An ecological remediation model combining optimal substrate amelioration and native hyperaccumulator colonization in non-ferrous metal tailings pond.

The vegetation deterioration and pollution expansion from non-ferrous metal tailings pond have been found in many countries leading to water soil erosion and human health risk. Conventional ecological remediation technologies of mine tailings such as capping were costly and elusive. This study provided an economic and effective model as an alternative by substrate amelioration and vegetation restoration. A field experiment was carried out on a silver tailings pond in southwest China. Tailings substrate was ameliorated by adding organic matter (decomposed chicken manure, DCM), structural conditioner (polyacrylamide, PAM), water-retaining agent (acrylic acid-bentonite water-retaining agent, AAB), and heavy metal immobilizer (biofuel ash, BFA), which were optimized by laboratory experiment. Native heavy metal hyperaccumulator, Bidens pilosa, was colonized. Vegetation coverage and plant height of Bidens pilosa reached about 80% and over 30 cm respectively after 3 months, and the turbidity of tailings leaching solution decreased by 60%. The practice showed that the proportion of available heavy metals in tailings substrate was significantly lower than that in the soil surrounding mining area. Immobilization didn't have stabilization effect on Cd, Zn, and Pb, and As was only 0.002%, phytoremediation had stabilization effect of Cd, Zn, As, and Pb were 2.5-3.5%, 1-2%, 0.25-0.5%, and 0.25-0.75%. Phytoremediation was more effective significantly in controlling heavy metal pollution risk of tailings than immobilization. These results provided a new ecological remediation OSA-NHC model, meaning a combination of optimal substrate amelioration and native hyperaccumulator colonization, which could achieve vegetation restoration and augment heavy metal pollution control in non-ferrous metal tailings pond.

Response and Adaptation of Microbial Community in a CANON Reactor Exposed to an Extreme Alkaline Shock.

Responses of a microbial community in the completely autotrophic nitrogen removal over nitrite (CANON) process, which was shocked by a pH of 11.0 for 12 h, were investigated. During the recovery phase, the performance, anaerobic ammonia oxidation (anammox) activity, microbial community, and correlation of bacteria as well as the influencing factors were evaluated synchronously. The performance of the CANON process deteriorated rapidly with a nitrogen removal rate (NRR) of 0.13 kg·m-3·d-1, and Firmicutes, spore-forming bacteria, were the dominant phyla after alkaline shock. However, it could self-restore within 107 days after undergoing four stages, at which Planctomycetes became dominant with a relative abundance of 64.62%. Network analysis showed that anammox bacteria (Candidatus Jettenia, Kuenenia, and Brocadia) were positively related to some functional bacteria such as Nitrosomonas, SM1A02, and Calorithrix. Canonical correspondence analysis presented a strong correlation between the microbial community and influencing factors during the recovery phase. With the increase of nitrogen loading rate, the decrease of free nitrous acid and the synergistic effects, heme c content, specific anammox activity (SAA), NRR, and the abundance of dominant genus increased correspondingly. The increase of heme c content regulates the quorum sensing system, promotes the secretion of extracellular polymeric substances, and further improves SAA, NRR, and the relative abundance of the dominant genus. This study highlights some implications for the recovery of the CANON reactor after being exposed to an alkaline shock.

Foliar application of selenium and zinc to alleviate wheat (Triticum aestivum L.) cadmium toxicity and uptake from cadmium-contaminated soil.

Due to the large area of agricultural soils contaminated by Cd worldwide, cost-effective and practical method for safety food production are necessary. The roles of micronutrient on reducing Cd accumulation in crops are recently introduced. In the current study, a pot-culture experiment in the greenhouse was conducted to study the foliar spraying of Se (Na2SeO4) and Zn (ZnSO4) on physiological and growth parameters, as well as Cd concentrations in wheat plants grown in Cd-contaminated soil. The foliar was sprayed with four concentration of Se and Zn (0, 10, 20, and 40 mg L-1) at different growth stage (tillering, elongating and heading) and whole wheat plants were collected after maturity. Both foliar spraying with Se and Zn significantly enhanced the photosynthesis, tissue biomass and antioxidant enzyme activity. Additionally, Se and Zn application can also increase Se and Zn concentrations in different plant tissues. Selenium and Zn decreased malondialdehyde (MDA) and Cd concentrations in wheat grains, hulks, leaves, stalks and root in a dose-additive manner. Overall, Se and Zn both efficiently enhanced the wheat growth and Se and Zn concentrations, and simultaneously decreased the Cd concentration in wheat plant. Compared with Zn, Se more efficiently improved wheat growth and reduced Cd concentration in the wheat in a Cd-contaminated soil. Present results suggest that use of foliar spraying, especially Se, could be a cost-effective strategy and could be recommended for remediation of light-or moderate-polluted soils contaminated by Cd.

Evaluation of anammox pathway recovery after high COD loading using water quality, molecular biology and isotope labelling analysis.

Anaerobic ammonium oxidation (anammox) pathway is sensitive to organic matter, and its recovery requires reliable evidence regarding the dominance of anammox in N-removal. This study showed that the anammox process deteriorated, with N-removal efficiencies rapidly decreasing from 87.2 to 45.7% when reactors were exposed to COD shocks of 1.12, 2.24 and 3.36 g L-1 (COD/N ratio 2, 4 and 6). Comprehensive assessments of water quality, microbial characteristics and isotope analysis were adopted to investigate anammox recovery. Operational performance took 8-20 days to recover; anammox relative abundance recovered after 20 days, based on the results of fluorescence in situ hybridisation and quantitative PCR; and the anammox pathway contributed to 80.0-91.5% of N-loss 40 days after COD shock terminated, based on the results of the isotope labelling experiment. Therefore, a complete recovery required 40 days. The isotope labelling method supplied a reliable reference for recovery assessment of anammox system in real-world applications.

Selection of cost-effective magnesium sources for fluidized struvite crystallization.

Struvite crystallization has been considered a promising approach to recover phosphorus from wastewater. However, its practical application is limited, probably because of the high cost of magnesium (Mg). In this study, a comprehensive economic analysis was conducted using five Mg sources (MgCl2, MgSO4, MgO, Mg(OH)2, and bittern) during the operation of a pilot-scale fluidized bed reactor (FBR), using swine wastewater as the case matrix. First, the economic operating conditions were investigated, and subsequently, the performance and the costs of the five Mg sources were compared. The results indicated that the FBR could be operated most economically at pH of 8.5 and Mg to phosphorus (Mg/P) molar ratio of 1.5. Under these conditions, no significant differences in phosphorus removal and product quality could be found between the five Mg sources. Selecting the most economical Mg source was thus highly dependent on the prices of the reagents and Mg sources. Low-solubility Mg sources were preferable when NaOH was priced higher, while high-solubility Mg sources proved more economical when HNO3 was expensive. The bittern was the most economical choice only when the distances for total inorganic orthophosphate removal and struvite recovery were shorter than 40 and 270km, respectively. The current study provides an overview of the economic selection of an Mg source, which can help reduce the cost of struvite crystallization.

Response of microbial communities to roxarsone under different culture conditions.

Roxarsone is a feed additive widely used in the broiler and swine industries that has the potential to contaminate the environment, mainly via the use of poultry manure as fertilizer, which results in release of inorganic arsenic to the soil and water. This study was conducted to investigate roxarsone degradation and the response of the microbial community under different culture conditions using high-throughput sequencing technology. Poultry litter was incubated for 288 h in the presence of roxarsone under light aerobic, dark aerobic, or dark anaerobic conditions. The results showed that roxarsone was completely degraded after 48 h of dark anaerobic incubation, while 79.9% and 94.5% of roxarsone was degraded after 288 h of dark aerobic and light aerobic incubation, respectively. Under dark aerobic conditions with microbial inhibitor sodium azide, roxarsone was rarely degraded during the 288 h of incubation, illustrating that microorganisms play an important role in roxarsone degradation. Microbial community structure was significantly different among various culture conditions. Olivibacter, Sphingobacterium, and Proteiniphilum were the top 3 genera in the control samples. Sphingobacterium and Alishewanella dominated the light aerobic samples, while the dominant microflora of the dark aerobic samples were Acinetobacter spp. Pseudomonas and Advenella were the predominant genera of dark anaerobic samples. This study emphasizes the potential importance of microbes in roxarsone degradation and expands our current understanding of microbial ecology during roxarsone degradation under different environmental conditions.

Response of soil microbial communities to roxarsone pollution along a concentration gradient.

The extensive use of roxarsone (3-nitro-4-hydroxyphenylarsonic acid) as a feed additive in the broiler poultry industry can lead to environmental arsenic contamination. This study was conducted to reveal the response of soil microbial communities to roxarsone pollution along a concentration gradient. To explore the degradation process and degradation kinetics of roxarsone concentration gradients in soil, the concentration shift of roxarsone at initial concentrations of 0, 50, 100, and 200 mg/kg, as well as that of the arsenic derivatives, was detected. The soil microbial community composition and structure accompanying roxarsone degradation were investigated by high-throughput sequencing. The results showed that roxarsone degradation was inhibited by a biological inhibitor, confirming that soil microbes were absolutely essential to its degradation. Moreover, soil microbes had considerable potential to degrade roxarsone, as a high initial concentration of roxarsone resulted in a substantially increased degradation rate. The concentrations of the degradation products HAPA (3-amino-4-hydroxyphenylarsonic acid), AS(III), and AS(V) in soils were significantly positively correlated. The soil microbial community composition and structure changed significantly across the roxarsone contamination gradient, and the addition of roxarsone decreased the microbial diversity. Some bacteria tended to be inhibited by roxarsone, while Bacillus, Paenibacillus, Arthrobacter, Lysobacter, and Alkaliphilus played important roles in roxarsone degradation. Moreover, HAPA, AS(III), and AS(V) were significantly positively correlated with Symbiobacterium, which dominated soils containing roxarsone, and their abundance increased with increasing initial roxarsone concentration. Accordingly, Symbiobacterium could serve as indicator of arsenic derivatives released by roxarsone as well as the initial roxarsone concentration. This is the first investigation of microbes closely related to roxarsone degradation.

Mercury Fractionation in Superficial Sediment and Paddy Soil Samples from Tianjin, Northern China.

Sediment and soil samples from the Beitang River (BR) and the Haihe River (HR) in Tianjin were analyzed to investigate the extent of mercury contamination. The results show that total mercury (THg) contents in the BR and HR sediments were 2241 ± 1024 and 653 ± 450 ng g(-1), and THg in rice paddy soils were 907 ± 345 and 328 ± 286 ng g(-1), respectively. Industrial and domestic sewage were regarded as the main sources of mercury in the two river basins. Sediment-bound mercury in the BR and the HR were found to be predominantly associated with the organic-bound fraction (55 %) and residual fraction and (54 %), while soil-bound mercury was mainly in organic-bound fraction in paddy soils (61 % and 57 %, respectively). The availability of this element (soluble and exchangeable and specifically sorbed fraction) seemed restricted, but significantly higher in the paddy soils than in sediments. Higher soluble and exchangeable, specifically sorbed fraction and organic-bound fraction may promote the higher toxic methylmercury and bioavailable fraction formation in the soils during the rice cultivation.

Phosphorus recovery from wastewater by struvite crystallization: property of aggregates.

Struvite crystallization is a promising method to remove and recover phosphorus from wastewater to ease both the scarcity of phosphorus rock resources and water eutrophication worldwide. To date, although various kinds of reactor systems have been developed, supporting methods are required to control the struvite fines flushing out of the reactors. As an intrinsic property, aggregation is normally disregarded in the struvite crystallization process, although it is the key factor in final particle size and therefore guarantees phosphorus recovery efficiency. The present study developed a method to analyze the characteristics of struvite aggregates using fractal geometry, and the influence of operational parameters on struvite aggregation was evaluated. Due to its typical orthorhombic molecular structure, struvite particles are prone to crystallize into needle or rod shapes, and aggregate at the corners or edges of crystals. The determined fractal dimension (Dpf) of struvite aggregates was 1.52-1.31, with the corresponding range of equivalent diameter (d0.5) at 295.9-85.4 µm. Aggregates formed in relatively low phosphorus concentrations (3.0-5.0 mmol/L) and mildly alkaline conditions (pH 9.0-9.5) displayed relatively compact structures, large aggregate sizes and high aggregation strength. Increasing pH values led to continuous decrease of aggregate sizes, while the variation of Dpf was insignificant. As to the aggregate evolution, fast growth in a short time followed by a long steady stage was observed.

Physiological and transcriptomic responses of seawater halobios to micro/nano-scale polystyrene-cadmium exposure in a marine food web.

Micro/nano-plastics (MPs/NPs) represent an emerging contaminant, posing a significant threat to oceanic halobios. While the adverse effects of joint pollutants on marine organisms are well-documented, the potential biological impacts on the food chain transmission resulting from combinations of MPs/NPs and heavy metals (HMs) remain largely unexplored. This study exposed the microbial loop to combined contaminants (MPs/NPs + HMs) for 48h, bacteria and contaminants are washed away before feeding to the traditional food chain, employing microscopic observation, biochemical detection, and transcriptome analysis to elucidate the toxicological mechanisms of the top predator. The findings revealed that MPs/NPs combined with Cd2+ could traverse both the microbial loop and classical food chain. Acute exposure significantly affected the carbon biomass of the top predator Tigriopus japonicus (75.8% lower). Elevated antioxidant enzyme activity led to lipid peroxidation, manifesting in increased malondialdehyde levels. Transcriptome sequencing showed substantial differential gene expression levels in T. japonicus under various treatments. The upregulation of genes associated with apoptosis and inflammatory responses, highlighting the impact of co-exposure on oxidative damage and necroptosis within cells. Notably, NPs-Cd exhibited stronger toxicity than MPs-Cd. NPs-Cd led to a greater decrease in the biomass of top predators, accompanied by lower activities of GSH, SOD, CAT, and GSH-PX, resulting in increased production of lipid peroxidation product MDA and higher oxidative stress levels. This investigation provides novel insights into the potential threats of MPs/NPs combined with Cd2+ on the microbial loop across traditional food chain, contributing to a more comprehensive assessment of the ecological risks associated with micro/nano-plastics and heavy metals.

Mechanisms of the novel pesticide sodium dodecyl benzene sulfonate in the mitigation of protozoan ciliated pathogens during microalgal cultivation.

Protozoan ciliates represent a common biological contaminant during microalgae cultivation, which will lead to a decline in microalgae productivity. This study investigated the effectiveness of sodium dodecyl benzene sulfonate (SDBS) in controlling ciliate populations within microalgae cultures. SDBS concentrations of 160 mg/L and 100 mg/L were found to effectively manage the representative species of ciliates contamination by Euplotes vannus and Uronema marinum during the cultivation of Synechococcus and Chlorella, and the growth vitality of microalgae has been restored. Additionally, SDBS at these concentrations reduced oxidative stress resistance and induced membrane damage to remove biological pollutants by modulating enzyme activity, affecting lipid, energy, amino acid metabolism pathways, and processes such as translation and protein folding. This research provides insights into the mechanisms through which SDBS effectively combats protozoan ciliates during the microalgal cultivation. This contributes to reduce biological pollution, ensure the overall productivity and healthy and sustainable management of microalgae ecosystems.

Micro-/nano-plastics as vectors of heavy metals and stress response of ciliates using transcriptomic and metabolomic analyses.

The escalating presence of microplastics and heavy metals in marine environments significantly jeopardizes ecological stability and human health. Despite this, research on the combined effects of microplastics/nanoplastics (MPs/NPs) and heavy metals on marine organisms remains limited. This study evaluated the impact of two sizes of polystyrene beads (approximately 2 µm and 200 nm) combined with cadmium (Cd) on the ciliate species Euplotes vannus. Results demonstrated that co-exposure of MPs/NPs and Cd markedly elevated reactive oxygen species (ROS) levels in ciliates while impairing antioxidant enzyme activities, thus enhancing oxidative damage and significantly reducing carbon biomass in ciliates. Transcriptomic profiling indicated that co-exposure of MPs/NPs and Cd potentially caused severe DNA damage and protein oxidation, as evidenced by numerous differentially expressed genes (DEGs) associated with mismatch repair, DNA replication, and proteasome function. Integrated transcriptomic and metabolomic analysis revealed that DEGs and differentially accumulated metabolites (DAMs) were significantly enriched in the TCA cycle, glycolysis, tryptophan metabolism, and glutathione metabolism. This suggests that co-exposure of MPs/NPs and Cd may reduce ciliate abundance and carbon biomass by inhibiting energy metabolism and antioxidant pathways. Additionally, compared to MPs, the co-exposure of NPs and Cd exhibited more severe negative effects due to the larger specific surface area of NPs, which can carry more Cd. These findings provide novel insights into the toxic effects of MPs/NPs and heavy metals on protozoan ciliates, offering foundational data for assessing the ecological risks of heavy metals exacerbated by MPs/NPs.

Transfer from ciliate to zebrafish: Unveiling mechanisms and combined effects of microplastics and heavy metals.

The impacts and toxicological mechanisms of microplastics (MPs) or heavy metals on aquatic ecosystems have been the subject of extensive research and initial understanding. However, the combined toxicity of co-pollutants on organisms and cumulative toxic effects along the food chain are still underexplored. In this study, the ciliate protozoan Paramecium caudatum and zebrafish Danio rerio were used to represent the microbial loop and the higher trophic level, respectively, to illustrate the progressive exposure of MPs and cadmium (Cd2+). The findings indicate that MPs (ca. 1 ×105 items/L) containing with Cd2+ (below 0.1 µg/L) could permeate the bodies of zebrafish through trophic levels after primary ingestion by ciliates. This could cause adverse effects on zebrafish, including alterations in bioindicators (total sugar, triglycerides, lactate, and glycogen) associated with metabolism, delayed hepatic development, disruption of intestinal microbiota, DNA damage, inflammatory responses, and abnormal cellular apoptosis. In addition, the potential risks associated with the transfer of composite pollutants through the microbial loop into traditional food chain were examined, offering novel insights on the evaluation of the ecological risks associated with MPs. As observed, understanding the bioaccumulation and toxic effects of combined pollutants in zebrafish holds crucial implications for food safety and human health.

Characterization of microbial community structure in a hybrid biofilm-activated sludge reactor for simultaneous nitrogen and phosphorus removal.

The microbial communities in a hybrid biofilm-activated sludge reactor (HY) for nitrogen and phosphorus removal were characterized by 16S rRNA-based clone libraries and phylogenetic analysis. The hybrid reactor removed over 90% of COD, 92% of total nitrogen (TN) and 95% of total phosphorus (TP) from the municipal wastewater, respectively. The mean removal rates of COD, TN, and TP in the conventional suspended activated sludge reactor were above 80%, 80% and 94%, respectively. Community structures were determined by phylogenetic analyses of six clone libraries (each nearly 100 clones). The dominant bacterial group with which clones were affiliated to the beta subclass of the Proteobacteria (31% to approximately 77%), following the Bacteroidetes group (10% to approximately 34%). In addition, several clone groups affiliated with unknown bacterial assemblages were identified in the clone libraries. Acinetobacter sp., which was thought to had played an important role in phosphate removal systems, was scarcely represented by clone sequences in both libraries. Differences in community structure were observed between the hybrid reactor and activated sludge reactors. Such differences may account for the differing wastewater treating capabilities of the two different systems.

The transformation of dissolved organic matter and formation of halogenated by-products during electrochemical advanced oxidation pretreatment for shale gas produced water.

Electrochemical advanced oxidation processes (EAOPs) have shown great potential for the treatment of shale gas produced water (SGPW). In this study, we investigated the transformation of dissolved organic matter (DOM) during EAOPs of SGPW and the formation of toxic halogenated by-products at various current densities, using fluorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry. We found that the priority of DOM removal was terrestrial humic-like > microbial humic-like > protein-like substances. Non-Halogenated organic compounds (non-HOCs) and HOCs were predominantly CHO, and CHOCl/CHOBr compounds in EAOP-treated SGPW, respectively. As applied current density and treatment time increased, the production of oxyhalides increased, with chlorate > bromate > perchlorate. Meanwhile, most DOM was mineralized, resulting in residual products with higher modified aromaticity index (AImod) and nominal oxidation state of carbon (NOSC). The resistants had lower mass-to-charge ratio (m/z), AImod, NOSC, and double bond equivalent minus oxygen per carbon ((DBE-O)/C). The dominant reactions were the addition of tri-oxygen and deallyl. Bromine addition dominated the reactions of halogenating addition, while chlorine addition took second place. Furthermore, the acute toxicity of SGPW was positively correlated with inorganic halogenated by-products. This study contributes to the understanding and improvement of EAOPs for the treatment of SGPW.

Generation, toxicity, and reduction of chlorinated byproducts: Overcome bottlenecks of electrochemical advanced oxidation technology to treat high chloride wastewater.

Electrochemical advanced oxidation process (EAOP) is recommended for high-strength refractory organics wastewater treatment, but the accompanying chlorinated byproduct generation becomes a bottleneck that limits the application of this technology to actual wastewater. In this study, we applied EAOP (0.4-40 mA cm-2) to treat ultrafiltration effluent of an actual landfill leachate, and quantitatively assessed the toxicities of the dominant chlorinated byproducts in EAOP-treated effluent. Considering both toxic effect and dose, it followed the order: active chlorine > chlorate > perchlorate > organochlorines. The toxic active chlorine could spontaneously decompose by settling. And secondary bioreactor originally serving for denitrification could be used to reduce perchlorate and chlorate. The effects of residual active chlorine and extra carbon addition on simultaneous denitrification, perchlorate, and chlorate reduction were investigated. It seemed that 20 mg of active chlorine was an acceptable level to bioactivity, and sufficient electron donors favored the removal of chlorate and perchlorate. Pseudomonas was identified as an active chlorine tolerant chlorate-reducing bacteria. And Thauera was responsible for perchlorate reduction under the conditions of sufficient carbon source supply. Our results confirmed that the perchlorate and chlorate concentrations in the effluent below their health advisory levels were achievable, solving the issue of toxic chlorinated byproduct generation during EAOP. This study provided a solution to realistic application of EAOP to treat high chloride wastewater.

Oxidation treatment of shale gas produced water: Molecular changes in dissolved organic matter composition and toxicity evaluation.

Produced water (PW) is the largest waste stream generated by hydraulic fracturing in an unconventional shale gas reservoir. Oxidation processes (OPs) are frequently used as advanced treatment method in highly complicated water matrix treatments. However, the degradation efficiency is the main focus of research, organic compounds and their toxicity have not been properly explored. Here, we obtained the characterization and transformation of dissolved organic matters of PW samples from the first shale gas field of China by two selected OPs using FT-ICR MS. CHO, CHON, CHOS, and CHONS heterocyclic compounds associated with lignins/CRAM-like, aliphatic/proteins, and carbohydrates compounds were the major organic compounds identified. Electrochemical Fe2+/HClO oxidation preferentially removed aromatic structures, unsaturated hydrocarbons, and tannin compounds with a double-bond equivalence (DBE) value below 7 to more saturated compounds. Nevertheless, Fe (VI) degradation manifested in CHOS compounds with low DBE values, especially single bond compounds. Oxygen- and Sulfur-containing substances, primarily O4-11, S1O3-S1O12, N1S1O4, and N2S1O10 classes, were the main recalcitrant components in OPs. The toxicity assessment showed that the free-radical-formed Fe2+/HClO oxidation could cause significant DNA damage. Therefore, the toxicity response byproducts need spcial attention when conducting OPs. Our results led to discussions on designing appropriate treatment strategies and the development of PW discharge or reuse standards.

Characteristic pollutant purification analysis of modified phosphogypsum comprehensive utilization.

The waste product phosphogypsum (PG) is produced in phosphoric acid production processes. Its storage requires large amounts of land resources and poses serious environmental risks. In this work, detailed experimental research was carried out to investigate the potential reuse of PG after calcination modification as a novel building material for cast-in-place concrete products. The calcination modification mechanism was studied, and the environmental risk assessment of modified PG was presented. The results showed that the calcination modification includes crystal phase transformation, removal of impurities, and modifying the pH value. The calcination was carried out at 280 °C for 5 h, where the resulting product was a pH value of 7.1, and the soluble fluorine and phosphorus removal rates reached up to 69.2% and 71.2%, respectively. These removal rates met the requirements of the China national standard Phosphogypsum (GB/T 23456-2018). To ensure the environmental safety, ecological risk assessment methods for determining the leaching toxicity of the modified PG were employed. The toxicity of Ba and P elements in the modified PG products was assessed, as well as the leaching toxicity concentrations of all particular heavy metals, which were found well below the limits set by the national standards. All the results presented strongly suggest that the 280 °C modified PG presented here has excellent application potential as a raw component in building materials.

Characterization of extracellular polymeric substances from biofilm in the process of starting-up a partial nitrification process under salt stress.

In this study, the characteristics of extracellular polymeric substance (EPS) fractions of biofilm during the process of establishing a partial nitrification under salt stress were analyzed in terms of concentrations, molecular weight distribution, and three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy. A partial nitrification was formed successfully with a salinity of 1%. Results indicated that the amount of total EPS increased from 54.2 mg g⁻¹ VSS⁻¹ on day 1 to 99.6 mg g⁻¹ VSS⁻¹ on day 55 due to the NaCl concentration changed from 0 to 10.0 g L⁻¹ in a biofilm reactor. The changes of loosely bound EPS (LB-EPS) compounds under different salt concentrations appeared to be more significant than those of the tightly bound EPS. A clear release of polysaccharides in the LB-EPS fraction was detected during the enhancement of salinity. This was considered as a protective response of bacteria to the salinity. Three fluorescence peaks were identified in the EEM fluorescence spectra of the EPS fraction samples. Two peaks were assigned to the protein-like fluorophores, and the third peak was located at the excitation/emission wavelengths of 275 nm/425-435 nm of the spectra of EPS fractions till the salinity maintained constant at 1%. This information is valuable for understanding the characteristics of EPS isolated from biomass in a saline nitrogen removal system.

Molecular-level variation of dissolved organic matter and microbial structure of produced water during its early storage in Fuling shale gas field, China.

Shale gas-produced water (PW), the waste fluid generated during gas production, contains a large number of organic contaminants and high salinity matrix. Previous studies generally focused on the end-of-pipe treatment of the PW and ignored the early collection process. In this study, the transformation of the molecular composition and microbial community structure of the PW in the transportation and storage process (i.e., from the gas-liquid separator to the storage tank) were investigated. As the PW was transported from the gas-liquid separator to the portable storage tank, the dissolved organic matter (DOM) showed greater saturation, less oxidation, and lower polarity. DOMs with high O/C and low H/C ratios (numbers of oxygen and hydrogen divided by numbers of carbon) were eliminated, which may be due to precipitation or adsorption by the solids suspended in the PW. The values of double-bond equivalent (DBE), DBE/C (DBE divided by the number of carbon), and aromatic index (AI) decreased, likely because of the microbial degradation of aromatic compounds. The PW in the gas-liquid separator presented a lower biodiversity than that in the storage tank. The microbial community in the storage tank showed the coexistence of anaerobes and aerobes. Genera related to biocorrosion and souring were detected in the two facilities, thus indicating the necessity of more efficient anticorrosion strategies. This study helps to enhance the understanding of the environmental behavior of PW during shale gas collection and provides a scientific reference for the design and formulation of efficient transportation and storage strategies to prevent and control the environmental risk of shale gas-derived PW.