Underwater light source changes microecosystem constructed by Vallisneria spinulosa Yan for water restoration: Efficiency of water purification, characteristics of growth, and rhizosphere.

Submerged macrophytes are effective in ecological restoration of water bodies polluted by nitrogen and phosphorus, and its restoration capacity depends on underwater illumination condition. This study explored the influencing mechanism of illumination on Vallisneria spinulosa Yan (V. spinulosa Yan) for water restoration. Addition of underwater light source increased the total nitrogen, ammonia nitrogen, total phosphorus, and phosphate removal loads of the V. spinulosa Yan growth system by 61.5, 39.2, 8.5, and 5.0 mg m-2 d-1, respectively. Meanwhile, the growth of V. spinulosa Yan was obviously promoted, even with high water turbidity. Although the biological nitrogen removal processes were inhibited by adding underwater light source, the growth of V. spinulosa Yan can be significantly improved, thus enhancing the efficiency of water purification via the absorption of nitrogen and phosphorus by V. spinulosa Yan. This study provides a theoretical foundation and technical support for application of submerged macrophytes in ecological water restoration.

Subtle magnesium liberation of self-fabricated functional filler actuates highly efficient phosphorus removal from source-separated urine by SBBR.

Domestic wastewater source-separated treatment has attracted wide attention due to the efficiency improvement of sewage treatment systems, energy saving, resource reuse, and the construction and operation cost saving of pipeline networks. Nonetheless, the excess source-separated urine still demands further harmless treatment. Sequencing batch biofilm reactor (SBBR), a new type of composite biofilm reactor developed by filling different fillers into the sequential batch reactor (SBR) reactor, has higher pollutant removal performance and simpler operation and maintenance. However, the phosphorus removal ability of the SBBR filling with conventional fillers is still limited and needs further improvement. In this study, we developed two new fillers, the self-fabricated filler A and B (SFA/SFB), and compared their source-separated urine treatment performance. Long-term treatment experimental results demonstrated that the SBBR systems with different fillers had good removal performance on the COD and TN in the influent, and the removal rate increased with the increasing HRT. However, only the SBBR system with the SFA showed excellent PO43--P and TP removal performance, with the removal rates being 83.7 ± 11.9% and 77.3 ± 13.7% when the HRT was 1 d. Microbial community analysis results indicated that no special bacteria with strong phosphorus removal ability were present on the surface of the SFA. Adsorption experimental results suggested that the SFA had better adsorption performance for phosphorus than the SFB, but it could not always have stronger phosphorus adsorption and removal performance during long-term operation due to the adsorption saturation. Through a series of characterizations such as SEM, XRD, and BET, it was found that the SFA had a looser structure due to the use of different binder and production processes, and the magnesium in the SFA gradually released and reacted with PO43- and NH4+ in the source-separated urine to form dittmarite and struvite, thus achieving efficient phosphorus removal. This study provides a feasible manner for the efficient treatment of source-separated urine using the SBBR system with self-fabricated fillers.

Enhanced water treatment performance of ceramic-based forward osmosis membranes via MOF interlayer.

Forward osmosis (FO) membrane processes could operate without hydraulic pressures, enabling the efficient treatment of wastewaters with mitigated membrane fouling and enhanced efficiency. Designing a high-performance polyamide (PA) layer on ceramic substrates remains a challenge for FO desalination applications. Herein, we report the enhanced water treatment performance of thin-film nanocomposite ceramic-based FO membranes via an in situ grown Zr-MOF (UiO-66-NH2) interlayer. With the Zr-MOF interlayer, the ceramic-based FO membranes exhibit lower thickness, higher cross-linking degree, and increased surface roughness, leading to higher water flux of 27.38 L m-2 h-1 and lower reverse salt flux of 3.45 g m-2 h-1. The ceramic-based FO membranes with Zr-MOF interlayer not only have an application potential in harsh environments such as acidic solution (pH 3) and alkaline solution (pH 11), but also exhibit promising water and reverse salt transport properties, which are better than most MOF-incorporated PA membranes. Furthermore, the membranes could reject major species (ions, oil and organics) with rejections ＞94 % and water flux of 22.62-14.35 L m-2 h-1 in the treatment of actual alkaline industrial wastewater (pH 8.6). This rational design proposed in this study is not only applicable for the development of a high-quality ceramic-based FO membrane with enhanced performance but also can be potentially extended to more challenging water treatment applications.

Electro-oxidation of Ibuprofen using carbon-supported SnOx-CeOx flow-anodes: The key role of high-valent metal.

Exploiting electrochemically active materials as flow-anodes can effectively alleviate mass transfer restriction in an electro-oxidation system. However, the electrocatalytic activity and persistence of the conventional flow-anode materials are insufficient, resulting in limited improvement in the electro-oxidation rate and efficiency. Herein, we reported a rational strategy to substantially enhance the electrocatalytic performance of flow-anodes in electro-oxidation by introducing the redox cycle of high-valent metal in a suitable carbon substrate. The characterization suggested that the SnOx-CeOx/carbon black (CB) featured well-distributed morphology, rapid charge transfer, high oxygen evolution potential, and strong water adsorption, and stood out among three kinds of SnOx-CeOx loaded carbon materials. Mechanistic analysis indicated that the redox cycle of Ce species played a key role in accelerating the electron transfer from SnOx to CB directionally and could continuously create the electron-deficient state of the SnOx, thereby sustainably triggering the generation of ·OH. All these features enabled the resulting SnOx-CeOx/CB flow-anode to accomplish a calculated maximum kinetic constant of 0.02461 1/min, a higher current efficiency of 47.1%, and a lower energy consumption of 21.3 kWh/kg COD compared with other conventional flow-anodes reported to date. Additionally, SnOx-CeOx/CB exhibited excellent stability with extremely low leaching concentrations of Sn and Ce ions. This study provides a feasible manner for efficient water decontamination using the electro-oxidation system with SnOx-CeOx/CB.

Effects of regular zooplankton supplement on the bacterial communities and process performance of biofilm for wastewater treatment.

Biofilm processing technologies were widely used for wastewater treatment due to its advantages of low cost and easy management. However, the aging biofilms inevitably decrease the purification efficiency and increase the sludge production, which limited the widely application of biofilms technologies in rural area. In this study, we proposed a novel strategy by introducing high-trophic organisms to prey on low-trophic organisms, and reduce the aged biofilms and enhance treatment efficiencies in rural wastewater treatment. The effect of three typical zooplankton (Paramecium, Daphnia, and Rotifer) supplement on the purification efficiency and biofilm properties in the contact oxidation process were investigated, and the reaction conditions were optimized by an orthogonal experiment. Under optimal conditions, the biofilms weight decreased 67.6%, the oxygen consumption rate of biofilms increased 9.4%, and wastewater treatment efficiency was obviously increased after zooplankton supplement. Microbial sequencing results demonstrated that the zooplankton optimize the contact oxidation process by altering the bacterial genera mainly Diaphorobacter, Thermomonas, Alicycliphilus and Comamonas. This research provides insight into mechanism of the zooplankton supplement in biological contact oxidation process and provides a feasible strategy for improving the rural sewage treatment technology.

Robust ceramic-based graphene membrane for challenging water treatment with enhanced fouling and scaling resistance.

Membrane fouling and scaling are two challenges for efficient treatment of hypersaline wastewater, greatly hindering separation performance and operation stability of desalination membranes. In this work, we report a smooth ceramic-based graphene desalination membrane, exhibiting enhanced anti-fouling and anti-scaling ability and operational performance for efficient treatment of both synthetic and real industrial wastewaters, outperforming polypropylene (PP) membrane. For treatment of hypersaline waters containing organic or inorganic substance, we demonstrate that the graphene membrane exhibits more stable water flux and almost complete salt rejection (>99.9%) during constant operation. Enhanced anti-fouling and desalination performance of graphene membrane could be attributed to the lower attractive interaction force with foulant (-4.65 mJ m-2), lower surface roughness (Ra = 2.2 ± 0.1 nm) and higher affinity with water than PP membrane. Furthermore, an anti-scaling mechanism enabled by graphene membrane is evidenced, with a highlight on the roles of smooth graphene surface with lower roughness, less nucleation sites and lower binding force with scaling crystals. Importantly, even for industrial petrochemical wastewater, such a graphene membrane also exhibits relatively more stable water flux and promising oil and ions rejection during long-term operation, outperforming PP membrane. This study further confirms a promising practical application potential of robust ceramic-based graphene membrane for efficient treatment of more challenging hypersaline wastewater with complicated compositions, which is not feasible by conventional desalination membranes.

Identification of microbial consortia for sustainable disposal of constructed wetland reed litter wastes.

Reed is a typical emerged plant in constructed wetlands (CWs). Its litters were used as raw materials for preparing Fe-C ceramic-filler (Fe-C-CF). The physical and chemical properties of Fe-C-CF were studied under different conditions, including the mass ration of Fe to carbon (Fe/C ratio), sintering temperature, and time, to determine the optimum preparing conditions. Meanwhile, the denitrification performance and CO2 emission flux of the surface flow constructed wetland (SFCW) systems were investigated when using Fe-C-CF as the matrix. The optimum preparing conditions for Fe-C-CF were Fe/C ratio of 1:1, sintering temperature and time of 500 °C and 20 min, respectively. The SFCW system with Fe-C-CF obtained a higher total nitrogen (TN), nitrate nitrogen (NO3--N), and ammonia nitrogen (NH3-N) removal efficiencies than the control SFCW system without Fe-C-CF. Compared with the heterotrophic denitrification process, the SFCW system with Fe-C-CF decreased CO2 emission by 67.9 g m-2 per year. The results of microbial community analysis indicated that addition of Fe-C-CF increased the diversity and abundance of microbial communities in the SFCW systems. The dominant genus of the SFCW system with Fe-C-CF was Bacillus, while Uliginosibacterium was the dominant genus in the system without the filler.

A comprehensive review on mixotrophic denitrification processes for biological nitrogen removal.

Biological denitrification is the most widely used method for nitrogen removal in water treatment. Compared with heterotrophic and autotrophic denitrification, mixotrophic denitrification is later studied and used. Because mixotrophic denitrification can overcome some shortcomings of heterotrophic and autotrophic denitrification, such as a high carbon source demand for heterotrophic denitrification and a long start-up time for autotrophic denitrification. It has attracted extensive attention of researchers and is increasingly used in biological nitrogen removal processes. However, so far, a comprehensive review is lacking. This paper aims to review the current research status of mixotrophic denitrification and provide guidance for future research in this field. It is shown that mixotrophic denitrification processes can be divided into three main kinds based on different kinds of electron donors, mainly including sulfur-, hydrogen-, and iron-based reducing substances. Among them, sulfur-based mixotrophic denitrification is the most widely studied. The most concerned influencing factors of mixotrophic denitrification processes are hydraulic retention times (HRT) and ratio of chemical oxygen demand (COD) to total inorganic nitrogen (C/N). The dominant functional bacteria of sulfur-based mixotrophic denitrification system are Thiobacillus, Azoarcus, Pseudomonas, and Thauera. At present, mixotrophic denitrification processes are mainly applied for nitrogen removal in drinking water, groundwater, and wastewater treatment. Finally, challenges and future research directions are discussed.

Electro-peroxone enables efficient Cr removal and recovery from Cr(III) complexes and inhibits intermediate Cr(VI) generation in wastewater: Performance and mechanism.

Available oxidation processes for removing Cr(III) complexes from water/wastewater usually encounter the formation of highly toxic Cr(VI) and the generation of Cr enriched waste sludge, posing challenges on the subsequent disposal. Herein, we achieve efficient removal of Cr(III)-organic complexes and simultaneous recovery of Cr from wastewater with enhanced curtailment of intermediate Cr(VI), by using an electrochemically driven peroxone (i.e., electro-peroxone) process with activated carbon fiber (ACF) electrodes. For Cr(III)-EDTA, electro-peroxone could remove ∼90% total Cr from 11.50 mg/L to 1.20 mg/L and ∼80% total organic carbon, with a strong curtailment of Cr(VI) to less than 0.2 mg/L. Additionally, the process could obtain a complete recovery of the removable Cr, of which 78.3% are enriched at ACF cathode as amorphous Cr(OH)3 deposits and the remaining 21.7% are adsorbed at the anode, thus avoiding the generation of Cr laden sludge. Mechanism studies show the electro-generated H2O2 reacts with O3 to generate abundant HO· for decomplexation, which sequentially oxidizes Cr(III) to Cr(VI), and degrades the released EDTA via stepwise decarboxylated process, as confirmed by HPLC analysis. Multiple pathways including electro-reduction, H2O2 reduction and electro-adsorption synergistically curtail and immobilize the formed intermediate Cr(VI). ACF characterizations and continuous 5-cycle experiments substantiate the excellent reusability of the ACF electrodes. Moreover, this process exhibits satisfactory effectiveness to Cr(III) complexed with other ligands (e.g., citrate and oxalate), and complexed Cr(III) in the real electroplating wastewater. We believe this study would provide an efficient and eco-friendly alternative for Cr(III) complexes removal from wastewater.

Roles of Surfactants in Oriented Immobilization of Cellulase on Nanocarriers and Multiphase Hydrolysis System.

Surfactants, especially non-ionic surfactants, play an important role in the preparation of nanocarriers and can also promote the enzymatic hydrolysis of lignocellulose. A broad overview of the current status of surfactants on the immobilization of cellulase is provided in this review. In addition, the restricting factors in cellulase immobilization in the complex multiphase hydrolysis system are discussed, including the carrier structure characteristics, solid-solid contact obstacles, external diffusion resistance, limited recycling frequency, and nonproductive combination of enzyme active centers. Furthermore, promising prospects of cellulase-oriented immobilization are proposed, including the hydrophilic-hydrophobic interaction of surfactants and cellulase in the oil-water reaction system, the reversed micelle system of surfactants, and the possible oriented immobilization mechanism.

Enhancement of cottonseed oil refining wastewater treatment by zero valent iron under sunlight irradiation and O2 bubbling.

This study is the first to apply a zero-valent iron (ZVI) system in the treatment of cottonseed oil (CTO) refining wastewater. The results indicated that the ZVI system can effectively degrade and mineralize CTO in the wastewater, whereas sunlight irradiation and O2 bubbling can considerably enhance CTO degradation, removing 93.5% of CTO and 69.0% of chemical oxygen demand within 180 min. In addition, a low concentration (0.1 mM) of SO42- and Cl- in the wastewater improved CTO degradation, whereas a high concentration (>1 mM) of these anions considerably inhibited the degradation process. However, NO3- at all concentrations hindered CTO degradation. Furthermore, OH and O2- were the main active species for CTO degradation in the ZVI system under dark conditions. However, in addition to these two species, photogenerated hole (h+) played a key role in CTO degradation under sunlight irradiation. This observation might be derived from the photocatalytic effect due to photoexcitation of the iron corrosion product, γ-FeOOH. Our findings show that the ZVI system assisted by sunlight irradiation and O2 bubbling is feasible for CTO-refining wastewater treatment and can guide the real wastewater treatment project.

Treatment of oily wastewaters by highly porous whisker-constructed ceramic membranes: Separation performance and fouling models.

Efficient treatment of challenging oily emulsion wastewater can alleviate water pollution to provide more chances for water reuse and resource recovery. Despite their promising application potential, conventional porous ceramic membranes have challenging bottleneck issues such as high cost and insufficient permeance. This study presents a new strategy for highly efficient treatment of not only synthetic but real oily emulsions via unexpensive whisker-constructed ceramic membranes, exhibiting exceptional permeance and less energy input. Compared with common ceramic membranes, such lower-cost mullite membranes with a novel whisker-constructed structure show higher porosity and water permeance, and better surface oleophobicity in water. Treatment performance such as permeate flux and oil rejection was explored for the oily emulsions with different properties under key operating parameters. Furthermore, classical Hermia models were used to reveal membrane fouling mechanism to well understand the microscopic interactions between emulsion droplets and membrane interface. Even for real acidic oily wastewater, such membranes also exhibit high permeance and less energy consumption, outperforming most state-of-the-art ceramic membranes. This work provides a new structure concept of highly permeably whisker-constructed porous ceramic membranes that can efficiently enable more water separation applications.

Isolation and thermo-acclimation of thermophilic bacteria in hyperthermophilic fermentation system.

Hyperthermophilic microorganisms play a key role in the hyper-thermophilic composting (HTC) technique. However, little information is available about the hyperthermophilic microorganisms prevalent in HTC systems, except for the Calditerricola satsumensis, Calditerricola yamamurae, and Thermaerobacter. To obtain effective hyper-thermophilic microorganisms, a continuous thermo-acclimation of the suitable thermophilic microorganisms was demonstrated in this study. Bacillus thermoamylovorans with high-temperature endurance (70 °C) were newly isolated from sludge composting, and an adequate slow heating rate (2 °C per cycle) was applied to further improve its thermostability. Finally, a strain with a maximum growth temperature of 80 °C was obtained. Moreover, structural and hydrophobic changes in cell proteins, the special amino acid content ratio, and the membrane permeability of the thermophilic bacterium after thermo-acclimation were evaluated for improved thermostability. In addition, the acclimated hyperthermophilic bacterium was further inoculated into the HTC system, and an excellent performance with a maximum operating temperature of 82 °C was observed.

Synergistic oxytetracycline adsorption and peroxydisulfate-driven oxidation on nitrogen and sulfur co-doped porous carbon spheres.

Metal-free carbonaceous catalysts are receiving increasing attention in wastewater treatment. Here, nitrogen and sulfur co-doped carbon sphere catalysts (N,S-CSs900-OH) were synthesized using glucose and L-cysteine via a hydrothermal method and high temperature alkali activation. The N,S-CSs900-10%-OH exhibited excellent catalytic performance for the degradation of oxytetracycline (OTC). The degradation rate was 95.9% in 60 min, and the reaction equilibrium rate constant was 0.0735 min-1 (k0-15 min). The synergistic effect of adsorption-promoting degradation was demonstrated in the removal process of OTC. The excellent adsorption capacity of N,S-CSs900-10%-OH ensured the efficient oxidation of OTC. N,S-CSs900-10%-OH reduced the activation energy of the OTC degradation reaction (Ea=18.23 kJ/mol). Moreover, the pyrrolic N, thiophene S and carbon skeleton played an important role in the degradation of OTC based on density function theory, and the catalytic mechanism was expounded through radical and nonradical pathways. The active species involved in the reaction were O2•-, 1O2, SO4•- and •OH, of which O2•- was the primary reactive species. This study provides a new insight into the reaction mechanism for efficient treatment of organic pollutants using metal-free doped porous carbon materials.

Optimisation of enzymatic saccharification of wheat straw pre-treated with sodium hydroxide.

To enhance the reducing sugar yield in enzymatic hydrolysis, various factors (NaOH concentration, solid content and pre-treatment time) that affect the pre-treatment process were investigated and evaluated based on the reducing sugar yield of the subsequent enzymatic hydrolysis. The enzymatic hydrolysis was based on the cellulase from Trichoderma reesi ATCC 26921, the optimum NaOH pre-treatment conditions were an NaOH concentration of 1.0% (w/w), a solid content of 5.0% (w/v) and a pre-treatment time of 60 min. Various parameters that affect the enzymatic hydrolysis of wheat straw, including the solid content, enzyme loading, pH and hydrolysis time, were investigated and optimized through a Box-Behnken design and response surface methodology. The predicted optimum conditions for enzymatic hydrolysis were a solid content of 8.0% (w/v), an enzyme loading of 35 FPU/g substrate, a temperature of 50 °C, a pH of 5.3 and a hydrolysis time of 96 h. The experimental result showed that the maximum reducing sugar yield was 60.73% (53.35% higher than the wheat straw without NaOH pre-treatment), which is in accordance with the predicted conditions.

Enhancement of algae ponds for rural domestic sewage treatment by prolonging daylight using artificial lamps.

Algal ponds (APs) are widely used as treatment facilities for domestic sewage in sparsely populated rural areas. However, few AP studies have focused on daylight length to enhance pollutants removal. In this study, four algae ponds were set up, daylight was prolonged by 0, 2, 4, and 6 h with an illuminating intensity of 3000 lx. The highest removal efficiencies of total nitrogen, ammonium, and total phosphorus were 37.36%, 41.20%, and 21.56% due to the highest microbial abundance under optimum conditions (2 h PD), respectively. Excessive PD (4 h and 6 h) could inhibit the removal abilities. PD also increased the maximum relative electron transport rate of algae, leading to an increase in the photosynthetic capacity of APs. Meanwhile, the high microbial abundance indicates that chemoheterotrophic bacteria are the main influencing factor for the removal of nitrogen and phosphorus by the APs. Moreover, the system with PD using artificial lamps was proven to be feasible for engineering applications and potentially utilized in rural domestic wastewater treatment.

Stable Zr-Based Metal-Organic Framework Nanoporous Membrane for Efficient Desalination of Hypersaline Water.

Treatment of hypersaline waters is a critical environmental challenge. Pervaporation (PV) desalination is a promising technique to address this challenge, but current PV membranes still suffer from challenging issues such as low flux and insufficient stability. Herein, we propose in situ nanoseeding followed by a secondary growth strategy to fabricate a high-quality stable metal-organic framework (MOF) thin membrane (UiO-66) for high-performance pervaporation desalination of hypersaline waters. To address the issue of membrane quality, a TiO2 nano-interlayer was introduced on coarse mullite substrates to favor the growth of a UiO-66 nanoseed layer, on which a well-intergrown UiO-66 selective membrane layer with thickness as low as 1 µm was finally produced via subsequent secondary growth. The PV separation performance for hypersaline waters was systematically investigated at different salt concentrations, feed temperatures, and long-term operation in different extreme chemical environments. Besides having nearly complete rejection (99.9%), the UiO-66 membrane exhibited high flux (37.4 L·m-2·h-1) for hypersaline waters, outperforming current existing zeolite and MOF membranes. The membrane also demonstrated superior long-term operational stability under various harsh environments (hypersaline, hot, and acidic/alkaline feed water) and mild fouling behavior. The rational design proposed in this study is not only applicable for the development of a high-quality UiO-66 membrane enabling harsh hypersaline water treatment but can also be potentially extended to other next-generation nanoporous MOF membranes for more environmental applications.

Reduced graphene oxide/TiO2(B) immobilized on nylon membrane with enhanced photocatalytic performance.

Taking advantage of the unique properties of reduced graphene oxide (rGO) and monoclinic crystalline titanium dioxide (TiO2(B)) nanomaterials, a novel rGO-TiO2(B) composite membrane (MrGO-TiO2(B)) was constructed by UV-light-assisted self-assembly of rGO and TiO2 on a nylon membrane. The structure of MrGO-TiO2(B) was characterized by scanning electron microscopy, transmission electron microscopy, UV-visible diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction analysis. Through 2D/2D self-assembly, rGO and TiO2(B) were more tightly combined, and then MrGO-TiO2(B) exhibited outstanding photocatalytic activity and an excellent methylene blue (MB) removal rate. MB was completely removed in 60 min at a constant rate of 0.042 min-1 by the MrGO-TiO2(B)/H2O2/MB system upon solar simulating Xe lamp irradiation. The synergistic effect of rGO and TiO2(B) facilitated the photocatalytic degradation of MB. TiO2(B) was excited and generated electrons and holes upon irradiation. Some electrons migrated to the surface of TiO2(B) to react with H2O2 to produce hydroxyl radicals (OH), while the other electrons migrated to the surface of rGO to react with H2O2, producing OH. In addition, a number of superoxide radicals (O2-) was detected. The holes in the valence band of TiO2(B) directly oxidized MB. The catalytic activity of MrGO-TiO2(B) toward MB degradation remained stable after four rounds of reuse. Therefore, the surface modification of a nylon membrane with TiO2(B) and rGO can serve as a promising route to fabricate photocatalytic membranes for use in the water treatment industry.

Application of constructed wetlands in treating rural sewage from source separation with high-influent nitrogen load: a review.

Constructed wetlands (CWs) are characterized by low construction cost, convenient maintenance and management, and environmentally friendly features. They have emerged as promising technologies for decentralized sewage treatment across rural areas. Source separation of black water and gray water can facilitate sewage recycling and reuse of reclaimed water, reduce the size of treatment facilities, and lower infrastructure investment and operating cost. This is consistent with the concept of sustainable development. However, black water contains high concentrations of ammonia nitrogen, and the denitrification capacity of CWs is not excellent due to insufficient carbon source. Therefore, application of CWs for black water treatment faces challenges. This article provides a review on the progress in CWs for treatment of the sewage with high-influent nitrogen load, with emphasis on the commonly used strengthening means and the role of plants in nitrogen removal via CWs. The current issues of rural sewage treatment with high-influent nitrogen load by CWs are also assessed. Finally, the challenges and perspectives are discussed for the optimization of CWs-enhanced denitrification strategies.

Combined process of bio-contact oxidation-constructed wetland for blackwater treatment.

In this study, a combined process of bio-contact oxidation and constructed wetland for blackwater treatment was assessed. The effects of hydraulic retention time and particle size on treatment performance were systematically studied. Additionally, microbial communities in the combined process were characterized. The results show that the removal efficiency of COD, TN, NH4+-N, and TP under optimum conditions in this study were 81.6%, 56.1%, 42.2%, and 73.7%, respectively. The maximum nitrogen removal rate reached 16.5 g m-2 d-1 (3 d). N and P removed via direct plant absorption accounted for only 19.7% and 16.1% of the total system, respectively. Plants play a crucial role in the microbial community of constructed wetlands and influence the overall performance of the system. The biofilm on roots favored aerobic and heterotrophic bacteria such as the aerobic denitrification microorganisms of Pelagibacterium, Halomonas, and Zoogloea. Overall, the combined process is a suitable technique for the treatment of blackwater.