Distribution, source and ecological risk of per- and polyfluoroalkyl substances in Chinese municipal wastewater treatment plants.

Municipal wastewater treatment plants (WWTPs) are sinks of per- and polyfluoroalkyl substances (PFASs) generated by human activities and are also sources of PFASs in aquatic environment. This study analyzed distribution, source and ecological risk of 14 PFASs in influent and effluent samples from 148 Chinese municipal WWTPs. Composition and concentrations of PFASs in the influents and effluents had obvious spatial differences. Fluoropolymer processing aids/wrappers and textile treatments/coatings were found to be the dominant sources in WWTP influents, which accounted for 78.34% of all sources. Consumption structure and metal and transportation equipment manufacturing affected the spatial differences of PFASs in WWTPs. Further, mean removal rate of total PFASs in all WWTPs was -5.45%. The conventional treatment processes can not effectively remove PFASs and no significant difference was found among different treatment processes. However, risk quotient values of PFASs in effluents were all below 0.1, indicating low risk or no risk to aquatic organisms. It should be noted that the composition, source and ecological risk of PFASs in east China were different from the other regions, which need more attentions. This study sheds insights into occurrencesof PFASs in municipal WWTPs, which should be helpful for their control strategy development.

Combined effects of arsenic and 2,2-dichloroacetamide on different cell populations of zebrafish liver.

Arsenic (As) and disinfection by-products are important health risk factors in the water environment. However, their combined effects on different cell populations in the liver are not well known. Here, zebrafish were exposed to 100 µg/L As, 300 µg/L 2,2-dichloroacetamide (DCAcAm), and their combination for 23 days. Then transcriptome profiles of cell populations in zebrafish liver were analyzed by single-cell RNA sequencing (scRNA-seq). A total of 13,563 cells were obtained, which were identified as hepatocytes, hepatic duct cells, endothelial cells and macrophages. Hepatocytes were the main target cell subtype of As and DCAcAm exposures. DCAcAm exposure induced higher toxicity in male hepatocytes, which specifically changed amino acid metabolism, response to hormone and cofactor metabolism. However, As exposure caused higher toxicity in female hepatocytes, which altered lipid metabolism, carbon metabolism, and peroxisome. Combined exposure to As and DCAcAm decreased toxicities in hepatocytes compared to each one alone. Female hepatocytes had higher tolerance to co-exposure of As and DCAcAm than male hepatocytes. Further, combined exposure to As and DCAcAm induced functional changes in macrophages similar to As alone groups, which mainly altered the transfer of sterol and cholesterol. Hepatic duct cells and endothelial cells were not influenced by exposures to As and DCAcAm. This study for the first time highlights the cell-specific combined responses of As and DCAcAm in zebrafish liver, which provide useful information for their health risk assessment in a co-exposure environment.

Toxicity of perfluorooctanoic acid on zebrafish early embryonic development determined by single-cell RNA sequencing.

The perfluorooctanoic acid (PFOA) poses a high risk for aquatic organisms. Nevertheless, the current toxicity studies rarely report how PFOA affects different cell populations during the embryonic development of fish. Here, the zebrafish embryos at 2-30 hpf were exposed to 1-100 µg/L PFOA. The heartbeat and locomotor behavior were significantly decreased after ≥ 25 µg/L PFOA exposure. The single-cell RNA sequencing showed that PFOA exposure influenced nine cell populations, including heart cells, hatching gland cells, macrophages, lens cells, ionocytes, melanoblasts, optic cup cells, periderm cells, and differentiating neurons cells. Among them, heart cells were the most affected cell population. Functions of cardiac muscle contraction, actin cytoskeleton and oxygen binding were significantly changed in the heart cells, which were involved in the altered expressions of tnni2a.4, acta1a, atp1a1a.2, mylpfa, and so on. Besides, the changes of apoptotic process, innate immune response, and translation in lens cells, hatching gland cells, macrophages and ionocytes should also be of concern. Our study indicates that 2-30 hpf of embryonic development is the sensitivity window for the PFOA exposure. Identification of the target cell population provides clear information of the toxic endpoint of PFOA, which sheds new light on the risk assessment of PFOA on aquatic organisms.

Developing a generally applicable electrochemical sensor for detecting macrolides in water with thiophene-based molecularly imprinted polymers.

Our screening data revealed the threat macrolide antibiotics, especially azithromycin (AZN), posed to human health with its increasing occurrence in water environment. The electrochemical sensor based on molecularly imprinted polymer (MIP) is a promising platform that caters for the next generation of intelligent wastewater treatment plants (WWTPs) by virtue of its wide tolerance to water from all sources and in-situ monitoring. However, low initiation potentials of cross-linking monomers contributed by the electron-rich circumstance allowed them to usurp sites designed for functional monomers when electrically stimulated, leading to an unsatisfactory binding capacity. Another uncertainty is that multiple reaction sites of cross-linking monomers granted them complex polymerization routes and made it difficult to ensure the consistency of preparation. Serval monomers had been investigated with electrochemical tools and the performance of sensors constructed with these monomers were compared in this study. Based on the results, we proposed a protocol in which a novel functional monomer possessing a stronger electron-donating group, phenyl, was adopted to compete for the dominance in electropolymerization. Beyond that, the cross-linking monomer was modified with electron-withdrawing groups to raise its initiation potential. A monothiophene with a moderate initiation potential was also recruited as the linker to address the steric hindrance. In this way, polymerization proceeded in a specific order. It is worth mentioning that the Marangoni flow is an ideal tool to deal with the Coffee-ring deposition while drop-casting. The resulting sensor showed good performance with a limitation of detection (LOD) of 0.120 µM for AZN and a satisfactory selectivity, and the design can be applied to constructing sensors for a variety of macrolide antibiotics.

Revisiting the Microscopic Processes of Biofilm Formation on Organic Carriers: A Study under Variational Shear Stresses.

The microscopic process of biofilm development on carriers is critical for interfacial regulation of biofilms in attached-growth wastewater treatment. However, the process under shear stress has not been well understood. The study purposed to revisit the processes of biofilm formation on organic carriers under different shear stresses with special highlights on bacterial reversible adhesion and pioneers in the microbial community. Biofilm formation on high-density polyethylene, polyamide, acrylonitrile butadiene styrene plastic, polyvinyl chloride, and polycarbonate carriers under shear stresses ranging from 1.0 to 2.5 Pa was investigated using Couette-Taylor reactors. Employing extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, the bacterial reversible adhesion regions ranging from 3.74 ± 0.20 to 5.51 ± 0.24 nm on an organic carrier were quantified for the first time, elucidating significant differences among different carriers (p < 0.01). The colonization of pioneers in the microbial community was significantly altered by shear stress rather than carrier properties (p < 0.01). In particular, the diversity of the biofilm microbial community was pronouncedly enhanced by a higher shear stress (p < 0.01). XDLVO analysis suggested that extracellular polymeric substances had a negative feedback on subsequent microbial adhesion and biofilm development, especially the transition from reversible to irreversible bacterial adhesion. This study contributed to a better understanding of the biofilm formation process at the microscopic scale and shed light on micro-interfacial manipulation for biofilm accumulation or renewal.

Microplastics enhance the developmental toxicity of synthetic phenolic antioxidants by disturbing the thyroid function and metabolism in developing zebrafish.

Coexposure of MPs and other contaminants adsorbed from the environment has raised many attentions, but the understanding of the combined effects of MPs and plastic additives are limited. Butylated hydroxyanisole (BHA), a widely used synthetic phenolic antioxidant in plastics, has gained high concerns due to their unintended environmental release and potential threat to aquatic organisms. This study was conducted to reveal the influences of MPs on the bioaccumulation and developmental toxicity of BHA in zebrafish larvae. As a result, MPs promoted the accumulation of BHA in zebrafish larvae and enhanced the toxicity of BHA in larvae development manifested by reduced hatching rates, increased malformation rates and decreased calcified vertebrae. Although the concentration of MPs was not sufficient to cause obvious developmental toxicity, the impacts of MPs on thyroid hormones status might contribute to the aggravated join toxicity. The metabolomic mechanism was revealed to be that the coexposure of BHA and MPs affected the development of zebrafish larvae via disturbing the metabolism of arachidonic acid, glycerophospholipid, and lipids. Our results emphasized that MPs, even at the nontoxic concentrations, in combination with additives caused health risk that should not be ignored.

Single-Cell RNA Sequencing Reveals Size-Dependent Effects of Polystyrene Microplastics on Immune and Secretory Cell Populations from Zebrafish Intestines.

Microplastics (MPs) as widespread contamination pose a high risk for aquatic organisms. However, the current understanding of MP toxicity is based on cell population-averaged measurements. Our aim was to gain a comprehensive understanding of the size-dependent effects of polystyrene MPs (PS-MPs) on intestinal cell populations in zebrafish and characterize the interplay of MPs, intestinal cells, and intestinal microbiota. Here, we used single-cell RNA sequencing to determine the transcriptome heterogeneity of 12 000 intestinal cells obtained from zebrafish exposed to 100 nm, 5 µm, and 200 µm PS-MPs for 21 days. Eight intestinal cell populations were identified. Combined with changes in intestinal microbiota, our findings highlight a previously unrecognized end point that all three sizes of PS-MPs induced dysfunction of intestinal immune cells (including effects on phagosomes and the regulation of immune system processes) and increased the abundance of pathogenic bacteria. However, only 100 nm PS-MPs altered the expression of genes related to phagocyte-produced reactive oxygen species (ROS) generation and increased mucus secretion by secretory cells. Microsize PS-MPs specifically changed the lysosome (5 µm) and cell surface receptor signaling (200 µm) processes of the macrophages. Our findings pinpoint to cell-specific and size-dependent responses to PS-MPs in fish intestine, which can provide a reference for future study directions.

Comparative analysis of toxicity reduction of wastewater in twelve industrial park wastewater treatment plants based on battery of toxicity assays.

Wastewater treatment plants (WWTPs) in industrial parks provide centralized treatment for industrial and domestic wastewater. However, the information on toxicity reduction of wastewater and its correlation with treatment process in industrial park is limited. This study compared the toxicity reduction of wastewater in 12 industrial park WWTPs based on battery of toxicity assays. Nine toxic endpoints involving microorganism, phytoplankton, zooplankton, plant and human cell lines were applied. All the influents of WWTPs induced high toxicities, which were significantly reduced after the treatments from 7 of the studied WWTPs. However, the effluents of five WWTPs induced higher toxicity in one or more toxic endpoints compared to the influents. This study also found that most of anaerobic-anoxic-oxic (A2/O)-based processes had good removal efficiency of wastewater toxicity, while the sequencing batch reactor (SBR)-based processes had the lowest removal efficiency. Moreover, low correlation coefficients were obtained among all toxic endpoints, indicating that battery of toxicity assays was necessary to completely characterize the toxicity and risk of wastewater in industrial parks. This study shed new lights to the toxicity reduction of wastewater and its correlation with treatment process, which is very useful for the design, management and operation of WWTPs in industrial parks.

Effect of mixing intensity on hydrolysis and acidification of sewage sludge in two-stage anaerobic digestion: Characteristics of dissolved organic matter and the key microorganisms.

Mixing should be optimized in anaerobic digestion (AD) systems to achieve excellent biomaterials production in the sewage sludge (SS) management in wastewater treatment plant. AD depends on the coordinated activity of hydrolysis, acidification and methanogenesis. However, the effect of mixing intensity on characteristics of hydrolysis and acidification in AD of SS is still poorly understood. This study focused on the mixing intensity (30, 60, 90 and 120 rpm) effect on the characteristics of dissolved organic matter (DOM) and the key microorganisms in the hydrolysis and acidification of SS. Results showed that enhanced hydrolysis and acidification efficiency was obtained at mixing of 90 and 120 rpm (p < 0.05), while the maximum acetic acid (388 ±â€¯21 mg/L) was produced at 90 rpm. Mixing at 90 rpm enhanced the release of protein and polysaccharide as well as humic acid. Further analyses of DOM molecular features revealed that 90 rpm led to the highest molecular diversity and easily biodegradable molecules (lipid and proteins/amino sugars), which contributed to the maximum hydrolysis and acidification efficiency. Firmicutes and Actinobacteria significantly increased with mixing intensity (p<0.05), and Chloroflexi and Fusobacteria were enriched at mixing of 90 rpm, which favored the hydrolysis of SS. The enrichment of Clostridium XI and Clostridium sensu stricto contributed to the acidification of DOM at 90 and 120 rpm. The results of this study can advance our knowledge about mixing intensity effects on the AD systems of SS. This research also showed how increasing mixing intensity to a relatively high speed can enhance the hydrolysis and acidification efficiency of SS.

[Impact of Nano Zero-Valent Iron (NZVI) on Methanogenic Activity, Physiological Traits, and Microbial Community Structure in Anaerobic Digestion].

Effects of short-term nano zero-valent iron (NZVI) and zero-valent iron (ZVI) exposure on methanogenic activity of anaerobic sludge, physiological traits, composition of phospholipid fatty acids (PLFA), and microbial community structure were investigated. Results show that accumulated methane production decreased with an increase of NZVI concentration; yet, methane production only changed slightly with the same concentration of ZVI. In the NZVI (100-5000 mg·L-1) sets, dissolved iron (DFe) concentrations were 1.6-7.4 times that of the control value at 5 d, whereas DFe was only slightly above the control in the ZVI set (5000 mg·L-1). The concentration of extracellular polymeric substances and cell viability decreased to 21.1% and 79.7%, respectively, of the control in the 5000 mg·L-1 NZVI treatments. Coenzyme F420 and coenzyme M decreased to 40.2% and 61.1%, respectively, of the control in the 5000 mg·L-1 NZVI treatments, which were significantly increased to 1.3 times that of the control value in the 100 mg·L-1 NZVI and 5000 mg·L-1 ZVI treatments. The order of unsaturation and branch PLFA content was ZVI-5000 (21.18%) > control (19.37%) > NZVI-1000 (16.69%) > NZVI-5000 (15.94%) > NZVI-100 (12.08%). High NZVI concentration (5000 mg·L-1) resulted in an increase of DFe and a decrease of cell membrane fluidity and key coenzyme activity of methanogenesis, which led to the inhibition of methane production. Principle component analysis and redundancy analysis indicated that differences in the microbial community existed among these treatments and that Nakamurella, Bacillus, Trichococcus, and Petrimonas showed tolerance to NZVI.

[Performance, Sludge Characteristics, and the Microbial Community Dynamics of Bulking Sludge Under Different Nitrogen and Phosphorus Imbalances].

In this paper, the performance, characteristics of the bulking sludge, and the variations in the microbial community (including the bulking bacteria) under different nitrogen and phosphorus imbalances were compared, using high-throughput sequencing (16S rRNA) and the high performance liquid chromatography (HPLC) technology. The results showed that after seeding bulking sludge in the A/O process and operating for a period of time, the sludge settleability of the nitrogen limitation alone reactor (RN) could recover to normal[sludge volume index (SVI)<150 mL·g-1], while the SVI of the phosphorus limitation alone reactor (RP) improved slightly; the control reactor (R0, C/N/P=100/5/1) exhibited the highest SVI index (SVI=1496 mL·g-1), followed by the reactor of simultaneous nitrogen and phosphorus limitations (RNP). Under normal nutritional conditions, Pearson correlation analysis showed a significant negative correlation between the lipopolysaccharide (LPS) relative content (LPS/MLVSS) and the settleability of bulking sludge (r=-0.625, P<0.05), while under nutrient limitation conditions, LPS showed high accuracy in reflecting the biomass of the activated sludge. Thiothrix was the dominant bulking bacteria in all the reactors. PCoA analysis showed that the migration of the community in the reactors experienced nitrogen limitation (RNP, RN) changes greatly during the stages Ⅱ and Ⅲ, while RDA analysis showed that the correlation of Thiothrix with the settling performance and oxygen consumption rate was significant.

Cell membrane characteristics and microbial population distribution of MBBR and IFAS with different dissolved oxygen concentration.

This paper investigated the influences of different dissolved oxygen (DO) concentration (0.71-1.32, 2.13-3.02 and 4.31-5.16 mg/L) on cell membrane characteristics and microbial population distribution of moving biofilm reactors. Two representative reactors, i.e., moving bed biofilm reactors and integrated fixed-film activated sludge were operated. Results indicated that both DO concentration of 0.71-1.32 mg/L and 4.31-5.16 mg/L could increase membrane lipid mobile fraction (49.4%-67.4%) of the microbes, however, through prompting the synthesis of branched fatty acids and unsaturated fatty acids, respectively. For the biofilms, the abundance of Bacteroidetes decreased and Actinobacteria increased with the increase of DO levels. The lowest EfOM content and the highest microbial diversities (1.14-1.52) was observed at DO of 2.13-3.02 mg/L. Redundancy analysis showed that changes of DO levels could alter cell membrane properties and bacterial community structures, and subsequently significantly influenced effluent organic matter composition of moving biofilm reactors.

Cytotoxicity and Efflux Pump Inhibition Induced by Molybdenum Disulfide and Boron Nitride Nanomaterials with Sheetlike Structure.

Sheetlike molybdenum disulfide (MoS2) and boron nitride (BN) nanomaterials have attracted attention in the past few years due to their unique material properties. However, information on adverse effects and their underlying mechanisms for sheetlike MoS2 and BN nanomaterials is rare. In this study, cytotoxicities of sheetlike MoS2 and BN nanomaterials on human hepatoma HepG2 cells were systematically investigated at different toxic end points. Results showed that MoS2 and BN nanomaterials decreased cell viability at 30 µg/mL and induced adverse effects on intracellular ROS generation (≥2 µg/mL), mitochondrial depolarization (≥4 µg/mL), and membrane integrity (≥8 µg/mL for MoS2 and ≥2 µg/mL for BN). Furthermore, this study first found that low exposure concentrations (0.2-2 µg/mL) of MoS2 and BN nanomaterials could increase plasma membrane fluidity and inhibit transmembrane ATP binding cassette (ABC) efflux transporter activity, which make both nanomaterials act as a chemosensitizer (increasing arsenic toxicity). Damage to plasma membrane and release of soluble Mo or B species might be two reasons that both nanomaterials inhibit efflux pump activities. This study provides a systematic understanding of the cytotoxicity of sheetlike MoS2 and BN nanomaterials at different exposure levels, which is important for their safe use.

Arsenic Metabolism and Toxicity Influenced by Ferric Iron in Simulated Gastrointestinal Tract and the Roles of Gut Microbiota.

Iron (Fe) is a common trace element in drinking water. However, little is known about how environmental concentrations of Fe affect the metabolism and toxicity of arsenic (As) in drinking water. In this study, influence of Fe at drinking water-related concentrations (0.1, 0.3, and 3 mg Fe (total)/L) on As metabolism and toxicity, and the roles of gut microbiota during this process were investigated by using in vitro Simulator of the Human Intestinal Microbial Ecosystem (SHIME). Results showed that Fe had ability to decrease bioaccessible As by coflocculation in small intestine. 0.1 and 0.3 mg/L Fe significantly increased As methylation in simulated transverse and descending colon. Gut microbiota played an important role in alteration of As species, and Fe could affect As metabolism by changing the gut microbiota. Bacteroides, Clostridium, Alistipes, and Bilophila had As resistance and potential ability to methylate As. Cytotoxicity assays of effluents from simulated colons showed that the low levels of Fe decreased As toxicity on human hepatoma cell line HepG2, which might be due to the increase of methylated As. When assessing the health risk of As in drinking water, the residual Fe should be considered.

Effects of DO levels on surface force, cell membrane properties and microbial community dynamics of activated sludge.

In this paper, we employ atomic force microscopy (AFM), fluorescence recovery after photobleaching (FRAP) technique, phospholipid fatty acids (PLFA) and MiSeq analysis to study the effects of traditional dissolved oxygen (DO) levels (0.71-1.32mg/L, 2.13-3.02mg/L and 4.31-5.16mg/L) on surface force, cell membrane properties and microbial community dynamics of activated sludge. Results showed that low DO level enhanced the surface force and roughness of activated sludge; the medium DO level decreased cell membrane fluidity by reducing the synthesis of branched fatty acids in the cell membrane; high DO level resulted in the highest protein content in the effluent by EEM scanning. Abundance of Micropruina, Zoogloea and Nakamurella increased and Paracoccus and Rudaea decreased with the increase of DO levels. RDA analysis suggested that saturated fatty acids (SFA), anteiso-fatty acids (AFA) and iso-fatty acids (IFA) were closely related to effluent quality as well as some genera.

Effect of low temperature on highly unsaturated fatty acid biosynthesis in activated sludge.

Low temperature is a limiting factor for the microbial activity of activated sludge for sewage treatment plant in winter. Highly unsaturated fatty acid (UFA) biosynthesis, phospholipid fatty acid (PLFA) constituents and microbial structure in activated sludge at low temperature were investigated. Over 12 gigabases of metagenomic sequence data were generated with the Illumina HiSeq 2000 platform. The result showed 43.11% of phospholipid fatty acid (PLFA) in the activated sludge participated in UFA biosynthesis, and γ-Linolenic could be converted to Arachidonic acid at low temperature. The highly UFA biosynthesis in activated sludge was n-6 highly UFA biosynthesis, rather than n-3 highly UFA biosynthesis. The microbial community structures of activated sludge were analyzed by PLFA and high-throughput sequencing (HiSeq) simultaneously. Acidovorax, Pseudomonas, Flavobacterium and Polaromonas occupied higher percentage at 5°C, and genetic changes of highly UFA biosynthesis derived from microbial community structures change.

Preconditioning of model biocarriers by soluble pollutants: a QCM-D study.

Preconditioning of a biocarrier surface is the first step in triggering biofilm formation in attached-growth bioreactors. However, the quantification and control of this step as influenced by solution conditions and biocarrier properties have been rarely explored. In this paper, deposition behaviors of soluble pollutants on the model biocarriers polystyrene (PS) and polyamide (PA) were performed using a quartz crystal microbalance with dissipation monitoring (QCM-D). Three types of wastewater from municipal and industrial wastewater treatment plants and 12 synthetic wastewaters with different configurations of model macromolecules (bovine serum albumin and sodium alginate) and ionic compositions (Na(+) and Ca(2+)) were prepared. Results showed that high organic contents (protein and humic acid) in real wastewater increased deposition compared to the impact of ions on the two types of carriers. For synthetic wastewater, an interesting phenomenon was observed in that the presence of Ca(2+) can transform a thin and rigid adlayer into a denser and viscoelastic one on the surface of PS with low organic contents, yet a viscoelastic adlayer can directly form on PS and an increase in the ionic strength hinders deposition in the presence of high organic contents. The deposition of solutes on PA produces a thicker and viscoelastic adlayer that is strengthened an elevated concentration of organic materials. Additionally, a weakening effect of Ca(2+) on deposition was revealed under high ionic strength. This is the first demonstration of control strategies for preconditioning hydrophilic and hydrophobic biocarriers under different water quality conditions and has important implications for the design of a start-up process for biofilm formation in attached-growth bioreactors.

Physicochemical characteristics and microbial community evolution of biofilms during the start-up period in a moving bed biofilm reactor.

This study aimed to investigate biofilm properties evolution coupled with different ages during the start-up period in a moving bed biofilm reactor system. Physicochemical characteristics including adhesion force, extracellular polymeric substances (EPS), morphology as well as volatile solid and microbial community were studied. Results showed that the formation and development of biofilms exhibited four stages, including (I) initial attachment and young biofilm formation, (II) biofilms accumulation, (III) biofilm sloughing and updating, and (IV) biofilm maturation. During the whole start-up period, adhesion force was positively and significantly correlated with the contents of EPS, especially the content of polysaccharide. In addition, increased adhesion force and EPS were beneficial for biofilm retention. Gram-negative bacteria mainly including Sphaerotilus, Zoogloea and Haliscomenobacter were predominant in the initial stage. Actinobacteria was beneficial to resist sloughing. Furthermore, filamentous bacteria were dominant in maturation biofilm.

Treating cardiovascular atherosclerotic plaques with Tongmaijiangzhi (TMJZ) capsule.

Atherosclerotic plaques can cause serious syndromes and mortality. Cholesterol accumulation in the plaques can disrupt the arterial flow, with lumen narrowing and stenosis, which contributes to heart attack and sudden cardiac death. The pharmacological treatment to atherosclerotic plaques can be anti-hypertensives, anti-cholesterol, and cleaning of the existed plaques. This work examined the effects of pharmacological Tongmaijiangzhi (TMJZ) capsule on atherosclerotic plaques. The radiological findings of the atherosclerotic plaques of 107 patients receiving TMJZ treatment were analyzed. We found that the TMJZ administration decreases plaque volume and alters the composition in a relatively short period, showing highly promising effects. TMJZ treatment is able to remove the existed atherosclerotic plaques with no side effects observed.

Characteristics of biofilm attaching to carriers in moving bed biofilm reactor used to treat vitamin C wastewater.

In order to investigate characteristics of biofilm attaching firmly to carriers in the moving bed biofilm reactor (MBBR) used for vitamin C wastewater treatment, experiments were undertaken with instrumental analysis methods. Scanning electron microscopy (SEM) micrographs of MBBR biofilms revealed that there were rod-shaped microbes and cocci in the biofilm, and microbes were embedded within medium substances and the biofilm matrix adhered firmly to carriers, leading to the formation of a smooth compacted surface at the base of the biofilm. Transmission electron microscopy (TEM) analysis revealed that extracellular polymeric substances (EPS) layer surrounded cell, sequestered inorganics to form a mixed structure, which ensured firm attachment of the biofilm to the carrier. X-ray diffraction (XRD) experiments and thermogravimetry analysis revealed that (i) the biofilm contained many inorganic substances, about 70.5%, and the inorganic substances contained multiple classes of inorganic with a high boiling point; (ii) inorganic elements such as calcium and phosphorous were selectively absorbed and accumulated in the biofilm as insoluble compounds with amorphous phases, rendering the biofilm highly resistant to detachment. Fourier-transform infrared (FTIR) spectroscopy showed carbohydrates were the main EPS.