium may mitigate environmental risk, obtain high biomass, and improve the efficiency of nutrient removal. The applied microalgae include Chlorella sp., Scenedesmus sp., Pediastrum sp., and Phormidium sp. among others, and most strains belong to Chlorophyta and Cyanophyta. The bacteria in microalgae-bacteria consortia are mainly from activated sludge and specific sewage sources. Bioengineer in CBB cycle in microalgae cells provide effective strategy to achieve improvement of CO2 fixation or a high yield of high-value products. The mechanisms of CO2 fixation and nutrient removal by different microbial systems are also explored and concluded, the importance of microalgae in the technology is proven. After cultivation, microalgae biomass can be harvested through physical, chemical, biological and magnetic separation methods and used to produce high-value by-products, such as biofuel, feed, food, biochar, fertilizer, and pharmaceutical bio-compounds. Although this technology has brought many benefits, some challenging obstacles and limitation remain for industrialization and commercializing.

Phycoremediation and valorization of hypersaline pickled mustard wastewater via Chaetoceros muelleri and indigenous bacteria

Hypersaline pickled mustard wastewater (PMW), a typical food wastewater with high nutrient content, was successfully bioremediated via the co-treatment of Chaetoceros muelleri and indigenous bacteria in this study. Chemical oxygen demand, ammonia nitrogen, total nitrogen and total phosphorus in 10 % PMW could be effectively reduced by 82 %, 90 %, 94 % and 96 %, respectively, after 12 days treatment. Oxygen species activities, malondialdehyde content, microalgal biomass, photosynthesis and extracellular polymeric substances were characterized during the treatment to determine the responses of the consortium when exposed to different concentration of PMW. Microbial community analysis demonstrated a significant increase in the relative abundance of Halomonas and Marinobacter in the 10 % PMW after 12 days treatment, which was beneficial for nutrients recycling by the diatoms. Meanwhile, C. muelleri was effective in reducing the relative abundance of potentially pathogenic bacteria Malaciobacter. In conclusion, the work here offers a promising and environmentally friendly approach for hypersaline wastewater treatment.

Advances in Algomics technology: Application in wastewater treatment and biofuel production

Advanced sustainable bioremediation is gaining importance with rising global pollution. This review examines microalgae's potential for sustainable bioremediation and process enhancement using multi-omics approaches. Recently, microalgae-bacterial consortia have emerged for synergistic nutrient removal, allowing complex metabolite exchanges. Advanced bioremediation requires effective consortium design or pure culture based on the treatment stage and specific roles. The strain potential must be screened using modern omics approaches aligning wastewater composition. The review highlights crucial research gaps in microalgal bioremediation. It discusses multi-omics advantages for understanding microalgal fitness concerning wastewater composition and facilitating the design of microalgal consortia based on bioremediation skills. Metagenomics enables strain identification, thereby monitoring microbial dynamics during the treatment process. Transcriptomics and metabolomics encourage the algal cell response toward nutrients and pollutants in wastewater. Multi-omics role is also summarized for product enhancement to make algal treatment sustainable and fit for sustainable development goals and growing circular bioeconomy scenario.

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.

The interplay between microalgae and toxic metal(loid)s: mechanisms and implications in AMD phycoremediation coupled with Fe/Mn mineralization

Acid mine drainage (AMD) is low-pH with high concentration of sulfates and toxic metal(loid)s (e.g. As, Cd, Pb, Cu, Zn), thereby posing a global environmental problem. For decades, microalgae have been used to remediate metal(loid)s in AMD, as they have various adaptive mechanisms for tolerating extreme environmental stress. Their main phycoremediation mechanisms are biosorption, bioaccumulation, coupling with sulfate-reducing bacteria, alkalization, biotransformation, and Fe/Mn mineral formation. This review summarizes how microalgae cope with metal(loid) stress and their specific mechanisms of phycoremediation in AMD. Based on the universal physiological characteristics of microalgae and the properties of their secretions, several Fe/Mn mineralization mechanisms induced by photosynthesis, free radicals, microalgal-bacterial reciprocity, and algal organic matter are proposed. Notably, microalgae can also reduce Fe(III) and inhibit mineralization, which is environmentally unfavorable. Therefore, the comprehensive environmental effects of microalgal co-occurring and cyclical opposing processes must be carefully considered. Using chemical and biological perspectives, this review innovatively proposes several specific processes and mechanisms of Fe/Mn mineralization that are mediated by microalgae, providing a theoretical basis for the geochemistry of metal(loid)s and natural attenuation of pollutants in AMD.

Enhanced degradation of bisphenol A: Influence of optimization of removal, kinetic model studies, application of machine learning and microalgae-bacteria consortia

Bisphenol A (BPA), a typical endocrine disruptor and a contaminant of emerging concern (CECs), has detrimental impacts not only on the environment and ecosystems, but also on human health. Therefore, it is essential to investigate the degrading processes of BPA in order to diminish its persistent effects on ecological environmental safety. With this objective, the present study reports on the effectiveness of biotic/abiotic factors in optimizing BPA removal and evaluates the kinetic models of the biodegradation processes. The results showed that BPA affected chlorophyll a, superoxide dismutase (SOD) and peroxidase (POD) activities, malondialdehyde (MDA) content, and photosystem intrinsic PSII efficiency (Fv/Fm) in the microalga Chlorella pyrenoidosa, which degraded 43.0 % of BPA (8.0 mg L^-1) under general experimental conditions. The bacteria consortium AEF21 could remove 55.4 % of BPA (20 mg L^-1) under orthogonal test optimization (temperature was 32 °C, pH was 8.0, inoculum was 6.0 %) and the prediction of artificial neural network (ANN) of machine learning (R² equal to 0.99 in training, test, and validation phase). The microalgae-bacteria consortia have a high removal rate of 57.5 % of BPA (20.0 mg L^-1). The kinetic study revealed that the removal processes of BPA by microalgae, bacteria, and microalgae-bacteria consortia all followed the Monod's kinetic model. This work provided a new perspective to apply artificial intelligence to predict the degradation of BPA and to understand the kinetic processes of BPA biodegradation by integrated biological approaches, as well as a novel research strategy to achieve environmental CECs elimination for long-term ecosystem health.

Effect of co-culture with Halomonas mongoliensis on Dunaliella salina growth and phenol degradation

The discharge of industrial phenol wastewater has caused great harm to the environment. This study aims to construct microalgae and bacteria co-culture system to remove phenol from simulated high-salt phenol wastewater and accumulate microalgae biomass. The degradation of phenol by marine microalgae Dunaliella salina (D. salina) and phenol-degrading bacteria Halomonas mongoliensis (H. mongoliensis) was investigated preliminarily, and then the effects of co-culture H. mongoliensis and D. salina on the degradation of phenol and the growth of D. salina were studied. The effects of D. salina/H. mongoliensis inoculation ratio, light intensity, temperature and pH on the performance of the co-culture system were systematically evaluated and optimized. The optimal conditions for phenol degradation were as follows: a D. salina/H. mongoliensis inoculation ratio of 2:1, a light intensity of 120 μmol m−2 s−1, a temperature of 25°C and a pH around 7.5. Under optimal conditions, this co-culture system could completely degrade 400 mg L−1 of phenol within 5 days. Correspondingly, the phenol degradation rate of D. salina monoculture was only 30.3% ± 1.3% within 5 days. Meanwhile, the maximum biomass concentration of D. salina in coculture was 1.7 times compared to the monoculture. This study suggested that this coculture system had great potential for the bioremediation of phenol contaminants and accumulate microalgae biomass.

Microalgae-based wastewater treatment - Microalgae-bacteria consortia, multi-omics approaches and algal stress response

Sustainable environmental management is one of the important aspects of sustainable development goals. Increasing amounts of wastewaters (WW) from exponential economic growth is a major challenge, and conventional treatment methods entail a huge carbon footprint in terms of energy use and GHG emissions. Microalgae-based WW treatment is a potential candidate for sustainable WW treatment. The nutrients which are otherwise unutilized in the conventional processes are recovered in the beneficial microalgal biomass. This review presents comprehensive information regarding the potential of microalgae as sustainable bioremediation agents. Microalgae-bacterial consortia play a critical role in synergistic nutrient removal, supported by the complex nutritional and metabolite exchange between microalgae and the associated bacteria. Design of effective microalgae-bacteria consortia either by screening or by recent technologies such as synthetic biology approaches are highly required for efficient WW treatment. Furthermore, this review discusses the crucial research gap in microalgal WW treatment - the application of a multi-omics platform for understanding microalgal response towards WW conditions and the design of effective microalgal or microalgae-bacteria consortia based on genetic information. While metagenomics helps in the identification and monitoring of the microbial community throughout the treatment process, transcriptomics, proteomics and metabolomics aid in studying the algal cellular response towards the nutrients and pollutants in WW. It has been established that the integration of microalgal processes into conventional WW treatment systems is feasible. In this direction, future research directions for microalgal WW treatment emphasize the need for identifying the niche in WW treatment, while highlighting the pilot sale plants in existence. Microalgae-based WW treatment could be a potential phase in the waste hierarchy of circular economy and sustainability, considering WWs are a rich secondary source of finite resources such as nitrogen and phosphorus.

Kinetics and molecular mechanism of enhanced fluoranthene biodegradation by co-substrate phenol in co-culture of Stenotrophomonas sp. N5 and Advenella sp. B9

Polycyclic aromatic hydrocarbons (PAHs) and phenol are persistent pollutants that coexist in coking wastewater (CWW). Fluoranthene (Flu) is the predominant PAH species in the CWW treatment system. Our work emphasized on distinguishing the effects of phenol on Flu biodegradation by co-culture of Stenotrophomonas sp. N5 and Advenella sp. B9 and illustrated the molecular mechanisms. Results showed Flu biodegradation by co-culture was enhanced by phenol. According to the first-order degradation kinetic analysis of Flu, phenol significantly increased the biodegradation rate constant and shortened the half-life of Flu. Transcriptome analysis pointed out the up-regulation of DNA repair activity and 3717 significantly differentially expressed genes (DEGs), were triggered by 800 mg/L phenol. GO enrichment analysis suggested these DEGs are mainly concentrated in biochemical processes such as metal ion binding and alpha-amino acid biosynthesis, which are closely associated with Flu biodegradation, indicating that phenol promotes DNA repair activity and reduces Flu genotoxicity. qRT-PCR was performed to detect the gene expression of aromatic ring-opening dioxygenase. Combined with transcriptome analysis, the qRT-PCR results suggested phenol did not induce the expression of related PAHs-degrading enzymes. RNA extraction and microbial growth curves of COC and COC + Ph provided further evidence that phenol serves as co-substrate which increases biomass and the concentration of degrading enzymes, therefore promoting the Flu degradation.

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.

A latest review on the application of microcosm model in environmental research

Microcosms are used experimentally to simulate ecosystems. This technology has received increasing attention and is widely used for environmental research. This review briefly introduces the origin and development of microcosm theory, summarizes classification and applications of microcosms across decades, and describes the advantages and limitations of microcosm technology in comparison with other methods. Finally, trends in the development of microcosm models are discussed.

Prospects and development of algal-bacterial biotechnology in environmental management and protection

The coexistence of algae and bacteria in nature dates back to the very early stages when life came into existence. The interaction between algae and bacteria plays an important role in the planet ecology, cycling nutrients, and feeding higher trophic levels, and have been evolving ever since. The emerging concept of algal-bacterial consortia is gaining attention, much towards environmental management and protection. Studies have shown that algal-bacterial synergy does not only promote carbon capture in wastewater bioremediation but also consequently produces biofuels from algal-bacterial biomass. This review has evaluated the optimistic prospects of algal-bacterial consortia in environmental remediation, biorefinery, carbon sequestration as well as its contribution to the production of high-value compounds. In addition, algal-bacterial consortia offer great potential in bloom control, dye removal, agricultural biofertilizers, and bioplastics production. This work also emphasizes the advancement of algal-bacterial biotechnology in environmental management through the incorporation of Industry Revolution 4.0 technologies. The challenges include its pathway to greener industry, competition with other food additive sources, societal acceptance, cost feasibility, environmental trade-off, safety and compatibility. Thus, there is a need for further in-depth research to ensure the environmental sustainability and feasibility of algal-bacterial consortia to meet numerous current and future needs of society in the long run.