Unplanted Systems Research Articles

The use of Bassia indica for salt phytoremediation in constructed wetlands

The treatment and reuse of wastewater in constructed wetlands offers a low-cost, environmentally-friendly alternative for common engineered systems. Salinity in treated wastewater is often increased, especially in arid and semi-arid areas, and may harm crops irrigated from wetlands. We have strong evidence that halophyte plants are able to reduce the salinity of wastewater by accumulating salts in their tissues. Bassia indica is an annual halophyte with unique adaptations for salt tolerance. We performed three experiments to evaluate the capability of B. indica for salt phytoremediation as follows: a hydroponic system with mixed salt solutions, a recirculated vertical flow constructed wetland (RVFCW) with domestic wastewater, and a vertical flow constructed wetland (VFCW) for treating goat farm effluents. B. Indica plants developed successfully in all three systems and reduced the effluent salinity by 20–60% in comparison with unplanted systems or systems planted with other wetland plants. Salinity reduction was attributed to the accumulation of salts, mainly Na and K, in the leaves. Our experiments were carried out on an operative scale, suggesting a novel treatment for green desalination in constructed wetlands by salt phytoremediation in desert regions and other ecosystems.

Leachate Characterization and Phytoremediation Using Water Hyacinth (Eichorrnia crassipes) in Pulau Burung, Malaysia

ABSTRACT Leachate from Pulau Burung landfill site was analyzed and treated using phytoremediation technique while water hyacinth (Eichhornia crassipes) was used as the phytoremediator. Some parameters analyzed included ammonia nitrogen (NH3-N), nitrate, nitrite, total Kjeldahl nitrogen (TKN), phosphate, and zinc. The range of values of nutrients such as the pH, ammonia nitrogen, TKN, phosphate and zinc during leachate characterization were 8.72 and 8.58, 1810 and 1070 mg/L, 1183 and 1120 mg/L, 46.4 and 31.2 mg/L, 11.1 and 5.4 mg/L, respectively. After phytoremediation, significant reduction was noticed in all the nutrients and zinc. Nitrite, phosphate and zinc values were between 91.9% and 98.2%, 4.4 to 0.6 mg/L and 1.1 and 0.1 mg/L, respectively. Statistical analyses showed significant differences between the planted and unplanted systems (p ≤ .05). It was established that Eichhornia crassipes had the capacity to remove nutrients and heavy metals from leachate, which requires treatment to minimize pollutants to an acceptable level before discharging into water courses.

Purification processes involved in sludge treatment by a vertical flow wetland system: Focus on the role of the substrate and plants on N and P removal

Vertical-flow wetland systems were tested for treatment of liquid waste activated sludge with high content of organic compounds from a soft drink factory. A mesocosm experiment was carried out on planted and unplanted systems to understand the relative importance of substrate and plants in purification processes and to compare three species: Phragmites australis Cav., Typha latifolia L., or Iris pseudacorus L. All planted mesocosms performed better than unplanted mesocosms and Phragmites showed the highest efficiencies, both in volumes and loads, closely followed by Typha. Removal efficiencies were very high in all cases, and physical filtration by the organic substrate was identified as the main processes for nutrient removal (>50%). We showed that plants played direct and indirect roles such as nutrients uptake (up to 23% of the N for Phragmites), evapotranspiration reducing outflow volumes; or improvement of filtration by the root systems and stimulation of microbial activities (respiration rate was double compared to unplanted mesocosms).

Plants in constructed wetlands help to treat agricultural processing wastewater

Over the past three decades, wineries in the western United States and sugarcane processing for ethanol in Central and South America have experienced problems related to the treatment and disposal of process wastewater. Both winery and sugarcane (molasses) wastewaters are characterized by large organic loadings that change seasonally and are detrimental to aquatic life. We examined the role of plants for treating these wastewaters in constructed wetlands. In the greenhouse, subsurface-flow flumes with volcanic rock substrates and plants steadily removed approximately 80% of organic-loading oxygen demand from sugarcane process wastewater after about 3 weeks of plant growth; unplanted flumes removed about 30% less. In field studies at two operational wineries, we evaluated the performance of similar-sized, paired, subsurface constructed wetlands with and without plants; while both removed most of the oxygen demand, removal rates in the planted system were slightly greater and significantly different from those of the unplanted system under field conditions.

Efficiency of Mesocosm-Scale Constructed Wetland Systems for Treatment of Sanitary Wastewater Under Tropical Conditions

Subsurface-flow constructed wetlands technology (SSFW) has been used successfully for treating sanitary wastewater throughout North America and Europe. However, treatment wetland technologies have not been used extensively in the tropics. To advance tropical studies, a pilot-scale SSFW was constructed on the campus of the University of the Atlantic in Barranquilla, Colombia. The systems performance was monitored from January to July of 2009. The treatment system consisted of a 760-L septic tank followed by three mesocsom-scale subsurface-flow constructed wetlands in parallel arrangement. Clarified wastewater was batch loaded to each unit at a rate of 53 L/m2/day to affect a hydraulic retention time of approximately 3 days. One of the treatment units served as a non-planted control (gravel only), while the other two treatment units were planted with either Eriochloa aristata or Eleocharis mutata. The objective of this study was to evaluate the comparative efficacy of the treatment units (planted vs. unplanted), with respect to their abilities to augment treatment of septic tank effluent (sanitary wastewater). Monitored parameters included plant biomass, oxidation–reduction potential, chemical oxygen demand (COD), temperature, dissolved oxygen, pH, ammonia–nitrogen (NH 4 + –N) nitrate– and nitrite–nitrogen (NO3–N, NO2–N), phosphates (PO 4 − ), and coliform bacteria. Total biomass (dry matter) was 2.84 and 0.87 Kg/m2 for E. aristata and E. mutata, respectively. Redox potential in the plant rizospheres averaged −172 mV (±164.1) in E. aristata, 29 mV (±251.1) in E. mutata, and 32 mV (±210.5) in the unplanted control. COD removal was superior in planted vs. non-planted systems (>75% vs. 47%). Ammonia and total phosphorus removal averaged 69% and 85%, respectively, in planted systems versus 31% and 59% in the unplanted system. Removal of total and fecal coliforms averaged 96%. Results of this pilot study revealed that SSFW technology in the tropics can provide significant removal of organic matter, nutrients, and bacteria from clarified sanitary wastewater.

Phytotoxicity and naphthenic acid dissipation from oil sands fine tailings treatments planted with the emergent macrophyte Phragmites australis

During reclamation the water associated with the runoff or groundwater flushing from dry stackable tailings technologies may become available to the reclaimed environment within an oil sands lease. Here we evaluate the performance of the emergent macrophyte, common reed (Phragmites australis), grown in chemically amended mature fine tailings (MFT) and simulated runoff/seepage water from different MFT drying treatments. The present study also investigated the phytotoxicity of the concentration of oil sands naphthenic acids (NAs) in different MFT drying chemical treatments, in both planted and unplanted systems. We demonstrate that although growth was reduced, the emergent macrophyte common reed was capable of growing in diluted unamended MFT runoff, as well as in diluted runoff from MFT amended with either 0.25% lime and gypsum or 0.5% gypsum. Common reed can thus assist in the dewatering process of oil sands MFT. However, simulated runoff or seepage waters from chemically amended and dried MFT were phytotoxic, due to combined levels of salts, naphthenic acids and pH. Phytoremediation of runoff water/ground water seepage from dry-land applied MFT will thus require pre-treatment in order to make conditions more favorable for plant growth.

Dynamics in the bacterial community-level physiological profiles and hydrological characteristics of constructed wetland mesocosms during start-up

The objective of this work was to study the effect of plant presence ( Phragmites australis) and inoculant origin on wetland mesocosm start-up dynamics. Eight mesocosms were studied based on a duplicated 2 2 factorial design tracking bacterial community and hydrological changes during an 8 month start-up period. The mesocosms were characterized in terms of their hydrological character based on evapotranspiration (ET), porosity, and a dispersion coefficient. The microbiological regime was characterized using a microbial activity measure and community-level physiological profiling (CLPP) employing BIOLOG™ ECO plates. CLPP-related indices such as substrate richness, substrate diversity, over-all community profile, and community divergence are also presented. It was found that mesocosm porosities decreased over time as a result of media-related biofilm development. This biofilm development also contributed to a substantial increase in the dispersion coefficient in the mesocosms over the start-up period. Dispersion coefficients in planted systems reached values of ∼50–55 cm 2/min whereas in the unplanted systems values of ∼30–35 cm 2/min were observed. Bacterial community divergence in the mesocosms was quantified using a Euclidean-based divergence metric. All mesocosms showed a sharp increase in community divergence until day 75, at which point a steady state was reached. The interstitial communities were also characterized in terms of similarity based on the experimental design treatments. Four stages of mesocosm development were identified that can be described by an initial community state based on the origins of the initial inoculum [days 0–6]; a dynamic period where adjustments and shifts in the bacterial community occurred in all mesocosms [days 7–26]; a period where all interstitial CLPPs were quite similar [days 27–73]; and finally a shift towards unplanted and planted mesocosm CLPP groupings [days 74–232].

Differences in phytotoxicity and dissipation between ionized and nonionized oil sands naphthenic acids in wetland plants

Naphthenic acids (NAs) are composed of alkyl-substituted acyclic and cycloaliphatic carboxylic acids and, because they are acutely toxic to fish, are of toxicological concern. During the caustic hot-water extraction of oil from the bitumen in oil sands deposits, NAs become concentrated in the resulting tailings pond water. The present study investigated if dissipation of NAs occurs in the presence of hydroponically grown emergent macrophytes (Typha latifolia, Phragmites australis, and Scirpus acutus) to determine the potential for phytoremediation of these compounds. Plants were grown with oil sands NAs (pKa approximately 5-6) in medium at pH 7.8 (predominantly ionized NAs) and pH 5.0 (predominantly nonionized NAs) to determine if, by altering their chemical form, NAs may be more accessible to plants and, thus, undergo increased dissipation. Whereas the oil sands NA mixture in its nonionized form was more toxic to wetland plants than its ionized form, neither form appeared to be sequestered by wetland plants. The present study demonstrated that plants may selectively enhance the dissipation of individual nonionized NA compounds, which contributes to toxicity reduction but does not translate into detectable total NA dissipation within experimental error and natural variation. Plants were able to reduce the toxicity of a NA system over 30 d, increasing the median lethal concentration (LC50; % of hydroponic solution) of the medium for Daphnia magna by 23.3% +/- 8.1% (mean +/- standard error; nonionized NAs) and 37.0% +/- 2.7% (ionized NAs) as determined by acute toxicity bioassays. This reduction in toxicity was 7.3% +/- 2.6% (nonionized NAs) and 45.0% +/- 6.8% (ionized NAs) greater than that in unplanted systems.

Treatment of high-strength wastewater in tropical vertical flow constructed wetlands planted with Typha angustifolia and Cyperus involucratus

The ability of vertical flow (VF) constructed wetland systems to treat high-strength ( ca. 300 mg L −1 of COD and ca. 300 mg L −1 total-nitrogen) wastewater under tropical climatic conditions was studied during a 5-month period. Nine 0.8-m diameter experimental VF units (depth 0.6 m) were used: three units were planted with Typha angustifolia L., another three units were planted with Cyperus involucratus Rottb and three units were unplanted. Each set of units were operated at hydraulic loading rates (HLRs) of 20, 50 and 80 mm d −1. Cyperus produced more shoots and biomass than the Typha, which was probably stressed because of lack of water. The high evapotranspirative water loss from the Cyperus systems resulted in higher effluent concentrations of COD and total-P, but the mass removal of COD did not differ significantly between planted and unplanted systems. Average mass removal rates of COD, TKN and total-P at a HLR of 80 mm d −1 were 17.8, 15.4 and 0.69 g m −2 d −1. The first-order removal rate constants at a HLR of 80 mm d −1 for COD, TKN and total-P were 49.8, 30.1 and 13.5 m year −1, respectively, which is in the higher range of k-values reported in the literature. The oxygen transfer rates were ca. 80 g m −2 d −1 in the planted systems as opposed to ca. 60 g m −2 d −1 in the unplanted systems. The number of Nitrosomonas was two to three orders of magnitude higher in the planted systems compared to the unplanted systems. Planted systems thus had significantly higher removal rates of nitrogen and phosphorus, higher oxygen transfer rates, and higher quantities of ammonia-oxidizing bacteria. None of the systems did, however, fully nitrify the wastewater, even at low loading rates. The vertical filters did not provide sufficient contact time between the wastewater and the biofilm on the gravel medium of the filters probably because of the shallow bed depth (0.6 m) and the coarse texture of the gravel. It is concluded that vertical flow constructed wetland systems have a high capacity to treat high-strength wastewater in tropical climates. The gravel and sand matrix of the vertical filter must, however, be designed in a way so that the pulse-loaded wastewater can pass through the filter medium at a speed that will allow the water to drain before the next dose arrives whilst at the same time holding the water back long enough to allow sufficient contact with the biofilm on the filter medium.

Dynamics of Arsenic Species in Laboratory‐Scale Horizontal Subsurface‐Flow Constructed Wetlands Treating an Artificial Wastewater

AbstractKnowledge regarding the dynamics of arsenic species and their interactions under gradient redox conditions in treatment wetlands is still insufficient. The aim of this investigation was to gain more information on the biotransformation of As and the dynamics of As species in horizontal subsurface‐flow constructed wetlands. Experiments were carried out in laboratory‐scale wetland systems, two planted with Juncus effusus and one unplanted, using an As‐containing artificial wastewater under defined organic C‐ and SO42–‐loading conditions. Immobilization of As was found in all systems under conditions of limited C, mainly due to adsorption and/or co‐precipitation. The removal efficiencies were substantially higher in the planted systems (60–70 %) as compared to the unplanted system (37 % on average). Immobilization under the conditions mentioned above appeared to decrease over time in all systems. At the beginning, the dosage of organic carbon immediately caused intensive microbial dissimilatory sulfate reduction in all systems (in the range of 85–95 %) and highly efficient removal of total arsenic (81–96 % on average). Later on, in this operation period, the intensity of sulfate reduction and simultaneous removal of As decreased, particularly in the planted wetlands (ranging from 30–46 %). One reason could be the re‐oxidation of reduced compounds due to oxygenation of the rhizosphere by the emergent wetland plants (helophytes). A significant amount of reduced As [As(III)] was found in the planted systems (> 75 % of total As) during the period of efficient microbial sulfate reduction, compared to the unplanted system (> 25 % of total As). The immobilization of arsenic was found to behave more stably in the planted beds than in the unplanted bed. Both systems (planted and unplanted) were suitable to treat wastewater containing As, particularly under sulfate reducing conditions. The unplanted system seemed to be more efficient regarding the immobilization of As, but the planted systems showed a better stability of immobilized As.

Constructed mangrove wetland as secondary treatment system for municipal wastewater

Intermittent subsurface flow mangrove microcosms were constructed to investigate their capabilities in treating primary settled municipal wastewater collected from a local sewage treatment work in Hong Kong SAR and the effect of hydraulic retention time (HRT). The study was carried out in a greenhouse and without any tidal flushing or tidal cycle, with half of the tanks planted with Kandelia candel and half without any plants. The removal percentages of dissolved organic carbon (DOC), ammonia-N, inorganic-N and total Kjeldahl nitrogen in the planted systems were 70.43–76.38%, 76.16–91.83%, 47.89–63.37% and 75.15–79.06%, respectively, significantly higher than in the unplanted system during the 6-month treatment period. More than 97% ortho -phosphate and 86.65–91.83% total phosphorus were removed by the planted microcosms. The HRT of 10 days had better removal than that of 5 days, and the best performance was obtained in the planted microcosms with 10 days of retention time. During the 6-month experimental period, the concentrations of all forms of nitrogen in the treated effluent were within the standards for effluents discharged into Group B inland waters and coastal zone with open waters. In terms of phosphorus, the effluents met the standards for effluents discharged into Group A inland waters. These results suggest that it is feasible to use the constructed mangrove wetland without tidal flushing as a secondary treatment process for municipal wastewater.

Effects of Plant Biomass, Plant Diversity, and Water Content on Bacterial Communities in Soil Lysimeters: Implications for the Determinants of Bacterial Diversity

Soils may comprise tens of thousands to millions of bacterial species. It is still unclear whether this high level of diversity is governed by functional redundancy or by a multitude of ecological niches. In order to address this question, we analyzed the reproducibility of bacterial community composition after different experimental manipulations. Soil lysimeters were planted with four different types of plant communities, and the water content was adjusted. Group-specific phylogenetic fingerprinting by PCR-denaturing gradient gel electrophoresis revealed clear differences in the composition of Alphaproteobacteria, Betaproteobacteria, Bacteroidetes, Chloroflexi, Planctomycetes, and Verrucomicrobia populations in soils without plants compared to that of populations in planted soils, whereas no influence of plant species composition on bacterial diversity could be discerned. These results indicate that the presence of higher plant species affects the species composition of bacterial groups in a reproducible manner and even outside of the rhizosphere. In contrast, the environmental factors tested did not affect the composition of Acidobacteria, Actinobacteria, Archaea, and Firmicutes populations. One-third (52 out of 160) of the sequence types were found to be specifically and reproducibly associated with the absence or presence of plants. Unexpectedly, this was also true for numerous minor constituents of the soil bacterial assemblage. Subsequently, one of the low-abundance phylotypes (beta10) was selected for studying the interdependence under particular experimental conditions and the underlying causes in more detail. This so-far-uncultured phylotype of the Betaproteobacteria species represented up to 0.18% of all bacterial cells in planted lysimeters compared to 0.017% in unplanted systems. A cultured representative of this phylotype exhibited high physiological flexibility and was capable of utilizing major constituents of root exudates. Our results suggest that the bacterial species composition in soil is determined to a significant extent by abiotic and biotic factors, rather than by mere chance, thereby reflecting a multitude of distinct ecological niches.

Effects of type of flow, plants and addition of organic carbon in the removal of zinc and chromium in small-scale model wetlands

Constructed wetlands are used for the treatment of wastewater containing metals. In order to clarify the role of plants, flow and the impact of organic matter, an investigation of three factors, each at two different levels, was carried out in small-scale model wetlands. The evaluated factors and levels were: type of flow (subsurface and surface); presence of plants (planted with Typha latifolia and unplanted) and addition of organic matter (with and without). Eight different experimental units were run for a year. The units were fed with synthetic wastewater containing chromium (VI) (1.5 mg L(-1)), zinc (1.5 mg L(-1)), macro, micronutrients and organic matter (to those units in which this factor was being investigated). Subsurface flow wetlands showed a significantly higher rate of chromium removal in comparison with surface flow systems (97 and 60 mg m(-2) d(-1), respectively). Planted systems removed significantly more chromium compared to unplanted systems (85 and 76 mg m(-2) d(-1), respectively), and the addition of organic matter increased the removal rate in a comparison with the units without it (88 and 69 mg m(-2) d(-1), respectively). Similar results were found for zinc; however, the addition of organic matter made no significant difference to zinc removal.

Characterisation of microbial biocoenosis in vertical subsurface flow constructed wetlands

In this study a quantitative description of the microbial biocoenosis in subsurface vertical flow constructed wetlands fed with municipal wastewater was carried out. Three different methods (substrate induced respiration, ATP measurement and fumigation-extraction) were applied to measure the microbial biomass at different depths of planted and unplanted systems. Additionally, bacterial biomass was determined by epifluorescence microscopy and productivity was measured via (14)C leucine incorporation into bacterial biomass. All methods showed that >50% of microbial biomass and bacterial activity could be found in the first cm and about 95% in the first 10 cm of the filter layer. Bacterial biomass in the first 10 cm of the filter body accounted only for 16-19% of the total microbial biomass. Whether fungi or methodical uncertainties are mainly responsible for the difference between microbial and bacterial biomass remains to be examined. A comparison between the purification performance of planted and unplanted pilot-scale subsurface vertical flow constructed wetlands (PSCWs) showed no significant difference with the exception of the reduction of enterococci. The microbial biomass in all depths of the filter body was also not different in planted and unplanted systems. Compared with data from soils the microbial biomass in the PSCWs was high, although the specific surface area of the used sandy filter material available for biofilm growth was lower, especially in the beginning of the set-up of the PSCWs, due to missing clay and silt fraction.

Effect of external organic matter on nutrient removal and growth of Phragmites australis in a laboratory-scale subsurface-flow treatment wetland

Coconut dust, which is used intensively in horticultural applications, was tested as an external organic additive in a series of laboratory-scale subsurface-flow constructed wetlands planted with Phragmites australis. The systems were fed with a mixture of NO3(-)-N, NH4+-N, and SRP in tap water to simulate high nutrient loads. In the absence of plants, TN removal efficiency was 66%, and the efficiency increased to > 80% in the microcosm wetlands. TN and NO3- removal efficiencies were marginally increased by coconut-dust treatment in comparison with sand-bed microcosms. Analysis by ANOVA showed that the TN removal from a coconut dust-supplemented sand-bed microcosm was significantly different from a sand-bed microcosm (0.0437 < p < 0.05). All the systems showed an equal capacity to treat NH4+ nitrogen under low influent concentration levels. Phosphorus removal efficiencies were > 98% in all three systems, and a difference between planted and unplanted systems was not observed. Shoot height and shoot densities of P. australis grown in the coconut dust-supplemented medium were significantly higher than those grown in the sand-bed medium. The difference in P. australis growth in response to the coconut dust addition revealed that the added material has the potential to create favourable conditions for plant growth.

An investigation of the potential to use street trees and their root zone soils to remove nitrogen from urban stormwater

Eutrophication in coastal ecosystems is often attributed to elevated nitrogen levels. Reducing the amount of nitrogen entering Port Phillip Bay is therefore an important objective for Melbournians. This article details the performance of a pilot scale street tree bioretention system in reducing nitrogen loads in urban stormwater. Three tree species (Eucalyptus polyanthemos, Lophostemon confertus and Platanus orientalis) and three sandy soils of different hydraulic conductivity (4, 95 and 170 mm/hr) were tested in a randomised block design. Over the course of the experiment, all species displayed seasonal height growth patterns with maximum growth rates occurring in late Spring and Summer. Applications of stormwater increased height growth and root length density compared with tapwater applications. Tree growth was similar in the three soils studied. During the warmer months, leachate volumes from the planted systems were significantly less than the unplanted systems due to transpirational drying. Leached nitrogen loads were significantly reduced in systems with a tree. Whilst there were some statistically significant differences in ammonium, oxidised nitrogen and organic nitrogen removal between species, these were not large in practical terms. In December, total nitrogen load removal from stormwater was 82 to 95% in planted systems (L. confertus), compared to 36 to -7% in the unplanted systems

Nitrogen and bacterial removal in constructed wetlands treating domestic waste water

The current study was carried out to compare the performances of two combined systems at pilot scale: the first one is composed of a vertical flow bed planted with Phragmites and a horizontal flow bed planted with Typha. The second combined system is an unplanted one. Each vertical flow bed, placed in the upstream of the horizontal flow bed is fed intermittently with a flow rate of 0.144 m 3 per day corresponding to an hydraulic application rate of a 0.24 m 3/m 2/day. Such parameters as Kjeldahl nitrogen, ammonia, and nitrate, nitrite, total and faecal coliform in the influent and effluent of the wetland system are examined, and their removal rates are determined. Nitrogen removal in planted system was greater than in unplanted one especially for nitrogen Kjeldahl (27 and 5%) and nitrogen ammonia (19 and 6%). Whereas, removal of nitrate-nitrite in planted system is less than in unplanted one (4 and 13%). However, bacterial removal in both planted and unplanted system was similar.

Vegetation effects on fecal bacteria, BOD, and suspended solid removal in constructed wetlands treating domestic wastewater

Constructed wetlands have emerged as a viable alternative for secondary treatment of domestic wastewater in areas with landscape limitations, poor soil conditions, and high water tables, which limit installation of full-scale adsorption fields. Existing information on the effects of macrophytes on treatment performance is contradictory and mostly derived from greenhouse mesocosm experiments. This study investigated the removal efficiency of fecal bacteria, biological oxygen demand (BOD), and total suspended solids (TSS) in 12 constructed wetlands treating secondary effluent from single household domestic wastewater in Kentucky. The wetlands were monoculture systems planted to cattails ( Typha latifolia L.) or fescue ( Festuca arundinacea Schreb.), polyculture systems planted with a variety of flowering plants, and unplanted systems. Influent and effluent samples were taken on a monthly basis over a period of 1 year and analyzed for fecal coliforms (FC), fecal streptococci (FS), BOD and TSS. The findings suggested no significant differences ( P<0.05) in the average yearly removal of fecal bacteria (>93%) between systems, with the vegetated systems performing best during warmer months and the unplanted systems performing best during the winter. The vegetated systems showed significantly greater ( P<0.05) removal efficiencies for BOD (>75%) and TSS (>88%) than the unplanted systems (63 and 46%, respectively) throughout the year. Overall, the polyculture systems seemed to provide the best and most consistent treatment for all wastewater parameters, while being least susceptible to seasonal variations. The performance of the cattail systems may improve by harvesting the plants at the end of the growing season, thus reducing additional BOD and TSS inputs from decaying biomass litter. The fescue systems were generally inferior to the polyculture and cattail systems because of their shallow rooting zone and limited biofilm surface area, while the unplanted systems were completely inefficient for BOD and TSS removal and should not be recommended.

Microcosm Wetlands for Wastewater Treatment with Different Hydraulic Loading Rates and Macrophytes

Constructed wetlands (CW) usually require large land areas for treating wastewater. This study evaluated the feasibility of applying CW with less land requirement by operating a group of microcosm wetlands at a hydraulic retention time (HRT) of less than 4 d in southern Taiwan. An artificial wastewater, simulating municipal wastewater containing 200 mg L(-1) of chemical oxygen demand (COD), 20 mg L(-1) of NH4+-N (AN), and 20 mg L(-1) of PO4(3-)-P (OP), was the inflow source. Three emergent plants [reed, Phragmites australis (Cav.) Trin. ex Steud.; water primrose, Ludwigia octovalvis (Jacq.) P.H. Raven; and dayflower, Commelina communis L.] and two floating plants [water spinach, Ipomoea aquatica Forssk.; and water lettuce, Pistia stratiotes L.] plants were tested. The planted systems showed more nutrient removal than unplanted systems; however, the type of macrophytes in CW did not make a major difference in treatment. At the HRTs of 2 to 4 d, the planted system maintained greater than 72,80, and 46% removal for COD, AN, and OP, respectively. For AN and OP removal, the highest efficiencies occurred at the HRT of 3 d, whereas maximum removal rates for AN and OP occurred at the HRT of 2 d. Both removal rates and efficiencies were reduced drastically at the HRT of 1 d. Removals of COD, OP, and AN followed first-order reactions within the HRTs of 1 to 4 d. The efficient removals of these constituents obtained with HRT between 2 and 4 d indicated the possibility of using a CW system for wastewater treatment with less land requirement.

Phosphate and ammonium distribution in a pilot-scale constructed wetland with horizontal subsurface flow using shale as a substrate

Phosphate (P) and ammonium (N) distributions were investigated in a pilot-scale constructed wetland system (CWS) with horizontal flow. Shale was selected as a substrate, on the basis of its P adsorption capacity as well as its suitability for plant growth, investigated in an earlier study. The system was set up in a greenhouse, and comprised of four tanks with and four tanks without Phragmites australis (common reed). Sampling ports were installed along the length of each tank, and at three different depths, in order to facilitate three-dimensional monitoring of nutrient distribution over the period of study (11 months). In the planted systems, H 2PO − 4-P (ortho-P) and NH + 4-N concentrations were low (0.5–1.0 g m −3) at all depths throughout their length. Generally, ortho-P and NH + 4-N concentrations decreased exponentially along the transect from the tank inlet to the outlet. In the unplanted systems, higher values (0.5–16.5 g m −3) of ortho-P were observed. NH + 4-N in the unplanted systems was relatively high (10–30 g m −3) throughout the period of investigation. In both planted and unplanted tanks, NO − 3-N concentrations were very low at the inlets (0.02–0.05 g m −3), and increased only slightly towards the outlets. Although the presence of P. australis had a significant effect ( p<0.05) on P and N concentrations at all depths and along the length of the tanks, the nutrient distribution followed the same trend as in unplanted tanks. The results were consistent with the theoretical removal model which predicts an exponential decrease in pollutant concentrations to a background value approaching zero along the transect from wetland inlet to the outlet. A modification of the model was suggested where a first order area-based reduction rate constant k (m d −1) would be replaced with ( k p+ k s), k p representing the rate constant for the removal by the plants, and k s the rate constant for the removal by the substrate, and associated microbial populations they support. Approximate values for k p+ k s of 0.084 m d −1 (P) and 0.065 m d −1 (N) and for k ṡ of 0.069 m d −1 (P) and 0.034 m d −1 (N) were obtained. The hydraulic residence time, flow characteristics and permeability of the shale was investigated by a bromide (Br −) tracer. The tracer breakthrough curves showed a similar pattern in all tanks, with about 66% of the flow occurring through the bottom zone (0.35 m). The actual hydraulic residence time (6 days) was slightly higher than the nominal one. The tracer study also enabled the calculation of the volumetric rate constants, k ν and approximate values of 0.075 d −1(P) and 0.060 d −1(N) were obtained for planted and 0.061 d −1(P) and 0.020 d −1(N) for unplanted tanks. The results obtained from this pilot scale study, provide a better understanding of nutrient distribution and flow patterns that take place within CWS, and should enable more rational design parameters to be developed that help to optimise future large-scale systems.