Robustness of the synergistic partial-denitrification, anammox, and fermentation process for treating domestic and nitrate wastewaters under fluctuating C/N ratios.

The synergistic partial-denitrification, anammox, and fermentation (SPDAF) process presents a promising solution to treat domestic and nitrate wastewaters. However, its capability to handle fluctuating C/N ratios (the ratios of COD to total inorganic nitrogen) in practical applications remains uncertain. In this study, the SPDAF process was operated for 236 days with C/N ratios of 0.7-3.5, and a high and stable efficiency of nitrogen removal (84.9 ± 7.8%) was achieved. The denitrification and anammox contributions were 6.1 ± 7.1% and 93.9 ± 7.1%, respectively. Batch tests highlighted the pivotal role of in situ fermentation at low biodegradable chemical oxygen demand (BCOD)/NO3- ratios. As the BCOD/NO3- ratios increased from 0 to 6, the NH4+ and NO3- removal rates increased, while the anammox contribution decreased from 100% to 80.1% but remained the primary pathway of nitrogen removal. The cooperation and balanced growth of denitrifying bacteria, anammox bacteria, and fermentation bacteria contributed to the system's robustness under fluctuating C/N ratios.

Facilitating effects of the synergy with zero-valent iron and peroxysulfate on the sludge anaerobic fermentation system: Combined biological enzyme, microbial community and fermentation mechanism assessment.

This study evaluated a synergetic waste activated sludge treatment strategy with environmentally friendly zero-valent iron nanoparticles (Fe0) and peroxysulfate. To verify the feasibility of the synergistic treatment, Fe0, peroxysulfate, and the mixture of peroxysulfate and Fe0 (synergy treatment) were added to different sludge fermentation systems. The study demonstrated that the synergy treatment fermentation system displayed remarkable hydrolysis performance with 435.50 mg COD/L of protein and 197.67 mg COD/L of polysaccharide, which increased 1.13-2.85 times (protein) and 1.12-1.49 times (polysaccharide) for other three fermentation system. Additionally, the synergy treatment fermentation system (754.52 mg COD/L) exhibited a well acidification performance which was 1.35-41.73 times for other systems (18.08-557.27 mg COD/L). The synergy treatment fermentation system had a facilitating effect on the activity of protease, dehydrogenase, and alkaline phosphatase, which guaranteed the transformation of organic matter. Results also indicated that Comamonas, Soehngenia, Pseudomonas, and Fusibacter were enriched in synergy treatment, which was beneficial to produce SCFAs. The activation of Fe0 on peroxysulfate promoting electron transfer, improving the active groups, and increasing the enrichment of functional microorganisms showed the advanced nature of synergy treatment. These results proved the feasibility of synergy treatment with Fe0 and peroxysulfate to enhance waste activated sludge anaerobic fermentation.

Insight into the potentiality of nano zero-valent iron on enhancing the nitrite accumulation and phosphorus removal performance of endogenous partial denitrification systems.

Endogenous partial denitrification (EPD) has drawn a lot of interest due to its abundant nitrite (NO2--N) accumulation capacity. However, the poor phosphate (PO43--P) removal rate of EPD restricts its promotion and application. In this study, the potentiality of various nano zero-valent iron (nZVI) concentrations (0, 20, 40, and 80 mg/L) on NO2--N accumulation and PO43--P removal in EPD systems had been investigated. Results showed that nZVI improved NO2--N accumulation and PO43--P removal, with the greatest nitrate-to-nitrite transformation ratio (NTR) and PO43--P removal rate of 97.74 % and 64.76 % respectively at the optimum nZVI level (80 mg/L). Microbial community analysis also proved that nZVI had a remarkable influence on the microbial community of EPD. Candidatus_Competibacter was contribute to NO2--N accumulation which was enriched from 24.74 % to 40.02 %. The enrichment of Thauera, Rhodobacteraceae, Pseudomonas were contributed to PO43--P removal. The chemistry of nZVI not only compensated for the deficiency of biological PO43--P removal, but also enhanced NO2--N enrichment. Therefore, nZVI had the huge potentiality to improve the operational performance of the EPD system.

Polystyrene size-dependent impacts on microbial decomposers and nutrient cycling in streams.

The particle size of plastic is one of the most important factors influencing its ecotoxicity, but we are unclear about the effect of polystyrene (PS) particle size on microbial decomposers and consequent nutrient cycling in streams. Here, using microcosm experiments, we assessed how three PS sizes (50 nm, 1 µm, and 20 µm) influenced the process and consequences of leaf litter decomposition. Under acute exposure to 1 µm and 20 µm PS, fungal biomass significantly decreased, but microbial biomass significantly increased, indicating compensations may work between fungi and other microbial decomposers. After chronic exposure to 50 nm and 1 µm PS, the leaf decomposition rate decreased by 19.27 % and 15.22 %, respectively, due to the reduced microbial enzyme activity, fungal diversity, and dominance of Anguillospora. As a result, the regeneration of nutrients, especially phosphorus, was significantly depressed, which might influence the primary productivity of streams. Therefore, our results suggest that nanoscale PS has a greater impact on microbial activity, thus affecting their functioning in leaf litter decomposition and consequent nutrient cycling. The findings provide a data support for the risk assessment of plastic pollution in freshwater systems.

Can titanium dioxide nanoparticles modulate the effects of zinc oxide nanoparticles on aquatic leaf litter decomposition?

The potential impacts of metallic nanoparticles (NPs) at environmental levels on freshwater ecosystems cannot be ignored due to their frequent release. The most widely used metallic oxide, ZnO NPs and TiO2 NPs (100 ng L-1) were applied to explore their single and combined effects on leaf litter decomposition. Although ZnO NPs and TiO2 NPs alone or in combination increased 22.68%-41.17% of the leaf decomposition rate, they performed different toxic mechanisms in ecological processes. The microbial mass and enzyme activities significantly increased after acute exposure, but significantly decreased after chronic exposure to ZnO NPs. The activity of BG was the most sensitive factor that was decreased by 66.22%, 56.97%, and 39.39% after 21-day exposure to ZnO NPs, TiO2 NPs, and in combination, respectively. In addition, the analysis of Fourier transform infrared spectroscopy suggested a novel perspective on understanding the promoting mechanism. The promotion effect of ZnO NPs relied on the enhanced decomposition of refractory organics and easily degradable substances due to the contribution of Anguillospora, Pyrenochaetopsis, and Bipolaris. The single exposure to TiO2 NPs and combined exposure with ZnO NPs promoted microbial mass and hydrolase activities, with the stimulating effect attributed to the enhanced decomposition of soluble substances. Therefore, the results highlight the importance of chemical analysis of decomposed leaves to evaluate the potential threat of metallic NPs to the function of freshwater ecosystems.

Effects of multiple key factors on the performance of petroleum coke-based constructed wetland-microbial fuel cell.

In this study, two constructed wetland-microbial fuel cells (CW-MFC), including a closed-circuit system (CCW-MFC) and an open-circuit system (OCW-MFC) with petroleum coke as electrode and substrate, were constructed to explore the effect of multiple key factors on their operation performances. Compared to a traditional CW, the CCW-MFC system showed better performance, achieving an average removal efficiency of COD, NH4+-N, and TN of 94.49 ± 1.81%, 94.99 ± 4.81%, and 84.67 ± 5.6%, respectively, when the aeration rate, COD concentration, and hydraulic retention time were 0.4 L/min, 300 mg/L, and 3 days. The maximum output voltage (425.2 mV) of the CCW-MFC system was achieved when the aeration rate was 0.2 L/min. In addition, the CCW-MFC system showed a greater denitrification ability due to the higher abundance of Thiothrix that might attract other denitrifying bacteria, such as Methylotenera and Hyphomicrobium, to participate in the denitrifying process, indicating the quorum sensing could be stimulated within the denitrifying microbial community.

Effects of biochar on the degradation of organophosphate esters in sewage sludge aerobic composting.

In this study, the impact of biochar on the degradation of organophosphate esters (OPEs) during the aerobic composting of sewage sludge was investigated. Three treatments were conducted with different percentages of biochar in the compost, including 5 %, 10 %, and 20 %. The treatment with 10 % of biochar showed the longest thermophilic phase compared to that of 5 % and 20 % of biochar, which greatly promoted the decomposition of organic matter. In addition, the degradation rate of the hard-to-degrade chlorinated-OPEs was significantly increased by 10 % biochar, reaching to 57.2 %. Correspondingly, approximately 43.6 % of the total concentration of OPEs (Σ6OPEs) was eliminated in the presence of 10 % of biochar, which was higher than the treatments with 5 % and 20 % of biochar. Biochar significantly influenced the microbial community structure of compost, but the previously reported organophosphorus-degrading bacteria did not play a major role in the degradation of OPEs. The redox ability of the increased oxygen-containing functional groups such as quinone on the surface of biochar and the biochar-mediated electron transfer ability may play an essential role in the degradation of OPEs during the composting process.

A scalable field study using leaves as a novel passive air sampler to evaluate the potential source of organophosphate esters in street dust.

Organophosphate esters (OPEs) are widely used as flame retardants and plasticizers in industrial and commercial products. It is generally believed that OPEs in street dust mainly originate from road traffic and anthropogenic activities. The influence of atmospheric deposition is still unknown. In this study, leaves were employed as a novel passive air sampler to collect particle matters (PM) in 12 cities in the central province of Henan, China. Similar compositional profiles of OPEs were found in street dust and PM samples. The concentrations of individual OPEs in PM were 1-4 times higher than in street dust. Chlorinated OPEs concentration in PM shows a moderate correlation (r2 = 0.538, p < 0.01) with that in street dust. The concentration of alkyl OPEs in PM has a high correlation (r2 = 0.843, p < 0.01) with that in street dust. No significant correlation (r2 = 0.133, p = 0.132) was found on the aryl OPEs concentrations between street dust and PM. Spearman correlation reveals that the emission sources of tricresyl phosphate (TCrP) and triethyl phosphate (TEP) may be different from other OPEs in dust and PM samples. Principle component analysis (PCA) provides an appropriate explanation that tris (2-chloroethyl) phosphate (TCEP), triphenyl phosphate (TPhP), tris (chloropropyl) phosphate (TCPP), tributyl phosphate (TnBP), and TEP in street dust and PM may be emitted from the same sources, suggesting that PM has a significant influence on the occurrence of OPEs in street dust. The estimated dry deposition fluxes of particle-bound OPEs show a significant correlation (R2 = 0.969, p < 0.01) with OPEs concentrations in street dust, revealing that the input of atmospheric deposition could be a major source of OPEs in street dust.

Simultaneous phosphorus and nitrogen removal with different C/N ratios in a low oxygen aeration system: Microorganisms and mechanisms.

In this study, a combined system with simultaneous nitrification, denitrification, and phosphorus removal was operated in continuous low oxygen aeration mode, and the effect of lower oxygen aeration (dissolved oxygen [DO] 0.5-1.5 mg/L) on its performance was examined. The combined system consisted of sludge and high-efficiency biological packing and was operated using four carbon/nitrogen ratios (C/N) with being 10:1, 8:1, 6:1, 10:1. Experimental results showed that the combined system could perform an efficient nitrogen and phosphorus removal under low DO and C/N ratio of 8:1 condition, and removal efficiencies of chemical oxygen demand (COD), NH4 + -N, and PO4 3- -P were 80.01%, 99.03%, and 89.51%, respectively. High-throughput analysis indicated that the functional species of denitrifying bacteria, including Ferruginibacter Azospira, Comamonas, Bacilli, Hyphomicrobium, Thauera, and Comamonadaceae, were important participants in biological nutrient removal. Meanwhile, Acinetobacter was enriched in the combined system, which contributed to phosphorus removal. PRACTITIONER POINTS: A combined system was operated firstly under continuous low oxygen condition. The lower dissolved oxygen (DO) of the combined system was maintained at 0.50-1.5 mg/L level. The combined system could realize simultaneous phosphorus and nitrogen removal under C/N ratio of 8:1. Several functional bacteria were enriched in the coupled systems.

The gas phase retention volume behavior of organophosphate esters on polyurethane foam.

In this study, the gas-phase retention volume behavior of four highly volatile organophosphate esters (OPEs) on polyurethane foam (PUF) was studied using a frontal chromatogram. The breakthrough volumes (VB) of trimethyl phosphate (TMP), triethyl phosphate (TEP), tripropyl phosphate (TPrP), and tri-n-butyl phosphate (TnBP) were 0.33, 0.59, 10.5, and 32.4 m3, respectively. A significant negative correlation was found between the logarithm value of VB and the subcooled liquid vapor pressure (PL) with an r2 of 0.905, indicating that the vapor penetration depends on both the volatility and total air volume. The enthalpy of desorption and vaporization (ΔHS-ΔHV) showed a significant difference between the tested OPEs and polycyclic aromatic hydrocarbons (PAHs), revealing that the strength of the sorption interaction of the tested OPEs vapor on PUF should be different from that of PAHs. The PUF-air partition coefficients (KPUF-air) of the tested OPEs ranged from 4.3 to 8.1, which were lower than those of three-to four-ring PAHs (7.02-10.2) and organochlorines (8.01-9.72), revealing that the partition of highly volatile OPEs on PUF is lower than that of low-volatile compounds. The PUF/XAD cartridge improved the absorption efficiency of the tested OPEs; however, its sorptive capacity was still limited.

Rapid and stable achievement of mainstream nitritation at low temperature using the competitive inhibition caused by the organics.

The unstability of mainstream nitritation at low temperature has always been a limiting factor for the nitrogen removal from domestic wastewater by anammox. In this study, the competitive inhibition caused by the organics has been demonstrated as an effective strategy to rapidly and stably achieve mainstream nitritation. This strategy was based on our novel discovery that nitrite-oxidizing bacteria (NOB) was more susceptible to the organics inhibition than ammonia-oxidizing bacteria (AOB). Batch tests showed while NOB activity gradually decreased by 66.5%, AOB activity only decreased by 31.6% with the initial C/N ratio raising from 0.0 to 3.0. Furthermore, treating the actual domestic wastewater at 14-18 °C, mainstream nitritation was rapidly established within 12 days and then the nitrite accumulation ratio was stable at ∼92.1% during a long-term operation. This strategy could be easily and effectively applied in urban WWTPs through modifying the operation mode.

Effects of combined 4-chlorophenol and Cu2+ on functional genes for nitrogen and phosphorus removal and heavy metal resistance genes in sequencing batch bioreactors.

The effects of combined 4-chlorophenol (4-CP) and Cu2+ on microbial community structures, functional genes for nitrogen and phosphorus removal, and heavy metal resistance genes (HMRGs) were explored in wastewater treatment using sequencing batch bioreactors (SBRs). Compared to influent 4-CP (2.3-4.5 mg/L), the removal of pollutants including chemical oxygen demands (COD), NH4+-N, PO43--P, and 4-CP was inhibited under Cu2+ stress (5 mg/L). The effects of Cu2+ on microbial community structures were more significant than those of 4-CP with respect to operational time, while the dominant function from gene information was not affected with or without influent 4-CP and Cu2+ via sequencing analysis. The influent 4-CP and Cu2+ largely influenced the dynamic changes of functional genes and HMRGs, and the abundance of partial HMRGs was correlated to the functional genes and dominant genera. This study provides insights into the treatment of combined chlorophenols and Cu2+ in wastewater.

New insights into denitrification and phosphorus removal with degradation of polycyclic aromatic hydrocarbons in two-sludge system.

Polycyclic aromatic hydrocarbons (PAHs) have led to failure of waste water treatment plant operations. In this study, a two-sludge system was used to solve this problem of simultaneously removing phosphorus, nitrogen, and PAHs. The results showed that increasing the maximum PAHs concentration to 15 mg/L did not have any negative effect on the removal rates of total nitrogen (79.68%) and chemical oxygen demand (75.94%); however, the phosphorus removal efficiency decreased to 61.16%. The system exhibited a stronger degradation ability for phenanthrene. Thauera, Hydrogenophaga, and Hyphomicrobium were enriched, which resulted in good denitrification, and contributed to PAHs removal. PAHs mixture promoted PAHs functional genes but restrained denitrification functional genes. However, single naphthalene enhanced denitrification functional genes, which confirmed the feasibility of denitrification coupled with PAHs degradation. In conclusion, for the removal of pollutants from sewage treatment, nitrogen and phosphorus removal coupled with PAHs could be maintained by selecting a two-sludge system.

Response of extracellular polymeric substances and microbial community structures on resistance genes expression in wastewater treatment containing copper oxide nanoparticles and humic acid.

The extracellular polymeric substances (EPS) and microbial community structures were investigated in wastewater treatment containing copper oxide nanoparticles (CuO NPs) (reactor R1) and CuO NPs and humic acid (HA) (reactor R2) using both sequencing batch bioreactors (SBRs), and their response on resistance genes expression was analyzed. The removal of influent chemical oxygen demands (COD) and NH4+-N was moderately influenced under CuO NPs (5 mg/L) stress, while the function of HA (10 mg/L) was not reflected. However, the EPS production and microbial community were affected by the HA addition. The expression of different antibiotic resistance genes (ARGs), metal-resistance genes (MRGs), and intI1 was related to the primary compositions of polysaccharides and proteins in EPS and different microbial communities at the genus level. Furthermore, the expression of resistance genes was not stimulated under CuO NPs stress, and supplying HA was suggested to reduce their expression in wastewater treatment.

In-site synthesis of an inorganic-framework molecular imprinted TiO2/CdS heterostructure for the photoelectrochemical sensing of bisphenol A.

In this study, we develop a highly sensitive and selective photoelectrochemical (PEC) sensor for bisphenol A (BPA) determination by combining a TiO2/CdS heterostructure with inorganic framework molecular imprinting (MI) technology. A MI-TiO2/CdS heterostructure was synthesized via successive ionic layer adsorption combined with an inorganic framework molecular imprinting method. Due to the matched energy level distribution of TiO2 with CdS, the formed heterojunction promotes photogenerated charge separation and enhanced PEC conversion. The MI-TiO2/CdS based PEC sensor exhibits higher photocurrent responses and perfect selectivity for BPA under simulated sunlight irradiation. Benefiting from the unique heterostructure and special recognition ability of MI-TiO2/CdS, the photocurrent is linear to the concentration of BPA (range from 1 to 100 pmol L-1), with a low limit detection of 0.5 pmol L-1 (S/N = 3). Meanwhile, the detection results show that the PEC sensor exhibits excellent sensitivity, high selectivity, and good stability. Furthermore, the PEC sensor was successfully applied to the real environmental sample detection of BPA, in lake and river water, domestic wastewater and tap water. This PEC sensor exhibits favourable BPA detection, and it is also a promising method by which to measure other similar environmental substances selectively and sensitively in future work.

Effect of sodium dichloroisocyanurate treatment on enhancing the biodegradability of waste-activated sludge anaerobic fermentation.

In the present study, a novel oxidant (sodium dichloroisocyanurate, NaCl2(NCO)3; SDIC) combined with microorganisms was employed to achieve a higher performance of waste-activated sludge (WAS) anaerobic fermentation. Four concentrations of SDIC (0, 0.3, 0.6, and 1.0 mg SDIC/mg SS) were studied in WAS fermentation systems. The results showed that the release of proteins and polysaccharides was enhanced by the addition of SDIC with values of 1002.25 mg COD/L and 680.25 mg COD/L, respectively, and these values increased 14.46-18.07 times (proteins) and 3.74-7.40 times (polysaccharides) compared with that of the blank test. Additionally, the short-chain fatty acids also increased 2.24 times. The rate of extraction of organic substances from the sludge increased from 3.03% to 33.33%. Furthermore, the fermented sludge with the SDIC treatment had higher hydrolytic acidification efficiencies for bovine serum albumin and glucose, increasing from 4.558% to 9.91% and 2.976%-6.764%, respectively. However, SDIC treatment of the conventional fermented sludge resulted in lower hydrolytic acidification efficiencies with values of 4.978%-1.781% and 3.334%-0.582%, respectively. Biological enzyme analysis also showed that SDIC enhanced α-glucosidase and protease activity but inhibited dehydrogenase, alkaline phosphatase, and acid phosphatase activity. Proteobacteria and Comamonas were the main microbial communities observed in the WAS anaerobic fermentation.

Effects of 2,4,6-trichlorophenol and its intermediates on acute toxicity of sludge from wastewater treatment and functional gene expression.

Considering the extensive usage of chlorophenols as well as their refractory and toxic characteristics, 2,4,6-trichlorophenol (2,4,6-TCP) and its metabolic intermediates that cause the acute toxicity of sludge were comprehensively evaluated using a bioassay including Photobacterium phosphoreum in a sequencing batch bioreactor (SBR), and the effects of 2,4,6-TCP wastewater treatment on mRNA expression were explored. The results showed that acute toxicity of sludge and effluent chemical oxygen demand greatly exceeded that of the other SBR without 2,4,6-TCP acclimation when 2,4,6-TCP wastewater treatment in the range of 10-50 mg/L was used. The identified intermediates and 2,4,6-TCP largely contributed to the acute toxicity of sludge, which favorably fitted the Fit Exponential Decay (R2 > 0.93). During the stable stages for treating 50 mg/L 2,4,6-TCP in the influent, the mRNA expression for encoding functional proteins based on the genus Pseudomonas was markedly inhibited after the completion of the SBR operation.

Effects of zinc oxide nanoparticles on sludge anaerobic fermentation: phenomenon and mechanism.

Zinc oxide nanoparticles (ZnO NPs) production and usage might lead to a large discharge of ZnO NPs into the natural environment, raising concerns of pollution and ecological security. The effects of ZnO NPs on waste activated sludge hydrolytic acidification and microbial communities were studied in semi-continuous fermentation systems. The fermentation performance of eight ZnO NPs concentrations including ZnO NPs normal [0.01, 0.1, 1 and 10 mg/g mixed liquor suspended solids (MLSS)] and ZnO NPs shock (10, 1000, 1000 and 10,000 mg/g MLSS) were discussed, and their biodegradability was also analyzed. The experimental results showed that proteins, polysaccharides and short-chain fatty acids were enhanced by ZnO NPs, particularly by ZnO NPs shock. Low ZnO NPs concentrations inhibited coenzyme 420 (F420) and dehydrogenase activities but enhanced α-glucosidase and protease activities. Illumina MiSeq sequencing revealed that ZnO NPs addition enriched Azospira, Ottowia and Hyphomicrobium but not Anaerolineaceae.

Long-term alkaline conditions inhibit the relative abundances of tetracycline resistance genes in saline 4-chlorophenol wastewater treatment.

Considering the occurrence and spread of antibiotic resistance genes (ARGs) pose significant risks to public health, the effects of long-term exposure to alkaline conditions on the relative abundances of tetracycline resistance genes (TRGs) were studied in saline 4-chlorophenol (4-CP) wastewater treatment. Alkaline conditions were maintained by supplying the co-metabolic carbon source of sodium acetate. Results showed that except for the 4-CP, the removal of pollutants was significantly inhibited, and the relative abundances of the most TRGs were repressed. In addition, the removal of pollutants and the relative abundances of TRGs were moderately affected by the NaCl addition. The proteins in the extracellular polymeric substances (EPS) played key roles in reducing the relative abundances of TRGs, which were altered by the microbial diversity. In conclusion, for the pollutants removal and ARGs reduction in refractory industrial wastewater treatment, alkaline conditions should be maintained by selecting suitable co-metabolic carbon sources.