The adsorption and absorption kinetics of BDE-47 by Chlorella sp. and the role of extracellular polymer substances influenced by environmental factors

Insights into the removal of antibiotics from livestock and aquaculture wastewater by algae-bacteria symbiosis systems

With the burgeoning growth of the livestock and aquaculture industries, antibiotic residues in treated wastewater have become a serious ecological threat. Traditional biological wastewater treatment technologies-while effective for removing conventional pollutants, such as organic carbon, ammonia and phosphate-struggle to eliminate emerging contaminants, notably antibiotics. Recently, the use of microalgae has emerged as a sustainable and promising approach for the removal of antibiotics due to their non-target status, rapid growth and carbon recovery capabilities. This review aims to analyse the current state of antibiotic removal from wastewater using algae-bacteria symbiosis systems and provide valuable recommendations for the development of livestock/aquaculture wastewater treatment technologies. It (1) summarises the biological removal mechanisms of typical antibiotics, including bioadsorption, bioaccumulation, biodegradation and co-metabolism; (2) discusses the roles of intracellular regulation, involving extracellular polymeric substances, pigments, antioxidant enzyme systems, signalling molecules and metabolic pathways; (3) analyses the role of treatment facilities in facilitating algae-bacteria symbiosis, such as sequencing batch reactors, stabilisation ponds, membrane bioreactors and bioelectrochemical systems; and (4) provides insights into bottlenecks and potential solutions. This review offers valuable information on the mechanisms and strategies involved in the removal of antibiotics from livestock/aquaculture wastewater through the symbiosis of microalgae and bacteria.

General performance, kinetic modification, and key regulating factor recognition of microalgae-based sulfonamide removal

Sulfonamides have been widely detected in water treatment plants. Advanced wastewater treatment for sulfonamide removal based on microalgal cultivation can reduce the ecological risk after discharge, achieve carbon fixation, and simultaneously recover bioresource. However, the general removal performance, key factors and their impacts, degradation kinetics, and potential coupling technologies have not been systematically summarized. To guide the construction and enhance the efficient performance of the purification system, this study summarizes the quantified characteristics of sulfonamide removal based on more than 100 groups of data from the literature. The biodegradation potential of sulfonamides from different subclasses and their toxicity to microalgae were statistically analyzed; therefore, a preferred option for further application was proposed. The mechanisms by which the properties of both sulfonamides and microalgae affect sulfonamide removal were comprehensively summarized. Thereafter, multiple principles for choosing optimal microalgae were proposed from the perspective of engineering applications. Considering the microalgal density and growth status, a modified antibiotic removal kinetic model was proposed with significant physical meaning, thereby resulting in an optimal fit. Based on the mechanism and regulating effect of key factors on sulfonamide removal, sensitive and feasible factors (e.g., water quality regulation, other than initial algal density) and system coupling were screened to guide engineering applications. Finally, we suggested studying the long-term removal performance of antibiotics at environmentally relevant concentrations and toxicity interactions for further research.

Reactive oxygen species mediated extracellular polymeric substances production assisting the recovery of Thalassiosira pseudonana from polystyrene micro and nanoplastics exposure

As emerging pollutants in the aquatic environments, micro- and nano-plastics (MNPs) aroused widespread environmental concerns for their potential threats to the ecological health. Previous research has proved that microalgae growth could recover from the MNPs toxicities, in which the extracellular polymeric substances (EPS) might play the key role. In order to comprehensively investigate the recovery process of microalgae from MNPs stress and the effecting mechanisms of EPS therein, this study conducted a series of experiments by employing two sizes (0.1 and 1 μm) of polystyrene (PS) MNPs and the marine model diatom Thalassiosira pseudonana during 14 days. The results indicated: the pigments accumulations and photosynthetic recovery of T. pseudonana under MPs exposure showed in the early stage (4-5 days), while the elevation of reactive oxygen species (ROS) and EPS contents lasted longer time period (7-8 days). EPS was aggregated with MNPs particles and microalgal cells, corresponding to the increased settlement rates. More increase of soluble (SL)-EPS contents was found than bound (B)-EPS under MNPs exposure, in which the increase of the protein proportion and humic acid-like substances in SL-EPS was found, thus facilitating aggregates formation. ROS was the signaling molecule mediating the overproduction of EPS. The transcriptional results further proved the enhanced EPS biosynthesis on the molecular level. Therefore, this study elucidated the recovery pattern of microalgae from MNPs stress and linked "ROS-EPS production changes-aggregation formation" together during the growth recovery process, with important scientific and environmental significance.

20 years of polybrominated diphenyl ethers on toxicity assessments

Polybrominated diphenyl ethers (PBDEs) serve as brominated flame retardants which continue to receive considerable attention because of their persistence, bioaccumulation, and potential toxicity. Although PBDEs have been restricted and phased out, large amounts of commercial products containing PBDEs are still in use and discarded annually. Consequently, PBDEs added to products can be released into our surrounding environments, particularly in aquatic systems, thus posing great risks to human health. Many studies and reviews have described the possible toxic effects of PBDEs, while few studies have comprehensively summarized and analyzed the global trends of their toxicity assessment. Therefore, this study utilizes bibliometrics to evaluate the worldwide scientific output of PBDE toxicity and analyze the hotspots and future trends of this field. Firstly, the basic information including the most contributing countries/institutions, journals, co-citations, influential authors, and keywords involved in PBDE toxicity assessment will be visualized. Subsequently, the potential toxicity of PBDE exposure to diverse systems, such as endocrine, reproductive, neural, and gastrointestinal tract systems, and related toxic mechanisms will be discussed. Finally, we conclude this review by outlining the current challenges and future perspectives in environmentally relevant PBDE exposure, potential carriers for PBDE transport, the fate of PBDEs in the environment and human bodies, advanced stem cell-derived organoid models for toxicity assessment, and promising omics technologies for obtaining toxic mechanisms. This review is expected to offer systematical insights into PBDE toxicity assessments and facilitate the development of PBDE-based research.

Photosynthetic response mechanism to polybrominated diphenyl ether exposure in Chlorella pyrenoidosa

Polybrominated diphenyl ether (PBDE) contamination is common in aquatic environments and can severely damage aquatic organisms. However, there is a lack of information on the response and self-adaptation mechanisms of these organisms. Chlorella pyrenoidosa was treated with 2,2',4,4'-tetrabromodiphenyl ether (BDE47), causing significant growth inhibition, pigment reduction, oxidative stress, and chloroplast atrophy. Photosynthetic damage contributed to inhibition, as indicated by Fv/Fm, Chl a fluorescence induction, photosynthetic oxygen evolution activity, and photosystem subunit stoichiometry. Here, Chl a fluorescence induction and quinone electron acceptor (QA-) reoxidation kinetics showed that the PSII donor and acceptor sides were insensitive to BDE47. Quantitative analyses of D1 and PsaD proteins illustrated that PSII and PSI complexes were the main primary targets of photosynthesis inhibition by BDE47. Significant modulation of PSII complex might have been caused by the potential binding of BDE47 on D1 protein, and molecular docking was performed to investigate this. Increased activation of antioxidant defense systems and photosystem repair as a function of exposure time indicated a positive resistance to BDE47. After a 5-day exposure, 23 % of BDE47 was metabolized. Our findings suggest that C. pyrenoidosa has potential as a bioremediator for wastewater-borne PBDEs and can improve our understanding of ecological risks to microalgae.

Sunlight-driven intimately coupled photocatalysis and biodegradation (SDICPB): A sustainable approach for enhanced detoxification of triclosan

Triclosan is considered as recalcitrant contaminant difficult to degrade from the contaminated wastewater. Thus, promising, and sustainable treatment method is necessary to remove triclosan from the wastewater. Intimately coupled photocatalysis and biodegradation (ICPB) is an emerging, low-cost, efficient, and eco-friendly method for the removal of recalcitrant pollutants. In this study BiOI photocatalyst coated bacterial biofilm developed at carbon felt for efficient degradation and mineralization of triclosan was studied. Based on the characterization of BiOI prepared using methanol had lower band gap 1.85 eV which favors lower recombination of electron-hole pair and higher charge separation which ascribed to enhanced photocatalytic activity. ICPB exhibits 89% of triclosan degradation under direct sunlight exposure. The results showed that production of reactive oxygen species hydroxyl radical and superoxide radical anion played crucial role in the degradation of triclosan into biodegradable metabolites further the bacterial communities mineralized the biodegradable metabolites into water and carbon dioxide. The confocal laser scanning electron microscope results emphasized that interior of the biocarrier shows a large number of live bacterial cells existing in the photocatalyst-coated carrier, where the little toxic effect on bacterial biofilm occurred on the exterior of the carrier. The extracellular polymeric substances characterization result remarkable confirms that which could act as sacrificial agent of photoholes further helped by preventing the toxicity to the bacterial biofilm from the reactive oxygen species and triclosan. Hence, this promising approach can be a possible alternative method for the wastewater treatment polluted with triclosan.