Aerobic biodegradation of p-nitrophenol in a nitrifying sludge bioreactor: System performance, sludge property and microbial community shift

Impact of pyroxasulfone on sugarcane rhizosphere microbiome and functioning during field degradation

Pyroxasulfone (PYR) is a widely used herbicide, but its effects on non-target organisms, particularly microorganisms, are largely unknown. Herein, we investigated the effects of various doses of PYR on the sugarcane rhizosphere microbiome by using amplicon sequencing of rRNA genes and quantitative PCR techniques. Correlation analyses indicated that several bacterial phyla (Verrucomicrobia and Rhodothermaeota) and genera (Streptomyces and Ignavibacteria) strongly responded to PYR application. Additionally, we found that both bacterial diversity and composition were significantly altered after 30 days, indicating a prolonged effect of the herbicide. Moreover, co-occurrence analyses of the bacterial community showed that the network complexity was significantly decreased by PYR at day 45. Furthermore, FAPROTAX analysis suggested that some functions with implications for carbon cycling groups were significantly altered after 30 days. Overall, we provide the first indications that PYR may not pose a significant risk for altering microbial communities in the short term (less than 30 days). However, its potential negative effects on bacterial communities in the middle and late stages of degradation deserve further attention. To our knowledge, this is the first study to provide insight into the effects of PYR on the rhizosphere microbiome, providing an extended basis for future risk assessments.

Simultaneous high p-nitrophenol concentration and nitrogen removal by two-stage membrane biofilm reactor

P-nitrophenol (PNP) is highly toxic and difficult to degrade, causing great harm to the ecological environment and human health. A two-stage bench-scale membrane biofilm reactor (MBfR) was constructed to treat wastewater containing high concentration of PNP and the generated nitrogen without external organic carbon sources. The two reactors were supplied with oxygen and methane, respectively. O₂-MBfR was used for the degradation of PNP and the improvement of wastewater biodegradability. CH₄-MBfR was used for the total nitrogen (TN) removal treatment from O₂-MBfR effluent. In this experiment, the performance of the two-stage MBfR process was evaluated and optimized by adjusting operational parameters (aeration pressure, HRT, and pH). Under the optimal operation parameters, the removal efficiencies of PNP (100 mg/L) and TN attained 89.70% and 69.24%, respectively, and the removal loads were 0.930 g·m^-2·d^-1 and 241.42 mg·m^-2·d^-1, respectively. The reactor was able to accommodate the concentrations of PNP up to 200-400 mg/L, and the reactor reached maximum efficiency throughout the process when the concentration of PNP in the wastewater was 250 mg/L. The removal rates of PNP and TN reached 95.0% and 69.48%, respectively, and the removal loads were 2.37 g·m^-2·d^-1 and 96.22 mg·m^-2·d^-1, respectively. This research provides a better solution for multi-MBfR to treat toxic industrial wastewater containing phenol, nitrophenol, and further TN removal, which would not release any air pollutants into the atmosphere.

Recent advances in biological removal of nitroaromatics from wastewater

Various nitroaromatic compounds (NACs) released into the environment cause potential threats to humans and animals. Biological treatment is valued for cost-effectiveness, environmental friendliness, and availability when treating wastewater containing NACs. Considering the significance and wide use of NACs, this review focuses on recent advances in biological treatment systems for NACs removal from wastewater. Meanwhile, factors affecting biodegradation and methods to enhance removal efficiency of NACs are discussed. The selection of biological treatment system needs to consider NACs loading and cost, and its performance is affected by configuration and operation strategy. Generally, sequential anaerobic-aerobic biological treatment systems perform better in mineralizing NACs and removing co-pollutants. Future research on mechanism exploration of NACs biotransformation and performance optimization will facilitate the large-scale application of biological treatment systems.

Submicron aerosols share potential pathogens and antibiotic resistomes with wastewater or sludge

Generation of size-segregated aerosols is an important eco-environmental problem in wastewater treatment plants (WWTPs), but the characteristics of potential pathogens and antibiotic resistomes in submicron aerosols (PM_1.0) were almost unknown. Here, 16S rRNA gene amplification and shotgun metagenome sequencing were respectively used to study the profiles of potential pathogens and antibiotic resistance genes (ARGs) in PM_1.0 from a full-scale WWTP. Acinetobacter and sul1 were respectively the predominant potential pathogens and ARG subtypes in PM_1.0 from aeration process. A total of 9 potential pathogens and 147 ARG subtypes, were shared among WWTP-PM_1.0, wastewater/sludge, and ambient air. Significant differences of potential pathogens or ARGs were found between WWTP-PM_1.0 and wastewater/sludge, however, wastewater/sludge had more crucial source contribution than the ambient air. Moreover, 13 potential pathogens and 40 ARG subtypes were easily aerosolized in PM_1.0 from at least one of the treatment units. ARGs were mainly harbored by Proteobacteria, and multidrug resistance genes were the most ARG type carried by potential pathogens. Taken together, this study indicates the prevalence of potential pathogens, ARGs, and ARG-carrying potential pathogens in WWTP-PM_1.0, which highlights the potential risk of PM_1.0 in spreading potential pathogens and antibiotic resistomes into the air environments.

Activity measurement of arylsulfatase and β-glucuronidase in activated sludge: HPLC-based versus classical spectrophotometric method

Arylsulfatase and β-glucuronidase are two important enzymes in wastewater and surface water, which play important roles on cleavage of sulfate/glucuronide estrogens. In this work, a high-performance liquid chromatography (HPLC)-based new method was firstly established for arylsulfatase/β-glucuronidase with determination of p-nitrophenyl sulfate (pNPS)/p-nitrophenyl-β-D-glucuronide (pNPG). The limits of detections (LODs) of the developed method for pNPS and pNPG were 0.164 and 0.098 μM, respectively. Intraday and interday reproducibility expressed as relative standard deviation (RSD) values of retention times and peak areas was 0.39%-3.68% and 0.23%-4.74%, respectively. The respective recovery efficiencies of this HPLC-based method spiking at three different concentrations for p-nitrophenol (pNP), pNPS, and pNPG in activated sludge were 76.5%-88.1%, 79.2%-93.1%, and 84.2%-96.1%, with RSD below 3.9%. The HPLC-based method was finally applied to estimate the enzyme activity of arylsulfatase/β-glucuronidase in one activated sludge system and along which the classical spectrophotometric method was also evaluated. Compared with the classic spectrophotometric analytical method, the HPLC-based new method could simultaneously measure arylsulfatase/β-glucuronidase one time, which was convenient and time-saving. Moreover, the developed method could effectively avoid possible underestimation that the spectrophotometric method might encounter. PRACTITIONER POINTS: A new HPLC-based method for activity estimation of arylsulfatase and β-glucuronidase was developed. The HPLC-based method can simultaneously estimate enzyme activity of both arylsulfatase and β-glucuronidase. The HPLC-based method can avoid possible underestimation that spectrophotometric method may encounter.

How phenol stresses anammox for the treatment of ammonia-rich wastewater: Phenomena, microbial community evolution and molecular modeling

Phenol is a biotoxic organic compound and found in large quantities in ammonia-rich wastewater discharged from coking and petrochemical industries. In this work, phenol was fed to the system of anaerobic ammonia oxidation (anammox), and the possible inhibitory mechanism was speculated using the characterization of granular sludge, analysis of microbial community and molecular docking simulations. The results showed that phenol (0-300 mg/L) did not significantly inhibit anammox. However, phenol did activate denitrification, which increased the nitrogen removal rate (NRR) by 0.94 kg N/(m³·d). Moreover, when phenol concentration reached t400 mg/L, the NRR was inhibited by 70%, while the extracellular polymeric substance (EPS) of granular sludge was reduced. Phenol resulted in the reduction of Candidatus_Kuenenia and promoted the proliferation of phenol-degrading denitrifying bacteria, Azoarcus and Thauera. Molecular docking indicated that phenol, 2-nitrophenol and 4-nitrophenol could bind the nitrite reductase (NirS), which prevented the first step of the anammox reaction.

Waste-Tire-Derived Activated Carbon as Efficient Adsorbent of P-Nitrophenol from Wastewater

In this work, a two-stage activation method was used to prepare adsorbents from scrap tire rubber. Firstly, KOH was mixed with rubber using different impregnation ratios (1–2) for primary activation; a second activation was performed after pyrolysis at 650°C and 750°C; and finally, the samples were acid-washed using HNO3. The prepared materials were characterized by elemental analysis, nitrogen adsorption isotherms, SEM, FTIR, and XPS. The adsorption capacity and mechanism of these materials on p-nitrophenol in wastewater were also investigated. It was found that after two-stage activation, the specific surface area of the materials can be effectively increased, and the surface of the materials can be enriched with oxygen-containing functional groups. The maximum adsorption capacity of PNP could reach 143.9 mg g−1, which is slightly higher than the literature data under the same conditions. The adsorption process is in the form of chemisorption and is dominated by hydrogen bonding and π-πEDA formation, but the adsorption tends to be monolayer, and the adsorption behavior can be described by a proposed secondary model. In addition, the adsorbent has a stronger adsorption capacity under acidic conditions.

Vacuum UV pre-treatment coupled with self-generated peroxide stimulation of biomass: An innovative hybrid system for detoxification and mineralization of toxic compounds

The degradation of p-nitrophenol (pNP) was investigated in the chemical-less UVC/VUV process (Advanced Oxidation/Reduction Process, AORP), the packed bed bioreactor (PBR), and the hybrid of AORP/PBR system. The control UVC/VUV process degraded and mineralized pNP with rate constants of 0.098 and 0.032 min^-1, respectively, at neutral initial pH. Operating the UVC/VUV process in a fluidized bed reactor improved the rate of pNP degradation by 21 % at a packing ratio of 0.5 %. The fluidized bed AORP was operated under continuous-flow mode, where 79 % degradation and 28 % mineralization of pNP were obtained along a significant improvement in the biodegradability (41 %) at a hydraulic retention time of 20 min. The oxidation with HO and reduction with e_aq^- simultaneously contributed to the degradation of pNP in the UVC/VUV process. In comparison, degradation and mineralization of pNP in a single PBR process (without pretreatment) was found to be 84.7 % and 47.2 %, respectively, during 30 h biotreatment. Coupling the fluidized bed UVC/VUV with the PBR attained complete biodegradation of the residual pNP within 1 h and over 89 % of TOC reduction during 3 h post treatment in the PBR. Accordingly, the hybrid, fluidized bed UVC/VUV reactor coupled with the PBR is an efficient and promising technology for treating toxic environmental contaminants.

Enhancing 2,6-dichlorophenol degradation and nitrate removal in the nano-zero-valent iron (nZVI) solid-phase denitrification system

Nano-zero-valent iron (nZVI), as a typical nano-material, has been recently used in wastewater treatment and combination with bioreactors. Using nZVI coupled denitrification system research the effect and influence of nZVI enhanced denitrification sludge on the degradation of toxic compounds and system performance. The nZVI coupled denitrification system showed better resistance to 2,6-DCP impact, and the concentrations of effluent NO₂^- and NO₃^- were below 2.0 mg/L. At the same time, the addition of nZVI enabled the denitrification system to quickly adapt to the toxic environment of 2,6-DCP within 15 days, and the degradation efficiency of 2,6-DCP reached 99.9%. The released SMP reduced after nZVI coupled with denitrification sludge in 2,6-DCP environment, which could improve the effluent water quality. Nuclear magnetic resonance spectroscopy showed that the addition of nZVI would change the structure of EPS in denitrification sludge. After 90 days of operation, the dominant bacteria in the denitrifying sludge have undergone great changes. Moreover, Thauera was responsible as the dominant bacteria for degrading 2,6-DCP in the denitrification system. The increased in the proportion of functional bacteria with nitrate_reduction, nitrogen_respiration, nitrate_respiration and nitrite_respiration in the presence of NZVI further reveals the mechanism of enhanced denitrification.

Single and joint inhibitory effect of nitrophenols on activated sludge

In this study, single and joint inhibitory effects of nitrophenols on activated sludge and variations on the content of extracellular polymeric substances (EPS) were investigated. Results indicate that the nitrophenols adversely affected the organic and NH₃-N removal of activated sludge and the adverse effect of nitrophenols on autotrophic bacteria was higher than that on heterotrophic bacteria. Further, 2,4-dinitrophenol (2,4-DNP) demonstrated the highest inhibitory effect, followed by 4-nitrophenol (4-NP) and 2-nitrophenol (2-NP), and the combined effects of binary and ternary nitrophenols induced additive toxicity. At various concentrations and toxicant ratios, 2,4-DNP, as the dominant toxic nitrophenol, was the major contributor to the joint inhibition effects of the mixed nitrophenols. At lower concentrations of 2-NP (below 100 mg/L), 4-NP (below 50 mg/L), and 2,4-DNP (below 10 mg/L), large amounts of both tightly bound EPS (TB-EPS) and loosely bound EPS (LB-EPS) were secreted for the normal physiological activities of the microbiological cells. After further stimulation with higher concentrations of 2-NP (above 100 mg/L), 4-NP (above 50 mg/L), and 2,4-DNP (above 10 mg/L), the inhibitory effect of nitrophenols on bacterial metabolism evidently increased. However, the EPS production sharply reduced, particularly with respect to protein production. Parallel factor analysis for TB-EPS and LB-EPS further confirmed that the major proteins were tyrosine, tryptophan, and aromatic proteins. Thus, this study provides new insights into the inhibitory effects of mixed nitrophenols, which are frequently found in pharmaceutical and petrochemical effluents.

Anaerobic semi-fixed bed biofilm reactor (An-SFB-BR) for treatment of high concentration p-nitrophenol wastewater under shock loading conditions

P-nitrophenol (PNP or 4-NP) has been widely used as a biorefractory raw material in chemical industry, whereas been highly concerned for its characteristics of mutagenic/carcinogenic activity and food chain bioaccumulation. In this study, an anaerobic semi-fixed bed biofilm reactor (An-SFB-BR) was constructed and used to treat PNP wastewater which discharged from chemical industries. Experimental results revealed that the An-SFB-BR was successfully cultivated with the gradually increasing of influent PNP from 0 to 540 mg/L (gradually increased 10 mg/L every time in stage II and 30-50 mg/L for stage III), with the observation of an average removal efficiency of 98% for PNP and 80% for chemical oxygen demand (COD), also a biogas production and biogas production rate of 2.1 L/(L·d) and 0.57 m³/kg-COD, respectively. Finally, the conversion rate of P-aminophenol (PAP), the primary intermediate of PNP reached 80% after An-SFB-BR biodegradation. A relatively stable pH was maintained throughout the entire process, and insignificant VFA accumulation. The reactor exhibited a strong toxic shock resistance, and 16S rRNA sequencing results demonstrated that the dominant microbial community changed slightly with the gradually increasing of PNP concentration, which guaranteed the PNP removal efficiency.