Improved anaerobic sludge fermentation mediated by a tryptophan-degrading consortium: Effectiveness assessment and mechanism deciphering.

The hydrolysis of extracellular polymeric substances (EPS) represents a critical bottleneck in the anaerobic fermentation of waste activated sludge (WAS), while tryptophan is identified as an underestimated constituent of EPS. Herein, we harnessed a tryptophan-degrading microbial consortium (TDC) to enhance the hydrolysis efficiency of WAS. At TDC dosages of 5%, 10%, and 20%, a notable increase in SCOD was observed by factors of 1.13, 1.39, and 1.88, respectively. The introduction of TDC improved both the yield and quality of short chain fatty acids (SCFAs), the maximum SCFA yield increased from 590.6 to 1820.2, 1957.9 and 2194.9 mg COD/L, whilst the acetate ratio within SCFAs was raised from 34.1% to 61.2-70.9%. Furthermore, as TDC dosage increased, the relative activity of protease exhibited significant increments, reaching 116.3%, 168.0%, and 266.1%, respectively. This enhancement facilitated WAS solubilization and the release of organic substances from bound EPS into soluble EPS. Microbial analysis identified Tetrasphaera and Soehngenia as key participants in WAS solubilization and the breakdown of protein fraction. Metabolic analysis revealed that TDC triggered the secretion of enzymes associated with amino acid metabolism and fatty acid biosynthesis, thereby fostering the decomposition of proteins and production of SCFAs.

High removal efficiencies of antibiotics and low accumulation of antibiotic resistant genes obtained in microbial fuel cell-constructed wetlands intensified by sponge iron.

Using microbial fuel cells with constructed wetlands (MFC-CWs) for eliminating antibiotics has recently attracted extensive attention. However, antibiotic removal efficiencies in MFC-CWs must be enhanced, and the accumulation of antibiotic resistant genes (ARGs) remains an unmanageable issue. This study tries to enhance the antibiotic removal in synthetic wastewater and reduce ARGs by adding sponge iron (s-Fe0) and calcium peroxide to the anode and cathode of MFC-CWs, respectively, and/or simultaneously. The results demonstrated that adding s-Fe0 and calcium peroxide to MFC-CWs could improve the removal efficiencies of sulfamethoxazole (SMX) and tetracycline (TC) by 0.8-1.3% and 6.0-8.7%. Therein, s-Fe0 also significantly reduced 84.10-94.11% and 49.61-60.63% of total sul and tet genes, respectively. Furthermore, s-Fe0 improved the voltage output, power density, columbic efficiency, and reduced the internal resistance of reactors. The intensification to the electrode layers posed a significant effect on the microbial community composition and functions, which motivated the shift of antibiotic removal, accumulation of ARGs and bioelectricity generation in MFC-CWs. Given the overall performance of MFC-CWs, adding s-Fe0 to the anode region of MFC-CWs was found to be an effective strategy for removing antibiotics and reducing the accumulation of ARGs.

Improving denitrification efficiency in constructed wetlands integrated with immobilized bacteria under high saline conditions.

Constructed wetlands (CWs) inoculated with exogenous microbes have great potential for removing pollutants in adverse environments. The rapid loss of functional bacteria and the high cost of repeated additions of inoculum, however, limit the practical application of this technology. In this study, C-F2 immobilized bacteria (i.e., immobilized salt-tolerant bacterium Alishewanella sp. F2 incorporated with a carbon source) were developed and utilized in CWs for solving the above problems. A 60-day experiment demonstrated that bioaugmented CWs (Bio-CWs) with the addition of C-F2 immobilized bacteria into the bottom gravel layer of CW microcosms (B-CF2 treatment) exhibited high nitrogen removal efficiency under a saline condition (electrical conductivity of 15 mS/cm). We measured mean nitrate nitrogen (NO3--N) and total nitrogen (TN) removal percentages of 97.8% and 88.1%, respectively, which were significantly (p < 0.05) higher than those in Bio-CWs with microbial inoculum (MI-F2 treatment, 63.5% and 78.2%) and unbioaugmented CWs (CK, 48.7% and 67.2%). The TN content of the entire plant was significantly (p < 0.05) increased in B-CF2 (636.06 mg/microcosm) compared with CK (372.06 mg/microcosm). The relative abundances of the genera Alishewanella (i.e., the exogenous bacterium, 5.5%), Clostridium-XlVa (8.8%) and Bacteroides (21.1%) in B-CF2 were significantly (p < 0.05) higher than in MI-F2 and CK, which improved the denitrification capacity of CWs. Overall, a high denitrification efficiency and durability were achieved in the newly developed Bio-CWs (i.e., B-CF2 treatment) with immobilized bacteria under saline conditions, which provides an alternative technology for the rapid removal of nitrogen from saline wastewater.

Removal of sulfamethoxazole and tetracycline in constructed wetlands integrated with microbial fuel cells influenced by influent and operational conditions.

Constructed wetlands integrated with microbial fuel cells (MFC-CWs) have been recently developed and tested for removing antibiotics. However, the effects of carbon source availability, electron transfer flux and cathode conditions on antibiotics removal in MFC-CWs through co-metabolism remained unclear. In this study, four experiments were conducted in MFC-CW microcosms to investigate the influence of carbon source species and concentrations, external resistance and aeration duration on sulfamethoxazole (SMX) and tetracycline (TC) removal and bioelectricity generation performance. MFC-CWs supplied with glucose as carbon source outperformed other carbon sources, and moderate influent glucose concentration (200 mg L-1) resulted in the best removal of both SMX and TC. Highest removal percentages of SMX (99.4%) and TC (97.8%) were obtained in MFC-CWs with the external resistance of 700 Ω compared to other external resistance treatments. SMX and TC removal percentages in MFC-CWs were improved by 4.98% and 4.34%, respectively, by increasing the aeration duration to 12 h compared to no aeration. For bioelectricity generation performance, glucose outperformed sodium acetate, sucrose and starch, with the highest voltages of 386 ± 20 mV, maximum power density (MPD) of 123.43 mW m-3, and coulombic efficiency (CE) of 0.273%. Increasing carbon source concentrations from 100 to 400 mg L-1, significantly (p < 0.05) increased the voltage and MPD, but decreased the internal resistance and CE. The highest MPD was obtained when the external resistance (700 Ω) was close to the internal resistance (600.11 Ω). Aeration not only improved the voltage and MPD, but also reduced the internal resistance. This study demonstrates that carbon source species and concentrations, external resistances and aeration duration, all play vital roles in regulating SMX and TC removal in MFC-CWs.

Constructed wetlands integrated with microbial fuel cells for COD and nitrogen removal affected by plant and circuit operation mode.

Organic matter and NH4+-N are two major pollutants in domestic sewage. This study evaluated the influence of plant and circuit operation mode on the performance of constructed wetlands integrated with microbial fuel cells (CW-MFCs) and investigated the removal mechanisms of organic matter and nitrogen. Better chemical oxygen demand (COD) removal was achieved in closed-circuit CW-MFCs regardless of planting or not, with average removal efficiencies of 83.19-86.28% (closed-circuit CW-MFCs) and 76.54-83.19% (open-circuit CW-MFCs), respectively. More than 70% organic matter was removed in the anaerobic region of all CW-MFCs. In addition, the planted CW-MFCs outperformed the unplanted CW-MFCs in ammonium, nitrate, and total nitrogen removal irrespective of circuit connection or not, for example, the NH4+-N removal efficiencies of 95.91-96.82% were achieved in planted CW-MFCs compared with 56.54-59.95% achieved by unplanted CW-MFCs. Besides, 33.14-55.69% of NH4+-N was removed in the anaerobic region. Throughout the experiment, the average voltages of planted and unplanted CW-MFCs were 264 mV and 108 mV, with the corresponding maximum voltage output of 544 mV and 321 mV, respectively. Furthermore, planted CW-MFCs, simultaneously producing a peak power density of 92.05 mW m-3 with a coulombic efficiency of 0.50%, exhibited better than unplanted CW-MFCs (3.29 mW m-3 and 0.21%, respectively) in bioelectricity generation characteristics. Graphical abstract.

Treatment of typical antibiotics in constructed wetlands integrated with microbial fuel cells: Roles of plant and circuit operation mode.

This study evaluated the removal efficiencies of sulfamethoxazole (SMX), tetracycline (TC) and their common co-existing contaminants, i.e., chemical oxygen demand (COD) and nitrogen in constructed wetlands integrated with microbial fuel cells (MFC-CWs), as affected by plant, circuit operation mode and influent antibiotic loads. The results demonstrated that MFC-CWs with plant and circuit connection exhibited the best performance in SMX and TC removal. The removal percentages for SMX and TC were 99.70-100% and 99.66-99.85% at HRT of 1 d, respectively, in MFC-CWs with plant and circuit connection when the influent SMX and TC concentrations were 5-100 µg L-1 and 5-50 µg L-1. The removal efficiencies of both SMX and TC were mainly enhanced by the circuit connection, compared to the plants. The presence of plant and circuit connection also accelerated the accumulation of SMX and TC in electrode layers, and the residues of both antibiotics in the anode layer were higher than in the cathode layer. Besides, closed-circuit MFC-CWs showed better COD removal performance than open-circuit MFC-CWs, irrespective of the increasing influent COD and antibiotic concentrations. The NH4+-N removal in MFC-CWs was mainly promoted by the presence of plants and decreased with increasing influent antibiotic concentrations. Additionally, the bioelectricity generation of planted MFC-CWs was better than in unplanted systems. The coulombic efficiencies in both planted and unplanted MFC-CWs decreased with increasing influent antibiotic concentrations. In summary, MFC-CWs with plant and circuit connection have potential for the treatment of wastewater containing SMX and TC.

Bioaugmented constructed wetlands for denitrification of saline wastewater: A boost for both microorganisms and plants.

The inhibition of salt stress on plant and microbial functions has led to the reduction of nitrogen removal capacity of constructed wetlands (CWs) under saline conditions. The mechanisms and effectiveness of bioaugmented CW (Bio-CW) microcosms with a salt-tolerant microbial inoculum were evaluated for nitrogen removal at different salinity levels. The results showed that the denitrification capacity of CWs was improved under saline conditions by adding the salt-tolerant microbial inoculum. At an EC of 15 mS/cm, the removal percentages of ammonia nitrogen (NH4+-N) and total nitrogen (TN) in Bio-CW microcosms (95.7% and 99.4%) on Day 5 were significantly (p < 0.05) higher than that in unbioaugmented CW (un-Bio-CW) microcosms (68.5% and 76.4%), respectively. The high throughput sequencing data of substrate samples indicated that the microbial community in the CWs was changed by the addition of the salt-tolerant microbial inoculum and the frequency of bacteria with nitrogen removal function was increased in the CWs. Furthermore, both growth and the TN accumulation capacity of plants in Bio-CW microcosms were promoted compared with the un-Bio-CW microcosms. In conclusion, the addition of the salt-tolerant microbial inoculum can enhance the nitrogen removal efficiency of CWs under saline condition via boosting the function of both microorganisms and plants.

Isolation and characterization of a salt-tolerant denitrifying bacterium Alishewanella sp. F2 from seawall muddy water.

A salt-tolerant denitrifying bacterium strain F2 was isolated from seawall muddy water in Dalian City, Liaoning Province, China. Strain F2 was identified by morphological observations, physiological and biochemical characteristics and 16 S rDNA identification. The salt tolerance of strain F2 was verified and the factors affecting the removal ability of strain F2 to nitrous nitrogen (NO2-N) and nitrate nitrogen (NO3-N) in saline conditions were investigated. Strain F2 was identified as Alishewanella sp., named Alishewanella sp. F2. Strain F2 can tolerate NaCl concentrations up to 70 g/L, and its most efficient denitrification capacity was observed at NaCl concentrations of 0-30 g/L. In the medium with NaCl concentrations of 0-30 g/L, strain F2 exhibited high removal efficiencies of NO2-N and NO3-N, with the removal percentages for both NO2-N and NO3-N of approximately 99%. In saline conditions with 30 g/L NaCl, the optimum culture pH, NaNO2 initial concentrations and inoculation sizes of strain F2 were 8-10, 0.4-0.8 g/L and 5-7%, respectively. Strain F2 was highly effective in removing NO2-N and NO3-N in saline conditions, and it has a good application potential in saline wastewater treatment.

[CH4 Uptake in Different Saline-alkaline Soils in Hetao Irrigation District, Inner Mongolia].

Soil salinization poses a great threat to sustainable land use and the limitation of greenhouse gas emissions. In this study, three saline alkali soils, saline soil[electrical conductivity (EC) 4.80 dS·m-1], high saline-alkaline soil (EC 2.60 dS·m-1), and low saline-alkaline soil (EC 0.74 dS·m-1) in the Hetao Irrigation District of Inner Mongolia were selected as research plots. Field experiments were conducted to study the uptake of methane (CH4) in the crop-growing season (April-October) for three years (2014-2016) using the static box method. There were significant differences in the soil CH4 uptake among the soil types in 2014 (F=18.0, P<0.001), 2015 (F=23.6, P<0.001), and 2016 (F=28.4, P<0.001). The uptake of CH4 by the soil decreases with increasing soil salinity. The accumulated CH4 uptake was 150.0 mg·m-2, 119.6 mg·m-2, and 99.9 mg·m-2 in the low saline-alkaline, high saline-alkaline, and saline soil in 2014, respectively. The cumulative uptake of CH4 was 27%, 28%, and 19% lower in the high saline-alkaline soil and 35%, 35%, and 53% lower in the saline soil than in the low saline-alkaline soil in 2014, 2015, and 2016, respectively. Redundancy analysis shows that the projection of the CH4 uptake flux and EC of saline-alkaline soil are in the positive direction, and in the opposite direction to the first principal component axis. The higher the soil EC, the lower the CH4 uptake flux. Soil EC was found to be the key factor controlling the uptakes of CH4, with a correlation coefficient (r) of -0.8809 (P<0.01, n=9).

Identification and denitrification characteristics of a salt-tolerant denitrifying bacterium Pannonibacter phragmitetus F1.

A salt-tolerant denitrifying bacterium F1 was isolated in this study, which has high nitrite (NO2--N) and nitrate (NO3--N) removal abilities. The salt tolerance capacity of strain F1 was further verified and the effects of initial pH, initial NaNO2 concentration and inoculation size on the denitrification capacity of strain F1 under saline conditions were evaluated. Strain F1 was identified as Pannonibacter phragmitetus and named Pannonibacter phragmitetus F1. This strain can tolerate NaCl concentrations up to 70 g/L, and its most efficient denitrification capacity was observed at NaCl concentrations of 0-10 g/L. Under non-saline condition, the removal percentages of NO2--N and NO3--N by strain Pannonibacter phragmitetus F1 at pH of 10 and inoculation size of 5% were 100% and 83%, respectively, after cultivation for 5 days. Gas generation was observed during the cultivation, indicating that an efficient denitrification performance was achieved. When pH was 10 and the inoculation size was 5%, both the highest removal percentages of NO2--N (99%) and NO3--N (95%) by strain Pannonibacter phragmitetus F1 were observed at NaCl concentration of 10 g/L. When the NaCl concentration was 10 g/L, strain Pannonibacter phragmitetus F1 can adapt to a wide range of neutral and alkaline environments (pH of 7-10) and is highly tolerant of NaNO2 concentration (0.4-1.6 g/L). In conclusion, strain Pannonibacter phragmitetus F1 has a great potential to be applied in the treatment of saline wastewater containing high nitrogen concentrations, e.g. coastal aquaculture wastewater.

Removal of chlorpyrifos and its hydrolytic metabolite 3,5,6-trichloro-2-pyridinol in constructed wetland mesocosms under soda saline-alkaline conditions: Effectiveness and influencing factors.

Chlorpyrifos (CP) is frequently detected in agricultural effluent worldwide. Both CP and its hydrolytic metabolite 3,5,6-trichloro-2-pyridinol (TCP) can cause serious environment hazards, and require removal before discharged into rivers and/or lakes. The effectiveness and main influencing factors of CP and TCP removal in mesocosm-scale subsurface flow constructed wetlands (SSFCWs) were evaluated. Results indicated that CP in SSFCWs reduced to less than detection limit in 4 d and TCP to 2 µg L-1 in 8 d. Higher influent CP concentrations lengthened the degradation process for both CP and TCP. The presence of co-existing inorganic nutrients restrained the degradation of CP during the hydraulic retention time of 2 h to 2 d. A higher pH resulting from the deterioration of soda saline-alkaline level accelerated the degradation of CP through the hydrolysis process. The SSFCWs with slag operating for another 88 d (i.e., 11 trails with HRT of 8 d for each trial) revealed a better and more stable treatment performance compared with previous studies. The results of this study demonstrated the positive feasibility of using SSFCWs with slag for the decontamination of CP-associated agricultural drainage or stormwater runoff.