Effects of pipe material on nitrogen transformation, microbial communities and functional genes in raw water transportation

Bidirectional potential effects of DON transformation in vadose zones on groundwater nitrate contamination: Different contributions to nitrification and denitrification

The main cause of groundwater nitrate contamination is the continual downward migration of dissolved nitrogen (N) in vadose zone with leachate. In recent years it has been found that dissolved organic N (DON) rise to forefront due to its great migration capacity and environmental effects. However, it remains unknown how the transformation behaviors of DONs with different properties in vadose zone profile may impact N forms distribution and groundwater nitrate contamination. To address the issue, we conducted a series of 60-day microcosm incubation experiments to investigate the effects of various DONs transformation behaviors on the distribution of N forms, microbial communities, and functional genes. The results revealed that urea and amino acids mineralized immediately after substrates addition. By contrast, amino sugars and proteins caused less dissolved N throughout entire incubation period. The transformation behaviors could substantially alter the microbial communities. Moreover, we discovered that amino sugars remarkably increased the absolute abundances of denitrification function genes. These results delineated that DONs with unique characteristics (such as amino sugar) promoted different N geochemical processes in distinct ways: different contributions to nitrification and denitrification. This can provide new insights for nitrate non-point source pollution control in groundwater.

Insights into the role of prechlorination in algae-laden raw water distribution process: Algal organic matter and microcystin-LR release, extracellular polymeric substances (EPS) aggregation, and pipeline biofilm communities

Prechlorination routinely applied for the treatment of algae-laden raw water has received extensive attention due to its influence on water quality and aquatic microbes. In this study, prechlorination experiments with different doses were conducted in sets of model raw water distribution systems. With the elevated dose of chlorine and prolonged hydraulic retention time (HRT), the ratio of intact algal cells decreased, and the stability of water enhanced. Dissolved organic carbon (DOC) and nitrogen (DON) increased when chlorine dose elevated from 0 to 0.5 mg/L but decreased with elevations from 0.5 to 2.0 mg/L, while UV₂₅₄ showed a monotonically increasing tendency. DOC, DON and extracellular microcystin-LR increase initially and decrease thereafter with the prolonged HRT. Notably, the effects of prechlorination on extracellular polymeric substances aggregation behavior on pipe walls and microbial community composition was revealed, providing more profound understanding of the community dynamics in this engineered system. This study helped optimize strategies to improve the stability and efficiency of pretreatment of algae-laden water.

Effects of silver nanoparticles on denitrification and anammox in sediments of hypertrophic and mesotrophic lakes

The abundant production and wide usage of silver nanoparticles (Ag NPs) inevitably lead to their release into aquatic ecosystems. However, it is still unclear about how Ag NPs influence denitrification and anammox (DA) in freshwater sediments. To address this, the sediments of hypertrophic and mesotrophic lakes were exposed to 0.5 and 50 mg/L Ag NPs under anaerobic conditions for 7 days to explore the effects of Ag NPs on environmental variables, including redox potential (Eh), pH, organic matter (OM) and acid volatile sulfide (AVS), and the resulting influence on DA. Experimental results indicated that NO₃^--N and NH₄⁺-N levels were increased by the low (p > 0.05) and high doses of Ag NPs (p < 0.05) in comparison with the non-Ag control, revealing an inhibitive impact on DA. The level of total nitrogen (TN) was notably increased by the low and high doses of Ag NPs (p < 0.05), perhaps due to inhibited enzyme activity and corresponding encoding gene abundance, which were related to generating gaseous nitrogen such as N₂O and N₂. In addition, environmental factor Eh was significantly raised by Ag NPs (p < 0.05), further inhibiting DA. Moreover, the quantitative analysis unveiled that denitrifying and anammox bacteria in hypertrophic lakes evinced a stronger resistance to Ag NPs toxicity than those in mesotrophic lakes. Overall, our study revealed that short-term exposure to Ag NPs could inhibit DA in sediments. These findings provide an understanding enabling evaluation and prediction of the environmental risks of Ag NPs in freshwater lakes.

Effect of microbial agents on maturity, humification, and stability and the bacterial succession of spent mushroom substrate composting

Two composting experiments were conducted to investigate the effects of commercial microbial agents on microbial succession and nutrient flow such as humification, maturation, and stability during the aerobic composting of the spent mushroom substrate (SMS). The cellulose degradation rate of T (added microbial agents at the initial stage) reached 41.8%, which was much significantly (p < 0.05) higher than that of CK (14.9%). The seed germination index (GI) in T (82.38%) was significantly (p < 0.05) higher than that in CK (74.74%) in the maturation phase. Moreover, the total organic carbon/total nitrogen ratio (C/N) and electrical conductivity (EC) value of T decreased to 10.5 and 2.37 mS/cm, respectively. Chemical detection and fluorescence excitation-emission region integration method (EEM-FRI) analysis showed that the microbial agents significantly accelerated the organic matter (OM) decomposition and promoted the quality of mature compost using SMS as a single raw material. The bacterial abundance of T was significantly richer than the CK due to the addition of microbial agents. The results could provide a comprehensive understanding of adding microbial agents into composting SMS and a scientific feasibility strategy to rational utilization of resources in the edible fungi industry, which was conducive to the waste management and sustainable development of the edible fungi industry.

A new LDH based sustained-release carbon source filter media to achieve advanced denitrogenation of low C/N wastewater at low temperature

Advanced denitrogenation of wastewater is now facing major challenges brought by low C/N ratio and low temperature. The development of sustained-release materials with good and stable carbon release properties was an effective countermeasure. FeNi-Layered double-metal hydroxides (LDH)- sodium carboxymethyl cellulose (CMC) filter media and its potential use in heterotrophic and sulfur-based mixotrophic denitrification biological filter (DNBF), was firstly reported. It demonstrated stable structure and good carbon release performance with a mass transfer coefficient (K) of 4.40 mg·L^-1·s^-1. When the influent NO₃^--N of 50 mg/L with the C/N ratio of 3 at 10 °C, the maximum nitrogen loading rate of 0.22 kg·N/(m³·d) and effluent TN close to 5 mg/L (nitrogen removal of almost 90 %) could be achieved. The slowly released carbon source and the leached iron increased the abundance of denitrifying bacteria and functional genes, and the augmentation of Sulfuritalea and the secretion of biofilm protein stimulated by sulfur also played a synergistic role. This study provided a new potentially effective strategy to enhance advanced denitrification of wastewater of low C/N wastewater at low temperature.

Effect of thermophilic microbial agents on nitrogen transformation, nitrogen functional genes, and bacterial communities during bean dregs composting

This study explored how a thermophilic microbial agent altered nitrogen transformation, nitrogen functional genes, and bacterial communities during bean dregs composting with (T) and without (CK) a thermophilic microbial agent for 15 days. The results showed that the maximum temperature in T reached 73 °C and remained above 70 °C for 8 days, while that in CK was only 65 °C. The pH in T had essentially stabilized on day 7, while that in CK was still increasing. On day 15, the seed germination index (GI) of T (95%) reached maturity (defined by GI ≥ 85%), while the GI of CK was only 36%. The concentrations of total nitrogen, water-soluble nitrogen, ammonia nitrogen, and nitrate nitrogen in T (2.5%, 18.9 g/kg, 8.75 g/kg, and 1.69 g/kg) were all lower than those in CK (3.6%, 28.9 g/kg, 12.75 g/kg, and 6.82 g/kg). During composting, Bacillus played a major role in nitrogen reduction, nitrogen mineralization, denitrification, and the conversion between nitrite and nitrate. Weissella played a major role in nitrogen assimilation. Komagataeibacter and Bacillus played a major role in nitrogen fixation in CK and T, respectively. Nitrification was not observed during composting. The nosZ gene, which converts nitrous oxide to nitrogen, was found only in T. Network analysis suggested that the average number of neighbours in T was 3.30% higher than that in CK and the characteristic path length in T was 14.15% higher than that in CK. Therefore, the thermophilic microbial agents could cause nitrogen loss but promote the maturity of bean dregs, which have great potential application.

Insights into the associations of copper and zinc with nitrogen metabolism during manure composting with shrimp shell powder

The application of shrimp shell powder (SSP) in manure composting can promote the maturation of compost and reduce the associated environmental risk. This study investigated the response of adding SSP at different levels (CK: 0, L: 5%, M: 10%, and H: 15%) on heavy metal resistance genes (MRGs), nitrogen functional genes, enzymes, and microorganisms. SSP inhibited nitrification and denitrification via decreasing the abundances of functional genes and key enzymes related to Cu, Zn, and MRGs. The nitrate reductase and nitrous-oxide reductase in the denitrification pathway were lower under H. Phylogenetic trees indicated that Burkholderiales sp. had strong relationships with OTU396 and OTU333, with important roles in the nitrogen cycle and plant growth. Redundancy analysis and structural equation modeling showed the complex response between heavy metal and nitrogen that bio-Cu and bio-Zn had positive significantly relationships with nirK-type and amoA-type bacteria, and amoA-type bacteria might be hotspot of cueO.

Dual roles of dissolved organic nitrogen in groundwater nitrogen cycling: Nitrate precursor and denitrification promoter

Dissolved organic nitrogen (DON) has been reported to be prevalent in groundwater worldwide. Owing to the diversity of physicochemical properties, DON plays complex roles in nitrogen cycling processes, which has further implications for nitrate (NO₃^--N) pollution control in groundwater. To characterize these crucial roles, we investigated the effects of three types of DON (amino acid, urea, and protein) on NO₃^--N accumulation in groundwater with a 60-day incubation experiment and established quantitative correlations between microbial indicators (bacterial communities and nitrogen functional genes) and nitrogen content. The results showed that NO₃^--N content increased by 30.3% and 38.8% and was strongly correlated with the presence of amino acid and urea; however, the addition of protein did not lead to an additional increase in NO₃^--N, possibly due to different extents of mineralization and denitrification caused by different types of DON. Molecular biological experiments demonstrated that Nitrospira (1.8-3.2%) contributed to nitrification in the urea treatment, whereas Arthrobacter (2.0-6.9%) and Thermomonas (11.9-13.1%) were key communities controlling denitrification in amino acid and protein treatments. amoA and nxrA were continuously enriched in the presence of urea; however, amino acid and protein were strongly correlated with napA-dominated and narG-dominated denitrification processes, with the path coefficient - 2.912 and - 2.450 respectively. Combined analyses showed that DON with distinct physicochemical properties played dual roles (NO₃^--N precursor and denitrification promoter) to varying degrees, which could have significant impacts on NO₃^--N accumulation in groundwater. This study may provide guidance for environmental risk evaluation and control strategies for NO₃^--N pollution in groundwater.

Storage tank as a pretreatment unit for rainwater cleaner production: Role of biofilm bacterial communities and functional genera in water quality improvement

This study investigated the water purification function and mechanism of biofilm in storage tank, with a view to using it as a pretreatment unit for rainwater cleaner production. Shortening the hydraulic retention time (HRT) of storage tank from 12 to 4 h improved the pollutants removal performance and reduced the suspended bacteria counts. The accumulation of abundant taxa and succession of rare taxa were observed with biofilm development. Positive correlations within and across different bacterial taxa were dominant in the network, and some rare genera (Ralstonia and Micropruina) were identified as hub bacteria. Candidatus Nitrospira nitrosa and Nitrospira sp. ENR4 were two identified complete ammonia oxidizers. Denitrifying bacteria tended to enrich and formed more complex interactions over time. The main nitrogen metabolism pathways may be ammonia assimilatory, complete denitrification and dissimilatory/assimilatory nitrate reduction. HRT was negatively correlated with most dominant genera, and contributed 20.35% to the variation of functional taxa. This study highlights the self-purification function and micro-ecology of storage tank, and provides a new insight for its role in rainwater cleaner production process.

Changes in microbial community diversity, composition, and functions upon nitrate and Cr(VI) contaminated groundwater

With the increasing occurrences of nitrate and Cr(VI) pollution globally, microbially driven pollutant reduction and its interaction effects were of growing interest. Despite the increasing number of experimental reports on the simultaneous reduction of nitrate and Cr(VI), a broad picture of the keystone species and metabolic differences in this process remained elusive. This study explored the changing of microorganisms with the introduction of Cr(VI)/NO₃^- through analyzing 242 samples from the NCBI database. The correlation between microbial abundance and environmental factors showed that, the types of energy substances and pollutants species in the environment had an impact on the diversity of microorganisms and community structure. The genus of Zoogloea, Candidatus Accumulibacter, and Candidatus Kapabacteria sp. 59-99 had the ability of denitrification, while genus of Alcaligenes, Kerstersia, Petrimonas, and Leucobacter showed effectively Cr(VI) resistance and reducing ability. Azoarcus, Pseudomonas, and Thauera were recognized as important candidates in the simultaneous reduction of nitrate and Cr(VI). Metagenomic predictions of these microorganisms using PICRUSt2 further highlighted the enrichment of Cr(VI)and nitrate reduction-related genes (such as chrA and norC). Special attention should therefore be paid to these bacteria in subsequent studies to evaluate their performance and mechanisms involved in simultaneous denitrification and chromium removal. The microbial co-occurrence network analysis conducted on this basis emphasized a strong association between community collaboration and pollution removal. Collectively, either site surveys or laboratory experiments, subsequent studies should focus on these microbial populations and the interspecific collaborations as they strongly influence the occurrence of simultaneous nitrate and Cr(VI) reduction.

Anaerobic biodegradation of four sulfanilamide antibiotics: Kinetics, pathways and microbiological studies

Large amounts of sulfanilamide antibiotics (SAs) have been excreted into the manure. In this study, the anaerobic biodegradation of four kinds of SAs including sulfaquinoxaline (SQX), sulfamethoxazole (SMX), sulfamethoxine (SMD) and sulfathiazole (STZ) was investigated. The degradation rates of SQX and STZ decreased with the increase of the concentrations of other organics, but those of SMX and SMD were less affected. The average degradation rates of SAs were in the order of SMX >SMD ≈QX >STZ, with the best degradation rate constants of 0.30125, 0.14752, 0.16696, and 0.06577 /d, respectively. STZ had the greatest effect on the population richness of microbes, whereas SQX had the largest impact on the population diversity. The degradation rates of SAs were positively correlated with the abundances of Proteobacteria and Bacteroidetes, and negatively correlated with the abundance of Firmicutes. The common degradation pathways of SAs were S-N cleavage and substitution. The specific functional groups of SQX, SMX and SMD, including quinoxaline, isoxazole and pyrimidine rings, could be opened, but the thiazole ring of STZ was difficult to be decomposed. After the rings of the specific functional groups were opened, they would be further substituted or decomposed to be products with small molecules.

Characterization of the synergistic relationships between nitrification and microbial regrowth in the chloraminated drinking water supply system

Deterioration of water quality is commonly found in secondary water supply systems (SWSSs), especially the growth of microbes. To explore the metabolic mechanism for rapid microbial regrowth in SWSSs, a regrowth potential assessment, flow cytometry, and quantitative PCR were conducted. Metagenomic and 16S rRNA gene sequencing were performed to better understand the microbial communities and metabolism. It was found that the increased biomass in the SWSS was significantly higher than that in the drinking water distribution system (DWDS). Statistical analysis revealed that ammonia oxidation was the dominant driver of increased biomass in the SWSS. The abundances of ammonia oxidation bacteria, concentration of nitrogen species, and related enzymes demonstrated that ammonia oxidation in the SWSS was more vigorous than that in the DWDS. In the SWSS, the metabolism of the ammonia oxidation cluster was more vigorous, and ammonia-oxidizing bacteria (AOB) were the dominant nitrifying bacteria. Incomplete nitrification products were involved in the metabolism of heterotrophic bacteria and promoted the growth of heterotrophic bacteria in the SWSS. More attention should be given to controlling incomplete nitrification to improve tap water quality.

Field study on the transportation characteristics of PFASs from water source to tap water

Perfluoroalkyl substances (PFASs) can occur in water sources, pass through drinking water treatment plants (DWTPs), drinking water distribution systems (DWDSs), to the consumer taps. This investigation was carried out to present the transportation behaviors of 17 PFASs, involving seven DWTPs with different water sources, raw water transportation modes, treatment processes, and DWDS structures in eastern and northern China. The results showed that the long-distance raw water transportation pipelines removed a certain extent of PFASs from raw water, probably due to the accumulation of loose deposits. The long-distance, open-channel South-to-North water diversion increased PFAS contamination risk. In the DWTPs, granular activated carbon (GAC) adsorption and ultraviolet radiation removed less than 25% of PFASs, but ozonation-biological activated carbon (O₃-BAC) was superior to GAC alone in removing PFASs. Loose deposits couldsignificantly influence PFAS accumulation and release within branch-structured DWDSs. In loop-structured DWDSs, finished water with different PFAS characteristics could mix along the pipeline, with the corresponding DWTP as the center, ultimately forming a relatively uniform distribution in the entire DWDS.

Occurrence and quantification of culturable and viable but non-culturable (VBNC) pathogens in biofilm on different pipes from a metropolitan drinking water distribution system

Waterborne pathogens have been found in biofilms grown in drinking water distribution system (DWDS). However, there is a lack of quantitative study on the culturability of pathogens in biofilms from metropolitan DWDS. In this study, we quantified culturable and viable but non-culturable (VBNC) Escherichia coli, Salmonella enterica, Pseudomonas aeruginosa and Vibrio cholerae in biofilms collected from five kinds of pipes (galvanized steel pipe, steel pipe, stainless steel clad pipe, ductile cast iron pipe and polyethylene pipe) and associated drinking water at an actual chlorinated DWDS in use from China. The results of these comprehensive analyses revealed that pipe material is a significant factor influencing the culturability of pathogen and microbial communities. Network analysis of the culturable pathogens and 16S rRNA gene inferred potential interactions between microbiome and culturability of pathogens. Although the water quality met the Chinese national standard of drinking water, however, VBNC pathogens were detected in both biofilms and water from the DWDS. This investigation suggests that stainless steel clad pipe (SSCP) was a better choice for pathogen control compared with other metal pipes. To our knowledge, this is the first study on culturable and VBNC pathogens in biofilms of different pipe materials in metropolitan DWDS.

Effect and mechanism of silver nanoparticles on nitrogen transformation in water-sediment system of a hypereutrophic lake

Industrialization and urbanization are expected to increase the release of silver nanoparticles (AgNPs) into aquatic ecosystems. However, it remains to be determined how AgNPs influence nitrogen transformation and the underlying mechanism in natural water bodies. Here, the impact of AgNPs on nitrogen cycling in water-sediment system of a hypereutrophic lake was studied and the mechanism of nitrogen transformation was investigated in terms of the nitrogen functional enzymes and genes. Following 7 days of water-sediment microcosm experiments, the levels of total nitroten (TN) and organic nitrogen (OrgN) were significantly increased by 50 mg/L Ag⁺ treatment when compared with the non-Ag control (P < 0.05). In contrast, the levels of TN and Org-N were both slightly decreased by AgNPs treatments (0.5 and 50 mg/L). Additionally, the levels of NO₃^--N were evidently reduced with the presence of AgNPs (P < 0.05). Further, our data proved that enzymes and those enzyme encoding genes involved in the nitrogen transformation may directly responsible for the alterations of nitrogen transformation. Overall, our work suggested that the short-term exposure to AgNPs might cause hormetic effects on nitrogen-transforming microorganisms in hypereutrophic lakes, and have a potential to result in non-negligible changes in the nitrogen cycling of hypereutrophic lakes.

Effects of phosphogypsum and medical stone on nitrogen transformation, nitrogen functional genes, and bacterial community during aerobic composting

This study explored the effects of adding phosphogypsum (PPG), medical stone (MS), and both (PPM) during composting on nitrogen transformation, nitrogen functional genes, the bacterial community, and their relationships with NH₃ and N₂O emissions. Adding MS and PPM reduced NH₃ emissions by 25.78-68.37% and N₂O emissions by 19.00-42.86%. PPG reduced NH₃ emissions by 59.74% but slightly increased N₂O emissions by 8.15%. MS was strongly correlated with the amoA-dominated nitrification process. PPG and PPM had strong correlations with nirS- and nirK-dominated, and nosZ-dominated denitrification processes, respectively. PPM promoted nitrification and denitrification processes more than PPG and MS. Different functional bacteria had key roles in nitrification and denitrification during different composting stages. Firmicutes probably contributed to the conversion and release of nitrogen in the thermophilic period, whereas Proteobacteria, Chloroflexi, Bacteroidetes, and other phyla might have played important roles in the cooling and maturation periods. PPM obtained the greatest reductions in NH₃ and N₂O release via the regulation of environmental variables, nitrogen functional genes, and the bacterial community. Overall, these results provide insights at a molecular level into the effects of PPG and MS on nitrogen transformation and NH₃ and N₂O emissions during composting.

Investigation of nitrogen pollutants transformation and its pathways along the long-distance prechlorinated raw water distribution system

Understanding the transformation pattern of nitrogen (N) pollutants and its pathways in the prechlorinated raw water distribution system (PRWDS) is vital for controlling the stablitiy and safety of raw water qulity. This study investigated the N transformation, N functional genes and their correlations to find the N transformation pathways along the PRWDS. Results suggested that simultaneous nitrification, anaerobic ammonium oxidation and denitrification (SNAD) contribute to the N transformationin the PRWDS. Along the pipeline, anammox 16S rRNA (9.18 × 10⁷-8.41 × 10⁸ copies/g), limited by prechlorination, was the most abundant N functional genes and anammox process was the main pathway of ammonia nitrogen (NH₄⁺-N). The decreasing NH₄⁺-N was connected with Planctomycetes, Nitrospira and abundance of nxrA attributing to the joint effort of anammox and declined nitrification. The concentration of nitrate (NO₃^--N) increasing at first and then decreasing, was correlated positively with Sphingomonas. because of the declined nitritication and increased denitrification. Besides, the NO₃^--N→NO₂^--N process was considered to be primary NO₃^--N transformation pathways. Increases in the concentration of dissolved organic nitrogen (DON) and nitrite (NO₂^--N) observed in the PRWDS had positive correlation with relative abundance of Pseudomonas. We believe that prechlorination shaped the particular bacterialcharacteristics in biofilms and influenced the N transformation pathways indirectly, resulting in the varying N transformation rules in PRWDSs. Moreover, systematic and extended research is particularly vital for determining the effects of changes in source water quality and environmental conditions on bacterial community structure and N conversion along PRWDSs.

Abundance, diversity, and distribution patterns along with the salinity of four nitrogen transformation-related microbes in the Yangtze Estuary

Purpose

The abundance and composition of nitrogen transformation-related microbes with certain environmental parameters for living conditions provide information about the nitrogen cycle in the Yangtze Estuary. The aim of this study was to explore the impacts of salinity on four N-related microbes and reveal the phylogenetic characteristics of microorganisms in the Yangtze Estuary ecosystem. A molecular biology method was used for the quantitation and identification of four microbes in the Yangtze River: ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA), denitrifying microbes (nirS-type), and anaerobic ammonia-oxidizing (anammox) bacteria. Sequence identification was performed on the levels of phylum, class, order, family, and genus, and the sequences were then matched to species.

Result

The results showed that the dominant species of AOA were crenarchaeote enrichment cultures, thaumarchaeote enrichment cultures, and Nitrosopumilus maritimus cultures, and the dominant AOB species were betaproteobacterium enrichment cultures and Nitrosomona sp. The denitrifying microbes were identified as the phylum Proteobacteria, classes Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria, and the species Thauera selenatis. The dominant species of the anammox bacteria was Candidatus Brocadia sp. In the estuarine sediments of the Yangtze River, the nirS gene abundance (1.31 × 107–9.50 × 108 copies g−1 sediments) was the highest among all the detected genes, and the abundance of bacterial amoA, archaeal amoA, and nirS was significantly correlated. Closely correlated with the abundance of the bacterial amoA gene, salinity was an important factor in promoting the abundance and restraining the community diversity of AOB. Moreover, the distribution of the AOB species exhibited regional patterns in the estuarine zone.

Conclusions

The results indicated that salinity might promote abundance while limiting the diversity of AOB and that salinity might have reverse impacts on AOA. Denitrifying microbes, which showed a significant correlation with the other genes, were thought to interact with the other genes during nitrogen migration. The results also implied that AOA has a lower potential nitrification rate than AOB and that both the anammox and denitrification processes (defined by nirS gene) account for N2 production.

Molecular Characteristics of Dissolved Organic Nitrogen and Its Interaction with Microbial Communities in a Prechlorinated Raw Water Distribution System

Dissolved organic nitrogen (DON) represents a unique challenge in prechlorinated raw water distribution systems (PRWDSs) because of its contribution to the formation of harmful nitrogen-disinfection byproducts, influence upon biogeochemical processes, and unclear molecular characteristics. Here, Fourier transform ion cyclotron resonance mass spectrometry in combination with high-throughput sequencing was applied to elucidate the molecular changes of DON and biofilm microbial communities in a PRWDS in Yixing, China. Our study revealed that dynamic characteristics of DON are significantly correlated with the biofilm. The accumulation of refractory lignin-like compounds and C_nH_mO_pN₁ contributes to the higher recalcitrance molecular characteristics of DON in the effluent associated with Alphaproteobacteria, Planctomycetes, and Bacteroidetes. Additionally, with the help of prechlorination, the biofilm may change the DON characteristics and lead to higher oxygenation, higher m/z, and lower saturation during transportation. Despite the promotion of C_nH_mO_pN₁ and C_nH_mO_pN₃ at the early stage, we suggest that appropriate concentration of chlorine can add to the front end of raw water distribution pipes. Prechlorination may control the nitrification process and stabilize the rapid growth of diversity and concentration of low molecular weight DON, especially the refractory C_nH_mO_pN₁ in the effluent, which may help to improve treatment efficiency of drinking water treatment plants.

A novel start-up strategy for mixotrophic denitrification biofilters by rhamnolipid and its performance on denitrification of low C/N wastewater

A novel start-up strategy for sulfur-based mixotrophic denitrification biofilters (mDNBFs) by rhamnolipid was investigated for the first time. Rhamnolipid with gradient concentrations (0-120 mg/L) was added into five lab-scale mDNBFs. Results showed that rhamnolipid could promote biomass yield and nitrogen removal rate (NRR) by 71.7% and 68.7%, respectively, while its effect on EPS and adhesion force was concentration-dependent. The spatial distribution characteristics of microbial communities demonstrated the enrichment of main heterotrophic denitrifying bacteria outcompeted that of the autotrophs, with a more pronounced difference in high concentration rhamnolipid-treated mDNBFs. Furthermore, highest abundance of napA, narG, nirK and nosZ genes was observed in 80 mg/L rhamnolipid-treated mDNBF. Interfacial processes including solubilizing effect and hydration repulse and variations of organics were discussed to explicate the underlying mechanism. The study enlightened that an appropriate concentration (∼80 mg/L) of rhamnolipid may be a good solution for accelerating biofilm formation and enriching denitrifying bacteria to promote denitrification performance of mDNBFs treating low C/N wastewater.

Genetic associations as indices for assessing nitrogen transformation processes in co-composting of cattle manure and rice straw

In this study, mechanism of nitrogen transformation was investigated in terms of genetic associations (nitrogen-related gene groups) in co-composting of cattle manure and rice straw. Mutual validation among KEGG, Pearson correlation, stepwise regression, and Path analyses indicated that the functional genes synergistically affected on nitrogen transformation in composting process. NxrA/qnorB (0.9419 ± 0.0334) and (amoA + anammox)/Bacteria (0.7187 ± 0.0334) were the key functional gene groups mediating NH₄⁺-N transformation. AmoA/(narG + napA) (-0.8400 ± 0.0129), amoA/bacteria (0.8692 ± 0.0273), and (nirK + nirS)/nosZ (1.1652 ± 0.0089) determined NO₃^--N, NO₂^--N and N₂O transformation, respectively. AmoA/(napA + narG) mediated both NO₃^--N and NO₂^--N transformation. AmoA/anammox (-0.7172 ± 0.0591) and (nirK + nirS)/nosZ (-0.6626 ± 0.0825) served as predominant factors for total nitrogen removal. These results provided a molecular-level insight that nitrification, anaerobic ammonia oxidation and denitrification (SNAD) might simultaneously contribute to nitrogen transformation during composting, rather than sequentially.

Transformation and fate of dissolved organic nitrogen in drinking water supply system: A full scale case study from Yixing, China

The transformation of dissolved organic nitrogen (DON) in the drinking water treatment plants could be closely associated with nitrogenous disinfection by-product (N-DBP) formation. In this study, we have assessed the molecular transformation of DON and its impact on N-DBP formation in a full scale drinking water treatment plant. Based on the result of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis, DON compounds with low molecular weight (<1 kDa) were classified as CHON, CHON₂ and CHON₃ according to the number of nitrogen atoms. Via the analytical window of van Krevelen diagrams, we found that the molecular structural features of CHON, CHON₂ and CHON₃ were not altered before the chlorination process. In detail, the CHON₂ and CHON₃ compositions were concentrated on the regions assigned to a lignin-structure while CHON compositions were also distributed in other compounds including proteins, carbohydrates and tannin. Furthermore, CHON formation was more difficult to be removed before the V-filter process. For N-DBP, chlorine-containing DON (Cl-DON) composition was likely to be removed through flocculation and sedimentation processes, whereas N-nitrosamine compounds were removed in V-filter and biological activated carbon filter processes. The health risks of aromatic structure N-nitrosamines due to the pre-chlorination of the raw water should be further studied.