Dynamics of nitrobenzene degradation and interactions with nitrogen transformations in laboratory-scale constructed wetlands

Treatment of pharmaceutical industry wastewater for water reuse in Jordan using hybrid constructed wetlands

Developing cost-efficient wastewater treatment technologies for safe reuse is essential, especially in developing countries simultaneously facing water scarcity. This study developed and evaluated a hybrid constructed wetlands (CWs) approach, incorporating tidal flow (TF) operation and utilising local Jordanian zeolite as a wetland substrate for real pharmaceutical industry wastewater treatment. Over 273 days of continuous monitoring, the results revealed that the first-stage TFCWs filled with either raw or modified zeolite performed significantly higher reductions in Chemical Oxygen Demand (COD, 58 %-60 %), Total Nitrogen (TN, 32 %-37 %), and Phosphate (PO4, 46 %-64 %) compared to TFCWs filled with normal sand. Water quality further improved after the second stage of horizontal subsurface flow CWs treatment, achieving log removals of 1.09-2.47 for total coliform and 1.89-2.09 for E. coli. With influent pharmaceutical concentrations ranging from 275 to 2000 μg/L, the zeolite-filled hybrid CWs achieved complete removal (>98 %) for ciprofloxacin, ofloxacin, erythromycin, and enrofloxacin, moderate removal (43 %-81 %) for flumequine and lincomycin, and limited removal (<8 %) for carbamazepine and diclofenac. The overall accumulation of pharmaceuticals in plant tissue and substrate adsorption accounted for only 2.3 % and 4.3 %, respectively, of the total mass removal. Biodegradation of these pharmaceuticals (up to 61 %) through microbial-mediated processes or within plant tissues was identified as the key removal pathway. For both conventional pollutants and pharmaceuticals, modified zeolite wetland media could only slightly enhance treatment without a significant difference between the two treatment groups. The final effluent from all hybrid CWs complied with Jordanian treated industry wastewater reuse standards (category III), and systems filled with raw or modified zeolite achieved over 95 % of samples meeting the highest water reuse category I. This study provides evidence of using hybrid CWs technology as a nature-based solution to address water safety and scarcity challenges.

Responses of nitrobenzene removal performance and microbial community by modified biochar supported zerovalent iron in anaerobic soil

Biochar-supported ZVI have received increasing attention for their potential to remove nitrobenzene in groundwater and soil. However, the capacity of this material to enhance the biological reduction of nitrobenzene and alter microbial communities in anaerobic groundwater have not been explored. In this study, the nitrobenzene removal performance and mechanism of modified biochar-supported zerovalent iron (ZVI) composites were explored in anaerobic soil. The results showed that the 700 °C biochar composite enhanced the removal of nitrobenzene and inhibited its release from soil to the aqueous phase. NaOH-700-Fe50 had the highest removal rate of nitrobenzene, reaching 64.4%. However, the 300 °C biochar composite inhibited the removal of nitrobenzene. Microbial degradation rather than ZVI-mediated reduction was the main nitrobenzene removal pathway. The biochar composites changed the richness and diversity of microbial communities. ZVI enhanced the symbiotic relationship between microbial genera and weakened competition between soil microbial genera. In summary, the 700 °C modified biochar composite enhanced the removal of nitrobenzene by increasing microbial community richness and diversity, by upregulating functional genes, and by promoting electron transfer. Overall, the modified biochar-supported ZVI composites could be used for soil remediation, and NaOH-700-Fe50 is a promising composite material for the on-site remediation of nitrobenzene-contaminated groundwater.

Horizontal flow aerated constructed wetlands for municipal wastewater treatment: The influence of bed depth

The influence of bed depth on the performance of aerated horizontal constructed wetlands was investigated at the pilot plant scale. Two horizontal flow subsurface constructed wetlands (HF) intensified units of different bed depth (HF1: 0.90 m and HF2: 0.55 m, 0.8 m and 0.5 m water level, respectively) were fitted with forced aeration, while a third one (HFc, 0.55 m bed depth, 0.5 m water level) was used as control and not aerated. The three HF units were operated in parallel, receiving the same municipal wastewater pre-treated in a hydrolytic up-flow sludge blanket anaerobic digester. Applied surface loading rates (SLR) ranged from 20 to 80 g biochemical oxygen demand (BOD5)/m2·d and from 3.7 to 6.7 g total nitrogen (TN)/m2·d, while it ranges from 6 to 23 g BOD5/m2·d and from 1.1 to 1.7 g TN/m2·d in the control unit. Removal of total suspended solids (TSS) and BOD5 was usually close to a 100 % in all units, whilst chemical oxygen demand (COD) removal was higher for the HF1 unit (97 % on average, range of 96-99 %) than for HF2 (92 %, 82-98 %) and HFc (94 %, 86-99 %). TN removal reached on average 33 % (16-43 %) in HFc, 37 % (10-76 %) in HF2 and 51 % (21-79 %) in HF1. High TN removal required a longer aeration time for nitrification and higher effluent recirculation ratio to enhance denitrification. The results indicate that artificial aeration and a high bed depth allows to increase the SLR by a factor of 4 in HF1 but only by a factor of 2 in HF2.

Evaluating the inhibitory effects of Nitrobenzene short-term stress on denitrification performance: Electron behaviors, bacterial and fungal community

Denitrifying system is a feasible way to remove nitro-aromatic compounds (NACs) in wastewater. However, the toxicity and mechanisms of NACs to denitrification remain unknown. This study investigated effects of nitrobenzene (NB, a typical NAC) on denitrification in short term. Results showed that NB in 10-50 mg/L groups decreased NO3--N removal efficiency by 9%-24%, but increased nitrous oxide (N2O) generation by 6-17fold. Mechanistic research indicated that NB could deteriorate electron behaviors and disturbed enzyme activities of microbial metabolism and denitrification, leading to a decline in denitrification performance. Structural equation modeling revealed that N2O reductase activity was the core factor in predicting denitrification performance at exposure of NB, with the indirect effects of NADH and electron transport system activity. High-throughput sequencing analysis demonstrated that NB had made an alteration on both bacterial and fungal community structure, as well as their interactions.

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.

Electrochemical Degradation of Nitrobenzene Wastewater: From Laboratory Experiments to Pilot-Scale Industrial Application

In this study, the electrochemical degradation of nitrobenzene (NB) was conducted on the Ti/SnO2-Sb/Ce-PbO2 anode with excellent functional performance. The effect of applied current density, electrode distance, pH value and initial concentration on the reaction kinetics of NB was systematically studied. The total organic carbon (TOC) removal rate reached 91.5% after 60 min of electrolysis under optimal conditions. Eight aromatic intermediate products of NB were identified by using a gas chromatography coupled with a mass spectrometer, and two aliphatic carboxylic acids were qualitatively analyzed using a high-performance liquid chromatograph. The electrochemical mineralization mechanism of NB was proposed based on the detected intermediates and the identified key active oxygen specie. It was supposed that the hydroxyl radical produced on an anode attacked NB to form hydroxylated NB derivatives, followed by the benzene ring opening reactions with the formation of aliphatic carboxylic acids, which mineralized to CO2 and H2O. In addition, NB was reduced to less stable aniline on the cathode surface, which resulted in actualized mineralization. The successful pilot-scale industrial application in combination with wastewater containing NB with the influent concentration of 80–120 mg L−1 indicated that electrochemical oxidation has great potential to abate NB in practical wastewater treatment.

Bacterial community response to different nitrogen gradients of swine wastewater in surface flow constructed wetlands

How sediment bacterial community structure and diversity responds to different gradients of nitrogen (N) in swine wastewater is poorly understood. Here, the effects of different total nitrogen (TN) concentrations in swine wastewater on the microbial diversity and community composition in surface flow constructed wetlands (SFCWs) were investigated. The five concentration gradients included 2, 250, 300, 350, and 400 mg L^-1. Under high N concentrations (>300 mg L^-1), the Ace and Chao1 indexes increased, however, the Shannon index declined with increasing N concentration. The relative abundance of Chloroflexi, Acidobacteria and Actinobacteria showed an increasing trend. In contrast, under relatively low N concentrations (≤300 mg L^-1), Shannon index increased with increasing N concentration. The relative abundance of Bacteroidetes and Verrucomicrobia exhibited an increasing trend with increasing N concentration. TN, NH₄⁺ and NO₃^- significantly influenced on the microbial community distribution and composition (P < 0.05). These findings provide evidence that N concentration of swine wastewater is powerful predictor of bacterial diversity and community composition in SFCWs.

Influence of plant radial oxygen loss in constructed wetland combined with microbial fuel cell on nitrobenzene removal from aqueous solution

This study investigated the effects of radial oxygen loss (ROL) of three different plants on nitrobenzene (NB) wastewater treatment and bioelectricity generation performance in constructed wetland-microbial fuel cell (CW-MFC). ROL and root biomass from wetland plants showed positive effects on NB wastewater compared to unplanted CW-MFC. Scirpus validus exhibited higher tolerance to NB than Typha orientalis and Iris pseudacorus at 20-200 mg/L NB. As NB concentration reached 200 mg/L, the CW-MFC with Scirpus validus had relatively high DO (2.57 ± 0.17 mg/L) and root biomass (16.42 ± 0.18 g/m²), which resulted in the highest power density and voltage (19.5 mW/m², 590 mV) as well as NB removal efficiency (93.9 %) among four reactors. High-throughput sequencing results suggested that electrochemically active bacteria (EAB) (e.g., Geobacter, Ferruginibacter) and dominant NB-degrading bacteria (e.g., Comamonas, Pseudomonas) could be enhanced by wetland plants, especially in CW-MFC with Scirpus validus. Therefore, Scirpus validus was a good option for simultaneously treating NB wastewater and producing bioelectricity.

Effects of glucose and starch on the toxicity of nitrobenzene to plants and microbes in constructed wetlands

Photosynthetic pigment content, antioxidant enzyme activities of plants, microbial enzyme activities and community structure were analyzed to investigate the effects of glucose and starch on the toxicity of nitrobenzene (NB) to plants and microbes in constructed wetlands (CWs). As the influent NB concentration increased from 10 mg/L to 100 mg/L, the NB removal efficiency of the blank group decreased from 97.1% to 75.02%. However, the NB removal efficiencies of the external carbon source groups were maintained at nearly 100%. External carbon sources accelerated the transformation process of NB to aniline (AN), thus decreasing NB toxicity to the microbes and plants. When the influent NB concentration reached 100 mg/L, the NB removal rates and NB reductase activities of the external carbon source groups were 2.4 times and 4 times higher, respectively, than those of the blank group. Most of the dominant genera found in the three CWs could reduce nitroaromatics to the corresponding aromatic amines according to the results of high-throughput sequencing. The performance of NB removal in the CWs indicated the potential of CWs for NB treatment and the necessity of external carbon sources under high NB concentrations.

Treatment of anaerobic digested effluent in biochar-packed vertical flow constructed wetland columns: Role of media and tidal operation

Three types of vertical flow constructed wetland columns (VFCWs), packed with corn cob biochar (CB-CW), wood biochar (WB-CW) and gravel (G-CW) under tidal flow operations, were comparatively evaluated to investigate anaerobic digested effluent treatment performance and mechanisms. It was demonstrated that CB-CW and WB-CW provide significantly higher removal efficiencies for organic matter (>59%), NH₄⁺-N (>76%), TN (>37%) and phosphorus (>71%), compared with G-CW (22%-49%). The higher pollutants removal ability of biochar-packed VFCWs was mainly attribute to the higher adsorption ability and microbial cultivation in the porous biochar media. Moreover, increasing the flooded/drained ratio from 4/8h to 8/4h of the tidal operation further improved around 10% of the removal of both organics and NH₄⁺-N for biochar-packed VFCWs. The phosphorus removal was dependent on the media adsorption capacities through the whole experiment. However, the NH₄⁺-N biodegradation by microbial communities was demonstrated to become the dominant removal mechanism in the long term treatment, which compensated the decreased adsorption capacities of the media. The study supported that the use of biochar would increase the treatment performance and elongate the lifespan of CWs under tidal operation.

Removal of organic matter, nitrogen and faecal indicators from diluted anaerobically digested slurry using tidal flow constructed wetlands

The rapid implementation of anaerobic digestion for renewable energy production has resulted in increased generation of anaerobically digested slurry, which contains a variety of pollutants and therefore has the potential to cause serious environmental problems. Tidal flow constructed wetlands, which could generate beneficial oxygen conditions, were investigated for their success in removing nitrogen, organic matter and pathogens in anaerobically digested slurry. The results indicated that tidal operation had a positive effect on promoting NH₄⁺-N and organic matter (chemical oxygen demand (COD)) removal. With an average influent NH₄⁺-N concentration of 288 mg/L and COD concentration of 839 mg/L, the average removal efficiency reached up to 93% (325 g/m² day) for NH₄⁺-N and 53% (603 g/m² day) for COD, with total inorganic nitrogen (TIN) removal efficiency of 51% (226 g/m² day). The nitrogen removal in the tidal-operated CWs is highly dependent on the flooded and drained (F/D) time ratio. Changing flooded time from 3 to 5 h enhanced denitrification (nitrite reductase-K (nirK) abundance) and further resulted in improved TIN removal efficiency of 62% (237 g/m² day). The removal of faecal indicators was also examined, with reduction rate of approximately 0.9 log₁₀ CFU/100 mL for both Escherichia coli and total coliforms, which was independent of the influent loadings and differing flooded/drained time ratio. Tidal flow CWs were demonstrated to have the high potential to treat diluted anaerobically digested slurry.

Facilitated biological reduction of nitroaromatic compounds by reduced graphene oxide and the role of its surface characteristics

How reduced graphene oxide (RGO) mediates the reductive transformation of nitroaromatic pollutants by mixed cultures and the role of its surface characteristics were evaluated in this study. Different electron donors were applied to investigate the interaction between RGO and anaerobic microbes. Moreover, the influence of the surface properties of RGO on biological nitroaromatic removal was further elucidated. The results show that RGO could achieve an approximate one-fold rate increase of nitrobenzene reduction by mixed culture with glucose as an electron donor. Selective elimination of oxygen moieties on the RGO surface, such as quinone groups, decreased the nitrobenzene transformation rate, whereas doping nitrogen into the RGO framework exhibited a positive effect. The study indicates that graphene-based carbon nanomaterials have the potential to accelerate the biological transformation of nitroaromatic compounds and that the functionalization of these carbon nanomaterials, especially through surface modification, would further enhance the conversion efficiency of contaminants.

Phytoremediation of imazalil and tebuconazole by four emergent wetland plant species in hydroponic medium

Pollution from pesticide residues in aquatic environments is of increasing concern. Imazalil and tebuconazole, two commonly used systemic pesticides, are water contaminants that can be removed by constructed wetlands. However, the phytoremediation capability of emergent wetland plants for imazalil and tebuconazole, especially the removal mechanisms involved, is poorly understood. This study compared the removal of both pesticides by four commonly used wetland plants, Typha latifolia, Phragmites australis, Iris pseudacorus and Juncus effusus, and aimed to understand the removal mechanisms involved. The plants were individually exposed to an initial concentration of 10 mg/L in hydroponic solution. At the end of the 24-day study period, the tebuconazole removal efficiencies were relatively lower (25%-41%) than those for imazalil (46%-96%) for all plant species studied. The removal of imazalil and tebuconazole fit a first-order kinetics model, with the exception of tebuconazole removal in solutions with I. pseudacorus. Changes in the enantiomeric fraction for imazalil and tebuconazole were detected in plant tissue but not in the hydroponic solutions; thus, the translocation and degradation processes were enantioselective in the plants. At the end of the study period, the accumulation of imazalil and tebuconazole in plant tissue was relatively low and constituted 2.8-14.4% of the total spiked pesticide in each vessel. Therefore, the studied plants were able to not only take up the pesticides but also metabolise them.

Pathways of nitrobenzene degradation in horizontal subsurface flow constructed wetlands: Effect of intermittent aeration and glucose addition

Intermittent aeration and addition of glucose were applied to horizontal subsurface flow constructed wetlands in order to investigate the effect on pathways of nitrobenzene (NB) degradation and interactions with microbial nitrogen and sulphur transformations. The experiment was carried out in three phases A, B and C consisting of different NB loading and glucose dosing. For each phase, the effect of aeration was assessed by intermittently aerating one wetland and leaving one unaerated. Regardless of whether or not the wetland was aerated, at an influent NB concentration of 140 mg/L, both wetlands significantly reduced NB to less than 2 mg/L, a reduction efficiency of 98%. However, once the influent NB concentration was increased to 280 mg/L, the aerated wetland had a higher removal performance 82% compared to that of the unaerated wetland 71%. Addition of glucose further intensified the NB removal to 95% in the aerated wetlands and 92% in the unaerated. Aeration of wetlands enhanced NB degradation, but also resulted in higher NB volatilization of 6 mg m(-2) d(-1). The detected high concentration of sulphide 20-60 mg/L in the unaerated wetland gave a strong indication that NB may act as an electron donor to sulphate-reducing bacteria, but this should be further investigated. Aeration positively improved NB removal in constructed wetlands, but resulted in higher NB volatilization. Glucose addition induced co-metabolism to enhance NB degradation.

Remediation of nitrobenzene contaminated soil by combining surfactant enhanced soil washing and effluent oxidation with persulfate

The combination of surfactant enhanced soil washing and degradation of nitrobenzene (NB) in effluent with persulfate was investigated to remediate NB contaminated soil. Aqueous solution of sodium dodecylbenzenesulfonate (SDBS, 24.0 mmol L^-1) was used at a given mass ratio of solution to soil (20:1) to extract NB contaminated soil (47.3 mg kg^-1), resulting in NB desorption removal efficient of 76.8%. The washing effluent was treated in Fe²⁺/persulfate and Fe²⁺/H₂O₂ systems successively. The degradation removal of NB was 97.9%, being much higher than that of SDBS (51.6%) with addition of 40.0 mmol L^-1 Fe²⁺ and 40.0 mmol L^-1 persulfate after 15 min reaction. The preferential degradation was related to the lone pair electron of generated SO₄•⁻, which preferably removes electrons from aromatic parts of NB over long alkyl chains of SDBS through hydrogen abstraction reactions. No preferential degradation was observed in •OH based oxidation because of its hydrogen abstraction or addition mechanism. The sustained SDBS could be reused for washing the contaminated soil. The combination of the effective surfactant-enhanced washing and the preferential degradation of NB with Fe²⁺/persulfate provide a useful option to remediate NB contaminated soil.

A novel "wastes-treat-wastes" technology: role and potential of spent fluid catalytic cracking catalyst assisted ozonation of petrochemical wastewater

Catalytic ozonation is a promising wastewater treatment technology. However, the high cost of the catalyst hinders its application. A novel "wastes-treat-wastes" technology was developed to reuse spent fluid catalytic cracking catalysts (sFCCc) for the ozonation of petrochemical wastewater in this study. Multivalent vanadium (V(4+) and V(5+)), iron (Fe(2+) and Fe(3+)) and nickel (Ni(2+)) oxides that are distributed on the surface of sFCCc and poisoned FCC catalysts are the catalytic components for ozonation. The sFCCc assisted catalytic ozonation (sFCCc-O) of nitrobenzene indicated that the sFCCc significantly promoted hydroxyl radical mediated oxidation. The degradation rate constant of nitrobenzene in sFCCc-O (0.0794 min(-1) at 298 K) was approximately doubled in comparison with that in single ozonation (0.0362 min(-1) at 298 K). The sFCCc-O of petrochemical wastewater increased chemical oxygen demand removal efficiency by three-fold relative to single ozonation. The number of oxygen-containing (Ox) polar contaminants in the effluent (253) from sFCCc-O treatment decreased to about 70% of the initial wastewater (353). The increased oxygen/carbon atomic ratio and decreased number of Ox polar contaminants indicated a high degree of degradation. The present study showed the role and potential of sFCCc for catalytic ozonation of petrochemical wastewater, particularly in an advantage of the cost-effectiveness through "wastes-treat-wastes".

Catalytic mechanism study on manganese oxide in the catalytic supercritical water oxidation of nitrobenzene

MnO₂and Mn₂O₃transform into each other, and the mixture acts as an electron relay to promote the generation of strong oxidizing agents and the catalytic oxidation of nitrobenzene during catalytic supercritical water oxidation.

How the novel integration of electrolysis in tidal flow constructed wetlands intensifies nutrient removal and odor control

Intensified nutrient removal and odor control in a novel electrolysis-integrated tidal flow constructed wetland were evaluated. The average removal efficiencies of COD and NH4(+)-N were above 85% and 80% in the two experimental wetlands at influent COD concentration of 300 mg/L and ammonium nitrogen concentration of 60 mg/L regardless of electrolysis integration. Effluent nitrate concentration decreased from 2.5mg/L to 0.5mg/L with the reduction in current intensity from 1.5 mA/cm(2) to 0.57 mA/cm(2). This result reveals the important role of current intensity in nitrogen transformation. Owing to the ferrous and ferric iron coagulant formed through the electro-dissolution of the iron anode, electrolysis integration not only exerted a positive effect on phosphorus removal but also effectively inhibited sulfide accumulation for odor control. Although electrolysis operation enhanced nutrient removal and promoted the emission of CH4, no significant difference was observed in the microbial communities and abundance of the two experimental wetlands.

Intensified nitrogen and phosphorus removal in a novel electrolysis-integrated tidal flow constructed wetland system

A novel electrolysis-integrated tidal flow constructed wetland (CW) system was developed in this study. The dynamics of intensified nitrogen and phosphorus removal and that of hydrogen sulphide control were evaluated. Ammonium removal of up to 80% was achieved with an inflow concentration of 60 mg/L in wetland systems with and without electrolysis integration. Effluent nitrate concentration decreased from 2 mg/L to less than 0.5 mg/L with the decrease in current intensity from 1.5 mA/cm(2) to 0.57 mA/cm(2) in the electrolysis-integrated wetland system, thus indicating that the current intensity of electrolysis plays an important role in nitrogen transformations. Phosphorus removal was significantly enhanced, exceeding 95% in the electrolysis-integrated CW system because of the in-situ formation of a ferric iron coagulant through the electro-dissolution of a sacrificial iron anode. Moreover, the electrolyzed wetland system effectively inhibits sulphide accumulation as a result of a sulphide precipitation coupled with ferrous-iron electro-dissolution and/or an inhibition of bacterial sulphate reduction under increased aerobic conditions.

Development of constructed wetlands in performance intensifications for wastewater treatment: a nitrogen and organic matter targeted review

The knowledge on the performance enhancement of nitrogen and organic matter in the expanded constructed wetlands (CWs) with various new designs, configurations, and technology combinations are still not sufficiently summarized. A comprehensive review is accordingly necessary for better understanding of this state-of-the-art-technology for optimum design and new ideas. Considering that the prevailing redox conditions in CWs have a strong effect on removal mechanisms and highly depend on wetland designs and operations, this paper reviews different operation strategies (recirculation, aeration, tidal operation, flow direction reciprocation, and earthworm integration), innovative designs, and configurations (circular-flow corridor wetlands, towery hybrid CWs, baffled subsurface CWs) for the intensifications of the performance. Some new combinations of CWs with technologies in other field for wastewater treatment, such as microbial fuel cell, are also discussed. To improve biofilm development, the selection and utilization of some specific substrates are summarized. Finally, we review the advances in electron donor supply to enhance low C/N wastewater treatment and in thermal insulation against low temperature to maintain CWs running in the cold areas. This paper aims to provide and inspire some new ideas in the development of intensified CWs mainly for the removal of nitrogen and organic matter. The stability and sustainability of these technologies should be further qualified.