Nitrogen removal in Myriophyllum aquaticum wetland microcosms for swine wastewater treatment: 15 N-labelled nitrogen mass balance analysis

Effects of multi-plant harvesting on nitrogen removal and recovery in constructed wetlands

The harvesting of plants is considered an effective method for nutrient recovery in constructed wetlands (CWs). However, excessive plant harvesting can lead to a decrease in plant biomass. It remains unclear what harvesting frequency can optimize plant nutrient uptake and pollutant removal. In this study, CWs planted with Myriophyllum aquaticum were constructed, and three different frequencies of plant harvesting (high: 45 days/time; low: 90 days/time; none: CK) were set to investigate nitrogen removal and its influencing mechanism, as well as the capacity for plant nutrient recovery. The results showed that the average removal efficiencies of ammonia nitrogen (NH4+-N) at 45 days/time, 90 days/time, and CK were 90.3%, 90.8%, and 88.3% respectively, while the corresponding total nitrogen (TN) were 61.2%, 67.4%, and 67.4%. Dissolved oxygen (DO) concentration and water temperature were identified as the main environmental factors affecting nitrogen removal efficiency. Low harvest frequency (90 days/time) increased DO concentration and NH4+-N removal efficiency without impacting TN removal. Additionally, TN recovery from plants under high and low harvest was found to be approximately 9.21-9.32 times higher than that from no harvest conditions. The above studies indicated that a harvest frequency of every 90 days was one appropriate option for M. aquaticum, which not only increased NH4+-N removal efficiencies but also facilitated more efficient nitrogen recovery from the wetland system.

Purification Effect of Water Eutrophication Using the Mosaic System of Submerged-Emerged Plants and Growth Response

Aquatic plants play a crucial role in the sustainable management of eutrophic water bodies, serving as a valuable tool for water purification. However, the effectiveness of using aquatic plants for improving water quality is influenced by landscape considerations. In practical applications, challenges arise concerning low purification efficiency and compromised aesthetic appeal when utilizing plants for water purification. To address these issues, this study aimed to examine the impact of aquatic plants on the purification of simulated landscape water bodies, specifically focusing on the effectiveness of the mosaic system of submerged-emerged plants in remediating eutrophic water bodies. Our findings indicated that individual aquatic plants exhibited limited efficacy in pollutant (total nitrogen, total phosphorus, ammonia nitrogen, and chemical oxygen demand) removal. However, when combined in appropriate proportions, submerged plants could enhance species growth and improve the purification efficiency of polluted water bodies. Notably, the mosaic system of submerged-emerged plants neither significantly promoted nor inhibited the growth of each other, but it effectively removed pollutants from the simulated water bodies and inhibited turbidity increase. The comprehensive evaluation ranked the purification capacity as Canna indica-submerged plants combination (C + S) > Thalia dealbata-submerged plants combination (T + S) > Iris pseudacorus-submerged plants combination (I + S) > Lythrum salicaria-submerged plants combination (L + S). Both C + S and T + S configurations effectively mitigated the rise of water turbidity and offered appealing landscape benefits, making them viable options for practical applications in urban landscape water bodies. Our study highlights that a submerged-emerged mosaic combination is a means of water purification that combines landscape aesthetics and purification efficiency.

Transformation mechanisms of ammonium and nitrate in subsurface wastewater infiltration system: Implication for reducing greenhouse gas emissions

Subsurface wastewater infiltration system (SWIS) has been recognized as a cost-effective and environmentally friendly tool for wastewater treatment. However, there is a lack of knowledge on the transformation processes of nitrogen (N), hindering the improvement of the N removal efficiency in SWIS. Here, the migration and transformation mechanisms of ammonium (NH4+-N) and nitrate (NO3+-N) over 10 days were explored by 15N labeling technique. Over the study period, 49% of the added 15NH4+-N remained in the soil, 29% was removed via gaseous N emissions, and 14% was leaked with the effluent in the SWIS. In contrast, only 11% of the added 15NO3--N remained in the soil while 65% of the added 15NO3--N was removed via gaseous N emissions, and 12% with the effluent in the SWIS. The main pathway for N2O emission was denitrification (52-70%) followed by nitrification (15-28%) and co-denitrification (9-20%). Denitrification was also the predominant pathway for N loss as N2, accounting for 88-96% of the N2 emission. The dominant biological transformation processes were different at divergent soil depths, corresponding to nitrification zone and denitrification zone along the longitudinal continuum in SWIS, which was confirmed by the expression patterns of microbial gene abundance. Overall, our findings reveal the mechanism of N transformation in SWIS and provide a theoretical basis for establishing a pollutant management strategy and reducing greenhouse gas emissions from domestic wastewater treatment.

Microbial community structure analyses and cultivable denitrifier isolation of Myriophyllum aquaticum constructed wetland under low C/N ratio

With the rapid expansion of livestock production, the amount of livestock wastewater accumulated rapidly. Lack of biodegradable organic matter makes denitrification of livestock wastewater after anaerobic digestion more difficult. In this study, Myriophyllum aquaticum constructed wetlands (CWs) with efficient nitrogen removal performance were established under different carbon/nitrogen (C/N) ratios. Analysis of community composition reveals the change of M. aquaticum CWs in microbial community structure with C/N ratios. The proportion of Proteobacteria which is one of the dominant phyla among denitrifier communities increased significantly under low C/N ratio conditions. Besides, to obtain cultivable denitrifier that could be added into CWs in situ, 33 strains belonging to phylum Proteobacteria were isolated from efficient M. aquaticum CWs, while the best-performing denitrification strain M3-1 was identified as Bacillus velezensis JT3-1 (GenBank No. CP032506.1). Redundancy analysis and quadratic models showed that C/N ratio had significant effects on disposal of nitrate (NO₃^--N) and the strains isolated could perform well in denitrification when C/N ratio is relatively low. In addition, they have relatively wide ranges of carbon sources, temperature and a high NO₃^- removal rate of 9.12 mg/(L·hr) at elevated concentrations of 800 mg/L nitrate. Thus, strains isolated from M. aquaticum CWs with low C/N ratio have a practical application value in the treatment of nitrate-containing wastewater. These denitrifying bacteria could be added to CWs to enhance nitrogen removal efficiency of CWs for livestock wastewater with low C/N ratio in the future.

Glutamine synthetase plays an important role in ammonium tolerance of Myriophyllum aquaticum

High-strength ammonium (NH₄⁺), the main characteristic of swine wastewater, poses a significant threat to the rural ecological environment. As a novel phytoremediation technology, Myriophyllum aquaticum wetlands have high tolerance and removal rate of NH₄⁺. Glutamine synthetase (GS), a pivotal enzyme in nitrogen (N) metabolism, is hypothesized to play an important role in the tolerance of M. aquaticum to high NH₄⁺. Herein, the responses of M. aquaticum to GS inhibition by 0.1 mM methionine sulfoximine (MSX) under 15 mM NH₄⁺ were investigated. After 5 days, visible NH₄⁺ toxicity symptoms were observed in MSX-treated plants. Compared with the control, the NH₄⁺ accumulation in the leaves increased by 20.99 times, while that of stems and roots increased by 3.27 times and 47.76 %, suggesting that GS inhibition had a greater impact on the leaves. GS inhibition decreased pigments in the leaves by 8.64 %-41.06 %, triggered oxidative stress, and affected ions concentrations in M. aquaticum. The concentrations of glutamine (Gln) and asparagine decreased by 63.46 %-97.43 % and 12.37 %-76.41 %, respectively, while the concentrations of most other amino acids increased after 5 days of MSX treatment, showing that GS inhibition reprogrammed the amino acids synthesis. A decrease in Gln explains the regulations of N-related genes, including increased expression of AMT in roots and decreased expression of GS, GOGAT, GDH, and AS, which would cause further NH₄⁺ accumulation via promoting NH₄⁺ uptake and decreasing NH₄⁺ assimilation in M. aquaticum. This study revealed for the first time that GS inhibition under high NH₄⁺ condition can lead to phytotoxicity in M. aquaticum due to NH₄⁺ accumulation. The physiological and molecular responses of the leaves, stems, and roots confirmed the importance of GS in the high NH₄⁺ tolerance of M. aquaticum. These findings provide new insights into NH₄⁺ tolerance mechanisms in M. aquaticum and a theoretical foundation for the phytoremediation of high NH₄⁺-loaded swine wastewater.

Physiological response and tolerance of Myriophyllum aquaticum to a wide range of ammonium concentrations

Myriophyllum aquaticum (M. aquaticum) can be used in constructed wetlands (CWs) to effectively purify swine wastewater with high-ammonia nitrogen (NH₃-N and NH₄⁺-N) concentrations. However, the understanding of its tolerance mechanism to ammonia nitrogen is limited. The physiological response and tolerance mechanism of M. aquaticum to a wide range of NH₄⁺ concentrations (0-35 mM) were investigated in the present study. The results indicated that M. aquaticum can tolerate NH₄⁺ concentrations of up to 30 mM for 21 days and grow well with high nutrient (N, P) uptake. A suitable concentration of NH₄⁺ for a better growth of M. aquaticum was 0.5-20 mM. The free NH₄⁺ content was no obviously increase at NH₄⁺ concentration below 15 mM, indicated there was no obviously ammonium accumulation. Exogenous NH₄⁺ inhibited K⁺ absorption and improved Ca²⁺ absorption, indicating mineral cation could mediate NH₄⁺ homeostasis under NH₄⁺ stress. Moreover, comparison with those in the control group, the activities of glutamine synthetase (GS), glutamate synthetase (GOGAT) in M. aquaticum increased by 52.7%-115% at 1-20 mM NH₄⁺, and superoxide dismutase (SOD) increased by 29.2-143% at 1-35 mM NH₄⁺. This indicated that the high NH₄⁺ tolerance of M. aquaticum was mainly due to the balance of free NH₄⁺ content in tissues, as well as improved nitrogen metabolism and antioxidant system. This could be attributed to the role of the GS-GOGAT cycle and SOD. In conclusion, M. aquaticum, which tolerates high NH₄⁺ concentration and has a high N uptake ability, can be used as a good candidate specie to help develop more efficient management strategies for treating high-NH₄⁺ wastewater in CW systems.

Fermentation Characteristics and Microbiota during the Ensiling of Myriophyllum aquaticum Inoculated with Lactic Acid Bacteria

Myriophyllum aquaticum (M. aquaticum) is a commonly used aquatic macrophyte for water purification and could be utilized as animal food. However, the high water content of M. aquaticum makes it difficult for long-term preservation, which leads to challenges as an ideal animal feed ingredient. The storage of Silage for long periods may be a proper method to solve the problem. In the present paper, we assess the effects of lactic acid bacteria Lactobacillus buchneri (LB), Lactobacillus plantarum (LP), or their combination on fermentation and microbial communities during the ensiling of M. aquaticum silage. The results show that the LP-treated silage displays a higher lactic acid concentration than that in the control silage. Both LB and LP increased the abundance of Lactobacillus, but decreased the abundance of Serratia and Prevotella_9 in M. aquaticum silage after 60 days of ensiling. Both LB and LP increased the diversity and richness of fungi. Therefore, the inoculation of LP improved silage fermentation during ensiling. These results show that the inoculation of lactic acid bacteria improves the fermentation quality of M. aquaticum silage, which makes it possible for the application of M. aquaticum to animal forage in the future.

Heterotrophic ammonium assimilation: An important driving force for aerobic denitrification of Rhodococcus erythropolis strain Y10

Studies on microbial ammonium removal have focused on the heterotrophic nitrification of microorganisms and have rarely studied the role of ammonium assimilation. In this study, Rhodococcus erythropolis strain Y10 with the capacity of aerobic denitrification was screened from the surface flow constructed wetlands that treat high-strength ammonium swine wastewater. Instead of through nitrification, this strain removed ammonium through heterotrophic ammonium assimilation, with the removal rate of 9.69 mg/L/h. The KEGG nitrogen metabolism pathway analysis combined with nitrogen balance calculation manifested that the removal of nitrate and nitrite by R. erythropolis Y10 was achieved through two pathways: 1) assimilation reduction to biomass nitrogen and 2) aerobic denitrification reduction to gaseous nitrogen. Ammonium addition improved the aerobic denitrification rate of nitrate and nitrite. The maximal reduction rates of nitrate and nitrite increased from 7.82 and 7.23 mg/L/h to 9.09 and 8.09 mg/L/h respectively, when 100 mg/L ammonium was separately added to 150 mg/L nitrate and nitrite. Furthermore, the removal efficiency of total nitrogen increased from 69.80% and 77.65% to 89.19% and 91.88%, respectively. Heterotrophic ammonium assimilation promoted the aerobic denitrification efficiency of Rhodococcus erythropolis strain Y10.

A comparison of the mechanisms and performances of Acorus calamus, Pontederia cordata and Alisma plantagoaquatica in removing nitrogen from farmland wastewater

This study examined the performances of Acorus calamus, Pontederia cordata, and Alisma plantagoaquatica in removing nitrogen (N) from farmland wastewater. P. cordata showed the fastest rate of N removal, followed by A. plantagoaquatica, whereas that of A. calamus was slowest. P. cordata and A. plantagoaquatica achieving a greater rate of TN reduction in soil than that by A. calamus. A. plantagoaquatica demonstrated the highest N adsorption capacity, 32.6% and 392.1% higher than that of P. cordata and A. calamus, respectively. The higher potential nitrification and denitrification rate, and abundance of functional genes in the P. cordata microcosm resulted in a stronger process of nitrification-denitrification, which accounted for 65.99% of TN loss. Plant uptake and nitrification-denitrification were responsible for 50.06% and 49.94% of TN removed within the A. plantagoaquatica. Nitrification-denitrification accounted for 86.35% of TN loss in A. calamus. These findings helped to insight into N removal mechanisms in different plants.

Removal effects of Myriophyllum aquaticum on combined pollutants of nutrients and heavy metals in simulated swine wastewater in summer

Swine wastewater (SW) treatment by Myriophyllum aquaticum is an important biotechnology for its resource utilization. However, some knowledge gaps remain in compound-pollutant removal in SW, especially in practical applications. To clarify the responses of M. aquaticum to the compound pollutants as well as the related operational parameters in SW treatment, three initial doses (0.5, 1.0, and 1.5 kg per pond in 150 L simulated SW) of M. aquaticum and a control (no plant; CK) were allocated to 12 ponds under a plastic roof in Nanjing city of Eastern China during 75 days in the summer of 2019. Results showed that M. aquaticum could be used as a pioneer plant to efficiently remove compounded pollutants of nitrogen (N), phosphorus (P), and especially for heavy metals in simulated SW. Compared with CK, M. aquaticum assisted in improving the total N, NH₄⁺-N, NO₃^--N, NO₂^--N, and dissolved organic N by 30.1%, 100%, 100%, 97.6%, 20.2%, 39.8% whereas Cu, Zn, and Cd by 50.4%, 36.4% and 47.9% on average during the 75-day experiment in summer, respectively. Moreover, concentrations of Cu and Cd at day 75 were in the ranges of 1.92-2.82 and 0.64-1.47 g kg^-1 DW, respectively, exceeding the corresponding limits of the heavy-metal hyperaccumulator. For the operational parameters, the optimized initial dose was 1.0 kg per pond with M. aquaticum harvested after 45 summer days, respectively. Given that M. aquaticum has been widely used as animal feed in recent years and limit values for Cu and Zn in animal feed are not set in China, the toxicities of Cu and Zn should be assessed and the guideline of their limit values needs to be established for safe feed production. Interestingly, NH₄⁺-N could dominate the removal of heavy metals especially Cd in the simulated SW, however, related mechanisms are needed for further study.

Potential of invasive watermilfoil (Myriophyllum spp.) to remediate eutrophic waterbodies with organic and inorganic pollutants

Watermilfoil (Myriophyllum) is one of the world's most troublesome invasive aquatic weeds. Although current management practices may inhibit its expansion, it also impacts not only the quality of water but habitat deterioration. Therefore, the need for developing highly efficient and low-cost biotechnologies with resource recovery into the agriculture field as a complementary management strategy cannot be overstated. Here, we reviewe the scientific/grey literature to offer readers a precise and panoramic view of the invasive watermilfoil ecology, regional problems, impacts, ecosystem services, and management. In this regard, an in-depth review aimed to assess the potential for reducing non-point source inorganic and organic pollutants using invasive watermilfoil, with the sustainable approaches, while offering other services and mitigating ecological trade-offs is presented. Global distributions, growth, and current progress on the management and utilization of invasive watermilfoil biomass are summarized to develop the aim, which is to convey challenges during the implementation of large-scale weed use. In short, pollutant assimilation in plant and bacterial communities linked to this weed considerably contribute to the reduction and degradation of pollutants from both natural and artificial systems. Although several considerations in recycling and reusing biomass need to be considered, the potential reuse of the harvested material for livestock feed, compost and direct use in farming systems offer an additional strategy to achieve sustainable ecosystem restoration. Further research and development may focus on a more detailed economic modeling approach that integrates the costs (worker's wage, harvesting, transportation, and energy consumption), legal and regulatory barriers, health risks and ecosystem service benefits (biodiversity improvement, and pollutant removal) to holistically evaluate the economic, environmental, and societal value of reusing and recycling this waste material.

Effect of ammonia stress on carbon metabolism in tolerant aquatic plant-Myriophyllum aquaticum

In this study, the tips of Myriophyllum aquaticum (M. aquaticum) plants were planted in open-top plastic bins and treated by simulated wastewater with various ammonium-N concentrations for three weeks. The contents of related carbohydrates and key enzyme activities of carbon metabolism were measured, and the mechanisms of carbon metabolism regulation of the ammonia tolerant plant M. aquaticum under different ammonium-N levels were investigated. The decrease in total nonstructural carbohydrates, soluble sugars, sucrose, fructose, reducing sugar and starch content of M. aquaticum were induced after treatment with ammonium-N during the entire stress process. This finding showed that M. aquaticum consumed a lot of carbohydrates to provide energy during the detoxification process of ammonia nitrogen. Moreover, ammonia-N treatment led to the increase in the activitives of invertase (INV) and sucrose synthase (SS), which contributed to breaking down more sucrose to provide substance and energy for plant cells. Meanwhile, the sucrose phosphate synthase (SPS) activity was also enhanced under stress of high concentrations of ammonium-N, especially on day 21. The result indicated that under high-concentration ammonium-N stress, SPS activity can be significantly stimulated by regulating carbon metabolism of M. aquaticum, thereby accumulating sucrose in the plant body. Taken together, M. aquaticum can regulate the transformation of related carbohydrates in vivo by highly efficient expression of INV, SPS and SS, and effectively regulate the osmotic potential, thereby delaying the toxicity of ammonia nitrogen and improving the resistance to stress. It is very important to study carbon metabolism under ammonia stress to understand the ammonia nitrogen tolerance mechanism of M. aquaticum.

Nitrogen removal in vertical flow constructed wetlands: influence of bed depth and high nitrogen loadings

The aim of the study was to evaluate the nitrogen removal and its effects on the plant's growth and leaves morphology. using two subsurface vertical flow (VF bed), with different depths (0.24 m² × 0.70 m; 0.24 m² × 0.35 m) and nitrogen load increments. The VF bed were planted with Vetiveria zizanioides, filled with light expanded clay aggregates (Leca®NR 10/20) and fed in parallel mode with synthetic wastewater. High ammonium nitrogen concentration ([NH₄ ⁺-N] from 68 ± 3 to 290 ± 8 mg L^-1) was used without toxicity symptoms in plants, although the effects of ammonium nitrogen load were stopped the growth of the plants. Significant differences between ammonium nitrogen removed in each VF bed obtained for total nitrogen (TN_infl.) ≥ 27 ± 0.8 g m^-2 d^-1. The nitrification was contributed to ammonium nitrogen removal because was found higher values of nitrate and nitrite in the effluent. These values were more higher in VF bed 1 than in the VF bed 2, since ammonium nitrogen removal were also more higher in VF bed 1 than in the VF bed 2. Total nitrogen mass balance was carried out and the results show that the nitrification/denitrification process occurred with nitrogen plants uptake. It was observed that the VF bed depth has an influence on all nitrogen removal processes. As higher the depth root system it is seemed to favour the creation of zones with different oxidations conditions that allow the nitrogen compounds to be removed intensively.

Nutrients release and greenhouse gas emission during decomposition of Myriophyllum aquaticum in a sediment-water system

Aquatic macrophytes play a significant role in nutrients removal in constructed wetlands, yet nutrients could be re-released due to plant debris decomposition. In this study, Myriophyllum aquaticum was used as a model plant debris and three debris biomass levels of 3 g, 9 g dry biomass, and 20 g fresh biomass (D3, D9, and F20, respectively) were used to simulate 120-d plant debris decomposition in a sediment-water system. The biomass first-order decomposition rate constants of D3, D9, and F20 treatments were 0.0058, 0.0117, and 0.0201 d^-1, respectively with no significant difference of decomposition rate among three mass groups (p > 0.05). Plant debris decomposition decreased nitrate and total nitrogen concentrations but increased ammonium, organic nitrogen, and dissolved organic carbon (DOC) concentrations in overlying water. The parallel factor analysis confirms that three components of DOC in overlying water changed over decomposition time. Emission fluxes of methane and nitrous oxide in the plant debris treatments were several to thousands of times higher than the control group within the initial 0-45 d, which was mainly attributed to DOC released from the plant debris. Plant debris decomposition can affect the gas emission fluxes for relatively shorter time (30-60 d) than water quality (>120 d). The 16S rRNA, nirK, nirS and hazA gene abundance increased in the early stage for plant debris treatments, and then decreased to the end of 120-d incubation time while ammonia monooxygenase α-subunit A gene abundance of ammonia-oxidizing archaea and bacteria had no large variations during the entire decay time compared with no plant debris treatment. The results demonstrate that decomposition of M. aquaticum debris could affect greenhouse gas emission fluxes and microbial gene abundance in the sediment-water system besides overlying water quality.

Nitrogen removal performance and needed area estimation of surface-flow constructed wetlands using a probabilistic approach

Pollutant concentrations in influents into constructed wetlands (CWs) are highly fluctuating and may vary over several orders of magnitude, leading to large uncertainties in removal performance assessment when using pollutant concentrations in the influent and effluent directly. Incorporating a probabilistic approach into removal performance assessment and needed area estimation of CWs could advantage decision making regarding wastewater treatment and engineering applications. A series of three-stage surface-flow CWs (SFCWs) were constructed for treating ammonium-rich swine wastewater. The surface removal rate and removal efficiency of ammonium nitrogen in the SFCWs using the probabilistic approach were 0.27-3.23 g m^-2 d^-1 and 43.0-99.9% (95% confidence interval (CI)), which were consistent with the deterministic approach (95% CI: 0.24-3.18 g m^-2 d^-1 and 70.4-99.9%). The needed SFCW area was estimated as 6.6 (95% CI: 1.4-17.8) to 29.7 (95% CI: 6.4-80.1) m² for required removal efficiency from 40% to 90% for 0.18 m³ d^-1 swine wastewater with different strengthens. For specific removal efficiency of 90%, the needed CW areas was 13.9 (95%CI: 4.9-42.7), 25.1 (95%CI: 5.9-66.0), 33.5 (95%CI: 13.5-87.1), and 40.8 (95%CI: 16.2-89.4) m² for influent ammonium loading rate of 0.18-2.7, 2.7-14.4, 14.4-36, and 36-60 g d^-1, respectively. The first-order removal constant of ammonium nitrogen decreased logarithmically with increasing influent and effluent concentration/loading rate in the SFCW units (p < 0.001), which was responsible for the needed SFCW areas covering a wide range. The reliability analysis confirmed the results from the probabilistic approach were appropriate. The present study shed new lights on the performance evaluation and design of CWs for treating wastewater with highly-fluctuating concentrations using a probabilistic approach.

Comprehensive evaluation of substrate materials for contaminants removal in constructed wetlands

Considerable number of studies have been carried out to develop and apply various substrate materials for constructed wetlands (CWs), however, there is a lack of method and model for comprehensive evaluation of different types of CWs substrates. To this end, this article summarized nearly all the substrate materials of CWs available in the literatures, including natural materials, agricultural/industrial wastes and artificial materials. The sources and physicochemical properties of various substrate materials, as well as their removal capacities for main water contaminants including nutrients, heavy metals, surfactants, pesticides/herbicides, emerging contaminants and fecal indicator bacteria (FIB) were comprehensively described. Further, a scoring model for the substrate evaluation was constructed based on likely cost, availability, permeability, reuse and contaminant removal capacities, which can be used to select the most suitable substrate material for different considerations. The provided information and constructed model contribute to better understanding of CWs substrate for readers, and help solve practical problems on substrates selection and CWs construction.

Rapid removal of tetracycline by Myriophyllum aquaticum: Evaluation of the role and mechanisms of adsorption

As a floating plant, Myriophyllum aquaticum provides a large surface area under water, and thus has high potential for the removal of pollutants through adsorption. The aim of this study was to evaluate the potential adsorption of tetracycline (TC) by M. aquaticum, and examine the underlying mechanisms. M. aquaticum exhibited a high potential for TC removal from water. Adsorption was the main mechanism for rapid TC removal by live M. aquaticum plants, due to its large contact area and ion exchange, accounting for about 99% and 54% of the total amount of TC removed within 2 h and 5 d, respectively. Further, the roots of M. aquaticum exhibited a higher adsorption capacity than the stems or leaves, as the roots had the largest specific surface area. Fourier transform infrared spectroscopy analysis and identification of functional groups showed that -OH, -COOH, and -NH₂ groups are involved in the adsorption process. The use of M. aquaticum may be a promising approach for TC removal from aquatic environments, especially in terms of shortening reaction times.

Effect of copper on the removal of tetracycline from water by Myriophyllum aquaticum: Performance and mechanisms

Pollution with antibiotics and heavy metals necessitates efficient approaches for their removal. This study was conducted to investigate the role of Cu in the tetracycline (TC) removal potential of the floating plant Myriophyllum aquaticum and determine the underlying mechanisms. Myriophyllum aquaticum exhibited high TC removal potential from water (60% at 50 mg·L^-1 TC and 10 g·L^-1M. aquaticum). Adsorption was the main mechanism of TC removal within 2 h, accounting for over 75% and 90% of total TC removal with and without Cu(II), respectively. Fourier-transform infrared spectroscopy and functional group identification showed that OH, COOH, and NH₂ were involved in TC adsorption through ion exchange. Cu(II) may act as a bridge during TC adsorption with M. aquaticum, but competitive adsorption of Cu(II) and TC on M. aquaticum occurs in case of excessive Cu(II). Myriophyllum aquaticum can serve as an important bioresource for effectively removing TC and Cu(II) from aquatic environments.

A wastewater treatment system combining Myriophyllum aquaticum and activated sludge: Optimization of construction conditions and evaluation of wastewater treatment performance

Although Myriophyllum aquaticum exhibits efficient nitrogen and phosphorus removal from wastewater, it has poor performance on organic matter removal. Here, a wastewater treatment system combining M. aquaticum and activated sludge was developed to improve its removal of organic matter. The Box-Behnken response surface methodology was used to optimize the construction conditions of the system, and the effects of time, temperature, illumination intensity, pollutant load, and dissolved oxygen (DO) on plant mass increment (PMI) and microbial biomass (MB) of the system were investigated. The wastewater remediation potential of the system was then evaluated. The results show that temperature and illumination intensity significantly affected PMI (p < 0.01), and that time, pollutant load, and DO were the most significant factors affecting MB (p < 0.01). The optimal construction conditions were 18.77 days in length, a temperature of 20.42 °C, an illumination intensity of 5827.61 Lx, a pollutant load of 120.61 mg/g plant, and a DO of 3.21 mg/L. The inoculation of activated sludge caused MB of the system to increase by four times relative to the non-inoculated system, suggesting successful formation of biofilms on M. aquaticum. Additionally, the removal of chemical oxygen demand (COD) from wastewater was significantly enhanced by the combined approach compared with a system relying solely on M. aquaticum. This study provides a new method for improving the remediation efficiency of M. aquaticum by combining the use of this species and activated sludge.

Complex regulatory network allows Myriophyllum aquaticum to thrive under high-concentration ammonia toxicity

Plants easily experience ammonia (NH₄⁺) toxicity, especially aquatic plants. However, a unique wetland plant species, Myriophyllum aquaticum, can survive in livestock wastewater with more than 26 mM NH₄⁺. In this study, the mechanisms of the M. aquaticum response to NH₄⁺ toxicity were analysed with RNA-seq. Preliminary analysis of enzyme activities indicated that key enzymes involved in nitrogen metabolism were activated to assimilate toxic NH₄⁺ into amino acids and proteins. In response to photosystem damage, M. aquaticum seemed to remobilize starch and cellulose for greater carbon and energy supplies to resist NH₄⁺ toxicity. Antioxidative enzyme activity and the secondary metabolite content were significantly elevated for reactive oxygen species removal. Transcriptomic analyses also revealed that genes involved in diverse functions (e.g., nitrogen, carbon and secondary metabolisms) were highly responsive to NH₄⁺ stress. These results suggested that a complex physiological and genetic regulatory network in M. aquaticum contributes to its NH₄⁺ tolerance.

Montmorillonite supported nanoscale zero-valent iron immobilized in sodium alginate (SA/Mt-NZVI) enhanced the nitrogen removal in vertical flow constructed wetlands (VFCWs)

Lacking of electron donor generally causes the low denitrification performance of constructed wetlands (CWs). Montmorillonite supported nanoscale zero-valent iron immobilized in sodium alginate (SA/Mt-NZVI) as novel electron donor-acceptor compounds were added in the denitrification zone of vertical flow constructed wetlands (VFCWs) to enhance the nitrogen removal. The key factors of the SA/Mt-NZVI dosage, the hydraulic retention time (HRT) of VFCWs, and the C/N ratios of influent were explored. SA/Mt-NZVI significantly improved the nitrogen (NO₃^--N) removal efficiency in VFCWs. When the optimal dosage of SA/Mt-NZVI was set as 2 g and the C/N was set as 6, the highest NO₃^--N removal efficiency was improved by 32.5 ± 1.0%. The microbial community analysis of by 16S rRNA had revealed that Proteobacteria and Bacteroidetes at phylum level and Betaproteobacteria, Gammaproteobacteria, and Alphaproteobacteria at class level played an important role in nitrogen removal.

Nitrogen removal and recovery from lagoon-pretreated swine wastewater by constructed wetlands under sustainable plant harvesting management

A series of three-stage pilot-scale surface flow constructed wetlands (CWs) planted with Myriophyllum aquaticum were fed with three strengths of lagoon-pretreated swine wastewater to study nitrogen (N) removal and recovery under sustainable plant harvesting management. The CWs had mean removal efficiency of 87.7-97.9% for NH₄⁺-N and 85.4-96.1% for total N (TN). The recovered TN mass via multiple harvests of M. aquaticum was greatest (120-222 g N m^-2 yr^-1) when TN concentrations were 21.8-282 mg L^-1. The harvested TN mass accounted for 0.85-100% of the total removal in the different CW units. Based on mass balance estimation, plant uptake, sediment storage, and microbial removal accounted for 13.0-55.0%, 4.9-8.0%, and 33.0-67.5% of TN loading mass, respectively. The results of this study confirm that M. aquaticum is appropriate for the removal and recovery of nutrients in CW systems designed for treating swine wastewater in conjunction with sustainable plant harvesting strategies.

Improving nutrient removal performance of surface flow constructed wetlands in winter using hardy submerged plant-benthic fauna systems

A novel hardy submerged plant-benthic fauna systems to enhance the performance of surface flow constructed wetlands in winter.

Purification and reuse of non-point source wastewater via Myriophyllum-based integrative biotechnology: A review

In this review, the applications of Myriophyllum-based integrative biotechnology to remove common non-point source (NPS) pollutants, such as nitrogen, phosphorus, heavy metals, and organic pollutants (e.g., pesticides and antibiotics) are summarized. The removal of these pollutants via various mechanisms, including uptake by plant and microbial communities in macrophyte-based treatment systems are discussed. This review highlights the potential use of Myriophyllum biomass to produce animal feed, fertilizer, and other valuable by-products, which can yield cost-effective returns and attract more attention to the regulation and recycling of NPS pollutants. In addition, it demonstrates that utilization of Myriophyllum species is a promising and reliable strategy for wastewater treatment. The future development of sustainable Myriophyllum-based treatment systems is discussed from various perspectives.

Nitrogen transformations and removal efficiency enhancement of a constructed wetland in subtropical Taiwan

Urbanization condenses reactive nitrogen into cities leaving threats of nitrogen pollution onto nearby environments when sewage is not properly treated. Constructed wetland is an ecological and economical way to remove reactive nitrogen. We investigated the seasonal nitrogen transformations and removal pathways in a surface-flow constructed wetland (93,000m² with five treatment cells), which treats domestic wastewater in subtropical Taiwan. By using isotopic pairing technique, we found denitrification exceeds anammox dominated the nitrogen removal pathway throughout seasons. The potential denitrification (0.09 to 2.84gNm^-2d^-1) in the overlying water was in the same magnitude relative to that in sediments (1.26 to 4.14gNm^-2d^-1). The denitrification rates in sediments were highest in summer followed by autumn and winter. The concentration removal efficiencies of ammonium and dissolved inorganic nitrogen (DIN) were both highest in summer, then decreased significantly in autumn and winter. Temperature is a significant regulator for seasonal nitrogen removal. However, a positive correlation was observed between the potential denitrification rates and the amount of ¹⁵NO₃^- addition, indicating that nitrate addition may still stimulate denitrification under low temperature condition in winter (15.2-16.3°C). Since nitrate concentrations in porewater were much lower than that in water column for autumn and winter, we speculated NO_x^--N (nitrite and nitrate) supply to the sediments was a limiting factor for low DIN removal efficiency. We proposed to enhance nitrate removal efficiency via denitrification by physically promoting NO_x^--N and oxygen exchanges through the sediment-water interface.