Comparison of four aquatic plant treatment systems for nutrient removal from eutrophied water

Hydrometeorological conditions drive long-term changes in the spatial distribution of Potamogeton crispus in a subtropical lake

Globally, anthropogenic disturbance and climate change caused a rapid decline of submerged macrophytes in lake ecosystems. Potamogeton crispus (P. crispus), a species that germinates in winter, explosively expanded throughout many Chinese lakes, yet the underlying mechanism remained unclear. Here, this study examined the long-term changes in the distribution patterns of P. crispus in Lake Gaoyou by combining remote sensing images and hydrometeorological data from 1984 to 2022 and water quality data from 2009 to 2022. It aims to unravel the relationships between the distribution patterns of P. crispus and hydrometeorological and water quality factors. The results showed that the area of P. crispus in Lake Gaoyou showed a slight increase from 1984 to 2009, a marked increase from 2010 to 2019, followed by a decline after 2020. Spatially, P. crispus was primarily distributed in the western and northern parts of Lake Gaoyou, with less distribution in the central and southeastern parts of the lake. Wind speed (WS), temperature (Temp), water level (WL), ammonia nitrogen (NH3-N), and Secchi depth (SD) were identified as the key factors regulating the variation in the P. crispus area in Lake Gaoyou. We found that the P. crispus area showed an increasing trend with increasing Temp, WL, and SD and decreasing WS and NH3-N. The influence of environmental factors on the area of P. crispus in Lake Gaoyou varied among seasons. The results indicated that hydrometeorology (WS, Temp, and WL) may override water quality (NH3-N and SD) in driving the succession of P. crispus distribution. The findings of this study offer valuable insights into the recent widespread expansion of P. crispus in shallow lakes across Eastern China.

Development and implementation of a novel mechanized planting method for ecological restoration of aquatic environments using degradable nutrition pots

Submerged plants play a significant role in the remediation and purification of polluted water bodies. Reconstruction of submerged plants has been considered as an important ecological method to restore aquatic ecosystems. However, large-scale and efficient plantation of submerged plants in water restoration is a huge challenge. This paper proposes a novel mechanized planting method for submerged plants utilizing nutrition pots as planting units. Firstly, the details of the mechanized planting method were introduced. The mechanized planting method involves pre-planting the reproductive bodies of submerged plants in degradable nutrition pots, and then implanting them into the underwater soil through a planting device. Secondly, the interaction force between the nutrition pot and the soil was measured. It was found that the implantation force of nutrition pots increases with planting velocity. The planting force shows a significant increase trend when the water content in the soil decreases. Thirdly, the deformation of the nutrition pot was studied through simulations. It was discovered that the deformation of the nutrition pot mainly occurs at the bottom and the side walls near the bottom, and the limited deformation ensures the integrity of the nutrition pot. Finally, a planting device with a linear motion mechanism was designed, and a typical submerged plant, Vallisneria natans was tested, using agricultural paper seedling containers as the nutrition pots. It was demonstrated that the mechanized device successfully planted submerged plant nutrition pots into the soil, and the submerged plants survived and showed a clear growth trend. The mechanized planting method of submerged plants proposed in this article is expected to provide a new and friendly technology for ecological restoration of water source.

The origins of odor (β-cyclocitral) under different water nutrient conditions: Algae or submerged plants?

Among the problems caused by water eutrophication, the issue of odor compounds has attracted notable attention. β-Cyclocitral, a widely distributed and versatile odor compound, is commonly derived from both algae and aquatic plants. Planting aquatic plants is a common method of water purification. However, there is limited study on their impact on β-cyclocitral levels in water. Here, we conducted a study on the β-cyclocitral levels in water and the submerged plant leaves under three nutrient levels and six plant density treatments. Our findings revealed the following: (1) Chlorophyll-a (Chla), β-cyclocitral in the water (Wcyc), β-cyclocitral in Potamogeton lucens leaves (Pcyc) and the biomass of the submerged plants increase with rising nutrient concentration, which increased about 83 %, 95 %, 450 %, 320 % from eutrophic treatment to oligotrophic treatment, respectively. (2) In water, β-cyclocitral is influenced not only by algae but also by submerged plants, with primary influencing factors varying across different nutrient levels and plant densities. The main source of β-cyclocitral in water becomes from plants to algae as the water eutrophication and plant density decrease. (3) As submerged plants have the capability to emit β-cyclocitral, the release of β-cyclocitral increases with the density of submerged plants. Hence, when considering planting submerged plants for water purification purposes, it is crucial to carefully manage submerged plant density to mitigate the risk of odor pollution emanating from aquatic plants. This study offers fresh insights into selecting optimal water density for submerged plants and their role in mitigating the release of β-cyclocitral.

Influence of enzyme activity on domestic wastewater amelioration in a hybrid subsurface flow constructed wetland

Wastewater treatment in a constructed wetland is achieved by the presence of plant species, the metabolism of microorganisms, and the enzyme activities. Three small-scale hybrid subsurface flow constructed wetlands (HSFCWs) planted with Arundo donax and one unplanted HSFCW were constructed near a water resource recovery facility at Guru Gobind Singh Indraprastha University. The purpose of the study was to determine the correlation between soil enzymatic activities and the removal of contaminants from domestic wastewater. Enzyme activity of phosphatase, protease, urease, and cellulase increased with an increase in temperature. A strong correlation between enzyme activities and TKN and surfactant removal was observed, whereas moderate correlation was observed with phosphate in planted HSFCW during the study. The correlation between COD removal and enzyme activities was low to moderate. In unplanted HSFCW, the correlation between enzyme activities and COD removal was negative, negligible to moderate to strong in the case of TKN, low to moderate in the case of phosphate, and negligible to low in the case of surfactants. The increased removal efficiency of the planted system compared with that of the unplanted system indicated a positive impact on enzyme activities with the growth of plants and their roots. PRACTITIONER POINTS: Protease, urease, and cellulase activities: Planted HSFCW exhibited higher protease, urease, and cellulase activities than unplanted, signifying enhanced breakdown. July displayed maximum enzyme activities, correlating with heightened biological breakdown in both systems. Fluctuations in enzyme activities reflected seasonal changes, influencing nutrient degradation rates. Planted HSFCW consistently showed higher enzymatic activities across protease, urease, and cellulase than unplanted.

Thirty years of experience in water pollution control in Taihu Lake: A review

Taihu Lake has suffered from eutrophication and algal blooms for decades, primarily due to increasing anthropogenic pollutants from human activities. Extensive research and widespread implementation of water pollution control measures have significantly contributed to the improvement of water quality of Taihu Lake. However, the relevant experience of Taihu Lake pollution control has not been well summarized to provide insight for future lake restoration. This review article seeks to address this gap by first providing a comprehensive overview of Taihu Lake's water quality dynamics over the past thirty years, characterized by two distinct stages: (I) water quality deterioration (1990s-2007); and (II) water total nitrogen (TN) improvement but total phosphorus (TP) fluctuation (2007-current). Subsequently, we conducted a thorough review of the experiences and challenges associated with water pollution control during these two stages. Generally, pollution control practices emphasized point source control but overlooked non-point sources before 2007, possibly due to point sources being easier to identify and manage. Accordingly, the focus shifted from industrial point sources to a combination of industrial point and agricultural non-point sources after 2007 to control water pollution in the Taihu Lake Basin. Numerous studies have delved into non-point source pollution control, including source control, transport intercept, in-lake measures, and the integration of these technologies. Taken together, this paper provides suggestions based on the needs and opportunities of this region. Further research is needed to better understand and model the underlying pollution processes, as well as to increase public participation and improve policy and law implementation, which will assist decision-makers in formulating better water management in Taihu Lake.

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.

Proper C/N ratio enhances the effect of plant diversity on nitrogen removal and greenhouse effect mitigation in floating constructed wetlands

Treating wastewater with low carbon-to-nitrogen (C/N) ratios by constructed wetlands (CWs) is still problematic. Adding chemicals is costly and may cause secondary pollution. Configuring plant diversity in substrate-based CWs has been found to be a better way to treat low-C/N wastewater, but wastewater treatment in floating CWs needs to be studied. In this study, wastewater with C/N ratios of 5 and 10 were set in simulated floating CWs, and 9 combinations with plant species richness (SR) of 1, 3, and 4 were configured. The results showed that (1) increasing SR improved the total N mass removal (NMR) by 29% at a C/N ratio of 5 but not 10; (2) the presence of Oenanthe javanica in the microcosms increased the NMR by 13% and 20% with C/N ratios of 5 and 10, respectively; (3) increasing SR mitigated the net global warming potential (GWP) by 120% at a C/N ratio of 5 but not 10; and (4) a Hemerocallis fulva × O. javanica × Echinodorus parviflours × Iris hybrids mixture resulted in a high NMR and low net GWP. In summary, assembling plant diversity in floating CWs is an efficient and clean measure during the treatment of wastewater with a C/N ratio of 5.

Phytosphere purification of urban domestic wastewater

Industrialization and overpopulation have polluted aquatic environments with significant impacts on human health and wildlife. The main pollutants in urban sewage are nitrogen, phosphorus, heavy metals and organic pollutants, which need to be treated with sewage, and the use of aquatic plants to purify wastewater has high efficiency and low cost. However, the effectiveness and efficiency of phytoremediation are also affected by temperature, pH, microorganisms and other factors. The use of biochar can reduce the cost of wastewater purification, and the combination of biochar and nanotechnology can improve the efficiency of wastewater purification. Some aquatic plants can enrich pollutants in wastewater, so it can be considered to plant these aquatic plants in constructed wetlands to achieve the effect of purifying wastewater. Biochar treatment technology can purify wastewater with high efficiency and low cost, and can be further applied to constructed wetlands. In this paper, the latest research progress of various pollutants in wastewater purification by aquatic plants is reviewed, and the efficient treatment technology of wastewater by biochar is discussed. It provides theoretical basis for phytoremediation of urban sewage pollution in the future.

Role of hydrophytes in constructed wetlands for nitrogen removal and greenhouse gases reduction

With the prominence of global climate change and proposal of carbon reduction concept, how to maximize the comprehensive effect of nitrogen removal and greenhouse gases (GHGs) reduction in constructed wetlands (CWs) has become crucial. As indispensable biological component of CWs, hydrophytes have received extensive attention owing to their application potential. This review comprehensively evaluates the functions of hydrophytes in nitrogen removal and GHGs reduction in CWs in terms of plants themselves, plant-mediated microbes and plant residues (hydrophyte carbon sources and hydrophyte-derived biochars). On this basis, the strategies for constructing an ideal CW system are put forward from the perspective of full life-cycle utilization of hydrophytes. Finally, considering the variability of plant species composition in CWs, outlooks for future research are specifically proposed. This review provides guidance and novel perspectives for the full life-cycle utilization of hydrophytes in CWs, as well as for the construction of an ideal CW system.

Microbial response to nitrogen removal driven by combined iron and biomass in subsurface flow constructed wetlands with plants of different ages

This study investigated the nitrogen removal enhanced by combined iron scraps and plant biomass, and its microbial response in the wetland with different plant ages and temperatures. The results showed that older plants benefitted the efficiency and stability of nitrogen removal, which could reach 1.97 ± 0.25 g m^-2 d^-1 in summer and 0.42 ± 0.12 g m^-2 d^-1 in winter. Plant age and temperature were the main factors determining the microbial community structure. Compared with temperature, plant ages affected more significantly on relative abundance of microorganisms such as Chloroflexi, Nitrospirae, Bacteroidetes and Cyanobacteria, and functional genera for nitrification (e.g., Nitrospira) and iron reduction (e.g., Geothrix). The absolute abundance of total bacterial 16S rRNA ranged from 5.22 × 10⁸ to 2.63 × 10⁹ copies g^-1 and presented extremely significant negative correlation to plant age, which would lead to a decline in microbial function on information storage and processing. The quantitative relationship further revealed that the ammonia removal was related to 16S rRNA and AOB amoA, while nitrate removal was controlled by 16S rRNA, narG, norB and AOA amoA jointly. These findings suggested that a mature wetland for nitrogen removal enhancement should focus on aging microbes caused by old plants and possible endogenous pollution.

Effects of Enrofloxacin on Nutrient Removal by a Floating Treatment Wetland Planted with Iris pseudacorus: Response and Resilience of Rhizosphere Microbial Communities

Constructed wetlands (CWs), including floating treatment wetlands (FTWs), possess great potential for treating excessive nutrients in surface waters, where, however, the ubiquitous presence of antibiotics, e.g., enrofloxacin (ENR), is threatening the performance of CWs. In developing a more efficient and resilient system, we explored the responses of the FTW to ENR, using tank 1, repeatedly exposed to ENR, and tank 2 as control. Plant growth and nutrient uptake were remarkably enhanced in tank 1, and similar phosphorus removal rates (86~89% of the total added P) were obtained for both tanks over the experimental period. Contrarily, ENR apparently inhibited N removal by tank 1 (35.1%), compared to 40.4% for tank 2. As ENR rapidly decreased by an average of 71.6% within a week after each addition, tank 1 took only 4 weeks to adapt and return to a similar state compared to that of tank 2. This might be because of the recovery of microbial communities, particularly denitrifying and antibiotic-resistance genes containing bacteria, such as Actinobacteria, Patescibacteria, Acidovorax and Pseudomonas. After three ENR exposures over six weeks, no significant differences in the nutrient removal and microbial communities were found between both tanks, suggesting the great resilience of the FTW to ENR.

Differential efficacy of water lily cultivars in phytoremediation of eutrophic water contaminated with phosphorus and nitrogen

Excessive inputs of phosphorus (P) and nitrogen (N) trigger eutrophication of the water bodies, which promotes the undesirable growth of algal bloom and deterioration of the water quality, and aquatic biodiversity. Macrophytes provide an environmentally benign and economically viable paradigm for the ecological restoration of eutrophic aquatic ecosystems. Water lily (Nymphaea) is largely used as ornamental plant for landscaping, and it has been documented that water lily possesses the potentiality in mitigating polluted aquatic environments. In the present study, water lily cultivars Nymphaea Texas Dawn (NTD), Nymphaea Colorado (NC), Nymphaea Madame Wilfron Gonnère (NMWG), and Nymphaea Sunshine Princess (NSP) were investigated for their potency in alleviating the eutrophication. The concentrations of total P and total N were significantly higher in the leaves of NC and NSP compared with NTD and NMWG. Therefore, NC and NSP were selected for subsequent studies to decipher their recuperation efficacy on eutrophic waters at different growth stages. NC and NSP significantly reduced the concentrations of eutrophication indicators i.e., total P, NH₄⁺-N, and chemical oxygen demand in different gradients of the simulated eutrophic water in a growth-dependent manner. On the contrary, NC and NSP triggered a significant increase in the concentration of dissolved oxygen particularly at the seedling stage. Notably, the concentrations of total P (shoot and root) and total N (root) were relatively higher in NSP than NC. The study thus revealed a growth-dependent differential efficacy of NSP and NC in mitigating the different eutrophic waters.

Stigmasterol root exudation arising from Pseudomonas inoculation of the duckweed rhizosphere enhances nitrogen removal from polluted waters

Rhizospheric microorganisms such as denitrifying bacteria are able to affect 'rhizobioaugmention' in aquatic plants and can help boost wastewater purification by benefiting plant growth, but little is known about their effects on the production of plant root exudates, and how such exudates may affect microorganismal nitrogen removal. Here, we assess the effects of the rhizospheric Pseudomonas inoculant strain RWX31 on the root exudate profile of the duckweed Spirodela polyrrhiza, using gas chromatography/mass spectrometry. Compared to untreated plants, inoculation with RWX31 specifically induced the exudation of two sterols, stigmasterol and β-sitosterol. An authentic standard assay revealed that stigmasterol significantly promoted nitrogen removal and biofilm formation by the denitrifying bacterial strain RWX31, whereas β-sitosterol had no effect. Assays for denitrifying enzyme activity were conducted to show that stigmasterol stimulated nitrogen removal by targeting nitrite reductase in bacteria. Enhanced N removal from water by stigmasterol, and a synergistic stimulatory effect with RWX31, was observed in open duckweed cultivation systems. We suggest that this is linked to a modulation of community composition of nirS- and nirK-type denitrifying bacteria in the rhizosphere, with a higher abundance of Bosea, Rhizobium, and Brucella, and a lower abundance of Rubrivivax. Our findings provide important new insights into the interaction of duckweed with the rhizospheric bacterial strain RWX31 and their involvement in the aquatic N cycle and offer a new path toward more effective bio-formulations for the purification of N-polluted waters.

High denitrification potential but low nitrous oxide emission in a constructed wetland treating nitrate-polluted agricultural run-off

Constructed wetlands (CW) can efficiently remove nitrogen from polluted agricultural run-off, however, a potential caveat is nitrous oxide (N₂O), a harmful greenhouse gas and stratospheric ozone depleter. During five sampling campaigns, we measured N₂O fluxes from a 0.53 ha off-stream CW treating nitrate-rich water from the intensively fertilized watershed in Rampillon, France, using automated chambers with a quantum cascade laser system, and manual chambers. Sediment samples were analysed for potential N₂ flux using the HeO₂ incubation method. Both inlet nitrate (NO₃^-) concentrations and N₂O emission varied significantly between the seasons. In the Autumn and Winter inlet concentrations were about 11 mg NO₃^--N L^-1, and < 6.5 mg NO₃^--N L^-1 in the Spring and Summer. N₂O emission was highest in the Autumn (mean ± standard error: 9.7 ± 0.2 μg N m^-2 h^-1) and lowest in the Summer (wet period: 0.2 ± 0.3 μg N m^-2 h^-1). The CW was a very weak source of N₂O emitting 0.32 kg N₂O-N ha^-1 yr^-1 and removing around 938 kg NO₃^--N ha^-1 yr^-1, the ratio of N₂O-N emitted to NO₃^--N removed was 0.033%. The automated and manual chambers gave similar results. From the potential N₂O formation in the sediment, only 9% was emitted to the atmosphere, the average N₂ N ₂O ratio was high: 89:1 for N₂-N_potential: N₂O-N_potential and 1353:1 for N₂-N_potential: N₂O-N_emitted. These results indicate complete denitrification. The focused principal component analysis showed strong positive correlation between the gaseous N₂O fluxes and the following environmental factors: NO₃^--N concentrations in inlet water, streamflow, and nitrate reduction rate. Water temperature, TOC and DOC in the water and hydraulic residence time showed negative correlations with N₂O emissions. Shallow off-stream CWs such as Rampillon may have good nitrate removal capacity with low N₂O emissions.

Process-based modeling to assess the nutrient removal efficiency of two endangered hydrophytes: Linking nutrient-cycle with a multiple-quotas approach

Hydrophytes have been widely used to reduce nutrient levels in aquatic ecosystems, but only limited species with high nutrient removal efficiencies have been implemented. Thus, it is necessary to continually explore new candidate species with high nutrient removal efficiencies. To effectively explore the nutrient removal ability of hydrophytes, a new process-based model combining the multiple-quotas approach and nutrient-cycle model was developed. The multiple-quotas approach provides a theoretical framework to conceptually explain the uptake and response of autotrophs to multiple nutrients. The developed process-based model was validated using observational data from microcosm experiments with two emergent hydrophytes, Menyanthes trifoliata and Cicuta virosa. The results showed that both M. trifoliata and C. virosa effectively reduced nitrogen (N) and phosphorus (P) in both water and sediment layers, but M. trifoliata showed a higher removal efficiency for both nutrients than C. virosa, particularly for total ammonia + ammonium-nitrogen (NH_x-N) and nitrate-nitrogen (NO₃-N) in the sediment layer (M. trifoliata: 0.579-0.976 for NH_x-N, 0.567-0.702 for NO₃-N; C. virosa: 0.212-0.501 for NH_x-N, 0.466-0.560 for NO₃-N). In addition, M. trifoliata achieved the maximum removal efficiency for N and P at higher nutrient exposure levels than C. virosa (M. trifoliata: exposure level of 0.725-0.775; C. virosa: exposure level of 0.550-0.575). The developed model well simulated the species-specific growth patterns of hydrophytes depending on the nutrient exposure level as well as the N and P dynamics in the water and sediment layers. The approach adopted in this study provides a useful tool for discovering candidate species to improve hydrophyte diversity and effectively remove nutrients from aquatic ecosystems.

Recycled utilization of Iris pseudacorus in constructed wetlands: Litters self-consumption and nitrogen removal improvement

Aquatic plants litters from constructed wetlands might become pollutants without proper treatment. Due to its high carbon and low nitrogen contained, Iris pseudacorus litters have potential to be used as carbon source to enhance denitrification process in advanced treatments of secondary effluent from wastewater treatment plants. This study investigated the characteristics of carbon release form Iris pseudacorus litters and its performance on enhancement of nitrogen removal. The batch experiment showed that the organic carbon release process can be simulated by combining dissolution and hydrolysis process, and it was found that dissolved organic matters mainly consisted of 60% sugar and 35% humic acid-like compounds from the neutral detergent solution and hemicellulose of litters. The long-term operation of lab-scale constructed wetlands revealed a high nitrogen removal of 78.81-90.39% in treating the synthetic wastewater treatment plants effluent with the equivalent dosage of 25-150 g litters m^-2 d^-1. Furthermore, it is possible to establish an Iris pseudacorus self-consumed constructed wetland to reuse all of the litters produced during the operation. These findings can contribute to the understanding of the dynamics of carbon release from Iris pseudacorus litters and recycled utilization of plant biomass in the constructed wetlands.

A comparison of nutrient uptake efficiency and growth rate between different macrophyte growth forms

Aquatic macrophytes grow abundantly in many lowland streams and play a key role in ecosystem functioning, such as nutrient retention. In this study, we performed a microcosm experiment to quantify and compare the contribution of two freshwater macrophyte growth forms to nutrient cycling. We measured and compared inorganic nitrogen (NH₄-N and NO₃-N) and phosphorus (PO₄-P) uptake kinetic parameters (V_max and C_min) in 12 submerged and seven amphibious plant species. We tested whether relative growth rate (RGR) was related to high V_max and low C_min, and quantified changes in nutrient uptake kinetic in a subset of six out of 19 plants species during the growth season. Uptake rates of NH₄-N were higher in submerged compared to amphibious plants, whereas uptake rates of NO₃-N were significantly higher in amphibious species; PO₄-P uptake kinetics were not significantly different between the two growth forms. There were also significant seasonal differences in V_max NH₄-N rate among both submerged and amphibious species and in V_max NO₃-N among amphibious species. Highest uptake rates were observed in summer for both submerged and amphibious species. Overall, we found that nutrient uptake kinetics differed between the two growth forms within and between seasons. Consequently, the presence of both growth forms should extend the period of nutrient uptake across the year and enhance nutrient uptake within seasons. We conclude that higher functional diversity enhances annual nutrient uptake in streams and that stream restoration efforts should consider increasing the niche space available for both submerged and amphibious species.

Myriophyllum elatinoides growth and rhizosphere bacterial community structure under different nitrogen concentrations in swine wastewater

In this study, Myriophyllum elatinoides growth under different nitrogen (N) concentrations (2, 250, 300, 350 and 400 mg L^-1) and changes in rhizosphere bacterial community structure were investigated. High N (>300 mg L^-1) concentrations caused reduction in M. elatinoides biomass. Growth tended to stabilize at 49 days. N concentration in roots were higher than that in stems and leaves under high N conditions. TN and NH₄⁺ removal efficiencies reached 84.0% and 87.2%, respectively, in M. elatinoides surface flow constructed wetlands (SFCWs). Rhizosphere bacterial diversity increased over time. Proteobacteria, Firmicutes, Cyanobacteria, and Bacteroidetes dominated at the phylum level. Genera Turicibacter, Allochromatium, and Methylocystis increased at low N (<300 mg L^-1) concentrations, while Pseudomonas increased at high N concentrations over the experimental period. Redundancy analysis showed that pH was strongly correlated with changes in rhizosphere bacterial community structure. These findings helped to insight into N removal mechanism in M. elatinoides.

Microbial diversity for the improvement of nitrogen removal in stormwater bioretention cells with three aquatic plants

The aquatic plants Iris pseudacorus L., Canna indica L. and Lythrum salicaria L. have been proved to be potential choices for nitrogen removal. However, little is known about microbial diversity for the improvement of nitrogen removal (nitrification and denitrification) in stormwater bioretention cells with the above plants. In this study, batch experiments were conducted to investigate nitrogen removal, substrate layer status, and bacterial community structure to understand microbial diversity and evaluate its effects on performances of nitrogen removal. Ammonia nitrogen removal in the bioretention cell with Lythrum salicaria L. was the highest (88.1%), which was consistent with oxidation reduction potential (ORP) in the bioretention cells. Whilst, removals for both total nitrogen and nitrate were the highest in the bioretention cell with Canna indica L., which was in line with urease activity in the mentioned cells. The used plants had different impact on top 11 dominant microflora at phylum level in the used bioretention cells. Ramlibacter and Nitrosomonadaceaea were both responsible for the difference of nitrogen removal in the bioretention cells with three aquatic plants, suggesting the enhancement of the above dominant microflora could strengthen nitrogen removal in the used bioretention cells.

Vegetated Ditch Habitats Provide Net Nitrogen Sink and Phosphorus Storage Capacity in Agricultural Drainage Networks Despite Senescent Plant Leaching

The utility of vegetated ditch environments as nutrient sinks in agricultural watersheds is dependent in part on biogeochemical transformations that control plant uptake and release during decomposition. We investigated nitrogen (N) and phosphorus (P) uptake and release across four P enrichment treatments in ditch mesocosms planted with rice cutgrass (Leersia oryzoides) during the summer growing and winter decomposition seasons. Measured N retention and modeled denitrification rates did not vary, but P retention significantly increased with P enrichment. At the end of the growing season, root biomass stored significantly more N and P than aboveground stem and leaf biomass. Decomposition rates were low (<10% organic matter loss) and not affected by P enrichment. Nitrogen and P export during winter did not vary across the P enrichment gradient. Export accounted for <10% of observed summer N uptake (1363 mg m−2), with denitrification potentially accounting for at least 40% of retained N. In contrast, net P retention was dependent on enrichment; in unenriched mesocosms, P uptake and release were balanced (only 25% net retention), whereas net retention increased from 77% to 88% with increasing P enrichment. Our results indicate that vegetated ditch environments have significant potential to serve as denitrification sinks, while also storing excess P in agricultural watersheds.

Assessment of the Nutrient Removal Potential of Floating Native and Exotic Aquatic Macrophytes Cultured in Swine Manure Wastewater

Although eutrophication and biological invasion have caused serious harm to aquatic ecosystems, exotic and even invasive plants have been used extensively in phytoremediation water systems in China. To identify native aquatic plants with excellent water restoration potential, two representative native floating aquatic plants from Guangdong Province, namely Ludwigia adscendens (PL) and Trapa natans (PT), were selected, with Eichhornia crassipes as a control, to study their growth status, adaptability, and nutrient removal potentials in swine manure wastewater. The results demonstrated that the two native plants offered greater advantages than E. crassipes in water restoration. Within 60 days, PL and PT exhibited excellent growth statuses, and their net biomass growth rates were 539.8% and 385.9%, respectively, but the E. crassipes decayed and died with an increasing HRT (hydraulic retention time). The PL and PT could adjust the pH of the wastewater, improve the dissolved oxygen and oxidation-reduction potential, and reduce the electrical conductivity value. The removal rates of NH₄⁺–N, NO₃⁻–N, NO₂⁻–N, total nitrogen, total phosphorus, chemical oxygen demand (COD), and Chl-a in the PL group reached 98.67%, 64.83%, 26.35%, 79.30%, 95.90%, 69.62%, and 92.23%, respectively; those in the PT group reached 99.47%, 95.83%, 85.17%, 83.73%, 88.72%, 75.06%, and 91.55%, respectively. The absorption contribution rates of total nitrogen (TN) and total phosphorus (TP) in the PL group were 40.6% and 43.5%, respectively, while those in the PT group were 36.9% and 34.5%, respectively. The results indicated that L. adscendens and T. natans are both promising aquatic plants for application to the restoration of swine manure wastewater in subtropical areas.

Effects of water level and vegetation on nitrate dynamics at varying sediment depths in laboratory-scale wetland mesocosms

Recent increases in the frequency of extreme floods and droughts associated with climate change can affect fluctuating groundwater or wetland water levels and wetland plant growth, and consequently cause redox condition changes in nitrogen dynamics in wetland sediments. Here, we studied the fate of nitrate (NO₃^-), dissolved organic carbon (DOC), and the microbial characteristics at different sediment depths in response to water levels (i.e., 5 or 2.5 cm) above the sediment surface and in the presence or absence of plants (Phragmites communis Trin) for four months in three wetland mesocosms. Results showed that mesocosm A (MA) with a high water level (5 cm above the surface) and plants had significantly higher DOC concentrations (17.57 ± 8.22 mg/L) in sediment that were actively consumed by microorganisms than other mesocosms with low water level (MB) and without plant (MC) (8.77 ± 2.38 mg/L and 7.87 ± 2.72 mg/L in MB and MC, respectively). Consequently, the most of influent NO₃^- (20 mg-N/L) dramatically reduced in the vicinity of plant roots (-20 to -15 cm sediment depth) where active denitrification was expected in MA. Moreover, the functional genes involved in denitrification such as narG (2.4 × 10⁸ -3.5 × 10⁸ copies·g^-1) and nirS (5.6 × 10⁶-1.1 × 10⁷ copies·g^-1) were more abundant in this mesocosm. The profile of the microbial community structure at the class level revealed that Alphaproteocbacteria (MA: 14.19 ± 1.19%; MB: 14.01 ± 0.51%; MC: 15.21 ± 2.76%) and Actinobacteria (MA: 8.21 ± 1.91%; MB: 13.91 ± 2.13%; MC: 11.75 ± 3.43%) were predominant in all three mesocosms. Interestingly, the clustered heatmap supported the obvious difference in microbial composition of MA from other mesocosms showing relatively more abundant Clostridia (6.71 ± 1.54%) and Deltaproteobacteria (7.05 ± 0.68%). These results can provide an insight to understand the biogeochemical nitrogen cycle associated with climate change in wetland systems.

A novel submerged Rotala rotundifolia, its growth characteristics and remediation potential for eutrophic waters

The vegetative growth and remediation potential of Rotala rotundifolia, a novel submerged aquatic plant, for eutrophic waters were investigated on different sediments, and under a range of nitrogen concentrations. Rotala Rotundifolia grew better on silt than on sand and gravel in terms of plant height, tiller number and biomass accumulation. Percent increment of biomass was enhanced at low water nitrogen (ammonium nitrogen concentration ≤10 mg/L). The maximum total nitrogen and total phosphorus removals in the overlying water were between 54% to 66% and 42% to 57%, respectively. Nitrogen contents in the sediments increased with increasing water nitrogen levels, whereas, nitrogen contents in the plant tissues showed no apparent regularity, and the greatest value was obtained at ammonium nitrogen concentration 15 mg/L. Both phosphorus contents in the sediments and tissues of plants were not affected significantly by additional nitrogen supply. Direct nitrogen uptake by plants was in the range of 16% to 39% when total phosphorus concentration was 1.0 mg/L. These results suggested that Rotala Rotundifolia can be used to effectively remove nitrogen and phosphorus in eutrophic waters.

Effectiveness of various wetland vegetation species on mitigating water pollution from highway runoff

This study selected and tested five submerged aquatic vegetation-based (SAV) wetlands to improve highway runoff treatment in best management practices. The removal efficiencies of suspended solid (SS), chemical oxygen demand (COD), total nitrogen (TN), ammonia nitrogen ( NH 4 + - N ), and total phosphorus (TP) in the five SAV wetlands were analyzed. Furthermore, the lead (Pb) and zinc (Zn) accumulation capabilities of five submerged macrophytes were determined. The obtained results show that Ceratophyllum demersum wetlands achieved the highest nutrient removal and had the heavy metal accumulation property. Vallisneria natans showed the highest bioaccumulation of Pb among all tested species. Ceratophyllum demersum wetlands showed the highest average removal efficiencies of SS (82.97%), COD (62.08%), TN (77.63%), NH 4 + - N (76.24%), TP (77.55%), Pb (96.24%), and Zn (91.23%). The tendencies of contaminant removal showed seasonal variation, and SAV wetlands performed better in summer than in spring and autumn. Consequently, SAV wetlands showed selectivity for contaminant removal. PRACTITIONER POINTS: Chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) in highway runoff were removed by submerged aquatic vegetation (SAV). Ceratophyllum demersum and Myriophyllum spicatum wetlands performed well on heavy metal removing. Ceratophyllum demersum showed the highest removal efficiencies of TSS, COD, TN, NH 4 + - N , and TP. The SAV wetlands performed better in summer than in other seasons.

Comparative study on nitrogen removal and functional genes response between surface flow constructed wetland and floating treatment wetland planted with Iris pseudacorus

Excessive nitrogen accumulated from wastewater with low C/N ratio is a new threat to water ecosystem. In this study, surface flow constructed wetland (SFCW) and floating treatment wetland (FTW) planted with Iris pseudacorus were set in parallel for nitrogen removal. The nitrogen removal efficiencies and pathways, as well as the abundance and functional diversities of the microbial community, were investigated. The results demonstrated that SFCW generally had better nitrogen removal performance than FTW did over four seasons. The average total nitrogen removal efficiency was 66.0% and 43.8% in SFCW and FTW, respectively. The plant uptake played a vital role in nitrogen reduction, which accounted for 29.3% and 7.7% of the total removed nitrogen in SFCW and FTW, respectively. A combination of high-throughput sequencing and quantitative polymerase chain reaction analysis revealed that the two wetland systems had complete nitrogen cycling, and the narG gene was the dominant nitrogen-transformation functional gene in both systems. More abundant denitrifying genes in SFCW than in FTW were also responsible for higher removal capacity of nitrogen. The results suggest that the planting pattern of wetland vegetation has an important impact on nitrogen removal efficiency by influencing the plant absorption and the development of microbial communities.

The response of nitrogen removal and related bacteria within constructed wetlands after long-term treating wastewater containing environmental concentrations of silver nanoparticles

The wide application of consumer products containing silver nanoparticles (AgNPs) inevitably results in their release into sewer systems and wastewater treatment plants, where they would encounter (and cause potential negative impacts) constructed wetlands (CWs), a complex biological system containing plants, substrate and microorganisms. Herein, the long-term effects of environmental AgNPs concentrations on nitrogen removal, key enzymatic activities and nitrogen-related microbes in constructed wetlands (CWs) were investigated. The short-term exposure (40 d) to AgNPs significantly inhibited TN and NH₄⁺-N removal, and the inhibition degree had a positive relationship with AgNPs levels. After about 450 d exposure, 200 μg/L AgNPs could slightly increase average TN removal efficiency, while presence of 50 μg/L AgNPs showed no difference, compared to control. The NH₄⁺-N removal in all CWs had no difference. The present study indicated that short-term AgNPs loading evidently reduced nitrogen removal, whereas long-term exposure to AgNPs showed no adverse impacts on NH₄⁺-N removal and slightly stimulated TN removal, which was related to the increase of corresponding enzymatic activities. After exposing AgNPs for 450 d, the abundance of relative functional genes and the composition of key community structure were determined by qPCR and high-throughput sequencing, respectively. The results showed that the abundance of amoA and nxrA dramatically higher than control, whereas the abundance of nirK, nirS, nosZ and anammox 16S rRNA was slightly higher than control, but had no statistical difference, which accorded with the TN removal performance. The microbial community analysis showed that different AgNPs concentrations could affect the microbial diversity and structure. The changes of the relative abundance of nitrogen-related genera were associated with the impacts of AgNPs on the nitrogen removal performance. Overall, the AgNPs loading had impacts on the key enzymatic activities, the abundance of nitrogen-related genes and microbial community, thus finally affected the treatment performance of CWs.

Effects of ofloxacin on nitrogen removal and microbial community structure in constructed wetland

Constructed wetlands (CWs) have emerged as a promising technology for the purification of micro-polluted water. However, their nitrogen removal performance can be significantly degraded by design, operational, and environmental factors. The present study investigates the effects of ofloxacin (OFL: 0.1, 10, and 1000 μg L^-1) and plants (Cyperus alternifolius L. and Typha angustifolia L.) on nitrogen removal in a micro-polluted CW system over a duration of 12 weeks. The effects were evaluated by investigating NH₄-N and NO₃-N removal efficiency, nitrification genes (amoA-AOA and amoA-AOB), denitrification genes (nirK and nirS), fungal 18S rRNA gene and microorganism community structure. The results showed that in unplanted CWs, OFL increased the NH₄-N removal efficiency (from 72.6% to 80.7-82.1%), the abundances of amoA-AOA, nirS, nirK and fungal 18S rRNA gene, and the bacterial diversity but decreased the abundance of both amoA-AOB and bacterial richness. In contrast, both the nitrogen removal efficiency (83.4-89.5% for NH₄-N and 33.8-38.5% for NO₃-N) and bacterial diversity/richness were not significantly affected by OFL in planted CWs. In planted systems, OFL increased the relative abundance of Arthrobacter, Pseudomonas, and Enterococcus, which are proven antibiotic-resistant bacteria. This study showed that CWs are able to remove nitrogen from antibiotic-contaminated micro-polluted water, which might primarily be attributed to the presence of plants that protect the microorganism community.

Nitrogen release and its influence on anammox bacteria during the decay of Potamogeton crispus with different values of initial debris biomass

Aquatic macrophytes play a significant role in the nutrient cycle of freshwater ecosystems. However, nutrients from plant debris release into both sediments and overlying water if not timely harvested. To date, minimal information is available regarding nutrient release and its subsequent influences on bacterial communities with decaying debris. In this study, Potamogeton crispus was used as a model plant. Debris biomass levels of 0 g (control, J-CK), 10 g dry weight (DW) (100 g DW/m², J-10 g), 40 g DW (400 g DW/m2, J-40 g) and 80 g DW (800 g DW/m², J-80 g) were used to simulate the different biomass densities of P. crispus in field. The physicochemical parameters of overlying water and sediment samples were analysed. The community composition of anammox bacteria in the sediment was also analysed using 16S rRNA genes as markers. The results showed that dissolved oxygen and pH dramatically decreased, whereas total nitrogen (TN) and NH₄⁺-N concentrations increased in the overlying water in the initial stage of P. crispus decomposition. However, NO₃^--N concentration changes in the overlying water were more complicated. The concentrations of organic matter, TN and NH₄⁺-N in the sediment all increased, but the rate of increase varied among the groups with different initial biomass levels, indicating that these physicochemical properties in sediment are significantly affected by debris biomass level and decay time. In addition, the order of anammox bacteria abundance was J-40 g > J-CK > J-80 g > J-10 g. Moreover, the community structure of anammox bacteria were simpler compared to that of J-CK as debris biomass level increased. The results demonstrate that P. crispus debris decomposition could affect the ecological distribution of anammox bacteria. Such influence clearly varies with varying amounts of P. crispus biomass debris. This information could be useful for the management of aquatic macrophytes in freshwater ecosystems.

Plant-microbial synergism: An effective approach for the remediation of shale-gas fracturing flowback and produced water

Effective and affordable treatment of hydraulic fracturing flowback and produced water (FPW) is a major challenge for the sustainability of unconventional shale-gas exploration and development. We investigated the effectiveness of different combinations of activated sludge (AS), three microbial preparations, and ten plants (ryegrass, water dropwort, typha, reed, iris, canna, water caltrop, rape, water spinach, and Alternanthera philoxeroides) on the treatment performance of FPW. Water quality parameters (NH₄-N, NO₃-N, NO₂-N, COD_cr, and BOD) and the algal toxicity of the treated FPW were used as metrics to assess the treatment efficiency. The results showed that AS had higher treatment efficiency than the prepared microorganisms, and water dropwort was the best plant candidate for boosting performance of AS treatment of FPW. The treated FPW showed improved water quality and microbial diversity. The Shannon-Wiener index increased from 4.76 to 7.98 with FPW treatment. The relative abundance of microbes with a greater resistance to high salt conditions, such as Bacteroidetes, Firmicutes, Chloroflexi, increased substantially in the treated FPW. The combination of water dropwort and AS showed the greatest improvement in water quality, the highest algal density and microbial diversity, thus indicating good potential for this candidate in the treatment of FPW.

Comparison of two different ecological floating bio-reactors for pollution control in hyper-eutrophic freshwater

The use of ecological floating beds (EFBs) to control water pollution has been increasingly reported worldwide due to the severe situation of eutrophication in water bodies. In this study, two kinds of EFBs were set up under similar condition to compare their purification efficiency in hyper-eutrophic water. The conventional ecological floating bed (CEFB) was made of polystyrene foam board, and the enhanced ecological floating bio-reactor (EEFB) was designed as an innovative hollow, thin floating bed integrated with substrates of zeolite and limestone. The results showed that the EEFB increased treatment efficiency of total nitrogen (TN), total phosphate (TP), and ammonia nitrogen (NH₄⁺-N) to 63.5%, 59.3%, and 68.0%, respectively. Plant accumulation was the main pathway for TN and TP removal in the CEFB. Microbial degradation played an increasingly important role in TN and TP removal in the EEFB. A higher concentration of nitrogen cycling bacteria was recorded in the EEFB than the CEFB (P < 0.05), suggesting that the substrates might enhanced the removal efficiency of the EEFB by promoting the growth of microorganisms rather than their absorption effect.

Comparison of Iris pseudacorus wetland systems with unplanted systems on pollutant removal and microbial community under nanosilver exposure

Rapidly developing industry raises concerns about the environmental risks of silver nanoparticles (AgNPs), but the effects of AgNPs on the performance and microbial community in the constructed wetlands remain unclear. In this study, long-term exposure of AgNPs in two VFCWs was conducted to determine the effects of AgNPs on the pollutant removal and microbial community structure. Before exposing AgNPs, the water quality of effluent was better in planted wetland (CW2), compared with unplanted wetland (CW1). After continuous exposure of 100μg/L AgNPs, the COD (chemical oxygen demand) removal of two CWs had no difference. However, addition of AgNPs reduced the nitrogen and phosphorus removal in two CWs, with decreasing average removal efficiencies of ammonia nitrogen from 46.31% to 32.09% and 59.66% to 51.06%, total nitrogen from 57.76% to 43.78% and 67.35 to 60.58%, total phosphorus from 71.29% to 59.31% and 67.35% to 60.58%, respectively. The vegetable wetlands showed higher resistances to AgNPs loading than unplanted wetlands. In addition, AgNPs accumulated in the wetland substrate, especially in the soil layer with the silver concentration of approximately 4.32μg/g. The small portion of silver was found in plant tissues, and plants played a minor role to remove the AgNPs from wastewater. Moreover, the constructed wetlands could effectively remove the AgNPs from the synthetic wastewater. The illumine high-throughput sequencing results demonstrated the variations of the bacterial community structure at the exposure of AgNPs. The results showed that the dominant phyla were Proteobacteria, Acidobacteria and Bacteroidetes. Compared with unplanted wetlands, the contents of several nitrifying bacteria such as Candidatus Nitrososphaera (AOA) and Nitrospira (NOB) at genus level increased, leading to the higher nitrogen removal in the planted wetlands.

Synergistic phytoremediation of wastewater by two aquatic plants (Typha angustifolia and Eichhornia crassipes) and potential as biomass fuel

The ability of a mixture of Typha angustifolia and Eichhornia crassipes to remove organics, nutrients, and heavy metals from wastewater from a Thailand fresh market was studied. Changes in physicochemical properties of the wastewater including pH, temperature, chemical oxygen demand, dissolved oxygen, biochemical oxygen demand (BOD), total P, TOC, conductivity, total Kjeldahl nitrogen, NO₃^--N, NH₃-N, and metal (Pb, Cd, and Zn) concentrations were monitored. In the aquatic plant (AP) treatment, 100% survival of both species was observed. Dry biomass production and growth rate of T. angustifolia were approximately 3.3× and 2.7× of those for E. crassipes, respectively. The extensive root system of the plants improved water quality as determined by a marked decrease in turbidity in the AP treatment after 7 days. BOD content served as a useful indicator of water quality; BOD declined by 91% over 21 days. Both T. angustifolia and E. crassipes accumulated similar quantities of metals in both roots and shoots. Accumulation of metals was as follows: Zn > Cd > Pb. A study of calorific value and biomass composition revealed that T. angustifolia and E. crassipes possessed similar carbon content (~ 35%), hydrogen content (~ 6%), and gross calorific value. E. crassipes contained up to 16.9% ash and 65.4% moisture. Both species are considered invasive in Thailand; however, they may nonetheless provide practical benefits: In addition to their combined abilities to treat wastewater, T. angustifolia holds potential as an alternative energy source due to its high biomass production.

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.

Effects of root exudates on denitrifier gene abundance, community structure and activity in a micro-polluted constructed wetland

In micro-polluted constructed wetland (CW), the low pollutant concentrations and the low COD/N ratios (chemical oxygen demand: total nitrogen in influent), make the biological treatment more difficult. It is expected that root exudates drive microbial-based transformations within plant rhizosphere. In this research, the roles of root exudates of three aquatic plants (Phragmites australis, Typha angustifolia and Cyperus alternifolius) in improving the growth of heterotrophic denitrifying bacteria were determined in a micro-polluted CW. In studied root rhizospheres, the total organic carbon (TOC) released from the plant roots varied significantly among plant species and seasons; the average TOC ranged from 0.1715 to 0.9221mgg^-1rootDMd^-1, which could fuel a denitrification rate of approximately 156-841kgNO₃^--Nha^-1year^-1 if all were used by the denitrifying bacteria; the abundances of nirK- and nirS-encoding bacteria were significantly influenced by the concentration of sucrose and glucose (0.869≤r≤0.933, p<0.05), and microbial community richness and diversity had response to root exudates. The results revealed that root exudates can act as endogenous carbon sources for heterotrophic denitrifying bacteria and ultimately determine the microbe distribution patterns in micro-polluted CW.

Bacterial communities and enzymatic activities in the vegetation-activated sludge process (V-ASP) and related advantages by comparison with conventional constructed wetland

A new-developed vegetation-activated sludge process (V-ASP) was implemented for decentralized domestic wastewater treatment, and studied in lab-scale and full-scale. The main purpose of this work was the investigation of biomass activities and microbial communities in V-ASP by comparison with conventional constructed wetland (CW), to unveil the causations of its consistently higher pollutants removal efficiencies. Compared with CWs, V-ASP has greater vegetation nitrogen and phosphorus uptake rates, higher biomass and enzymatic activities, and more bacteria community diversity. The microbial community structure was comprehensively analyzed by using high-throughput sequencing. It was observed that Proteobacteria was dominated in both CWs and V-ASPs, while their subdivisions distribution was rather different. V-ASPs contained a higher nitrite-oxidizing bacteria (Nitrospira) abundances that resulted in a consistently better nitrogen removal efficiency. Hence, a long-term experiment of full-scale V-ASP displayed stably excellent capability in resistance of influent loading shocks and seasonal temperature effect.

Comparative bioavailability of ammonium, nitrate, nitrite and urea to typically harmful cyanobacterium Microcystis aeruginosa

Phosphorus is generally considered as the prime limiting nutrient responsible for cyanobacterial blooms. However, recent research is drawing attention to the importance of bioavailable nitrogen (N) in freshwater eutrophication. This study investigated the bioavailability of NO3(-)-N, NO2(-)-N, NH4(+)-N and Urea-N under different concentrations of 1.2, 3.6 and 6.0mgL(-1) to Microcystis aeruginosa. Overall, Urea-N ranked the first in promoting M. aeruginosa growth, followed by NO3(-)-N and NO2(-)-N. However, the algal growth cultured in NH4(+)-N was depressed under test N levels. The bioavailability of N to M. aeruginosa was seriously influenced by both N forms and N concentrations (p<0.01). Total N concentrations in Urea-N treatment decreased the fastest, which were corresponding with the μ values of M. aeruginosa. The high enzymic activities of nitrate reductase, nitrite reductase and glutamine synthetase indicated that the decomposition process for urea is effective, which contributed in N assimilation and utilization in M. aeruginosa cells.

Enhancing the water purification efficiency of a floating treatment wetland using a biofilm carrier

Floating treatment wetlands (FTWs) and biofilm carriers are widely used in water purification. The objective of the present work was to explore whether and to what extent an FTW integrated with plants and biofilm carriers (FTW-I) could enhance the nutrient removal efficiency. Significantly higher removal rates of ammonia nitrogen (85.2 %), total phosphorus (82.7 %), and orthophosphate (82.5 %) were observed in the FTW-I treatment relative to the FTW with plants (FTW-P; 80.0, 78.5, and 77.6 %, respectively) and the FTW with biofilm carriers (FTW-B; 56.7, 12.9, and 13.4 %, respectively) (p < 0.05). The mass balance results indicated that plant uptake was the main pathway for N and P removal (accounting for 58.1 and 91.4 %, respectively) in FTW-I, in which only 1.2 % of the N and 5.7 % of the P was deposited on the bottom of the tank. In addition, the plants translocated 43.9 and 80.2 % of the N and P in the water and 83.5 and 88.3 % of the absorbed N and P, respectively, into their aboveground tissues. The combination of an FTW and biofilm carriers can improve the efficiency of water purification, and nutrients can be rapidly removed from the system by harvesting the aboveground plant tissues.

Effect of orthophosphate and bioavailability of dissolved organic phosphorous compounds to typically harmful cyanobacterium Microcystis aeruginosa

Results show that Microcystis aeruginosa can utilize both dissolved organic phosphorus (DOP) and orthophosphate (DIP) even under low phosphorus (P) conditions to sustain its growth. Total P concentrations decreased markedly in all three P source treatments. Alkaline phosphatase activity (APA) in the different P sources tested changed in response to the DOP and DIP. The APA of DOP groups remained low after decreasing significantly, but the APA in the DIP treatments remained high during the period of culture. Changes in APA at different PO4(3-)-P concentrations in a culture medium revealed negative correlations between APA and DIP. However, a positive relationship was observed between APA and DOP under low P concentrations. These findings indicate that M. aeruginosa can regulate its physiological metabolism to acclimate to low ambient DIP environments.