Enhanced nitrogen removal using solid carbon source in constructed wetland with limited aeration

Effective remediation of agricultural drainage at three influent strengths by bioaugmented constructed wetlands filled with mixture of iron‑carbon and organic solid substrates: Performance and mechanisms

Agricultural drainage containing a large quantity of nutrients can cause quality deterioration and algal blooming of receiving water bodies, thus needs to be effectively remediated. In this study, iron‑carbon (FeC) composite-filled constructed wetlands (Fe-C-CWs) were employed to treat farmland drainage at three pollution levels, and organic solid substrates (walnut shells) and phosphate-accumulating denitrifying bacteria (Pseudomonas sp. DWP1) were supplemented to enhance the treatment performance. The results showed that the Fe-C-CWs exhibited notably superior removal efficiency for total nitrogen (TN, 52.0-58.2 %), total phosphorus (TP, 67.8-70.2 %) and chemical oxygen demand (COD, 56.7-70.4 %) than the control systems filled solely with gravel (28.5-32.5 % for TN, 33.2-40.5 % for TP and 30.2-55.0 % for COD) at all influent strengths, through driving autotrophic denitrification, Fe-based dephosphorization, and organic degradation processes. The addition of organic substrates and functional bacteria markedly enhanced pollutant removal in the Fe-C-CWs. Furthermore, use of FeC and organic substrates and denitrifier inoculation decreased CO2 and CH4 emissions from the CWs, and reduced global warming potential of the CWs at low influent strength. Pollutant removal efficiencies in the CWs were only marginally impacted by the increasing influent loads except for NO3--N, and pollutant removal mass was largely increased with the increase of influent strengths. The microbial community in the FeC composite-filled CWs exhibited distinct distribution patterns compared to the gravel-filled CWs regardless of the influent strengths, with obviously higher proportions of dominant genera Trichococcus, Geobacter and Ferritrophicum. Keystone taxa associated with pollutant removal in the Fe-C-filled CWs were identified to be Pseudomonas, Geobacter, Ferritrophicum, Denitratisoma and Sediminibacterium. The developed augmented Fe-C-filled CWs show great promises for remediating agricultural drainage with varied pollutant loads.

Plant-microbe involvement: How manganese achieves harmonious nitrogen-removal and carbon-reduction in constructed wetlands

Carbon deficits in inflow frequently lead to inefficient nitrogen removal in constructed wetlands (CWs) treating tailwater. Solid carbon sources, commonly employed to enhance denitrification in CWs, increase carbon emissions. In this study, MnO2 was incorporated into polycaprolactone substrates within CWs, significantly enhancing NH4+-N and NO3--N removal efficiencies by 48.26-59.78 % and 96.84-137.23 %, respectively. These improvements were attributed to enriched nitrogen-removal-related enzymes and increased plant absorption. Under high nitrogen loads (9.55 ± 0.34 g/m3/d), emissions of greenhouse gases (CO2, CH4, and N2O) decreased by 147.23-202.51 %, 14.53-86.76 %, and 63.36-87.36 %, respectively. N2O emissions were reduced through bolstered microbial nitrogen removal pathways by polycaprolactone and MnO2. CH4 accumulation was mitigated by the increased methanotrophs and dampened methanogenesis, modulated by manganese. Additionally, manganese-induced increases in photosynthetic pigment contents (21.28-64.65 %) fostered CO2 sequestration through plant photosynthesis. This research provides innovative perspectives on enhancing nitrogen removal and reducing greenhouse gas emissions in constructed wetlands with polymeric substrates.

Carbon slow-release and enhanced nitrogen removal performance of plant residue-based composite filler and ecological mechanisms in constructed wetland application

Stable carbon release and coupled microbial efficacy of external carbon source solid fillers are the keys to enhanced nitrogen removal in constructed wetlands. The constructed wetland plant residue Acorus calamus was cross-linked with poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) to create composite solid carbon source fillers (Ac-BDPs). The study demonstrated the slow release of carbon sources from Ac-BDPs with 35.27 mg/g under an average release rate of 0.88 mg/(g·d). Excellent denitrification was also observed in constructed wetlands with Ac-BDPs. Moreover, the average removal rate of nitrate nitrogen (NO3--N) was increased by 1.94 and 3.85 times of the blank groups under initial NO3--N inputs of 5 and 15 mg/L, respectively. Furthermore, the relatively high abundances of nap, narG, nirKS, norB, qnorZ and nosZ guaranteed efficient denitrification performance in constructed wetlands with Ac-BDPs. The study introduced a reliable technique for biological nitrogen removal by using composite carbon source fillers in constructed wetlands.

Characterization of simultaneous ammonium and nitrate removal and microbial communities in airlift reactor using 3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV) as carbon source and biofilm carrier

As a novel trend, solid carbon sources are applied to act as electron donors and biofilm carrier in biological denitrification process. In this study, simultaneous nitrate and ammonium removal process in an airlift sequencing batch reactor using 3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV) as carbon source and biofilm carrier under intermittent aeration conditions was established to treat effluent of synthetic marine recirculating aquaculture system. The results showed that maximum nitrate and ammonia nitrogen removal rates of 0.45 and 0.09 kg m-3 d-1 were achieved. No significant nitrite accumulation was found during 200-day operation, while effluent dissolved organic carbon accumulation and particle size reduction significantly increased. Microbial community analysis and batch tests illuminate that the generated sludge and attached biofilm played important roles in nitrogen removal. This study demonstrates the potential mechanism for the nitrogen removal process mediated by 3-hydroxybutyrate-co-3-hydroxyvalerate and provide a new idea for the alternative solutions of solid carbon sources.

Small ponds have stronger potential for net nitrogen removal: Insight from direct dissolved N2 measurement

Growing demands for watershed nitrogen (N) removal have called attention to abundant small bodies of water such as ponds, which have long been heralded as efficient storage and processing systems. Although pond conservation, restoration, and creation have been widely implemented to mitigate N pollution, information is limited regarding the impact of size-that is, whether N removal potential and efficiency are dependent upon pond size. We investigated the dynamics of N removal rates in 56 ponds from a hilly watershed by studying their bimonthly N2 concentrations and fluxes. Our results showed that smaller ponds performed better in net N removal. This can be discerned from the areal N2 fluxes, which were the highest in small ponds (< 4, 000 m2). The corresponding N2 fluxes (4.73 ± 4.53 mmol N2 m-2 d-1) were 2 to 14 times greater than those observed in larger ponds. The N removal efficiency, a metric used to describe the portions of the substrates released as N2, was also significantly higher in the small ponds (∼8.7 %) than in the larger ponds (∼5.0 %). Further regression analysis showed that both areal N2 flux and N removal efficiency were negatively correlated with pond area. The underlying mechanisms behind the size effects of N removal could be attributed to small ponds having larger sediment contact area to water volume ratios. Thus, smaller ponds allow more opportunities for N to interact with bioactive sediments than larger ponds. Overall, our findings contribute to the understanding of the distal role of pond size in affecting N removal. This research also provides a strong rationale for considering the effects of system size when implementing management practices dedicated to maximizing N removal.

Application of alkali-heated corncobs enhanced nitrogen removal and microbial diversity in constructed wetlands for treating low C/N ratio wastewater

Lack of carbon source is the main limiting factor in the denitrification of low C/N ratio wastewater in the constructed wetlands (CWs). Agricultural waste has been considered as a supplementary carbon source but research is still limited. To solve this problem, ferric carbon (Fe-C) + zeolite, Fe-C + gravel, and gravel were used as substrates to build CWs in this experiment, aiming to investigate the effects of different carbon sources (rice straw, corncobs, alkali-heated corncobs) on nitrogen removal performance and microbial community structure in CWs for low C/N wastewater. The results demonstrated that the microbial community and effluent nitrogen concentration of CWs were mainly influenced by the carbon source rather than the substrate. Alkali-heated corncobs significantly enhanced the removal of NO2--N, NH4+-N, NO3-N, and TN. Carbon sources addition increased microbial diversity. Alkali-heated corncobs addition significantly increased the abundance of heterotrophic denitrifying bacteria (Proteobacteria and Bacteroidota). Furthermore, alkali-heated corncobs addition increased the copy number of nirS, nosZ, and nirK genes while greenhouse gas fluxes were lower than common corncobs. In summary, alkali-heated corncobs can be considered as an effective carbon source.

Performances and mechanisms of simultaneous removal of nitrate and phosphate by biofilter assembled with sponge iron/copper and corn cobs

Sponge iron (SI) is a potential material for removing nitrate and phosphate from water. We decorated the SI with copper (Cu) to enhance its removal performance. To gain insight into the nitrate and phosphate removal utilizing SI/Cu and microbial coupling systems, three biofilters filled with corn cob (CC), corn cob + sponge iron (CS) and corn cob + sponge iron/copper (CSCu) were constructed. The results showed that the effluent NO3--N and PO43--P concentrations of CSCu remained consistently below 1 and 0.1 mg/L. The introduction of SI/Cu led to the enrichment of the Dechloromonas genus, making it the dominant microbial group, occupying 42.65% of the effective sequences. Modification of SI with Cu increased nitrogen cycle-related functional genes abundance in CSCu, with a 634% increase in nirS compared to CS. These findings proved that SI/Cu was a promising material, providing an approach to concomitantly removing nitrate and phosphate.

Performance and mechanism of sacrificed iron anode coupled with constructed wetlands (E-Fe) for simultaneous nitrogen and phosphorus removal

Three anodic biofilm electrode coupled CWs (BECWs) with graphite (E-C), aluminum (E-Al), and iron (E-Fe), respectively, and a control system (CK) were constructed to evaluate the removal performance of N and P in the secondary effluent of wastewater treatment plants (WWTPs) under different hydraulic retention time (HRT), electrified time (ET), and current density (CD). Microbial communities, and different P speciation, were analyzed to reveal the potential removal pathways and mechanism of N and P in BECWs. Results showed that the optimal average TN and TP removal rates of CK (34.10% and 55.66%), E-C (66.77% and 71.33%), E-Al (63.46% and 84.93%), and E-Fe (74.93% and 91.22%) were obtained under the optimum conditions (HRT 10 h, ET 4 h, CD 0.13 mA/cm²), which demonstrated that the biofilm electrode could significantly improve N and P removal. Microbial community analysis showed that E-Fe owned the highest abundance of chemotrophic Fe(II) (Dechloromonas) and hydrogen autotrophic denitrifying bacteria (Hydrogenophaga). N was mainly removed by hydrogen and iron autotrophic denitrification in E-Fe. Moreover, the highest TP removal rate of E-Fe was attributed to the iron ion formed on the anode, causing co-precipitation of Fe(II) or Fe(III) with PO₄^3--P. The Fe released from the anode acted as carriers for electron transport and accelerated the efficiency of biological and chemical reactions to enhance the simultaneous removal of N and P. Thus, BECWs provide a new perspective for the treatment of the secondary effluent from WWTPs.

Improving the removal efficiency of nitrogen and organics in vertical-flow constructed wetlands: the correlation of substrate, aeration and microbial activity

Four vertical-flow CWs (VFCWs) with different substrates and aeration conditions were studied on nutrient-removal capacity from synthetic wastewater. Zeolite substrate VFCWs (none-aerated: VFCW-1, aerated: VFCW-3) paralleled with ceramsite (none-aerated:VFCW-2, aerated: VFCW-4) were used to study the removal efficiencies of N and organics, the bacterial community, and the related functional genes. The results indicated that the pollutant removal efficiency was significantly enhanced by intermittent aeration. VFCW-4 (ceramsite with aeration) demonstrated a significant potential to remove NH₄⁺-N (89%), NO₃^--N (78%), TN (71%), and COD (65%). VFCW-3 and VFCW-4 had high abundances of Amx, amoA, and nirK genes, which was related to NH₄⁺-N and NO₂^--N removal. The microbial diversity and structure varied with aeration and substrate conditions. Proteobacteria, Actinobacteria, Candidatus, and Acidobacteria were the main bacteria phyla, with the average proportion of 38%, 21%, 19%, and 7% in the VFCWs. Intermittent aeration increased the abundance of Acidobacteria, which was conducive to the removal of organic matters. Overall, ceramsite substrate combined with intermittent aeration has a great potential in removing pollutants in VFCWs.

Simultaneous nitrification and denitrification in a PCL-supported constructed wetland with limited aeration

Considerable advances have been made in the substrate design and operation strategies of constructed wetlands to facilitate nitrogen elimination. However, few studies examined the complicated interaction between solid organic substrates and limited aeration on nitrogen removal. A vertical flow constructed wetlands in gradient distribution of inorganic and solid organic substrates (polycaprolactone/PCL) (P-VFCW) and a controlled vertical flow constructed wetland without PCL (C-VFCW) were developed for the tertiary treatment of municipal tailwater. Results indicated that ammonia was nearly converted to nitrate, while the total nitrogen removal efficiencies (TNREs) in C-VFCW were negligible. In P-VFCW, however, optimal TNREs approached 95% with an aeration rate of 0.06 mL·min^-1 and hydraulic retention time (HRT) of 24 h, and simultaneous nitrification and denitrification process (SND) in aerobic conditions was confirmed. As for the spatial microbial community structure evolution, Comamonas, which is associated with heterotrophic nitrification and anoxic/aerobic denitrification, was enriched along the vertical profiles of P-VFCW. Autotrophic nitrifier (Nitrospira), aerobic denitrifier (Bradyrhizobium and Azospira), and anoxic denitrifier (Ignavibacterium and Methyloversatilis) were dominated in different depths of P-VFCW, respectively. Besides, Canna indica biomass in P-VFCW was significantly larger than that in C-VFCW, which was attributed to the plant adaption response to diverse nitrogen. The P-VFCW in gradient distribution of inorganic and solid carbon sources under limited aeration is a promising technology for advanced nitrogen removal.

Direct measurements of dissolved N2 and N2O highlight the strong nitrogen (N) removal potential of riverine wetlands in a headwater stream

Increasing levels of nitrogen (N) in aquatic ecosystems due to intensified human activities is focusing attention on N removal mechanisms as a means to mitigate environmental damage. Important N removal processes such as denitrification can resolve this issue by converting N to gaseous emissions. Here, the spatiotemporal variability of N removal rates in China's Zhongtian River, a headwater stream that contains wetlands, was investigated by quantifying gaseous emissions of the main end products, N₂ and N₂O, using the water-air exchange model. Excess concentrations of these gases relative to their saturations in the water column generally varied within 1.4-8.7 μmol L^-1 and 8.7-20.3 nmol L^-1, with mean values of 4.5 μmol L^-1 and 13.7 nmol L^-1, respectively, demonstrating significant N removal in the river. The reach with wetlands was characterized by higher in-stream N₂ production than the non-wetland reach, especially in July, when aquatic vegetation is most abundant. High N₂O emissions during the same period in the non-wetland reach indicate that environmental conditions associated with vegetation are conducive to N₂ production and likely constrain N₂O emission. Changes in dissolved oxygen, pH, temperature, and carbon to nitrogen ratios are correlated with the observed spatiotemporal variabilities in gaseous N production. The mean N removal rate in the wetland reach was roughly twice that in the non-wetland reach, i.e., 22.4 vs. 10.3 mmol N m^-2 d^-1, while the corresponding efficiency was about five times as high, i.e., 15 % vs. 3 %. This study reveals the spatiotemporal patterns of in-stream N removal in a headwater stream and highlights the efficacy of wetlands in N removal. The data provide a strong rationale for constructing artificial wetlands as a means to mitigate N pollution and thereby optimize riverine environmental conditions.

The mechanism of C-N-S interconnection degradation in organic-rich sediments by Ca(NO3)2 - CaO2 synergistic remediation

The rebound of black-odorous occurred in organic-rich sediments has become a critical issue due to its great harm to the ecological environment. Elements such as S, C, and N play a crucial role in the biogeochemical cycle of black-odorous rivers. As electronic acceptors, Ca(NO₃)₂ and CaO₂ can effectively remove acidified volatile sulfide (AVS) and organic matter to control the black-odorous rebound. However, the remediation mechanisms in organic-rich sediments by Ca(NO₃)₂ and CaO₂ are unclear. The present study explored the mechanism of C-N-S interconnection degradation in organic-rich urban river sediments by adding different ratios and sequences of Ca(NO₃)₂ and CaO₂. The results showed that Ca(NO₃)₂ remediation followed by CaO₂ and the accepted electron ratio 1:1 of Ca(NO₃)₂ to CaO₂ is an effective method for controlling the rebound of black-odorous and reducing the accumulation NO₂^--N. Mainly attributed to that, CaO₂ enhanced the degradation of organic matter by stimulating enzymatic activities in the sediments, which is also the main reason for controlling the rebound of black-odorous. Since CaO₂ releases O₂ and •OH, which inhibit nosZgenes, NO₂^--N accumulates when remedied simultaneously with Ca(NO₃)₂ and CaO₂. Co-occurrence network analysis illustrated that sulfur-driven autotrophic denitrification bacteria, heterotrophic denitrifying bacteria, and sulfate-reducing bacteria interact strongly inside one module, clarifying a solid interaction of C-N-S substances among these bacteria. Our results reveal the C-N-S interconnection degradation mechanism and provide a new perspective on applying biochemical remediation in organic-rich urban river sediments.

Performance intensification of constructed wetland technology: a sustainable solution for treatment of high-strength industrial wastewater

The objectives of this study were to: (1) assess the intensification of chemical oxygen demand (COD) and phosphate (PO₄-P) removal; and (2) generate a set of rate constants of COD degradation (k_COD) and phosphate (k_PO4-P) removal for the treatment of industrial wastewater (WW) using intensified adsorption beds. Two horizontal subsurface flow constructed wetlands (HSSFCWs) filled with coal ash and alum sludge and two conventional HSSFCWs packed with gravels were operated with different loadings of COD and PO₄-P at a hydraulic retention time (HRT) of 24 hrs at water depth of 0.40 m. The bed performance was analysed for COD and PO₄-P removal efficiency. The intensified HSSFCWs outperformed the control beds by a mean COD and PO₄-P removal efficiency of 43 and 49%, respectively. The progression of COD and PO₄-P removal along the system was fitted into the first-order plug flow model (K-C model). In this study the k_COD values ranged from 0.36 to 0.65 m/d with a mean of 0.46 ± 0.08 m/d (n = 30). The k_PO4-P values ranged from 0.74 to 1.76 m/d and averaged to 1.23 ± 0.37 m/d (n = 30), irrespective of the condition applied. Hence, these data can be used for future projects using HSSFCWs to treat industrial wastewater.

Treatment try of simulated agricultural surface runoff pollution by using a novel biomass concentrator reactor

Increased agricultural surface runoff in rural watersheds is a leading cause of nonpoint source pollution. In this study, a new biomass concentrator reactor (BCR) is conducted to degrade simulated agricultural surface runoff for both start-up process and treatment process. The results show that both in the start-up phase and in the stable phase, BCR had a good degradation effect on simulated agricultural surface runoff. Within 13 days-15 days of completed start-up of BCR, degradation of COD can be considered to the first-order kinetics: lnC_t=lnC₀-0.1377t (R² = 0.78). During the stabilization phase, the average removal rate of COD, NH₄⁺-N, NO₃^--N, TN and TP from the effluents through the BCR membrane was 94.58%, 85.79%, 53.58%, 37.87%, and 60.62%, respectively, which was increased by 7.4%, 2.5%, 5.1%, 0.18% and 11.4%, respectively, compared to control experiment which the effluents without membrane. The pollutants degradation by BCR in stable phase show a partly relative model of Lawrence-McCarty equation, which the nitrogen and phosphorus degradation is v_N=(4.1+S)/(2.53×S) (R² = 0.69) and v_P=(8.78+S)/(3.0×S) (R² = 0.67), respectively. In the stable phase, the operation cost of BCR is about $0.08/(L•d). Future research on improved BCR maybe focus on the membrane pollution and cleaning, optimized operation conditions, new materials of membrane.

Constructed wetland substrates: A review on development, function mechanisms, and application in contaminants removal

Constructed wetlands (CWs) are economical, efficient, and sustainable wastewater treatment method. Substrates in CWs inextricably link with the other key components and significantly influence the performance and sustainability of CWs. Gradually, CWs have been applied to treat more complex contaminants from different fields, thus has brought forward new demand on substrates for enhancing the performance and sustainability of CWs. Various materials have been used as substrates in CWs, and their individual characteristics and application advantages have been extensively studied in recent years. Therefore, this review summarizes the development, function mechanisms (e.g., filtration, adsorption, electron supply, supporting plant growth and microbial reproduction), categories, and applications of substrates in CWs. The interaction mechanisms of substrates with contaminants/plants/microorganisms are comprehensively described, and the characteristics and advantages of different substrate categories (e.g., Natural mineral materials, chemical products, biomass materials, industrial and municipal by-products, modified functional materials, and novel materials) are critically evaluated. Meanwhile, the influences of substrate layer arrangement and synergism on contaminants removal are firstly systematically reviewed. Furthermore, further research about substrates (e.g., clogging, life cycle assessment/management, internal relationship between components) should be systematically carried out for improving efficiency and sustainability of CWs.

Stability and nutrients removal performance of a Phanerochaete chrysosporium-based aerobic granular sludge process by step-feeding and multi A/O conditions

A Phanerochaete chrysosporium-based aerobic granular sludge (PC-AGS) was developed by inoculating fungal mycelial pellets into a lab-scale aerobic granular sequencing batch reactor (AGSBR). A strategy using step-anaerobic feeding coupled with multi A/O conditions was adopted. The results showed that the removal efficiencies for total phosphorus (TP) and total inorganic nitrogen (TIN) were 94.56 ± 2.92% and 75.20 ± 7.74%, respectively, under relatively low aeration time. Compared with original AGS, the content of extracellular proteins for PC-AGS obviously increased from 18.61 to 41.44 mg/g MLSS by the end of phase I. Moreover, the mature granules had a larger size and better stability during the 100 days operation. Furthermore, the analysis of microbial diversity detected many key functional groups in PC-AGS granules that were beneficial to nutrients removal. This work demonstrated that the addition of fungal pellets not only enhanced the removal performance, but also improved the stability of the AGS system.

Enhanced Denitrification of Integrated Sewage Treatment System by Supplementing Denitrifying Carbon Source

Integrated sewage treatment system (ISTY) is a new technology for rural domestic sewage treatment. In the ISTY, the carbon source in the denitrification stage is often insufficient, affecting the denitrification efficiency. In order to improve the denitrification efficiency, several commonly available agricultural wastes, peanut shell (PS), sawdust (SD), peat (PT), and their mixtures (MT), were selected as supplementary carbon sources in the denitrification stage of ISTY to study the denitrification efficiency. Results show that PS exhibited a high carbon release capacity. PS released an enormous amount of carbon in 144 h, and the cumulative total organic carbon was 41.99 ± 0.7 mg/(g·L). The optimum carbon source dosage was 3 g/L, the nitrate removal rates of PS exceeded 95% after 48 h, and the denitrification rates were 9.35 mg/(g·L), which were 63.92% higher than that of the control group. After running the ISTY for 120 h, and with PS as supplementary carbon sources, the removal rate of TN increased from 29.76% to 83.86%. At the genus level, the dominant denitrifying bacteria in ISTY, after adding PS, were Pseudomonas and Cupriavidus, accounting for 78.68%, an increase of 72.90% compared with the control group. This evidence suggested that PS can obviously enhance the denitrification efficiency of the ISTY as a supplementary carbon source.

Pilot-scale two-stage constructed wetlands based on novel solid carbon for rural wastewater treatment in southern China: Enhanced nitrogen removal and mechanism

Constructed wetlands (CWs) have been proved to be an alternative to the treatment of various wastewater. However, there are few studies focused on the removal performance and mechanisms of pollutants in pilot-scale CWs packed with novel solid carbon. In this study, we investigated the effect of poly-3-hydroxybutyrate-co-3-hydroxyvalerate/polyacetic acid (PHBV/PLA) blends as carbon source on pollutant's transformation, microbial communities and functional genes in pilot-scale aeration-anoxic two-stage CWs for polishing rural runoff in southern China. Results showed a striking improvement of TN removal in CWs with PHBV/PLA blends (64.5%) compared to that in CWs with ceramsite (52.9%). NH₄⁺-N (61.3-64.6%), COD (40.4-53.8%) and TP (43.6-47.1%) were also removed effectively in both two CWs. In addition, the strains of Rhodocyclaceae and Bacteroidetes were the primary denitrifiers on the surface of PHBV/PLA blends. Further, the aerobic stage induced gathering of 16 S and amoA genes and the anoxic zone with PHBV/PLA blends increased the nirS genes, which fundamentally explained the better denitrification performance in CW based on PHBV/PLA blends. Consequently, this study will provide straightforward guidance for the operation of engineering CWs packed with polymers to govern the low-C/N rural wastewater.

Insights into heterotrophic denitrification diversity in wastewater treatment systems: Progress and future prospects based on different carbon sources

Nitrate, as the most stable form of nitrogen pollution, widely exists in aquatic environment, which has great potential threat to ecological environment and human health. Heterotrophic denitrification, as the most economical and effective method to treat nitrate wastewater, has been widely and deeply studied. From the perspective of heterotrophic denitrification, this review discusses nitrate removal in the aquatic environment, and the behaviors of different carbon source types were classified and summarized to explain the cyclical evolution of carbon and nitrogen in global biochemical processes. In addition, the denitrification process, electron transfer as well as denitrifying and hydrolyzing microorganisms among different carbon sources were analyzed and compared, and the commonness and characteristics of the denitrification process with various carbon sources were revealed. This study provides theoretical support and technical guidance for further improvement of denitrification technologies.

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.

The use of pumice amended with sand media for domestic wastewater treatment in vertical flow constructed wetlands planted with lemongrass (Cymbopogon citratus)

The performance efficiency in constructed wetlands (CWs) technology is primarily affected by the media material and the types of plants used. Recently, investigations into the usage of local materials and plants in CWs has increased. Pumice is a material which is potential used as a media. However, research on amendment of pumice with other media in CWs is still limited. Therefore, this study aims to evaluate the potential of pumice amended with sand media and planted with lemongrass (Cymbopogon citratus) in CWs to remove organic matter, suspended solids, nutrients, and coliform. The adsorbents were characterized using X-ray diffraction, FTIR and XRF followed by adsorption experiments for PO₄-P. Furthermore, Six vertical flow (VF) mesocosms with a diameter of 10.2cm and 55cm depth were established over six months. The treatments were based on percentage of sand media amended with pumice and planted with lemongrass. Furthermore, the barren media were applied to investigate the effect of lemongrass. The loading rate of domestic wastewater into the VF mesocosms was 2 L/day while inflows and outflows were determined for nutrients, organic matter, suspended solids and coliform. The adsorption of PO₄-P followed the Langmuir model with adsorption capacity was 0.089 and 0.067 mol/g for pumice and sand, respectively. The results also showed that the removal efficiency of TSS, COD, NO₃-N, NO₂-N, PO₄-P and total coliforms were in the range of 93.7-97.3 %, 52-83 %, 63-86 %, 51-74%, 81-88 % and 92-97 %, respectively. Based on the results, the highest removal efficiency was observed in the sand media amended with 50 % pumice and planted with lemongrass, while the lowest was found in the barren sand media.

Characterization of dissolved organic matter and carbon release from wetland plants for enhanced nitrogen removal in constructed wetlands for low C-N wastewater treatment

The effects of pretreatment methods on the structure of functional groups and denitrification promotion capacity of solid carbon sources derived from reeds and cattails were elucidated. Alkaline treatment improved the relative content of carbon in the plant tissues, as well as prolonged the high denitrification rate of 0.40 mg/(L·h) from 6 days up to circa 28 days. Moreover, alkaline-heated cattails (ALH-C) showed high denitrification promotion capacity, and increased the removal rate of TN, NO₃^--N and NH₄⁺-N in the CW by 24.41%, 31.80% and 8.80%, respectively. Furthermore, the quantity, quality and migration of dissolved organic matter (DOM) released from ALH-C in CW analyzed via fluorescence excitation-emission matrix spectrophotometry showed mainly humic acid-like, tyrosine-like, and tryptophan-like components. These DOM components were highly bioavailable and had minimal effects on COD removal. These results provide insights into the preparation and environmental applications of plant carbon sources.

The Use of Constructed Wetland for Mitigating Nitrogen and Phosphorus from Agricultural Runoff: A Review

The loss of nitrogen and phosphate fertilizers in agricultural runoff is a global environmental problem, attracting worldwide attention. In the last decades, the constructed wetland has been increasingly used for mitigating the loss of nitrogen and phosphate from agricultural runoff, while the substrate, plants, and wetland structure design remain far from clearly understood. In this paper, the optimum substrates and plant species were identified by reviewing their treatment capacity from the related studies. Specifically, the top three suitable substrates are gravel, zeolite, and slag. In terms of the plant species, emergent plants are the most widely used in the constructed wetlands. Eleocharis dulcis, Typha orientalis, and Scirpus validus are the top three optimum emergent plant species. Submerged plants (Hydrilla verticillata, Ceratophyllum demersum, and Vallisneria natans), free-floating plants (Eichhornia crassipes and Lemna minor), and floating-leaved plants (Nymphaea tetragona and Trapa bispinosa) are also promoted. Moreover, the site selection methods for constructed wetland were put forward. Because the existing research results have not reached an agreement on the controversial issue, more studies are still needed to draw a clear conclusion of effective structure design of constructed wetlands. This review has provided some recommendations for substrate, plant species, and site selections for the constructed wetlands to reduce nutrients from agricultural runoff.

Changes in the nitrification-denitrification capacity of pilot-scale partially saturated vertical flow wetlands (with corncob in the free-drainage zone) after two years of operation

This six-month study aimed to evaluate the removal of total nitrogen (TN) in two duplicated partially saturated (PS) vertical flow (VF) wetlands added with corncob in two different heights of the free-drainage zone (FDZ) after two years in operation. Both PS VF wetlands efficiently removed organic matter measured as biochemical oxygen demand (BOD₅) and chemical oxygen demand (COD) as well as total suspended solids (TSS) achieving average mass removal efficiencies of 95.3%, 83.2% and 92.9%, respectively, in system I (SI) and 96.3%, 84.0% and 94.9%, respectively, in system II (SII); with no significant differences (p > 0.05) between the systems. Measurements of oxidation-reduction potential (ORP), dissolved oxygen (DO), pH and electrical conductivity (EC) showed suitable conditions in the saturated zone (SZ) of the systems for denitrification process. TN removal was similar in both systems (p > 0.05) (51.5% and 52.9% in SI and SII), and decreased in 15% with respect to the first year. This decrease was due to the lower denitrification capacity of the FDZ as a result of the reduction in the supply of biodegradable carbon by corncob. Denitrification occurred in the SZ, but not at a sufficient level to increase TN removal. NoveltyFirst, the use of lignocellulosic residues in partially saturated vertical wetlands to promote total nitrogen removal is very recent. Furthermore, to the best of our knowledge, this is the first study evaluating TN removal after two years of operation in this type of wetland. Therefore, this study allows us to better understand the function of these systems, in a relatively long term. Thanks to this study: it is possible to confirm that the main process of TN elimination is through the simultaneous nitrification-denitrification process in the free drainage zone (denitrification in the saturated zone is irrelevant) and that TN elimination decreases due to the reduction in carbon supply from the corn, in this area.

Enhanced nitrogen removal by simultaneous nitrification-denitrification and further denitrification (SND-DN) in a moving bed and constructed wetland (MBCW) integrated bioreactor

With the main objective of improving the removal of nitrogen from domestic wastewater and more sustainably, a moving bed and constructed wetland (MBCW) integrated bioreactor was fabricated and evaluated with continuous and intermittent aeration operations. The hybrid system achieves average removal efficiencies up to 90.4 ± 0.8% of chemical oxygen demand (COD), 91.8 ± 1.2% of ammonia nitrogen (NH₄⁺-N), and 77.0 ± 2.6% of total nitrogen (TN), respectively, through a simultaneous nitrification-denitrification and further denitrification (SND-DN) process. This occurs through an intermittent aeration operation followed by continuous aeration with a dissolved oxygen (DO) of 4.0 mg L^-1 due to the complementary and coordinated action of mixed biocarriers. It has resulted in the improvement of the efficiency of SND from 5.9 to 35.3% and in the removal via wetland for DN, between 2.42 and 2.45 g m^-2·d^-1, respectively. The analysis of extracellular polymeric substances (EPS) and high-throughput sequencing demonstrated the enhanced SND mechanism and the evolution of microbial species within the biofilm structure. The total relative abundance of nitrifying bacteria, more aggregated outside the biofilm, decreased by 7.66% compared to denitrifying bacteria, mostly accumulated inside, which increased by 5.49%, respectively.

High-rate nitrogen removal from carbon limited wastewater using sulfur-based constructed wetland: Impact of sulfur sources

This study aims to explore the application of sulfur-based constructed wetlands (CWs) for effective nitrogen (N) removal from wastewater. Two solid sulfur sources namely elemental sulfur (S⁰) and pyrite (FeS₂) were used as substrates in two CWs, i.e. S-CW and P-CW, respectively. The CWs were vegetated with a common wetland plant Iris pseudacorus, and were operated to investigate the effects of hydraulic retention time (HRT) and temperature on N removal. The use of S⁰ resulted in the highest denitrification rate (19.0 ± 7.5 g m^-2 d^-1), whereas up to 20 times slower total inorganic nitrogen (TIN) removal was observed with FeS₂. Different sulfur sources had negligible effects on the growth of I. pseudacorus, but the element contents (e.g., N, S, and P) within the plant tissues were different. Iris roots in S-CW had higher S content compared with those in P-CW, which resulted in the difference in shoots colors. The characteristics of rhizospheric microbial communities were closely related to the sulfur and nitrogen sources. Briefly, denitrifying and sulfur-oxidizing genera (e.g., Denitratisoma, Sulfurimonas, Thiobacillus) were dominating in the S-CW, suggesting the occurrence of both autotrophic and heterotrophic denitrification processes in the wetland. On the other hand, nitrifying bacteria were more abundant (e.g. Nitrospira, Piscinibacter) in the P-CW. S⁰ layer and rhizosphere accounted for 99.3% of nitrogen removal and the former part most likely played important roles with a decrease in HRT. Low temperature strongly affected the rate and efficiency of denitrification but recovered to 49.2 ± 25.8% when added with 30 mg L^-1 sodium acetate. This study broadens the applications of sulfur-based CWs and provides a promising management strategy for denitrification at low temperatures.

Design, Operation and Optimization of Constructed Wetland for Removal of Pollutant

Constructed wetlands (CWs) are affordable and reliable green technologies for the treatment of various types of wastewater. Compared to conventional treatment systems, CWs offer an environmentally friendly approach, are low cost, have fewer operational and maintenance requirements, and have a high potential for being applied in developing countries, particularly in small rural communities. However, the sustainable management and successful application of these systems remain a challenge. Therefore, after briefly providing basic information on wetlands and summarizing the classification and use of current CWs, this study aims to provide and inspire sustainable solutions for the performance and application of CWs by giving a comprehensive review of CWs' application and the recent development of their sustainable design, operation, and optimization for wastewater treatment. To accomplish this objective, thee design and management parameters of CWs, including macrophyte species, media types, water level, hydraulic retention time (HRT), and hydraulic loading rate (HLR), are discussed. Besides these, future research on improving the stability and sustainability of CWs are highlighted. This article provides a tool for researchers and decision-makers for using CWs to treat wastewater in a particular area. This paper presents an aid for informed analysis, decision-making, and communication. The review indicates that major advances in the design, operation, and optimization of CWs have greatly increased contaminant removal efficiencies, and the sustainable application of this treatment system has also been improved.

Comparison of agricultural wastes and synthetic macromolecules as solid carbon source in treating low carbon nitrogen wastewater

This paper investigated the feasibility of using agricultural wastes and synthetic macromolecules as solid carbon sources and studied the effects of improvement of denitrification by the selected agricultural wastes. The carbon release capacity and denitrification performance of corncob (CC), peanut shell (PS), obsolescent rice (OR) and polycaprolactone (PCL), poly butylene succinate (PBS), polyvinyl alcohol sodium alginate (PVA-SA) were systematically analyzed. The results showed that for each carbon source, the first-order kinetic equation was basically followed during the carbon release process. PVA-SA, CC and PS had higher carbon release capacity with accumulative dissolved organic carbon (DOC) of 16.22-20.63 mg·g^-1 and chemical oxygen demand (COD) of 100.86-134.10 mg·g^-1. Correspondingly, they showed excellent denitrification performance with almost no residual NO₃^--N, and the denitrification process well followed the Monod equation. PCL, PBS and OR had lower carbon release capacity with accumulative DOC of 2.06-3.14 mg·g^-1 and COD of 13.29-24.13 mg·g^-1, respectively. Nevertheless, these materials can also improve the denitrification performance, with the residual NO₃^--N in the range of 6.02-6.36 mg·L^-1, and the effluent DOC was in the range of 10-15 mg·L^-1. Synthetic polymers are more suitable for nitrogen removal in groundwater treatment, while agricultural wastes are ideal carbon sources for secondary effluent treatment.

Microbial coupling mechanisms of nitrogen removal in constructed wetlands: A review

Nitrogen removal through microorganisms is the most important pathway in constructed wetlands (CWs). In this review, we summarize the microbial coupling mechanisms of nitrogen removal, which are the common methods of nitrogen transformation. The electron pathways are shortened and consumption of oxygen and energy is reduced during the coupling of nitrogen transformation functional microorganisms. The highly efficient nitrogen removal mechanisms are cultivated from the design conditions in CWs, such as intermittent aeration and tidal flow. The coupling of microorganisms and substrates enhances nitrogen removal mainly by supplying electrons, and plants affect nitrogen transformation functional microorganisms by the release of oxygen and exudates from root systems as well as providing carriers for microbial attachment. In addition, inorganic elements such as Fe, S and H act as electron donors to drive the autotrophic denitrification process in CWs.

Enhanced nitrogen removal in filled-and-drained vertical flow constructed wetlands: microbial responses to aeration mode and carbon source

For the purpose of enhancing the removal rate of nitrogen (N) and organic matters, intermittent aeration and carbon source were used in filled-and-drained vertical flow constructed wetlands (VFCWs). The results showed that the best removal of COD (74.16%), NH₄⁺-N (93.56%), TN (86.88%), and NO₃^--N (79.65%) was achieved in VFCW1 (aerated with carbon source system). Illumina MiSeq300 high-throughput sequencing showed that carbon source aerated system increases the diversity and richness of the microbial community. The copy numbers of nitrification functional genes (nxrA, amoA), denitrification functional genes (nirS, nirK, nosZ), and anammox functional gene (anammox 16S rRNA) displayed various changes when applied different aeration modes and additional carbon source to each system. An increase of the DO concentration and carbon source facilitated the absolute abundance of microbial nitrification and denitrification functional genes, respectively. All in all, these results demonstrate that carbon source combined with intermittent aeration is valid to improve the pollutant treatment performance in these systems.

Advanced treatment of effluent from municipal wastewater treatment plant by strengthened ecological floating bed

The performance of eological floating bed (EFB) with novel carbon source (CS) and reed biochar substrate (RBS) derived from reed straw (RS) was evaluated for the advanced treatment of effluent from wastewater treatment plants (WWTPs). The average carbon releasing capacity of CS was 4.50 mg/g, and the P adsorption capacity of RBS was 0.39 mg/g. The additional CS and RBS increased the average removal efficiencies of total nitrogen (TN) and total phosphorus (TP) by 57.6% and 46.7%, respectively. Furthermore, the high-throughput sequencing results revealed significantly different microbial species richness and diversity due to the CS and RBS. Some genera related to nitrogen removal, such as Pseudomonas, Rhodobacter, Hydrogenophaga, Bradyrhizobium, Acinetobacter and Thiobacillus, were enriched in the EFB with CS and RBS. This study provided a suitable method for effectively treating low C/N wastewater such as WWTPs effluent using EFB strengthened by processed wetland plant.

Simulation and engineering demonstration of the advanced treatment of rainy overflow wastewater using a combined system of storage tank-wastewater treatment plant-wetland

We propose a new technology to advanced treat overflow wastewater from a combined sewer system using a storage tank-wastewater treatment plant (STP)-constructed wetland (CW) system. The engineering demonstration (a 7,500 m³ storage tank and a 3,436 m² CW) has been built to treat the combined sewer overflows (CSOs) at the largest combined rainwater/wastewater overflow outlet in the middle reaches of the Xinbaoxiang River, which is the second largest river in the Dianchi Lake Basin. During the rainfall period, CSOs enter the storage tank. After sedimentation purification, the higher concentration CSOs at the bottom enter the STP, and the upper low-concentration CSOs enter CWs, thereby linking the multiple means of treating CSOs and minimizing the impact of CSOs on the STP. During the dry season, CWs can also assist in purification of polluted river water. The supernatant (COD <80 mg/L) and the bottom part water (COD >200 mg/L) of the storage tank were sent to CWs and STP, respectively, for treatment. The project was stably operated over 6 months. The final effluent qualities were 12, 1.79, and 0.18 mg/L for COD, TN, and TP, respectively, which achieved the surface water class V standard. PRACTITIONER POINTS: A combined system of storage tank-wastewater treatment plant-wetland was proposed to advanced treat overflow wastewater of rainy season. The SWMM could calculate the water quality and volume of overflow under different rainfall conditions in the runoff area. The effluent of the engineering demonstration reached the standard of surface water class V.

Seasonal habitat drives intestinal microbiome composition in anadromous Arctic char (Salvelinus alpinus)

Intestinal microbial communities from 362 anadromous Arctic char (Salvelinus alpinus) from the high Arctic Kitikmeot region, Nunavut, Canada, were characterized using high-throughput 16S rRNA gene sequencing. The resulting bacterial communities were compared across four seasonal habitats that correspond to different stages of annual migration. Arctic char intestinal communities differed by sampling site, salinity and stages of freshwater residence. Although microbiota from fish sampled in brackish water were broadly consistent with taxa seen in other anadromous salmonids, they were enriched with putative psychrophiles, including the nonluminous gut symbiont Photobacterium iliopiscarium that was detected in >90% of intestinal samples from these waters. Microbiota from freshwater-associated fish were less consistent with results reported for other salmonids, and highly variable, possibly reflecting winter fasting behaviour of these char. We identified microbiota links to age for those fish sampled during the autumn upriver migration, but little impact of the intestinal content and water microbiota on the intestinal community. The strongest driver of intestinal community composition was seasonal habitat, and this finding combined with identification of psychrophiles suggested that water temperature and migratory behaviour are key to understanding the relationship between Arctic char and their symbionts.

Intensified simultaneous nitrification and denitrification performance in integrated packed bed bioreactors using PHBV with different dosing methods

To explore an effective approach of simultaneous nitrification and denitrification in wastewater with low C/N ratios, integrated packed bed bioreactors based on poly(3-hydroxybutyrate-hydroxyvalerate) (PHBV) with different dosing methods were designed. The removal efficiency of NH₄⁺-N in bioreactor with aeration was 88.62%, and higher NO₃^--N removal efficiency was observed in bioreactor filled with grainy PHBV (95.21%) than bioreactor filled with strip PHBV (93.34%). Microbial study indicated that microbes harboring amoA and nirS genes preferred to attach on the surface of ceramsite, and significant differences in microbial community compositions at phylum and genus levels were observed. To summarize, it is feasible to utilize grainy PHBV for simultaneous and efficient removal of NH₄⁺-N and NO₃^--N from wastewater with low C/N ratios.

Microporous intermittent aeration vertical flow constructed wetlands for eutrophic water improvement

To enhance eutrophic water improvement effect, three parallel lab-scale oxidation pond-vertical subsurface flow constructed wetland-stable pond combined systems with different microporous intermittent aeration positions were constructed. The purification effect of each system was determined, and the contribution rate of each part of the system was also calculated. The characters of bacterial community under different aeration positions were also analyzed. Microporous intermittent aeration rate of 5 mg/L was chosen as the aeration rate for follow-up experiment. The result showed that the best COD_Cr, total nitrogen, and total phosphorus removal efficiencies were achieved by the combined system with bottom microporous intermittent aeration, and the efficiencies were 71.04%, 79.52%, and 95.10%, respectively. The best ammonium nitrogen removal efficiency was 92.62% and was achieved by the combined system with surface microporous intermittent aeration. After analyses, 14 strains of bacteria associated with the removal of N elements were found and 8 strains of bacteria associated with P element cycle were found.

Sludge alkaline fermentation enhanced anaerobic- multistage anaerobic/oxic (A-MAO) process to treat low C/N municipal wastewater: Nutrients removal and microbial metabolic characteristics

This study aimed to present a strategy that utilizing semi-continuous flow primary sludge fermentation liquor as carbon source for anaerobic- multistage anaerobic/oxic (A-MAO) process to treat low chemical oxygen demand (COD) and total nitrogen (TN) (C/N) ratio municipal wastewater. The results showed that adding fermentation liquor resulted in average TN and total phosphorus (TP) concentration in effluent decreased from 33 and 2.80 mg L^-1 to 9.2 and 0.23 mg L^-1, respectively, which met wastewater discharge standard. High-throughput sequencing results indicated that bacterial richness increased and diversity decreased with fermentation liquor adding, and the dominant genera varied from Methylophilaceae and Methylotenera to unclassified_f_Rhodocyclaceae, noran k_f__env.OPS_17, and Azospira. Meanwhile, the abundance of metabolism and organismal systems in A-MAO process rose from 48.42% and 0.74% to 49.52% and 0.78%. The improvement of nitrogen and phosphorus removal with fermentation adding was based on the increment of enzyme coding genes in nitrogen and phosphorus pathway.

Enhanced optimal removal of nitrogen and organics from intermittently aerated vertical flow constructed wetlands: Relative COD/N ratios and microbial responses

Carbon source and dissolved oxygen are the critical factors which sustain the stable redox environment for the microbes to implement the removal of nitrogen and organics in vertical flow constructed wetlands (VFCWs). The effect mechanisms of the COD/N ratios in intermittently aerated VFCWs are needed to be investigated in order to increase the synchronous removal efficiency of pollutants. In this study, the combined effects of COD/N ratios (3, 6, 12) and intermittent aeration in VFCWs on pollutant removal, microbial communities and related function genes were studied. The results showed the increase of COD/N ratios from 3 to 12 enhanced the removal efficiency of TN, NO₃^--N and COD. The removals of NH₄⁺-N decreased as the COD/N ratio increased. The optimal removals of TN (87.65%), NH₄⁺-N (93.20%), NO₃^--N (80.80%) and COD (73.93%) were obtained in VFCW2 (COD/N ratios was 6). Illumina Miseq High-throughput sequencing analysis showed that high COD/N ratios increased the richness and diversity of microbial communities. The absolute abundance of nirK, nosZ, nirS, amoA, nxrA, and anammox bacterial 16S rRNA presented various changes under the different ratios of COD/N. The increase of COD/N ratios enhanced the copy numbers of nirS, nirK and nosZ, which participate in denitrification process. High COD/N ratios (6 and 12) were in favor of Actinobacteria, Firmicutes and Chloroflexi, which mainly play important roles in the process of denitrification. This paper implies that the combination of carbon source and aeration is necessary to sustain high microbial activities during pollutant removal in VFCWs.

Startup and stable operation of advanced continuous flow reactor and the changes of microbial communities in aerobic granular sludge

In this study, the granular sludge was operated under low aeration condition in sequencing batch reactor (SBR) and advanced continuous flow reactor (ACFR), respectively. Through increasing the sludge retention time (SRT) from 22 days to 33 days, the ACFR was successful startup in 30 days and achieved long term stable operation. Under SBR operation condition, the aerobic granular sludge (AGS) showed good nitrogen (60%), phosphorus (96%) and COD removal performance. During stable operation of continuous-flow, the nitrogen removal efficiency was increasing to 70%, however, the phosphorus removal efficiency could only be restored to 65%. Meanwhile, the sludge discharge volume from ACFR was about half of that in SBR. Results of high-throughput pyrosequencing illustrated that methanogenic archaea (MA), ammonia oxidizing archaea (AOA), denitrifying bacteria (DNB), denitrifying polyphosphate-accumulating organisms (DPAOs) played an important role in the removal of nutrients in ACFR. This study could have positive effect on the practical application of AGS continuous flow process for simultaneous biological nutrient removal (SBNR).

In-situ remediation of sediment by calcium nitrate combined with composite microorganisms under low-DO regulation

In this work, in-situ remediation of sediment was carried out by combining various methods. The results showed that the treatment effect of Calcium nitrate + composite functional microorganisms + Low-DO (dissolved oxygen) aeration (CN/CFM/LDA) was the best, in which 2.5 g calcium nitrate, 1 g functional bacteria and intermittent aeration (0.1 m³/h, 3 h per day) were utilized for the remediation of 500 g sediments within 40-day experimental period. The DO and oxidation reduction potential (ORP) in overlying water have been improved from 3.23 mg/L to 4.4 mg/L and 25.8 mV to 112.4 mV, respectively. The release fluxes of ammonia nitrogen (NH₄⁺-N), nitrite nitrogen (NO₂^--N) and nitrate nitrogen (NO₃^--N) were respectively reduced by 30.51%, 13.11% and 77.45% compared with the control and the removal rate of the acid volatile sulfide (AVS) in sediments was 94.14% compared with the original sample. The results of high-throughput sequencing show that the dominant bacterial community in CN/CFM/LDA was transformed into Proteobacteria (relative abundance of 74.17%) at the phylum level and Thiobacillus (relative abundance of 38.52%) at the genus level. The results of 16S functional prediction indicated that the remediation method can enhance the numbers of microbial key enzymes (92360) in the nitrification and denitrification process, where Low-DO aeration can mediate the growth of denitrifying bacteria and promote the performance of key enzymes. In conclusion, the experimental results show that the use of calcium nitrate and composite functional microorganisms under low-DO regulation has a promising remediation effect on sediments of black-malodorous water.

Zero valent iron supported biological denitrification for farmland drainage treatments with low organic carbon: Performance and potential mechanisms

In this work, the feasibility and performance of zero valent iron (ZVI) coupled anaerobic microorganisms in nitrogen removal under low organic carbon condition were investigated, through the comparison of mono-ZVI system and mono-cell system. Coupled system showed the highest total nitrogen (TN) removal efficiency of 67.85% with the addition of 15 g L^-1 iron shavings at pH 7.0, which was higher than 29.62% in the mono-ZVI system and 43.86% in the mono-cell system. Besides, the activities of nitrate reductase (NAR), nitrite reductase (NIR), nitric oxide reductase (NOR) and nitrous oxide reductase (N₂OR) were significantly improved at ZVI dosage of 15 g L^-1 and pH 7.0, which contributed to the higher TN removal efficiency in coupled system. The extent of sludge granulation was greater in the coupled system than mono-cell system, which benefited to the high operational performance and stability of coupled system. The promoted generation of extracellular polymeric substances (EPS) and formation of iron oxides in the coupled system also took advantages on nitrogen removal through adsorption. In addition, ZVI could largely enrich the functional species related to nitrogen removal in the system at phyla and genera level, which could be reasoned for the enhanced nitrogen removal efficiency. In conclusion, this study will improve the understandings of nitrogen removal in the coupled system and be useful to ensure the application of ZVI-supported biological process in the remediation of farmland drainage.

Emerging pollutants-Part II: Treatment

Recently, emerging pollutants (EPs) have been frequently detected in urban wastewater, surface water, drinking water, and other water bodies. EPs mainly usually include pharmaceuticals and personal care products, endocrine-disrupting chemicals, antibiotic resistance genes, persistent organic pollutants, disinfection by-products, and other industrial chemicals. The potential threat of EPs to ecosystems and human health has attracted worldwide attention. Therefore, how to treat EPs in various water bodies has become one of the research priorities. In this paper, some research results on treatment of EPs published in 2018 were summarized. PRACTITIONER POINTS: At present, more attention has been paid to emerging pollutants (EPs), including pharmaceuticals and personal care products (PPCPs), endocrine-disrupting chemicals (EDCs), antibiotic resistance genes, persistent organic pollutants, disinfection by-products, etc. Existing EPs disposal technologies mainly include: engineered wetlands and natural systems, biological treatment, physical and physicochemical separation, chemical oxidation, catalysis, etc. This paper reviews some research results on the treatment technologies of EPs published in 2018.

Effect of temperature on tertiary nitrogen removal from municipal wastewater in a PHBV/PLA-supported denitrification system

In this study, a poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/poly(lactic acid) (PHBV/PLA)-supported denitrification system was built to remove nitrogen from municipal wastewater treatment plant secondary effluent, and the influence of operating temperature on nitrogen removal was further investigated. Results indicated that a PHBV/PLA-supported denitrification system could effectively fulfill the tertiary nitrogen removal. The nitrogen removal efficiency gradually declined with the operating temperature decreasing, and the denitrification rate at 30 °C was 5 times higher than that at 10 °C. Meanwhile, it was found that a slight TOC accumulation only occurred at 30 °C (with an average of 2.03 mg/L) and was avoided at 10~20 °C. The reason for effluent TOC variation was further explained through the consumption and generation pathways of TOC in this system. Furthermore, the temperature coefficient was about 0.02919, indicating that the PHBV/PLA-supported denitrification system was a little sensitive to temperature. A better knowledge of the effect of operating temperature will be significant for the practical application of the solid-phase denitrification system.

Simultaneous removal of nitrogen and pharmaceutical and personal care products from the effluent of waste water treatment plants using aerated solid-phase denitrification system

Nowadays, waste water treatment plants (WWTPs) are regarded as the pollution sources of nitrogen and pharmaceutical and personal care products (PPCPs). In the present study, the simultaneous removal of nitrogen and typical PPCPs, ibuprofen and triclosan, was evaluated in a poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV) based solid-phase denitrification (SPD) system. Results after 602 days showed that simultaneous nitrification and denitrification (SND) process occurred with average 83.85 ± 13.09% NH₄⁺-N and 93.88 ± 10.19% NO₃^--N removals in the SPD system. Interestingly, the system achieved average 79.69 ± 6.35% and 65.96 ± 7.62% removals of ibuprofen and triclosan, respectively, under stable influent conditions of 50 μg L^-1. Cometabolic activities of heterotrophic denitrifying bacteria and ammonia oxidizing bacteria (AOB) probably played a role in the biodegradation of the two PPCPs. Illumina MiSeq sequencing results revealed that microbial composition enhanced the simultaneous removal of nitrogen and PPCPs in the SPD system.

Nutrients removal performance and sludge properties using anaerobic fermentation slurry from food waste as an external carbon source for wastewater treatment

Enhancement of nitrogen and phosphate removal using thermophilic fermentation slurry from food waste (FSFW) as external carbon source was investigated. Based on the batch tests, the soluble and particulate fractions of the FSFW acted as easily and slowly biodegradable carbon sources, respectively, and the fermented slurry showed the combined nutrients removal properties of soluble and solid organics. During the long-term operation of a sequencing batch reactor (SBR) with FSFW for wastewater treatment, the sludge particle size increased obviously, the bacterial metabolic capacity improved significantly, and some functional microorganisms were enriched selectively, which significantly promoted the nitrogen removal efficiency (approximately 90%) by enhancing the anoxic denitrification and simultaneous nitrification and denitrification (SND) processes. Moreover, high phosphate removal efficiency (above 98%) was achieved through the aerobic and anoxic phosphate accumulation processes. Thus, using the FSFW as supplementary carbon source is a suitable solution for both food waste disposal and wastewater treatment.

The use of biochar and crushed mortar in treatment wetlands to enhance the removal of nutrients from sewage

An experimental study was carried out using in pilot-scale constructed wetland systems, operated in parallel to treat raw sewage. Each system consisted of a vertical flow (VF) unit that was filled with biochar as the main media, followed by a horizontal flow (HF) unit filled with crushed cement mortar. Hydraulic loading (HL) ranged 340-680 mm/day was applied on the VF wetland units, where high total nitrogen (TN) mass removal rate (20-23 g N/m² d) was obtained, demonstrating that biochar media had a beneficial effect on the degradation of nitrogenous pollutants. Total phosphorus (TP) removal percentage (concentration based) was ≥ 86% in HF wetlands packed with mortar materials. In one system, the flow direction of the sewage was directed by the deployment of downflow pipes and vertical baffles, aiming to facilitate the formation of aerobic and anaerobic zones in the wetland matrices. The effects of such arrangement were analyzed by comparing pollutant removal efficiencies in the two systems. On average, 99, 96, 93, and 86 percentage removals were obtained for ammonia (NH₄-N), TN, biochemical oxygen demand (BOD), and TP, respectively, during the experiments. Biochar and crushed mortar proved to be a highly effective combination as media in subsurface flow constructed wetlands for wastewater treatment.

Hydrodynamic shear force shaped the microbial community and function in the aerobic granular sequencing batch reactors for low carbon to nitrogen (C/N) municipal wastewater treatment

The lab-scale aerobic granules process was applied for low carbon to nitrogen (C/N < 4) wastewater treatment under different hydrodynamic shear forces. Results revealed that aerobic granules exhibited strong adaptability and stability. The aerobic granules might adopt an extracellular polymeric substances (EPS) regulating mechanism to address the changes in operational conditions, especially through growing secretion of fluorescence protein. The hydrodynamic shear force determinedly shaped and regulated the diversity and structure of dominant microbial community, briefly, reduced aeration intensity with increased time led to higher microbial richness, lower diversity and evenness, and shifts of predominant microorganisms. Phylogenetic classification of the key functional groups including bacteria related to carbon and nutrients removal, EPS production and quorum sensing (QS) presented much more differences among the reactors subject to different conditions. Therefore, the present work adds insight into the comprehensive understanding of the effect of aeration induced hydrodynamic shear force on aerobic granules.

Nitrogen removal in pilot-scale partially saturated vertical wetlands with and without an internal source of carbon

The aim was to evaluate and compare total nitrogen (TN) removal in pilot-scale partially saturated vertical wetlands (PSVWs) with and without an internal solid source of organic carbon (corncob) in order to distinguish the role of nitrification-denitrification and ANAMMOX in the removal process. The height of the free-drainage zone (FDZ) was 40 cm and the saturated zone (SZ) was 30 cm in system I (SI) and system II (SII) and 40 cm in system III (SIII) and system IV (SIV). In SII and SIV, approximately 30 kg of dry, 5 cm-length corncob was added. The systems were evaluated during two periods, that is, P1 and P2. Measurements of water quality parameters including BOD₅, COD, organic nitrogen (Org-N), ammonium, nitrate and nitrite were taken in the influent and effluents on a weekly basis; nitrate measurements were also taken at the interface. Measurements of pH, dissolved oxygen (DO) and oxidation-reduction potential (ORP) were taken in the SZ. The height of both SZ (40 cm vs. 30 cm in P1) and FDZ (40 vs. 25 and 30 cm in SI/SIII in P2) did not affect the efficiencies (p > 0.05) but the presence or absence of corn cob did (p < 0.05). Thus, SII and SIV were superior when compared to SI and SIII (p < 0.05) with TN average removal efficiencies of 72.9% and 73.2% in P1, and 59.8% and 64.2% in P2, respectively; showing a tendency to lower values when the biodegradable organics supplied by the corncob diminished. In SI and SIII, TN removals were 47.6% and 40.3% in P1, and 46.1% and 44.1% in P2, respectively. In SII and SIV, denitrification took place in both the lower semi-saturated part of the FDZ (probably also ANAMMOX) and SZ; whereas in SI and SIII, ANAMMOX took place in the lower semi-saturated part of the FDZ.

Molecular characterization of long-term impacts of macrophytes harvest management in constructed wetlands

There is little understanding of constructed wetlands (CWs) microbial community patterns in response to harvest management. Therefore, long-term impacts of harvesting Phragmites australis (Cav.) Trin. ex Steudel annually in November on the activity and community structure of microorganisms critical to the treatment efficiency of CW are elucidated. Findings show exponential increases in P. australis density and biomass with continuous harvesting, up to three times over unharvested CW. High-throughput pyrosequencing analysis demonstrates that plants harvesting improves the microbial community diversity and richness significantly, and more particularly, the relative abundance of Flavobacterium, Paenisporosarcina, and Povalibacter, which are extensively associated with CW performance. Consequently, increased plants biomass resulted in enhanced plants nutrients uptake in harvested (56.5 g N/m², 5.5 g P/m²) than unharvested CWs (17.5 g N/m², 1.8 g P/m²), whereas improved rhizosphere microclimates significantly enhanced nutrients removals in harvested CW (TN 109.9 g/m² vs 67.4 g/m², TP 18.0 g/m² vs 13.0 g/m²).

Intensified heterotrophic denitrification in constructed wetlands using four solid carbon sources: Denitrification efficiency and bacterial community structure

Biodenitrification using solid carbon sources is a cost-effective way for nitrate removal. In the study, wheat straw, cotton, poly(butylene succinate), and newspaper was chosen as the carbon source to compare the denitrification efficiency and bacterial communities in constructed wetlands. Parameters including COD, NO₃^--N, NO₂^--N and total nitrogen (TN) were analyzed. Results indicated that newspaper provided significantly higher NO₃^--N and TN removal efficiency than the other three solid carbon sources in low-temperature condition. Moreover, both newspaper and wheat straw allowed high NO₃^--N and TN removal efficiency in high-temperature condition. According to pyrosequencing analysis, denitrifying bacteria Dechloromonas and Thauera were the predominant genus in the anaerobic zone of CO- (3.92 and 2.35%, respectively), WS- (1.97 and 1.02%, respectively) and NP-CWs (1.71 and 1.31%, respectively). Genus of Levilinea was enriched in NP- (1.02%) and WS-CWs (0.91%). Furthermore, genus Paludibacter (2.69%) and Saccharofermentans (3.14%) showed high relative abundance in WS-CWs.