Plants In Constructed Wetlands Research Articles

Effects of Cattails and Hydraulic Loading on Heavy Metal Removal from Closed Mine Drainage by Pilot-Scale Constructed Wetlands

This study demonstrated heavy metal removal from neutral mine drainage of a closed mine in Kyoto prefecture in pilot-scale constructed wetlands (CWs). The CWs filled with loamy soil and limestone were unplanted or planted with cattails. The hydraulic retention time (HRT) in the CWs was shortened gradually from 3.8 days to 1.2 days during 3.5 months of operation. A short HRT of 1.2 days in the CWs was sufficient to achieve the effluent standard for Cd (0.03 mg/L). The unplanted and the cattail-planted CWs reduced the average concentrations of Cd from 0.031 to 0.01 and 0.005 mg/L, Zn from 0.52 to 0.14 and 0.08 mg/L, Cu from 0.07 to 0.04 and 0.03 mg/L, and As from 0.011 to 0.006 and 0.006 mg/L, respectively. Heavy metals were removed mainly by adsorption to the soil in both CWs. The biological concentration factors in cattails were over 2 for Cd, Zn, and Cu. The translocation factors of cattails for all metals were 0.5–0.81. Sulfate-reducing bacteria (SRB) belonging to Deltaproteobacteria were detected only from soil in the planted CW. Although cattails were a minor sink, the plants contributed to metal removal by rhizofiltration and incubation of SRB, possibly producing sulfide precipitates in the rhizosphere.

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

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

Increasing plant diversity to mitigate net greenhouse effect of wastewater treatment in floating constructed wetlands

Constructed wetlands (CWs) are an effective wastewater treatment technology but also an important source of greenhouse gases. Converting CW plant biomass to biofuel as an alternative to fossil fuels can reduce carbon dioxide emissions, and plant diversity influences this mitigation effect. However, the impact of plant diversity on net global warming potential combining carbon dioxide and non-carbon dioxide emissions in CWs is less studied, especially in floating CWs where the substrate is absent and both above- and below-ground biomass can be harvested easily for biofuel production. In this paper, four species richness levels were assembled in 90 hydroponic microcosms that simulated floating CWs to explore the effect of plant diversity on global warming potential. The results showed that: (1) increasing species richness increased the aboveground and total biomass but had no effect on belowground biomass, and carbon dioxide emissions were reduced by converting both above- and belowground biomass to biofuel to replace fossil fuels; (2) increasing species richness increased non-carbon dioxide emissions but decreased the overall global warming potential of combined carbon dioxide and non-carbon dioxide emissions; (3) communities containing Oenanthe javanica had lower overall global warming potential; and (4) some species (Oenanthe javanica) had a stronger mitigating effect on global warming potential than species richness. Our observations suggest that it is economically feasible to produce biofuel from hydroponically grown plants in floating CWs, and net energy gain can be achieved. Assembling high species richness and carefully selecting species in floating CWs alongside converting plant biomass to biofuel offers a greener form of wastewater treatment that can contribute to cleaner production strategies.

Regulation of heavy metals accumulated by Acorus calamus L. in constructed wetland through different nitrogen forms

Improving accumulation of heavy metals (HMs) by plants is an important pathway for constructed wetland (CW) to alleviate the environmental risks caused by their release. This study aims to regulate HMs (Cr, Ni, Cu, Zn, and Cd) accumulated by Acorus calamus L. in the sandy substrate CW with different nitrogen forms, including ammonia (NH4+), nitrate (NO3‾), and NH4+/NO3‾ (1:1) in synthetic tailwaters. In general, the removal efficiency of HMs by CW could reach 92.4% under the initial concentrations below 500 μg/L. Accumulation percentages of HMs in the shoots and roots of plants in CW with NH4+ and NH4+/NO3‾ influents increased by 52–395% and 15–101%, respectively, when compared with that of NO3‾ treatment. Influents with NH4+ promoted plant growth of Acorus calamus L. and metabolic functions, such as carbohydrate metabolism/amino acid metabolism, related to HMs mobilization of rhizosphere bacterial communities, which might induce more organic acids and amino acids secreted by plants and microbes during their metabolic processes. These are the main reasons for the enhancive mobilization of HMs from their precipitation fractions and their uptake by plants in CW with NH4+ treatments. Moreover, the enhancement of organics secreted from plants and microbes also led to the high denitrification efficiency and nitrogen removal in CW. Overall, this study could provide a feasible method for the enhancive accumulation of HMs by wetland plants via the regulation water treatment process to appropriately increase NH4+ for CW.

Microbial abundance and community in constructed wetlands planted with Phragmites australis and Typha orientalis in winter

In winter, the withering of plants in constructed wetlands (CWs) limits the removal of pollutants by plants. It is prospective to improve performance of CWs through targeted transformation of the microbial abundance and community. This research characterized the purification performance of CWs planted with Phragmites australis (P. australis, PA) and Typha orientalis (T. orientalis, TO) and those in the unplanted constructed wetland (CT, control). PA showed some superiority in the removal rates of COD and NH4 +-N (42.06% ± 4.25% and 70.51% ± 1.46%, respectively). The 16S rRNA gene copy numbers (7.60 ± 0.57 × 104 copies/g) and the ammonia oxygen bacteria (5.30 ± 0.06 × 103 copies/g) were the highest in PA. In microbial structure, compared with TO and CT, in addition to common microorganisms that can remove contaminants, many specific functional genera were detected in PA (Rhodobacter, Catellibacterium, Hydrogenophaga, Geothrix and Aeromonas), which promoted the removal of NH4 +-N and COD. Novelty statement The microbial abundance and communities were characterized in CWs with different plant species during winter. Better removal efficiency with high microbial abundance and diversified microbial community were found in CWs planted with Phragmites australis. This study confirmed that in winter, withered plants in CWs can effectively remove NH4 +-N and COD by affecting microbial abundance and community structure.

Enhancing nitrogen removal from anaerobically-digested swine wastewater through integration of Myriophyllum aquaticum and free nitrous acid-based technology in a constructed wetland.

Despite of low operation costs and convenient maintenance, the application of natural systems for swine wastewater treatment has been limited by large construction area and unsatisfactory effluent quality. Introducing ammonium high uptake aquatic plants and shifting nitrogen removal pathway from nitrate to nitrite in constructed wetlands (CWs) has been regarded as promising approach to promote their performances. This study aimed to establish nitrite pathway and enhance N removal via free nitrous acid (FNA)-sediment treatment and Myriophyllum aquaticum vegetation in the CWs treating anaerobically digested swine wastewater. Nitrite pathway was successfully and stably achieved in the M. aquaticum CW with FNA-treated sediment. The overall removal efficiencies of ammonium nitrogen and total nitrogen were 42.3±10.2% and 37.7±9.3% in the planted CWs with FNA-treated sediment, which were 76.3% and 65.4% higher than those in the conventional oxidation pond system, respectively. Microbial community analysis (qPCR and metagenomics) suggested that the nitrite pathway established through FNA-sediment treatment was based on the inactivation of nitrite oxidizing bacteria (lower nxrA gene abundance) and the reduction of relative abundances of NOB (especially Nitrobacter and Nitrospira). During the denitrification processes, the integration of M. aquaticum vegetation with FNA-sediment treatment can lower the nitrate reduction by decreasing narG gene abundances and decreasing the relative abundances of napA affiliated bacteria (especially Bradyrhizobium), while strengthening reduction of nitrite and nitrous oxide by increasing nirK and nosZ gene abundances and enriching the corresponding affiliated microbial taxa, Mycobacterium and Bacillus, respectively. Our findings suggest that applying FNA-based technology in CW systems is technically and economically feasible, which holds promise for upgrading current CW systems treating swine wastewater to meet future water quality requirements.

Enhanced Benzofluoranthrene Removal in Surface Flow Constructed Wetlands with the Addition of Carbon.

Polycyclic aromatic hydrocarbons (PAHs), as hazardous pollutants, could be removed by constructed wetlands (CWs). While the traditional substrate of CWs has a weak adsorption capacity for PAHs, in this study, the carbonous fillers—activated carbon (AC) and biochar—were added into the substrate of surface flow CWs to improve the removal performance of benzofluoranthrene (BbFA), a typical PAH. The results showed that the BbFA removal efficiencies in CWs with the addition of AC and biochar were 11.8 and 1.2% higher than those in the Control group, respectively. Simultaneously, the removal efficiencies of NO3––N were 42.8 and 68.4% in these two CWs, while the BbFA content in the substrate and plants with the addition of carbon was lower than that in the Control group. The addition of carbonous filler reduced the absorption of PAHs by plants in CWs and enhanced microbial degradation. The microbial community results showed that the relative abundance of Proteobacteria, especially γ-proteobacteria, was higher with the addition of fillers, which related to PAH degradation.

Effects of salinity on the treatment of synthetic petroleum-industry wastewater in pilot vertical flow constructed wetlands under simulated hot arid climatic conditions

Petroleum-industry wastewater (PI-WW) is a potential source of water that can be reused in areas suffering from water stress. This water contains various fractions that need to be removed before reuse, such as light hydrocarbons, heavy metals and conditioning chemicals. Constructed wetlands (CWs) can remove these fractions, but the range of PI-WW salinities that can be treated in CWs and the influence of an increasing salinity on the CW removal efficiency for abovementioned fractions is unknown. Therefore, the impact of an increasing salinity on the removal of conditioning chemicals benzotriazole, aromatic hydrocarbon benzoic acid, and heavy metal zinc in lab-scale unplanted and Phragmites australis and Typha latifolia planted vertical-flow CWs was tested in the present study. P. australis was less sensitive than T. latifolia to increasing salinities and survived with a NaCl concentration of 12 g/L. The decay of T. latifolia was accompanied by a decrease in the removal efficiency for benzotriazole and benzoic acid, indicating that living vegetation enhanced the removal of these chemicals. Increased salinities resulted in the leaching of zinc from the planted CWs, probably as a result of active plant defence mechanisms against salt shocks that solubilized zinc. Plant growth also resulted in substantial evapotranspiration, leading to an increased salinity of the CW treated effluent. A too high salinity limits the reuse of the CW treated water. Therefore, CW treatment should be followed by desalination technologies to obtain salinities suitable for reuse. In this technology train, CWs enhance the efficiency of physicochemical desalination technologies by removing organics that induce membrane fouling. Hence, P. australis planted CWs are a suitable option for the treatment of water with a salinity below 12 g/L before further treatment or direct reuse in water scarce areas worldwide, where CWs may also boost the local biodiversity.Graphical abstract

Effect of wastewater depth to the performance of short-term batching-experiments horizontal flow constructed wetland system in treating domestic wastewater

Constructed wetland (CW) is one of alternative technologies to treat domestic wastewater rather than using physico-chemical processes. In this research, the efficiency of CW to treat domestic wastewater was analyzed.Short-term batching-experiments of horizontal flow CW under different wastewater depth (35 cm and 45 cm) planted with native plants of Lepironia articulata and Scirpus grossus was tested for 5 days to remove Biological Oxygen Demand (BOD 5 ), Chemical Oxygen Demand (COD), Total Suspended Solid (TSS), ammonium and phosphate. Results showed that all planted CW showed high removal of BOD 5 , COD, TSS, ammonium and phosphate with values up to 99.70%, 96.94%, 99.03%, 100% and 99.5%, respectively. The addition of plants significantly increases the BOD 5 , COD and TSS removal up to 27%, 38.5% and 40% compared to the non-planted beds, respectively. The wastewater depth of 45 cm had a significantly lower dissolved oxygen concentration inside CW as compared to the 35 cm depth, resulting in lower efficiency of BOD 5 and COD removals. The addition of plants showed a significant increase in ammonium and phosphate removal, indicating both plants performance in up taking nutrients from wastewater. S. grossus showed a slightly higher capability in up taking phosphate compared to the L. articulata. No significant difference was obtained for nutrient removal under different wastewater depth. The result of this research showed that short-term planted CW was reliable in treating domestic wastewater with high organic and nutrient concentration characteristics.

Aromatic Compounds and Organic Matter Behavior in Pilot Constructed Wetlands Treating Pinus Radiata and Eucalyptus Globulus Sawmill Industry Leachate

The objective of this research was to evaluate the fate of aromatic compounds and organic matter in pilot constructed wetlands (CW) treating Pinus radiata and Eucalyptus globulus sawmill industry leachate. Six lab-scale surface flow CW were built and fed in batches. Three CW were fed with P. radiata leachate, while the other three CW were fed with E. globulus leachate. Each group of three CW included two CW planted with Phragmites australis and one unplanted CW as control unit. A stable hydraulic retention time of seven days was maintained in each CW. The organic loading rate was gradually increased in three phases in the CW fed with P. radiata leachate (i.e., from 12 to 19 g COD/m2/day) and with E. globulus leachate (i.e., from 14 to 40 g COD/m2/day). The operation of the six CWs lasted 98 days. The CW treating P. radiata and E. globulus leachate had a similar performance. The highest performance was obtained by the unplanted CW (approximately 10–20% higher than the planted CW), without significant differences observed between the P. radiata and E. globulus leachate treatment, regarding the removal efficiencies of organic matter and total phenolic compounds. The planted systems were probably affected by the high concentrations of these compounds applied, which probably created a toxic environment hindering the microbial community growth.

The Potential of Constructed Wetland Plants for Bioethanol Production

Five plant species from two Chinese constructed wetland (CW) environments were studied for the production of bioethanol using simultaneous saccharification and fermentation (SSF). Fourteen CW plant species were found in the constructed wetlands and four species (Phragmites australis, Fargesia spathacea F., Thalia dealbata, and Juncus effusus L.) containing the highest contents of holocellulose (between 50 and 55% d.b.) as well as a highly abundant invasive species (Eupatorium adenophorum) were selected for further study of bioethanol production. Among the selected species, P. australis, T. dealbata, and J. effusus L. exhibited high glucose conversion efficiencies between 42 and 46% of the sample dry mass. These three species were then subjected to SSF at 38 °C with Saccharomyces cerevisiae BY4742 and obtained ethanol titers between 30 and 35 g/L. These results indicate promise for the application of CW plants in second-generation biofuel production.

Role of Wetland Plants and Use of Ornamental Flowering Plants in Constructed Wetlands for Wastewater Treatment: A Review

The vegetation in constructed wetlands (CWs) plays an important role in wastewater treatment. Popularly, the common emergent plants in CWs have been vegetation of natural wetlands. However, there are ornamental flowering plants that have some physiological characteristics similar to the plants of natural wetlands that can stimulate the removal of pollutants in wastewater treatments; such importance in CWs is described here. A literature survey of 87 CWs from 21 countries showed that the four most commonly used flowering ornamental vegetation genera were Canna, Iris, Heliconia and Zantedeschia. In terms of geographical location, Canna spp. is commonly found in Asia, Zantedeschia spp. is frequent in Mexico (a country in North America), Iris is most commonly used in Asia, Europe and North America, and species of the Heliconia genus are commonly used in Asia and parts of the Americas (Mexico, Central and South America). This review also compares the use of ornamental plants versus natural wetland plants and systems without plants for removing pollutants (organic matter, nitrogen, nitrogen and phosphorous compounds). The removal efficiency was similar between flowering ornamental and natural wetland plants. However, pollutant removal was better when using ornamental plants than in unplanted CWs. The use of ornamental flowering plants in CWs is an excellent option, and efforts should be made to increase the adoption of these system types and use them in domiciliary, rural and urban areas.

Purification of water contaminated with Hg using horizontal subsurface constructed wetlands.

As a global pollutant, Hg (Hg) since the turn of the last century has received increased attention. Decreasing the emission of Hg into the food chain and the atmosphere is an effective way to reduce the Hg damage. The current study provided information about pilot-scale horizontal subsurface flow (HSSF) constructed wetlands (CWs) to remove different Hg species in polluted water. Synthetic wastewater was fed to two HSSF CWs, one was planted with Acorus calamus L and the other was unplanted as a control. The total Hg (THg), dissolved Hg (DHg), and particulate Hg (PHg) from five sites along the HSSF CWs were analyzed to describe the process of Hg removal. Results show that the CWs have high removal efficiency of Hg which is more than 90%. The removal efficiencies of THg and DHg from the unplanted CW were 92.1 ± 3.6% and 72.4 ± 13.1%, respectively. While, the removal efficiencies of THg and DHg in planted CW were 95.9 ± 7.5% and 94.9 ± 4.9%, which were higher than that in blank CW. The PHg was mainly removed in the first quarter of the CWs, which was also revealed by the partition coefficient Kd. To a certain extent, the effect of plants depends on the hydraulic retention time (HRT). The results in the current study show the potential of the HSSF-CWs for restoration from Hg-contaminated water.

Purification of leachate from sludge treatment beds by subsurface flow constructed wetlands: effects of plants and hydraulic retention time.

Sludge treatment beds (STBs) have been used widely in many countries due to low energy consumption, low operating and maintenance costs, and better environmental compatibility. Penetration, evaporation, and transpiration are the main processes for sludge dewatering in STBs. However, the leachate quality from STBs usually cannot meet discharge limits. Moreover, such leachate has very low COD/N ratio, which makes it difficult to treat. In the present study, two subsurface flow (SSF) constructed wetlands (CWs) were investigated for the treatment of leachate from STBs under three different hydraulic retention time (HRT) (3days, 4days, 6days), aiming for evaluating the effects of plants and HRT on treatment performance, as well as the potential of SSF CWs to treat sludge leachate with low COD/N ration. The results showed that plants play an important role in leachate treatment. The best treatment performance was achieved with HRT of 4days. In this condition, the mean removal efficiencies of COD (chemical oxygen demand), NH4+-N, TN (total nitrogen), and TP (total phosphorus) in the planted and the unplanted CWs were 61.6% (unplanted - 3.7%), 76.6% (unplanted 43.5%), 70% (unplanted 41%), and 65.6% (unplanted 6%), respectively. Heavy metal concentrations were below the Chinese integrated wastewater discharge standard during the experimental period in the planted CW, and the removal efficiencies in the planted CW system were higher than in the unplanted CW system. In all, planted SSF CWs can be an effective approach in removing leachate from sludge treatment beds. Furthermore, considering to temperature and seasonal variation, the leachate from STBs needs to be further studied in pilot- and full-scale condition.

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.

Review of Constructed Wetlands for Acid Mine Drainage Treatment

The mining industry is the major producer of acid mine drainage (AMD). The problem of AMD concerns at active and abandoned mine sites. Acid mine drainage needs to be treated since it can contaminate surface water. Constructed wetlands (CW), a passive treatment technology, combines naturally-occurring biogeochemical, geochemical, and physical processes. This technology can be used for the long-term remediation of AMD. The challenge is to overcome some factors, for instance, chemical characteristics of AMD such a high acidity and toxic metals concentrations, to achieve efficient CW systems. Design criteria, conformational arrangements, and careful selection of each component must be considered to achieve the treatment. The main objective of this review is to summarize the current advances, applications, and the prevalent difficulties and opportunities to apply the CW technology for AMD treatment. According to the cited literature, sub-surface CW (SS-CW) systems are suggested for an efficient AMD treatment. The synergistic interactions between CW components determine heavy metal removal from water solution. The microorganism-plant interaction is considered the most important since it implies symbiosis mechanisms for heavy metal removal and tolerance. In addition, formation of litter and biofilm layers contributes to heavy metal removal by adsorption mechanisms. The addition of organic amendments to the substrate material and AMD bacterial consortium inoculation are some of the strategies to improve heavy metal removal. Adequate experimental design from laboratory to full scale systems need to be used to optimize equilibria between CW components selection and construction and operational costs. The principal limitations for CW treating AMD is the toxicity effect that heavy metals produce on CW plants and microorganisms. However, these aspects can be solved partially by choosing carefully constructed wetlands components suitable for the AMD characteristics. From the economic point of view, a variety of factors affects the cost of constructed wetlands, such as: detention time, treatment goals, media type, pretreatment type, number of cells, source, and availability of gravel media, and land requirements, among others.

Enhanced removal of Microcystis bloom and microcystin-LR using microcosm constructed wetlands with bioaugmentation of degrading bacteria

The prevalence of cyanobacterial bloom (Cyano-bloom) and hepatotoxic microcystin (MC) pollution caused by eutrophication poses serious problems to aquatic ecosystems and public health. However, conventional water treatment technologies are inefficient for removing cyanotoxins. In this study, the performance of microcosm constructed wetlands (CWs) in the removal of Cyano-bloom, microcystin-LR (MC-LR), and nutrients was investigated following repeated loading of pollutants. The effects of plant and bioaugmentation of selected MC-LR degrading bacteria on removal efficiency, degrading gene mlrA abundance, and bacterial community structure were examined. More than 90% of the MC-LR and chlorophyll-a was eliminated by CWs after 3 d of hydraulic retention time (HRT) without a lag phase. No significant differences between planted and unplanted CWs were found in the MC-LR and Cyano-bloom removal and mlrA gene abundance. Nevertheless, the plants improved nutrient removal to reduce eutrophication. Bioaugmentation markedly enhanced the degradation of MC-LR from 16.7 μg L−1 to below the threshold value within 12 h, which could help shorten the HRT of CWs by increasing functional MC-LR degrading bacteria. In the soil of CWs, the following six bacterial genera with MC-LR-degrading potential were found: Sphingopyxis, Methylotenera, Pseudomonas, Methylosinus, Novosphingobium, and Sphingomonas. Among them, the first three also significantly proliferated in CWs with bioaugmentation during MC-LR degradation, indicating their high adaptability and MC-LR removal contribution. These results suggested that CWs could provide suitable conditions for MC-LR degrading microorganism proliferation, and CWs with bioaugmentation could be effective and practical measures for the remediation of eutrophication and MC pollution.

Performance of a coupling device combined energy-efficient rotating biological contactors with anoxic filter for low-strength rural wastewater treatment

Abstract In order to meet the requirements of decentralized sewage treatment in rural China, a source-sorted treating method was proposed, including a black water pre-treating anaerobic baffled reactor (ABR), an anoxic filter (ANF), a novel multi-stair waterwheel driving rotating biological contactors (ms-wdRBCs) and constructed wetlands (CW). The ms-wdRBCs were utilized to post-treat mixture of digested black water and raw grey water with the ANF. Key parameters of ANF/ms-wdRBCS were identified founded on the nutrient removal performance, especially nitrogen removal, for further application in the project. Besides, the ANF/ms-wdRBCs coupling device was operated 10 weeks at the optimum parameters to confirm its performance on contamination removal. The coupling device performed well on chemical oxygen demand (COD), total nitrogen (TN), and ammonia (NH4+-) removal. When running under 150% reflux ratio, 1 h HRT of each-stair wdRBC and 7.11 h HRT of ANF, the removal efficiency of COD, TN, NH4+- and total phosphorus (RTP) were 88.40 ± 2.16%, 52.33 ± 3.80%, 88.14 ± 2.30% and 34.11 ± 7.00%, respectively. The NH4+-/ NO3−- concentration ratio of effluent was approximately 3 which was certificated to be beneficial to plants growth in CW. Although the removal efficiency of TP was only 34.11 ± 7.00%, the phosphorus was partly retained to contribute to plants growth in CWs. Overall, the entire four-part system achieved outstanding pollutant removal efficiencies, while the selected plants in CW also gained benefits back. Low construction and operating cost, simple management and easy maintenance of the system ensure the application in rural areas.

Preliminary study on the dynamics of heavy metals in saline wastewater treated in constructed wetland mesocosms or microcosms filled with porous slag.

This study aims to evaluate the practical potential of using constructed wetlands (CWs) for treating saline wastewater containing various heavy metals. The results demonstrated that CWs growing Canna indica with porous slag as substrate could efficiently remove heavy metals (Cu, Zn, Cd, and Pb) from saline wastewater at an electrical conductivity (EC) of 7mS/cm, especially under low influent load. Salts with salinity level (characterized as EC) of 30mS/cm suppressed the removal of some heavy metals, dependent on heavy metal species and their influent concentrations. The presence of salts in CWs can improve the accumulation of Cu, Zn, and Pb in plant tissues as compared to control treatment, irrespective of metal concentrations in solution. The influence of salts on Cd accumulation depended on both salinity levels and Cd concentrations in solution. Although more heavy metals were accumulated in roots than in shoots, the harvesting of aboveground plant materials is still efficient addition for heavy metal removal due to the greater biomass and growth rate of aboveground plant material. Furthermore, replacing all plants instead of preserving roots from harvested plants in CWs over a period of time is essential for heavy metal removal, because the continued accumulation by roots can be inhibited by the increasing accumulated heavy metals from saline wastewater.

Biochar enhances plant growth and nutrient removal in horizontal subsurface flow constructed wetlands

Biochar has shown great potential as an amendment to improve soil quality and promote plant growth, as well as to adsorb pollutants from water. However, information about the effect of biochar on the wastewater treatment efficiency in horizontal subsurface flow (HSSF) constructed wetlands (CWs) is still scarce. In this study, we assessed the effect of biochar amendment on the purification efficiency of pretreated municipal wastewater in planted (Typha latifolia) experimental horizontal subsurface flow filters filled with lightweight expanded clay aggregates (LECA). The addition of wood-derived biochar (10% v/v) to LECA significantly increased plant biomass production and enhanced the wastewater treatment efficiency of the planted filters. Both the aboveground plant biomass and belowground plant biomass were higher (1.9- and 1.5-fold, respectively) in the filters of the LBP (LECA + biochar + plants) treatments compared to the LP (LECA + plants) filters. The water pH was significantly lower in the planted filters (LBP < LP < LB-LECA + biochar). The efficiencies of TN and TP removal from wastewater were highest in the LBP filters (20.0% and 22.5%, respectively), followed by the LP (13.7% and 16.2%, respectively) and LB (9.5% and 15.6%, respectively) filters. More N and P were incorporated into the plant biomass from wastewater in the presence of biochar in the filter medium. The study results confirm that biochar can be an advantageous supplement for planted HSSF CWs to enhance the treatment efficiency of these systems.