Treatment Performance Of Constructed Wetland Research Articles

Simulation and optimization of magnetic and experimental study of magnetic field coupling constructed wetland.

AbstractThis study developed a novel constructed wetland (CW) coupled with a magnetic field for treating domestic wastewater, and the magnetic field distribution was solved and optimized by the finite element method. Herein, we investigated the effects of optimizing magnetic field optimization and studied its impact on CW treatment performance and the responses of a microbial community. The optimization results showed that the average magnetic field strength of the CW unit increases from 3mT to 8mT, and the proportion of areas with magnetic field strength greater than 5mT also increases from 30% to 74%. The water quality analysis results showed that the removal of chemical oxygen demand (COD) and NH4+-N (p < 0.01) was significantly increased by the magnetic field (average 3mT), increasing by 12.2% and 8.49%, respectively. Moreover, the removal of COD and NH4+-N (p < 0.01) was more significantly increased by M-VFCW(O) (average 8mT), increasing by 15.58% and 49.1%, respectively. The magnetic field application shifted significantly the abundance of dominant bacteria in CWs. Relative abundance of dominant bacteria such as Proteobacteria (63.3%), Firmicutes (4.72%) and Actinobacteria (2.11%) that played an important role in organics removal and nitrification and denitrification-related bacteria such as Nitrospirae (1.48%) and Planctomycetes (9.58%) significantly promoted in M-VFCW(O). These results suggest that introducing a magnetic field into CWs may improve organics and nitrogen removal via the biological process, and the optimization of the magnetic field was significant in enhancing the performance of VFCWs.

Recent Advances in the Effects of Biochar on Constructed Wetlands: Treatment Performance and Microorganisms

Constructed wetlands (CWs) are a kind of green environmental protection technology, which are widely used in sewage treatment. Traditional CWs are faced with the problem of a low treatment effect of high-concentration sewage. In recent years, biochar, as a new type of adsorption material, has been used in CWs because of its advantages of large specific surface area, strong adsorption capacity, and wide material sources. This paper systematically summarized the characteristics of biochar and the preparation of biochar by studying the changes in microorganisms added to CWs and compared the effects of different treatment methods coupled with biochar on the treatment performance of CWs. The effects of biochar coupled with CWs on enzyme activity, functional genes, metabolites, and microbial communities were investigated. This review summarizes how different preparation methods affect the properties of biochar and how these biochar properties cause changes in the microorganisms added to CWs. It provides a new theoretical basis for the treatment of pollutants in CWs.

White hard clam (Meretrix lyrata) shells as novel filter media to augment the phosphorus removal from wastewater

It is well recognized that filter media play a crucial role in constructed wetlands (CWs) for decontamination of phosphorus (P)-rich wastewater. This study investigates the suitability of raw white hard clam shells (WHC) and white hard clam shells thermally modified at 800 °C (WHC-M800) as potential media to enhance P treatment performance in CWs. The results indicated that both WHC and WHC-M800 displayed appropriate physicochemical properties, such as high porosity, excellent hydraulic conductivity, and rich Ca content. WHC-M800 exhibited a superior P adsorption capacity (38.7 mg/g) to WHC (12.8 mg/g). However, the practical utilization of WHC-M800 as filter media in CWs may be compromised, due to certain limitations, for example: extremely high pH values in the post-adsorption solutions; high weight losses during calcination and adsorption processes; low mechanical strength; and intensive energy consumption. In contrast, the WHC demonstrated significant advantages of reasonably high P adsorption capacity, locally abundant availability, low cost, and marginal side effects. The fractionation of inorganic P of WHC and WHC-M800 revealed that Ca-bounded P was the most dominant binding form, followed by loosely bound P, Fe-P, occluded P, and Al-P. The present study demonstrates that recycling of WHC shells as a potential substrate in CWs provides a feasible method for upgrading P removal in CWs. Additionally, it helps to reduce waste WHC shells in a simple, cheap, and eco-friendly way, thus can double environmental benefits.

Impacts of carbon-based nanomaterials on nutrient removal in constructed wetlands: Microbial community structure, enzyme activities, and metabolism process

The increasing use of raw carbon-based nanomaterials (CBNs) will inevitably affect wastewater treatment systems. Constructed wetlands (CWs) are ecological wastewater treatment facilities and can intercept the vast particles pollutant, including CBNs. However, the impacts of CBNs on the treatment performance of CWs have no available knowledge. Therefore, we systematically inspected the effects of single-walled and multi-walled carbon nanotubes (SWCNTs and MWCNTs) and fullerene nanoparticles (C60) on CW performance under 180-day exposure to 0, 10 and 1000 μg/L concentrations. The results showed that CBNs had marginally adverse impacts on chemical oxygen demand (COD) and total phosphorus (TP) removal, whereas nitrogen removal declined by 24.1 %–42.7 % following long-term exposure to CBNs. MWCNTs had the greatest inhibition effect on nitrogen removal, followed by SWCNTs and C60. The CBNs also induced reactive oxygen species (ROS) overproduction as the increasing concentration, which confirmed that CBNs have biotoxic effects in CWs. The variation of functional microbial community and the inhibition of enzyme activities were the dominant reasons for the decline in nitrogen removal efficiency. Furthermore, predictive functional profiling showed that CBNs affected functional gene abundance, and caused a decline in the enzymes abundance connected to nitrogen removal by the end of the 180-day exposure period.

Can biochar application improve nitrogen removal in constructed wetlands for treating anaerobically-digested swine wastewater?

In this study, aerated constructed wetlands (CWs) modified with biochar were used to treat anaerobically-digested swine wastewater. Nitrogen removal performance and mechanisms were comparatively investigated by exploring the dynamic transformation of dissolved organic matter (DOM) in water. It was demonstrated that removal efficiencies of chemical oxygen demand (COD) and ammonium nitrogen (NH4+-N) were 63.06–77.18% and 87.19–96.54% in aerated CWs with and without biochar application under various influent strengths. However, total nitrogen (TN) removal could not be enhanced in aerated CWs with biochar application (30.92–40.12%) compared that in conventional aerated CWs (40.83–48.70%), which might be related to insufficient carbon sources and lower pH values in systems. More average N2O emission fluxes (185.43–443.33 μg m−2 h−1) were detected in aerated CWs with biochar application at higher influent strengths. Humic-like substances were identified as major components of DOM in water by using fluorescence excitation-emission-matrix combined with parallel factor analysis (EEM-PARAFAC), which could result in insufficient carbon source for denitrification due to the refractory characteristics. The results suggested that the high-temperature biochar may be inappropriate to effectively increase anaerobically-digested swine wastewater treatment performance in CWs under intermittent aeration operations.

Assessment of uncertainty in constructed wetland treatment performance and load estimation methods.

Constructed wetlands (CWs) are commonly established to reduce pollution load from different sources. In environmental permits, the load remaining after CW purification is typically estimated through concentration and flow measurements. This load monitoring is often carried out using long water quality sampling intervals, which causes uncertainty in load estimation. In this study, a large suspended solids (SSs) and dissolved organic carbon (DOC) dataset was used to quantify the uncertainty in load estimation at the inlet and outlet of a CW with different sampling frequencies (sampling every 1, 2, 3 or 4weeks). A method to reduce the uncertainty by dividing the CW flow duration curve (FDC) into four equal categories and assigning mean/median concentration for each category according to the measured concentrations was also tested. The results showed that estimated SS load was associated with considerable uncertainty and that this uncertainty increased with lower sampling frequency. The FDC method was able to decrease the uncertainty, but much still remained, especially when concentrations of the measured variable showed great variation. In such cases, sensor technology might be a feasible option for further reducing the uncertainty.

Benzene Removal in Laboratory Scale Model Wetland under Different Electron Acceptor Conditions Treating Sulfate-Rich Wastewater

Constructed wetlands (CWs) are shown to be suitable for the treatment of water contaminated with benzene. However, due to the high sulfate concentration (around 850 mg/L) in influent, sulfate reduction will be stimulated in CWs. Subsequently, the toxicity of sulfide will be a catastrophe to the plants, and the treatment performance of CWs will be impaired. In this study, nitrite and nitrate were used as competitor with sulfate for electron acceptor to prevent the sulfate reduction. With the inflow benzene concentration ranged from 21.6-103 μg, and the accumulation of sulfide reached up to 39%, the removal efficiency of benzene decreased from 86% to 27%. However, with the addition of nitrite and nitrate, the sulfide accumulation was inhibited successfully, and the benzene removal efficiency recovered to 85%. In conclusion, both nitrite and nitrate can be an option for preventing sulfate reduction and sulfide toxicity in CWs treating sulfate-rich wastewater.

Influence of the Microbial Community in the Treatment of Acidic Iron-Rich Water in Aerobic Wetland Mesocosms

ABSTRACT Microbial communities certainly have an influence on the treatment performance of constructed wetlands (CWs); however, microbial community structure or microbial activity (MA) is rarely concurrently or comparatively quantified in relation to treatment performance. The objective of this study was to better understand the influence of the resident CW microbial community on water treatment performance in CWs. Using laboratory-scale mesocosm wetlands, several CW design variables and water chemistry variables were quantitatively and comparatively determined to assess their role in Fe(II) removal from simulated acid mine drainage (AMD). Initial AMD pH, initial AMD Fe(II) concentration, and overall wetland MA had a significant effect on an apparent first-order iron removal rate constant. Under the aerobic conditions used in this study, the presence of Phragmites australis did not have a significant effect on treatment performance. Of all the factors studied, the MA associated with the fixed microbial community had the greatest influence on the rate of iron removal. The presence of a microbiological component was shown to increase the first-order iron removal rate by a factor of 10. Following exposure to AMD, partial detachment of the fixed microbial regime was also observed, highlighting the potential consequences of AMD on the microbial community.