Ammonia, phosphate, phenol, and copper(II) removal from aqueous solution by subsurface and surface flow constructed wetland

Effects of pH on simultaneous Cr(VI) and p-chlorophenol removal and electrochemical performance in Leersia hexandra constructed wetland-microbial fuel cell

Cr(VI) and p-chlorophenol (4-CP) are common pollutants in the aquatic environment but are difficult to degrade and have complex toxic effects. A downflow Leersia hexandra microbial fuel cell (DLCW-MFC) system was constructed to purify Cr(VI) and 4-CP polluted wastewater, as well as to investigate the effects of different pHs on Cr(VI) and 4-CP removal, electrochemical performance, physiological and biochemical responses, and Cr enrichment status of L. hexandra. The results showed that the DLCW-MFC had the highest Cr(VI) and 4-CP removal rates at pH 6.5, which were 99.0% and 78.6%, respectively. At the same time, 543 mV output voltage and 72.25 mW/m2 power density of the system were generated at pH 6.5, which were better than those at pH 7.4 and pH 5.8. The electrochemical performance result showed that pH 6.5 enhanced charge transfer ability and ion diffusion ability of the system. pH 6.5 also promoted growth and photosynthesis, and enhanced the Cr enrichment capacity (4.56 mg/10 plants) of L. hexandra. These results demonstrate that pH 6.5 was the optimum pH for the DLCW-MFC synchronous treatment of Cr(VI) and 4-CP as well as the generation of electricity. The DLCW-MFC designed in this study will provide a reference for purifying polluted wastewater and generating electricity.

Removal of Cr(vi) and p-chlorophenol and generation of electricity using constructed wetland-microbial fuel cells based on Leersia hexandra Swartz: p-chlorophenol concentration and hydraulic retention time effects

Heavy metals and phenolic compounds existing in polluted wastewater are a threat to the environment and human safety. A downflow Leersia hexandra Swartz constructed wetland-microbial fuel cell (DLCW–MFC) was designed to treat polluted wastewater containing Cr(vi) and p-chlorophenol (4-CP). To determine the effect of 4-CP concentration and hydraulic retention time (HRT) on the performance of the DLCW–MFC system, the wastewater purification, electricity generation, electrochemical performance, and L. hexandra growth status were studied. Addition of 17.9 mg L⁻¹ 4-CP improved the power density (72.04 mW m⁻²) and the charge transfer capacity (exchange current, 4.72 × 10⁻³ A) of DLCW–MFC. The removal rates of Cr(vi) and 4-CP at a 4-CP concentration of 17.9 mg L⁻¹ were 98.8% and 38.1%, respectively. The Cr content in L. hexandra was 17.66 mg/10 plants. However, a 4-CP concentration of 35.7 mg L⁻¹ inhibited the removal of Cr(vi) and the growth of L. hexandra, and decreased the electricity generation (2.5 mW m⁻²) as well as exchange current (1.21 × 10⁻³ A) of DLCW–MFC. An increase in power density and removal of Cr(vi) and 4-CP, along with an enhanced transport coefficient of L. hexandra, was observed with HRT. At an optimal HRT of 6.5 d, the power density, coulomb efficiency, and exchange current of DLCW–MFC were 72.25 mW m⁻², 2.38%, and 4.99 × 10⁻³ A, respectively. The removal rates of Cr(vi) and 4-CP were 99.0% and 78.6%, respectively. The Cr content and transport coefficient of L. hexandra were 4.56 mg/10 plants and 0.451, respectively. Thus, DLCW–MFC is a promising technology that can be used to detoxify polluted wastewater containing composite mixtures and synchronously generate electricity.

A downflow Leersia hexandra Swartz constructed wetland-microbial fuel cell is used to treat polluted wastewater containing composite mixtures and synchronously generate electricity.

The Partial Contribution of Constructed Wetland Components (Roots, Gravel, Microorganisms) in the Removal of Phenols: A Mini Review

Constructed wetlands (CW) have attracted growing interest in wastewater treatment research in the last 20 years, and have been investigated intensively worldwide. Many of the basic processes occurring in CWs have been qualitatively established; however, much quantitative knowledge is still lacking. In this mini review, the proportionate contributions of the different system components to removal of contaminants are examined. The main objective of this mini review is to provide a more in-depth assessment of the interactions between the porous bed, plants, and microorganisms during the removal of organic contaminants from the water in a subsurface flow CW system. In addition, a unique technique to study the partial contribution to the total removal of contaminants in a CW is described. Future studies in this field will expand our knowledge of any synergistic or antagonistic interactions between the components and facilitate improved CW construction and operation. Here, phenol will be used as a model industrial organic contaminant to illustrate our current understanding of the contributions of the different components to total removal. I will also discuss the various factors influencing the efficacy of bacteria, whether planktonic or as biofilm (on porous bed or plant roots), in subsurface flow CWs.

Removal effects of different emergent-aquatic-plant groups on Cu, Zn, and Cd compound pollution from simulated swine wastewater

Aquatic plants play effective in removing heavy metal (HM) as a prominent factor of bioremediations, however, there are still knowledge gaps in species selection and configuration for high removal efficiency (RE) of compound HM and ornamental value. In this study, seven emergent-aquatic-plant species were configured into seven groups and planted in a simulated swine wastewater (SW) with Cu, Zn, and Cd for 75 days in summer. REs of Cu, Zn, and Cd were 45.06-86.93%, 42.40-87.22%, and 73.85-85.52% at day 75, respectively. Higher REs were observed from day 30-45 for Cu and Zn, whereas days 15-30 for Cd. The synergistic removal of Zn and Cu or Zn and Cd was almost observed (p < 0.05). The configuration of G5 (S. tabernaemontani, I. sibirica, and P. cordata) was generally efficient roles in the removal at day 45, with REs of 85.14%, 87.06%, and 83.56% for Cu, Zn, and Cd, respectively. The dry weight of roots, water NH₄⁺-N, temperature, pH, and dissolved oxygen acted on heavy-metal removal. During days 45-75, concentrations of Cu, Zn, and Cd in G5 were 0.52-0.66, 0.54-0.65, and 0.23-0.33 mg L^-1. The former two were below the limits of Grade Ⅱ (1.0 mg L^-1) and the latter was above the limits of Grade Ⅴ (0.1 mg L^-1; GB3838-2002). Thus, G5 could be optimal for Cu and Zn removal from simulated SW, however, efficient Cd removal is required to ensure efficient SW recycling.

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.

Implementation of a full-scale constructed wetland to treat greywater from tourism in Suluban Uluwatu Beach, Bali, Indonesia

This original research examines a full-scale subsurface Constructed Wetland (CW) system in Indonesia, where most CW research has been limited to laboratory scale experiments. The CW system was located in Bali and built in 2015 in a single series formation. This study aims to demonstrate the performance of the system in treating greywater and examine the nutrient content plants' above-ground biomass. The CW was arranged in linear sequence composed of one unplanted (CW1) and five planted treatments of Iris pseudacorus (CW2), Caladium bicolor (CW3), Rhoe discolor (CW4), Sansevieria trifasciata (CW5) and Heliconia psittacorum (CW6). There has been little research on Caladium bicolor, Rhoe discolor and Sansevieria trifasciata in a full-scale CW application. Our results showed fluctuating efficiency (%) in the reduction of Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Suspended Solid (TSS), Oil and Grease (O&G), Nitrate and Phosphate. The highest removal efficiency for CW1, CW2, CW3, CW4, CW5, CW6 were O&G (63.63%), BOD (90.66%), Nitrate (83.55%), BOD (80%), BOD (82.88%) and Phosphate (89.93%) respectively. After the experimental period, S. trifasciata and H. psittacorum experienced a decrease in Total N concentration, while H. psittacorum experienced a decrease in phosphate in above-ground biomass. Species of R. discolor, C. bicolor and I. pseudacorus showed good performance in terms of their growth and development. Although high removal efficiency was observed at certain times, this study showed the negative removal efficiencies at times among parameters as a consequence of the low Hydraulic Retention Time (HRT) and high Hydraulic Loading Rate (HLR).

Nutrient removal, methane and nitrous oxide emissions in a hybrid constructed wetland treating anaerobic digestate

A pilot hybrid constructed wetland (CW) planted with reeds (Phragmite australis) and rice (Oryza sativa L.) was designed to treat liquid anaerobic digestate in the Yangtze River Delta, China. The hybrid CW system was composed of four stages: two reed vegetated vertical subsurface flow beds (VSSF: U1 and U2) in sequence, followed by a reed vegetated horizontal subsurface flow bed (HSSF: U3) and a rice vegetated surface flow bed (SF: U4). The average loading rate of digestate was 3.6 m³ per day during the experimental period. The average concentrations of TN and TP in the influent were 379 ± 58 mg L^-1 and 29.6 ± 9.2 mg L^-1, while the average removal efficiencies of TN and TP were 94.6% and 88.4%. Both TN and TP removal efficiencies in the second VSSF containing zeolite gave the highest removal performance, in which the mass removal rates were 21.3 ± 8.0 g-N m^-2 d^-1 and 0.99 ± 0.69 g-P m^-2 d^-1, respectively. Similarly, the highest removal performance for COD was also observed in the second VSSF with a mass removal rate of 79.9 ± 72.4 g-COD m^-2 d^-1. On the other hand, the average CH₄ and N₂O fluxes were highest in the first VSSF, at 31.8 ± 12.9 mg m^-2 h^-1 and 3.7 ± 2.8 mg m^-2 h^-1, respectively. There was a significant linear relationship between CH₄ flux and DOC concentration in the pore water as well as a correlation between N₂O flux and TN concentration. Total GWP of the hybrid CWs, derived from CH₄ and N₂O emissions, was 792.4 kg CO₂-eq, of which CH₄ and N₂O emissions accounted for 66.0% and 34.0%, respectively. Consequently, the hybrid CWs emitted on average 0.93 kg CO₂-eq to remove 1 kg COD while the average EF of TN_in was 0.34%, suggesting that the use of multistage hybrid CWs could be efficiency-wise and environmentally a promising strategy for anaerobic digestate treatment.

Optimization of reactive media for removing organic micro-pollutants in constructed wetland treating municipal landfill leachate

The removal of organic micro-pollutants (OMPs) from landfill leachate in constructed wetland (CW) media having different material mixtures of sand (S), clay (C), and iron powder (Fe) was investigated using experimental column study. The use of S:C:Fe media consisting of 60:30:10% (w/w) and cattail as vegetation was found optimum for the removals of 2,6-DTBP, BHT, DEP, DBP, and DEHP at 67.5-75.4% during long-term operation of 373 days. Adsorption and biodegradation were confirmed as predominant mechanisms for their removal in CW media but their contribution in total removal varied depending on chemical properties of OMPs. Adsorption kinetic could be well explained by pseudo-second-order whereas biodegradation kinetic followed first-order reaction. The adsorption affinity of OMPs to CW media was S:C:Fe > S:C > S in descending order. This study demonstrated high and sustainable removal of OMPs during long-term operation of CW with the optimized reactive media.

Removal of ammoniacal nitrogen from municipal landfill leachate with floating Typha domingensis (Typhaceae)

 A promising method for the treatment of effluents is the use of floating macrophytes. Ammoniacal nitrogen is a typical compound present in urban landfill leachates and its removal is important due its toxicity to several organisms. Therefore, the study evaluated Typha domingensis survival and nitrification potential artificially floating in domestic solid waste leachate. Plants were exposed for 35 days to leachate (100, 75 and 50 %) and to rainwater with N:P:K (control). Dissolved oxygen (DO) of the treatments was periodically measured, and ammoniacal nitrogen, nitrite and nitrate were analyzed before and after exposure. At the end of the experiment, plant survival rate was calculated. After two weeks, DO increased twice in the control, three times in 50 % leachate, four times in 75 % leachate, and eight times in 100 % leachate. At the end of the experiment, ammoniacal nitrogen was no longer detected, there was a significant reduction of nitrite, and a significant increase of nitrate in the treatments containing leachate. Plant survival was higher in those individuals exposed to 100 % leachate and decreased at lower leachate concentrations: 98 %, 94 %, 92 %, and 86 %. The study demonstrated that the ammoniacal nitrogen concentration of the leachate was not toxic to T. domingensis, and that it was efficient in the removal of this compound from the effluent, indicating that the species may be used artificially floating for the removal of this contaminant from domestic solid waste landfill leachate when in low concentrations.

Optimization process of organic matter removal from wastewater by using Eichhornia crassipes

This study aimed to determine the optimal conditions for organic matter removal from wastewater by Eichhornia crassipes (E.C). As a matter of fact, a complete factorial design was used to determine the effect of residence time (X₁), plant density (X₂) and initial chemical oxygen demand (COD) concentration (X₃) on the phytoremediation process. The process's performance was measured on COD (Y₁), NH₄⁺ (Y₂) and PO₄^3- (Y₃), with the results indicating a reduction of 8.59-81.71% of COD (Y₁); 22.53-95.81% of NH₄⁺ (Y₂) and 0.54-99.35% of PO₄^3- (Y₃). Then, the first-order models obtained for COD, NH₄⁺ and PO₄^3- removal were validated using different statistical approaches such as statistical and experimental validation. Moreover, multi-response optimization was carried out through different scenarios. On the whole, the results obtained indicated that two serial ponds are required for an optimum organic matter removal by Eichhornia crassipes. Indeed, for the first pond, a residence time of 15 days is needed with a plant density of 60 ft/m² and an initial concentration of about 944 mg/L. The second was the same residence time as the first with similar plant density of 60 ft/m² and an initial load 192 mg/L (> 200 mg/L). Optimal organic matter removal from wastewater using Eichhornia crassipes requires two ponds arranged in chain.

Municipal wastewater treatment potential and metal accumulation strategies of Colocasia esculenta (L.) Schott and Typha latifolia L. in a constructed wetland

This paper elucidates phytoremediation potential of two wetland plants (Colocasia esculenta (L.) Schott and Typha latifolia L.) for municipal wastewater treatment using constructed wetland (CW) mesocosms. The concentrations (mg L^-1) of chemical oxygen demand (COD), total kjeldahl nitrogen (TKN), Cu, Cd, Cr, Zn, and Pb in municipal wastewater were higher than permissible Indian standards for inland surface water disposal; however, Mn and Ni were within the permissible limits. The pollutant removal efficiencies of planted CWs varied as electrical conductivity (EC) 67.8-71.4%; COD 70.7-71.1%; TKN 63.8-72.3%; Cu 75.3-83.4%; Cd 73.9-83.1%; Mn 74.1-74.5%; Cr 64.8-73.6%; Co 82.2-84.2%; Zn 63.3-66.1%; Pb 71.4-77.9%; and Ni 76-80%. Mass balance analysis revealed that the loss of metals from wastewater was equivalent to net accumulation in plants and natural degradation of metals. Metal accumulation strategies of plants were investigated using bioconcentration factor (BCF) and translocation factor (TF) of metals which indicated that both plants could be employed for phytostabilization (BCF > 1 and TF < 1) of Cu, Cd, Co, Pb, and Ni and phytoextraction (BCF > 1 and TF > 1) of Mn and Zn. The study demonstrated that a reduction of pollutants (except Pb) was observed within permissible levels (BIS) and suggested disposal of municipal wastewater into the inland surface water bodies after 20 days of treatment. The study concluded that both the plants could potentially be used for an efficient municipal wastewater treatment using constructed wetlands.