Comparative study of microbial community structure in different filter media of constructed wetland

An innovative reuse of bottom ash from municipal solid waste incinerators as substrates of constructed wetlands

The incineration of municipal solid waste has been important in waste management, but it raises another environmental issue concerning residue treatment. This study describes an innovative use of naturally aged incineration bottom ash (AIBA) as an alternative substrate for horizontal subsurface flow (HSSF) constructed wetlands (CW). Although experimental results from a period lasting for 396 days only revealed slightly higher removal ratios in HSSF with AIBA (HSSF-E) than in HSSF-traditional pebble beds (HSSF-C), increasing from 67% to 76% for BOD, 44%-51% for TKN, 47%-54% for NH₃-N, and 44%-52% for TN. The data indicate that the use of AIBA in HSSF CW can achieves a certain removal efficiency of BOD and nitrogen species. Interestingly, the total phosphorus removal rates also increased significantly from 20% in HSSF-C to 36% in HSSF-E. These observations on the use of AIBA in HSSF CW confirmed that AIBA is a suitable alternative for use as a substrate for HSSF CWs and identified an additional way to reuse incineration bottom ash. Design criteria for a CW using AIBA as a partial substrate is proposed to improve the pollutant removal performance of HSSF CWs.

Current Progress in Natural Degradation and Enhanced Removal Techniques of Antibiotics in the Environment: A Review

Antibiotics are used extensively throughout the world and their presence in the environment has caused serious pollution. This review summarizes natural methods and enhanced technologies that have been developed for antibiotic degradation. In the natural environment, antibiotics can be degraded by photolysis, hydrolysis, and biodegradation, but the rate and extent of degradation are limited. Recently, developed enhanced techniques utilize biological, chemical, or physicochemical principles for antibiotic removal. These techniques include traditional biological methods, adsorption methods, membrane treatment, advanced oxidation processes (AOPs), constructed wetlands (CWs), microalgae treatment, and microbial electrochemical systems (such as microbial fuel cells, MFCs). These techniques have both advantages and disadvantages and, to overcome disadvantages associated with individual techniques, hybrid techniques have been developed and have shown significant potential for antibiotic removal. Hybrids include combinations of the electrochemical method with AOPs, CWs with MFCs, microalgal treatment with activated sludge, and AOPs with MFCs. Considering the complexity of antibiotic pollution and the characteristics of currently used removal technologies, it is apparent that hybrid methods are better choices for dealing with antibiotic contaminants.

The Potential Application of Natural Clinoptilolite-Rich Zeolite as Support for Bacterial Community Formation for Wastewater Treatment

The aim of this study was to investigate the use of natural zeolite as support for microbial community formation during wastewater treatment. Scanning electron microscopy (SEM), thermal decomposition and differential thermogravimetric curves (TGA/DGT) techniques were used for the physicochemical and structural characterization of zeolites. The chemical characterization of wastewater was performed before and after treatment, after 30 days of using stationary zeolite as support. The chemical composition of wastewater was evaluated in terms of the products of nitrification/denitrification processes. The greatest ammonium (NH4+) adsorption was obtained for wastewater contaminated with different concentrations of ammonium, nitrate and nitrite. The wastewater quality index (WWQI) was determined to assess the effluent quality and the efficiency of the treatment plant used, showing a maximum of 71% quality improvement, thus suggesting that the treated wastewater could be discharged into aquatic environments. After 30 days, NH4+ demonstrated a high removal efficiency (higher than 98%), while NO3+ and NO2+ had a removal efficiency of 70% and 54%, respectively. The removal efficiency for metals was observed as follows (%): Mn > Cd > Cr > Zn > Fe > Ni > Co > Cu > Ba > Pb > Sr. Analysis of the microbial diversity in the zeolite samples indicated that the bacteria are formed due to the existence of nutrients in wastewater which favor their formation. In addition, the zeolite was characterized by SEM and the results indicated that the zeolite acts as an adsorbent for the pollutants and, moreover, as a support material for microbial community formation under optimal conditions. Comparing the two studied zeolites, NZ1 (particle size 1−3 mm) was found to be more suitable for wastewater treatment. Overall, the natural zeolite demonstrated high potential for pollutant removal and biomass support for bacteria community growth in wastewater treatment.

Improving the quality of stabilization pond effluents using hybrid constructed wetlands

Water shortage and excessive use of water resources in arid and semi-arid regions, such as Iran, highlights the importance of using treated wastewater, especially for the highly demanding agricultural sector. Constructed wetlands (CWs) are among green technologies that offer an efficient and cost-effective wastewater treatment. This study investigates the complementary treatment of effluent from the Fooladshahr wastewater treatment plant, Isfahan, Iran, using pilot-scale CWs with horizontal (H-CW) and horizontal-vertical flow (HV-CW). The performance of two substrates, pumice and gravel, and the effect of using plants (Phragmites australis) was compared. Maximum removal efficiencies of total suspended solids (TSS) and biochemical oxygen demand (BOD₅) were observed in the case of unplanted and planted HV-CW with pumice bed, respectively. In the case of gravel bed, planted H-CWs demonstrated maximum chemical oxygen demand (COD) removal efficiency. The highest mean outflow concentrations for TSS, BOD₅ and COD were obtained in unplanted H-CW with pumice bed, likely due to shorter retention times compared to HV-CWs, as well as due to the absence of plants providing the required physicochemical and biological conditions for high performance treatment. Phosphate (PO₄^3-) removal efficiency demonstrated seasonal dependency, where the highest values were obtained in warm seasons. In the case of fecal coliforms (FC), no significant differences were observed between the studied HV-CWs during the whole study period. Based on our results, planted H-CW with gravel bed provided an optimum removal efficiency while requiring a smaller footprint and lower expenditure than HV-CWs. This study demonstrates the application of CWs as an affordable solution for treating domestic wastewater for various reuse application in developing countries with water crisis, such as Iran.

Materials in constructed wetlands for wastewater remediation: A review

The wastewater treatment industry is constantly evolving to abate emerging contaminants and to meet stringent legislative requirements. The existing technologies need to be modified, or new innovative treatment techniques need to be developed to ensure environmental protection and secure sustainability in the future. Emphasis is mainly on nutrient recovery, energy-efficient systems, zero waste generation, and environmentally friendly techniques. Constructed wetlands (CWs) have evolved as natural, eco-friendly, economical, and low-maintenance alternatives for wastewater remediation. These wetlands employ several materials as adsorbents for the treatment, commonly known as media/substrate. This review paper presents an assessment of various materials that can be used as substrates in CWs for the efficient removal of organic and non-biodegradable pollutants in different types of wastewaters. The effect of pH, mineral composition, specific surface area, and porosity of various natural materials and agricultural and industrial wastes used as media in CWs for wastewater remediation was discussed. The study showed that different substrates like alum sludge, limestone, coal slags, rice husk, and sand had removal efficiency for chemical oxygen demand (COD): 71.8%-82%, total phosphorous (TP): 77%-80%, and total nitrogen (TN): 52%-82% for different types of wastewaters. It also highlights the challenges related to the long-term sustainability of these materials. PRACTITIONER POINTS: Physicochemical characteristics influence the removal efficiency of the materials Life of media is also important along with removal efficiency and cost The sustainability of materials is very crucial for the overall performance of the system.

Effect of intermittent induced aeration on nitrogen removal and denitrifying-bacterial community structure in Cork and gravel vertical flow pilot-scale treatment wetlands

In this work, we have evaluated the impact of intermittent induced aeration in total nitrogen (TN), ammonia (NH₄-N) and nitrate-nitrogen (NO₃-N) removal in four pilot-scale vertical flow constructed wetlands (VFCW) (two aerated two non-aerated) using cork by-product or gravel as the filter material and planted with Phragmites australis. Both aerated and non-aerated systems achieved high COD and BOD₅ elimination rates (≥ 90%) at the end of the 5-month test period. However, the aerated systems presented maximal COD and BOD₅ removal from the third month of operation onwards since air supply favored the oxidative bioprocesses occurring within the wetlands. Cork and gravel aerated VFCW also proved to be more efficient (p < 0.05) in NO₃-N removal than the non-aerated systems and this upgraded performance was correlated with a significant higher relative abundance of the nirS gene. The aerated systems also showed a slightly improved NH₄-N removal. Noticeably, cork VFCW showed higher TN removal mean values (∼35%) than gravel wetlands (27-28%) regardless aeration. Moreover, cork VFCW showed higher relative abundance of the nosZ gene. Our results demonstrated a better nitrogen elimination for the aerated cork pilot-scale VFCW, and this behavior was correlated with a higher abundance of both nirS and nosZ, two of the key functional genes involved in nitrogen metabolism.

Constructed wetland, an eco-technology for wastewater treatment: A review on types of wastewater treated and components of the technology (macrophyte, biolfilm and substrate)

Constructed wetland (CW) represents an efficient eco-technological conglomerate interweaving water security, energy possibility and environmental protection. In the context of wastewater treatment technologies requiring substantial efficiency at reduced cost, chemical input and low environmental impact, applications of CW is being demonstrated at laboratory and field level with reasonably high contaminant removal efficiency and ecological benefits. However, along with the scope of applications, role of individual wetland component has to be re-emphasized through related research interventions. Hence, this review distinctively explores the concerns for extracting maximum benefit of macrophyte (focusing on interface of pollutant removal, root radial oxygen loss, root iron plaque, endophyte-macrophyte assisted treatment in CW, and prospects of energy harvesting from macrophyte) and role of biofilm (effect on treatment efficiency, composition and factors affecting) in a CW. Another focus of the review is on recent advances and developments in alternative low-cost substrate materials (including conventional type, industrial by-products, organic waste, mineral based and hybrid type) and their effect on target pollutants. The remainder of this review is organized to discuss the concerns of CW with respect to wastewater type (municipal, industrial, agricultural and farm wastewater). Attempt is made to analyze the practical relevance and significance of these aspects incorporating all recent developments in the areas to help making informed decisions about future directions for research and development related to CW.

The effect of hydrodynamics on the succession of autotrophic and heterotrophic organisms of biofilms in river ecosystems

Biofilms were cultivated for a 68-day period under different hydrodynamic conditions, and the effect of hydrodynamics on the succession of autotrophic and heterotrophic organisms of biofilms was investigated. Five obvious stages were observed during biofilm formation. At Stage I, the attachment of algae was delayed, especially under turbulent conditions. After Stage II, algal density and heterotrophic biomass of biofilms increased, which were obvious under turbulent flow. Therefore, the algal density and heterotrophic biomass of biofilms were largest under turbulent condition, followed by laminar condition, and then transitional condition. Diatoms were dominant in all flumes and were most abundant under turbulent conditions. The proportion of cyanobacteria was highest under laminar conditions. The ratio of aerobic to anaerobic bacteria decreased and their co-existence could facilitate the nitrification and denitrification in the biofilm. The ratio of monounsaturated fatty acids to saturated fatty acids was highest under turbulent conditions on the 15th day. While the ratio was highest under laminar condition on the 48th day, the high ratio indicates the high ability of biofilm to obtain nutrients, which affect the growth of algae. The regulation of hydrodynamics is a useful technology which can affect the growth of the microorganisms of biofilm, and further improve water quality.

Changes of substrate microbial biomass and community composition in a constructed mangrove wetland for municipal wastewater treatment during 10-years operation

Constructed wetlands (CWs) have been used for wastewater treatment for decades, but research on microorganisms involved, especially long-term changes, is still limited. In this study, we evaluated changes in the substrate microbial community in a pilot-scale horizontal subsurface-flow constructed mangrove wetland during 10-years operation. In the 3rd year of operation, microbial biomass carbon and phospholipid fatty acids (PLFAs) reached peak values in two vegetated belts planted with Aegiceras corniculatum (Ac) and Kandelia obovata (Ko), respectively, then stabilized or declined in the 9th and 10th years of operation. PLFA profiles reflecting microbial community compositions varied significantly in the Ac belt during the operation period. Principal component (PCA) and redundancy analyses (RDA) revealed that microbial community compositions were significantly correlated with organic matter content, especially in the 9th and 10th years of operation, implying that the substrate microbial community in constructed mangrove wetland is sensitive to substrate characteristics and can be used as an indicator for long-term performance of CWs.

Interactive effect of carbon source with influent COD/N on nitrogen removal and microbial community structure in subsurface flow constructed wetlands

Carbon source and influent COD/N (chemical oxygen demand: total nitrogen) pose distinct effects on nitrogen removal efficiency and microbial community structure of constructed wetlands. To investigate the interactive effect of carbon source with COD/N on nitrogen removal and microbial community structure in subsurface flow constructed wetlands, glucose (C₆H₁₂O₆) and sodium acetate (C₂H₃NaO₂) were used to determine five COD/N ratios in nine groups of constructed wetlands divided into glucose constructed wetlands and sodium acetate constructed wetlands. Results showed that efficiency in COD removal increased with COD/N, and peak value reached 92.7%. Interactive effect of carbon source with COD/N on system pH and ammonium removal was notably significant. Differences in ammonium removal performance between treatments were achieved by the variation of influent COD/N ratio and the change of system pH resulted from different carbon sources, and the result suggested that glucose was a better choice at high COD/N ratio. System microbial community structure was significantly affected by carbon source, influent COD/N ratio and their interaction. Microbial biomass in constructed wetlands significantly increased with increasing COD/N ratio. Higher density and diversity of fungus were observed in glucose constructed wetlands, particularly at COD/N ratio of 7 and 10.

Effects of layered combined substrates on plant growth and treatment performance and its spatiotemporal variation of vertical-flow constructed wetlands

Layered combined bio-ceramic, zeolite, and anthracite were used as substrates in vertical-flow constructed wetlands (VFCWs) for enhancing contaminant removal from synthetic municipal wastewater. Plant growth and propagation and the removal of organic matter, nitrogen, and phosphorus as well as its spatiotemporal variation were evaluated systematically. The results demonstrated that three different substrates were adequate for the establishment of Canna indica L., especially for zeolite. All small-scale VFCW units were simultaneous efficient in removing COD_Cr (73.9-78.7%), NH₄⁺-N (83.8-89.9%), TN (88.3-91.5%), SRP (93.8-98.6%), and TP (87.1-90.9%) with a little significant difference on treatment performance. Different pollution removal processes followed a different trend because of their different removal mechanisms driven by the synergy of substrate, plant, and microorganism. Purification space moved down due to the adsorption capacity consumption of upper layer substrate over time. It was concluded that VFCWs filled with layered combined bio-ceramic, zeolite, and anthracite had great potential for treating municipal wastewater.

Microbial nitrate removal efficiency in groundwater polluted from agricultural activities with hybrid cork treatment wetlands

Agricultural practices have raised the level of nutrients reaching aquifers. In Europe, nitrate pollution is considered as one of the main threats for the quality of groundwater in agricultural areas. Treatment wetlands (TWs), also known as Constructed Wetlands, are used for groundwater treatment in areas with an important concentration of nitrogen compounds; total nitrogen removal depends on the type and operation scheme. Cork by-product from the industry has shown clear adsorbent properties to remove organic pollutants. The work is focused on the characterization of microbial communities involved in the nitrate‑nitrogen removal process in groundwater polluted from agricultural activities. The experimental design allowed the comparison of nitrate removal efficiency depending on the filter media material, cork by-product or gravel, used in two hybrid TWs (a vertical flow cell followed by a horizontal subsurface flow cell), installed in areas close to two irrigated agricultural plots at the Lleida plain area (Spain). Both physicochemical and microbial results were consistent and confirm the nitrate removal efficiency using cork as a filter media. A significant (p = 0.0025) higher removal in Bellvís TW using cork compared with the Vilanova de la Barca gravel system was observed, achieving a removal rate from 80 to 99% compared to the 5-46%, respectively. Regarding the community composition of the two different TWs, microorganisms were mainly related to the phylum Proteobacteria, and included members found to be key players in the nitrogen cycle, such as ammonia and nitrite oxidizers, as well as denitrifiers. Also, the group Bacteroidetes turns to be another abundant phylum from our bacterial dataset, whose members are suggested to be strongly involved in denitrification processes. Some groups showed to prevail depending on the type of media (cork or gravel); Firmicutes and Delta and Epsilonproteobacteria had a significant higher abundance in the TW with cork, while Acidobacteria and Planctomyces were prevalent in gravel. Therefore, cork could be an alternative material used by treatment wetlands to minimize the impact in the environment caused by nitrogen pollution in groundwater bodies.

Effects of pharmaceuticals on microbial communities and activity of soil enzymes in mesocosm-scale constructed wetlands

Cyperus alternifolius based mesocosm-scale constructed wetland was employed to remove pharmaceuticals. We investigated the microbial community composition using phosphor lipid fatty acids (PFLAs) analysis and substrate enzyme activity during long-term exposure to pharmaceuticals in mesocosm-scale constructed wetlands. The results showed that there was no visible inhibition effect of pharmaceuticals on CW substrate enzymes activities in the experimental range (0-500 μg/L). Microbial communities, as revealed by PFLAs, were enhanced by the presence of plants, while the PFLAs content was highest when the pharmaceutical concentration was 10 μg/L or 30 μg/L at CWs. Except for anaerobic bacteria and Saturated fatty acids, the maximum PLFAs levels were reached when the pharmaceuticals were 10 μg/L or 30 μg/L, while Bacteria, G (-), fungal bacteria, Aerobic bacteria and Monounsaturated fatty acids were remarkably affected by high pharmaceuticals (100-500 μg/L). However, the main microbial florae were not changed among the treatments. In this study, the removal efficiencies of the studied pharmaceuticals in Planted (30) was greatest, which could be attributed to the higher microbial biomass. These results indicate that C. alternifolius can phytoremediate pharmaceutical-contaminated waters in CWs. Individual fatty acid cannot be used to represent specific species; therefore, more approaches to species identification such as rRNA-based methods must be included in future studies to better understand the metabolic mechanisms of microorganisms involved in the removal of studied pharmaceuticals and improve the performance of CWs.

Insights into the role of earthworms on the optimization of microbial community structure during vermicomposting of sewage sludge by PLFA analysis

In this study, the influences of earthworms on the structure of microbial community as well as the metabolic function in vermicomposting (VPs, with earthworms) for excess sludge stabilization were investigated. Comparison between the dynamic variation of PLFA profiles in VPs and common composting (CPs, with no earthworms) was conducted. The Shannon index was increased in VPs, while it was decreased in CPs with time, indicating earthworm activity enhanced microbial community diversity. The fungal and protozoal biomasses were significantly increased in VPs compared with CPs. Further researches by principal component analysis (PCA) indicated that earthworms benefited certain microorganisms containing biomarkers of 18:1ω9c, 18:3ω3, 18:3ω6, 20:1ω9, 20:2ω6 and 20:3ω6. Moreover, the ratios of monounsaturated to branched PLFAs in VPs were larger than those in CPs, suggesting the aeration condition was promoted by the burrowing behaviors of earthworms and therefore facilitated the growth and propagation of aerobic microorganisms, such as protozoa. Those results indicated that earthworm activity led to the general optimization of vermicomposting for excess sludge stabilization.

Constructed Wetlands Revisited: Microbial Diversity in the -omics Era

Constructed wetlands (CWs) constitute an interesting alternative option to conventional systems for wastewater treatment. This technology is based on the utilization of the concerted activity of microorganisms for the removal of contaminants. Consequently, knowledge on the microbial assemblages dwelling CWs and the different environmental factors which can alter their activities is crucial for understanding their performance. In the last decades, the use of molecular techniques to characterize these communities and more recently, application of -omics tools, have broaden our view of microbial diversity and function in wastewater microbiology. In this manuscript, a review of the current knowledge on microbial diversity in CWs is offered, placing particular emphasis on the different molecular studies carried out in this field. The effect of environmental conditions, such as plant species, hydraulic design, water depth, organic carbon, temperature and substrate type on prokaryotic communities has been carefully revised, and the different studies highlight the importance of these factors in carbon, nitrogen and sulfur cycles. Overall, the novel -omics open a new horizon to study the diversity and ecophysiology of microbial assemblages and their interactions in CWs, particularly for those microorganisms belonging to the rare biosphere not detectable with conventional molecular techniques.

Vertical flow-constructed wetlands for domestic wastewater treatment under tropical conditions: effect of different design and operational parameters

This study assessed the treatment of domestic wastewater to find the optimum vertical flow-constructed wetland (VFCW) configuration under tropical conditions. Eight pilot-scale configurations units were studied to compare between fine sand and medium gravel used as substrate, two feeding frequencies (20 pulses d^-1 and 10 pulses d^-1), and the presence or absence of tropical plants (Heliconia psittacorum). The results showed that the sand beds were significantly more efficient in the removal of organic matter, ammonia nitrogen, and total suspended solids than gravel beds, presenting average removal rates of 48 and 24 g m^-2 d^-1 of COD; 35 and 16 g m^-2 d^-1 of BOD₅; 7 and 4 g m^-2 d^-1 of [Formula: see text]; 9 and 0 g m^-2 d^-1 for sand and gravel, respectively. The oxygen consumption rates were calculated and a value of 65 g m^-2 d^-1 was obtained for sand beds while for the gravel beds the consumption rate was 30 g m^-2d^-1. The assessment of different kinds of nitrogen showed interesting dynamics in the nitrification processes. The presence of H. psittacorum showed positive effects in the total nitrogen (TN) removal. The different loading frequencies applied did not show significant statistical differences in the removal of the tested contaminants. Preliminary results were found in the pathogen removal, where the sand is favorable as the substrate. This work represents the first step in the research of optimum VFWC design and operation parameters for Colombia as well as the use of plants of the genus Heliconia.

Comparative study of microbial community structure in integrated vertical-flow constructed wetlands for treatment of domestic and nitrified wastewaters

Microbial processes play a vital important role in the removal of contaminants in constructed wetland (CW). However, the microbial physiology and community structure can be influenced by environmental conditions. In this study, four pilot-scale integrated vertical-flow constructed wetlands (IVCWs) were employed to treat domestic and nitrified wastewaters. The microbial properties, along with their response to wastewater quality characteristics and seasonal variation, were determined. The results showed higher Shannon-Weiner diversity (H) and evenness (E) index of fatty acids (FAs), and relative abundances of signature FAs in down-flow cells and in the systems fed with domestic wastewater (DW). The relative abundances of fungi and gram-negative and aerobic bacteria were greater in up-flow cells. The dominant anaerobic bacteria found in most cells might be accounted for the prevailing anaerobic environment within the wetland beds, which could mean that the system fed with nitrified wastewater (NW) should perform better in nitrogen removal. The redundancy analysis (RDA) showed that pollutant concentrations, especially organic matter, influence the FA compositions greatly, and the most significant difference of microbial community structures was detected in down-flow cells fed with DW and up-flow ones with NW. The branched FAs, which could be used to represent anaerobic bacteria, were observed in down-flow cells treating DW and had a significant positive correlation with chemical oxygen demand (COD) concentration, probably suggesting the important role of anaerobic bacteria in organic matter degradation in the IVCWs. Seasonal variation, however, did not greatly influence the microbial community structure in the IVCWs.

Enhanced biodegradation of phthalate acid esters in marine sediments by benthic diatom Cylindrotheca closterium

Cylindrotheca closterium, a marine benthic diatom, was inoculated on the surface of marine sediments spiked with diethyl phthalate (DEP) and dibutyl phthalate (DBP) to investigate the effects of benthic microalgae on the degradation of the contaminants. The elimination of DEP and DBP from unsterilized sediments with C. closterium (treatment BA) was compared with that from unsterilized sediments without C. closterium (treatment B), sterilized sediments with C. closterium (treatment A) and sterilized sediments without C. closterium (treatment N). The results showed that during the 8-day experiment, inoculation with C. closterium increased the removal rates of the contaminants from the sediments, and more significantly from the surface layer (top 0.5 cm) of sediments than from the bottom layer of sediments. In the surface sediments, the first-order elimination rate constants (k) of DEP and DBP were in the order of treatment BA (2.098 and 0.309 d(-1))>treatment B (0.460 and 0.256 d(-1))>treatment A (0.216 and 0.039 d(-1))>treatment N (nil (no data)), indicating that microbial degradation played a major role in the removal of the contaminants from the sediments. A similar trend was also observed in bottom sediments (0.444 and 0.165 d(-1) in treatment BA, 0.329 and 0.194 d(-1) in treatment B, 0.129 d(-1) and nil in treatment A), but the difference of k values between treatments BA and B was relatively small. The positive effect of C. closterium on total phospholipid fatty acid (PLFA) content in sediments was observed, which was mainly related to the increase of biomass of aerobic bacteria as a result of improved sediment oxygenation and release of exudates (e.g. exopolysaccharides) by C. closterium. Moreover, Pearson correlation analysis showed a significant positive correlation between the elimination ratios of the contaminants and abundance of total aerobic bacterial PLFAs, suggesting that aerobic bacteria played a key role in C. closterium-promoted degradation of the contaminants in sediments.

Influence of environmental variables on the structure and composition of soil bacterial communities in natural and constructed wetlands

Bacteria are key players in wetland ecosystems, however many essential aspects regarding the ecology of wetland bacterial communities remain unknown. The present study characterizes soil bacterial communities from natural and constructed wetlands through the pyrosequencing of 16S rDNA genes in order to evaluate the influence of wetland variables on bacterial community composition and structure. The results show that the composition of soil bacterial communities was significantly associated with the wetland type (natural or constructed wetland), the type of environment (lagoon, Typha or Salix) and three continuous parameters (SOM, COD and TKN). However, no clear associations were observed with soil pH. Bacterial diversity values were significantly lower in the constructed wetland with the highest inlet nutrient concentrations. The abundances of particular metabolic groups were also related to wetland characteristics.

A review on removing pharmaceutical contaminants from wastewater by constructed wetlands: design, performance and mechanism

This paper presents a comprehensive review of the current state of research activities on the application of constructed wetlands for removing pharmaceutical contaminants from wastewater. The focus of the review was placed on the application of constructed wetlands as an alternative secondary wastewater treatment system or as a wastewater polishing treatment system. The design parameters of the reported constructed wetlands including the physical configuration, hydraulic mode, vegetation species, and targeting pharmaceuticals were summarized. The removal efficiencies of pharmaceuticals under different conditions in the wetlands were evaluated at the macroscopic level. In addition, the importance of the three main components of constructed wetlands (substrate, plants and microbes) for pharmaceutical removal was analyzed to elucidate the possible removal mechanisms involved. There is a general consensus among many researchers that constructed wetlands hold great potential of being used as an alternative secondary wastewater treatment system or as a wastewater polishing treatment system for the removal of pharmaceuticals, but relevant reported studies are scarce and are not conclusive in their findings. Current knowledge is limited on the removal efficiencies of pharmaceuticals in constructed wetlands, the removal mechanisms involved, the toxicity to constructed wetlands caused by pharmaceuticals, and the influences of certain important parameters (configuration design, hydraulic mode, temperature and seasonality, pH, oxygen and redox potential, etc.). This review promotes further research on these issues to provide more and better convincing evidences for the function and performance of larger laboratory-scale, pilot-scale or full-scale constructed wetlands.

Microbial community structure and metabolic property of biofilms in vermifiltration for liquid-state sludge stabilization using PLFA profiles

To investigate effects of earthworms on microbial community structure and metabolic properties of biofilms in vermifiltration for liquid-state sludge stabilization, a vermifilter (VF) with earthworms and a conventional biofilter (BF) without earthworms were compared. The Shannon index of fungi in VF was 16% higher than that in BF, which indicated earthworm activities significantly enhanced fungi diversity. The ratio of monounsaturated to saturated (mono:sat) PLFAs of VF biofilms was higher than that of BF biofilms, which indicated the physiological and nutritional stress for microbial community in VF was relieved due to the increasing of soluble substances caused by the earthworm ingestion. Further investigation showed that the burrowing action of earthworms promoted the aeration condition and led to aerobic microorganisms were predominant in VF. Those results indicated earthworms improved microbial community structure and metabolic properties of biofilms and thus resulted in the overall optimization of the vermifiltration system for liquid-state sludge stabilization.

Rhizosphere effect of Scirpus triqueter on soil microbial structure during phytoremediation of diesel-contaminated wetland

Though phytoremediation has been widely used to restore various contaminated sites, it is still unclear how soil microbial communities respond microecologically to plants and pollutants during the process. In this paper, batch microcosms imitating in situ phytoremediation of petroleum-contaminated wetland by Scirpus triqueter were set up to monitor the influence of plant rhizosphere effect on soil microbes. Palmitic acid, one of the main root exudates of S. triqueter, was added to strengthen rhizosphere effect. Abundances of certain microbial subgroups were quantified by phospholipid fatty acid profiles. Results showed that diesel removal extents were significantly higher in the rhizosphere (57.6 +/-4.2-65.5 +/- 6.9%) than those in bulk soil (27.8 +/-6.5-36.3 +/- 3.2%). In addition, abundances of saturated, monounsaturated, and polyunsaturated fatty acids were significantly higher (P < 0.05) in planted soil than those in the bulk soil. When it was less than 15,000 mg diesel kg soil-1, increasing diesel concentration led to higher abundances of fungi, Gram-positive and Gram-negative bacteria. The addition of palmitic acid amplified the rhizosphere effect on soil microbial populations and diesel removal. Principal component analysis revealed that plant rhizosphere effect was the dominant factor affecting microbial structure. These results provided new insights into plant-microbe-pollutant coactions responsible for diesel degradation, and they were valuable to facilitate phytoremediation of diesel contamination in wetland habitats.

Organic xenobiotics removal in constructed wetlands, with emphasis on the importance of the support matrix

Constructed wetlands (CWs) are increasingly popular as an efficient and economical alternative to conventional wastewater treatment processes for removal, among other pollutants, of organic xenobiotics. In CWs, pollutants are removed through the concerted action of their components, whose contribution can be maximized by careful selection of those components. Specifically for non-biodegradable organic pollutants, the materials used as support matrix of CWs can play a major role through sorption phenomena. In this review the role played by such materials in CWs is examined with special focus on the amount of research that has been conducted to date on their sorption properties relatively to organic compounds. Where available, the reports on the utilization of some of those materials on pilot or full-scale CWs are also recognized. Greatest interest has been directed to cheaper and widely available materials. Among these, clays are generally regarded as efficient sorbents, but materials originated from agricultural wastes have also gained recent popularity. Most available studies are lab-scale batch sorption experiments, whereas assays performed in full-scale CWs are still scarce. However, the available lab-scale data points to an interesting potential of many of these materials for experimentation as support matrix of CWs targeted for organic xenobiotics removal.

Diversity of microbial communities in an attached-growth system using Bauxsol™ pellets for wastewater treatment

Columns of Bauxsol™ pellets were used in a field experiment as biomass support particle for wastewater microbial communities. The attached microbial community structure was analysed using denaturing gradient gel electrophoresis (DGGE), targeting the 16S rDNA gene's V3 region. DGGE profiles showed that the type and composition of support particles used (i.e. Bauxsol™ pellets or gravel) had a significant impact on the attached bacterial communities (64% dissimilarity). In addition, ecological indices revealed a more heterogeneous bacterial community structure on the Bauxsol™ pellets. TOC/TN ratios post-experiment (6.5-9.3) suggested a good level of biological activity (i.e. active biofilm) in the Bauxsol™ columns. Moreover, Bauxsol™ pellets were mostly made of inorganic carbon, suggesting insoluble carbonate biomineralisation. Polymerase chain reaction (PCR) amplification of specific marker genes (i.e. bacterial and archaeal amoA genes, nosZ gene, and hzo gene) were used to identify the presence of attached bacterial communities associated with nitrogen transformation. The results along with geochemical data (i.e. up to 50% nitrogen removal) revealed co-existence of ammonia-oxidising bacteria, denitrifiers, and anammox organisms. This study conclusively demonstrates that microbial communities are well-adapted to Bauxsol™ pellets and bacterial communities involved in the nitrogen cycle are present.

Responses of Scirpus triqueter, soil enzymes and microbial community during phytoremediation of pyrene contaminated soil in simulated wetland

The aim of this study was to determine the enhancement of Scirpus triqueter in the dissipation of pyrene and the interaction of pyrene with plant, soil enzymes and microbial community. The results indicated that the dissipation ratios of pyrene in the rhizospheric and non-rhizospheric soil were 64.65 ± 3.86% and 54.49 ± 2.74%, respectively, and were higher than that in the unplanted soil (42.60 ± 0.71%) at 80 d after planting S. triqueter. The pyrene was toxic to S. triqueter, as evidenced by growth inhibition in height, diameter, shoot number and biomass during the planting period. The activities of dehydrogenase decreased significantly at the presence of pyrene in soils, and increased remarkably with the introduction of S. triqueter. It was found that the pyrene addition increased the ratios of fungal/total fatty acids and gram-positive/gram-negative, but the presence of S. triqueter decreased the ratios of gram-positive/gram-negative. A larger stress level was found in the pyrene treated soils without S. triqueter. The ratio of aerobic/anaerobic bacteria decreased with increasing pyrene concentration, but increased when S. triqueter was planted. The principal analysis of phospholipid fatty acid signatures revealed that microbial community structures in the rhizospheric and non-rhizospheric soil were similar, but different from those in the unplanted and control soil.

Functional community analysis of brain: a new approach for EEG-based investigation of the brain pathology

Analysis of structure of the brain functional connectivity (SBFC) is a fundamental issue for understanding of the brain cognition as well as the pathology of brain disorders. Analysis of communities among sub-parts of a system is increasingly used for social, ecological, and other networks. This paper presents a new methodology for investigation of the SBFC and understanding of the brain based on graph theory and community pattern analysis of functional connectivity graph of the brain obtained from encephalograms (EEGs). The methodology consists of three main parts: fuzzy synchronization likelihood (FSL), community partitioning, and decisions based on partitions. As an example application, the methodology is applied to analysis of brain of patients with attention deficit/hyperactivity disorder (ADHD) and the problem of discrimination of ADHD EEGs from healthy (non-ADHD) EEGs.