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The Use of Artificial Wetlands to Treat Greenhouse Effluents
Abstract
Untreated greenhouse effluents or leak solution constitute a major environmental burden because their nitrate and phosphate concentrations may induce eutrophication. Artificial wetlands may offer a low cost alternative treatment of greenhouse effluents and consequently improve the sustainability of greenhouse growing systems. The objectives of this study were to 1) characterize the efficiency of different types of wetland to reduce ion content of greenhouse tomato effluent, and 2) improve the wetland efficiency by adding carbon of 0-800 mg L -1 sucrose. Experiments were conducted at Laval University where 30 pilot scale horizontal subsurface flow artificial wetlands (0.81 m 3) were built. Two types of aquatic macrophytes, Pragmites australis and Typha latifolia, and a control group without plants were tested. The hydraulic retention time was 10 days. During the study, EC of the greenhouse effluent ranged between 1.5 to 5.5 mS cm -1 , while 0 to 800 mg L -1 of sucrose was provided to improve the biological activity of the wetland. The macro-and micro-elements, the greenhouse gases (CH 4 , CO 2 , N 2 O) and the population of bacteria were measured for each unit. At commercial scale, two vertical subsurface wetlands (43.2 m 3) were installed at Ste-Sophie Québec, on the production site of Les Serres Nouvelles Cultures (Sagami). According to our results, 50-90% of nitrate (NO 3
... Although VSS were reported to be less efficient than HSS to remove NO 3 load (Lee et al., 2009), large reductions in NO 3 -(86%), PO 4 3-(100%), and SO 4 2-(63%) were observed when greenhouse wastewater at the commercial level was treated in serial VSS during summer, fall, and winter in Eastern Canada (Lévesque et al., 2011). In HSS, a gravel bed (5 to 20 mm) provides high hydraulic conductivity and poses low risks of clogging, whereas in VSS, sand (0.25 and 4 mm) provides good contact between wastewater and bacteria growing on the medium (Vymazal, 2008a). ...
... Phragmite australis (common reed) largely used in CWs is tolerant of high salinity (Vymazal, 2013a), while Typha latifolia (cattail) was found to be more tolerant to high SO 4 2concentrations present in greenhouse effluent (Lévesque et al., 2011). Maximum Na + uptake rates by macrophytes in wetland microcosms was estimated at 0.072 g m -2 day -1 , equivalent to less than 7% of the Na + removal from wastewater (Tanner, 1996). ...
... Moreover, E. crassipes is not adapted to treat greenhouse wastewater rich in nutrients. Our previous study using three serial VSS CWs and treating greenhouse wastewater at the commercial scale shown a high efficiency to remove nitrate and phosphate from wastewater by up to 90% and 100%, respectively (Lévesque et al., 2011). So, although HSS has shown a good efficiency to remove NO 3 from greenhouse wastewater with low N 2 O emissions during treatment, the use of multiple and hybrid (VSS combined to HSS) CWs operated in series should be tested to improve the efficiency of removing nutrients, such as NO 3 and SO 4 2than single HSS or VSS CWs (Vymazal, 2013b). ...
In the current study, three constructed wetlands
(CWs) were tested as a sustainable method of treating
highly ion charged greenhouse wastewater before
disposal. Because of their anaerobic conditions, it was
hypothesized that free water surface flow (FWS) and
horizontal-subsurface flow (HSS) CWs would be more
efficient at removing NO3- and SO42- from greenhouse
wastewater than the vertical-flow (VSS) CW, but that
FWS and HSS would emit more greenhouse gases.
To test this hypothesis and propose the most sustainable
CW for the greenhouse industry, this study
compared three types of CWs (FWS, HSS and VSS) for
their nutrient removal performance and nitrous oxide
(N2O) emissions. The experiment was conducted
in a greenhouse and consisted of 36 wetland units
(12 replicates) of 0.8 m3 operated with reconstituted
greenhouse wastewater enriched with sucrose (C:N
ratio of 2.9) at a 10-day hydraulic retention time,
corresponding to the effluent loading rate coming
from commercial greenhouse vegetable crops. The
CWs were filled with water (FWS), gravel (HSS), or
sand (VSS) and planted with Eichhornia crassipes
(FWS) or Typha latifolia (HSS, VSS), two macrophytes
largely used to treat wastewaters heavily loaded
in nutriment. Results showed that HSS performed
better than the FWS and VSS at reducing pollutants
from the greenhouse wastewater, with 45% total N
load removed. Although 59% of the NO3‑N load was
removed in the FWS and HSS, a high accumulation of
NO2- (1.28 g N m-2 d-1) occurred in FWS. The removal
of ammonium (NH4‑N) (~26%) loadings was similar
in all CWs. Only 4% of the SO4‑S load was removed
in the FWS and HSS, and no SO4‑S reduction was
observed in VSS. Mean cumulative N2O emissions were
7 and 59 times higher in FWS (1.59 g m-2 d-1) than in
HSS and VSS, respectively. Although VSS emitted less
N2O than the other CWs tested in this study, HSS was
the best option in terms of reducing CO2 emissions
and nutrient pollutants from greenhouse wastewater
before disposal.
... However, organic C present in greenhouse wastewaters derived from damaged roots, microorganisms, and other organic debris (Park et al., 2008; Prystay and Lo, 2001) is generally insufficient to provide a significant C source for optimal wetland activity. Studies have found a significant effect of sucrose input in wetlands on NO 3 Gagnon et al., 2010; Lévesque et al., 2011). Denitrification is the most energetically favorable form of anaerobic respiration; sulfate reduction yields less energy and hence tends to occur when NO 3 ...
... 400 mg L -1 , respectively (Ingersoll and Baker, 1998; Lévesque et al., 2011; Lin et al., 2002). As Baker (1998) reported, when sufficient DOC is present, constructed wetlands are very efficient at promoting denitrification, and NO 3 ...
... 2- occurred, the C source was insufficient for sustaining both metabolic processes, namely denitrification followed by sulfate reduction. Greenhouse wastewaters have a low content in dissolved organic C (DOC » 10–20 mg L -1 ) (Martine Dorais, personal communication) and therefore are only a small source of external C. Similar studies show that planted constructed wetlands with added organic C (sucrose) represent the best combination for hydroponics wastewater treatment (Gagnon et al., 2010; Lévesque et al., 2011). The most important biotic reaction for sulfate removal is catalyzed by SRB; however, SO 4 2- concentration can also be lowered through abiotic mineral precipitation (such as gypsum [CaSO 4 ]), adsorption (Kadlec and Wallace, 2009), or biological assimilation into plant or microbial tissue (Sturman et al., 2008; Willow and Cohen, 2003). ...
This study evaluated the effectiveness of C-enriched subsurface-flow constructed wetlands in reducing high concentrations of nitrate (NO) and sulfate (SO) in greenhouse wastewaters. Constructed wetlands were filled with pozzolana, planted with common cattail (), and supplemented as follows: (i) constructed wetland with sucrose (CW+S), wetland units with 2 g L of sucrose solution from week 1 to 28; (ii) constructed wetland with compost (CW+C), wetland units supplemented with a reactive mixture of compost and sawdust; (iii) constructed wetland with compost and no sucrose (CW+CNS) from week 1 to 18, and constructed wetland with compost and sucrose (CW+CS) at 2 g L from week 19 to 28; and (iv) constructed wetland (CW). During 28 wk, the wetlands received a typical reconstituted greenhouse wastewater containing 500 mg L SO and 300 mg L NO. In CW+S, CW+C, and CW+CS, appropriate C:N ratio (7:3.4) and redox potential (-53 to 39 mV) for denitrification resulted in 95 to 99% NO removal. Carbon source was not a limiting factor for denitrification in C-enriched constructed wetlands. In CW+S and CW+CS, the dissolved organic carbon (DOC)/SO ratios of 0.36 and 0.28 resulted in high sulfate-reducing bacteria (SRB) counts and high SO removal (98%), whereas low activities were observed at DOC/SO ratios of 0.02 (CW) to 0.11 (CW+C, CW+CNS). On week 19, when organic C content was increased by sucrose addition in CW+CS, SRB counts increased from 2.80 to 5.11 log[CFU+1] mL, resulting in a level similar to the one measured in CW+S (4.69 log[CFU+1] mL). Consequently, high sulfate reduction occurred after denitrification, suggesting that low DOC (38-54 mg L) was the limiting factor. In CW, DOC concentration (9-10 mg L) was too low to sustain efficient denitrification and, therefore, sulfate reduction. Furthermore, the high concentration of dissolved sulfides observed in CW+S and CW+CS treated waters were eliminated by adding FeCl.
... The result of meta-analysis suggests that the presence of plants decre sion in HSSF CWs but increases N2O emission in FWS and VSSF CWs (Fi HSSF CWs provide more anaerobic conditions and favor the denitrificatio pared to FWS and VSSF CWs. The presence of plants in CWs can provide c for metabolic activities such as denitrification [60]. When the influent C/N cient to support denitrification, the available carbon from plants may be a m factor than the O2 level to control the denitrification process and reduce N This process may partially explain the lower N2O production in vegetated H in unvegetated HSSF CWs. ...
... The HSSF CWs provide more anaerobic conditions and favor the denitrification process compared to FWS and VSSF CWs. The presence of plants in CWs can provide carbon required for metabolic activities such as denitrification [60]. When the influent C/N ratio is insufficient to support denitrification, the available carbon from plants may be a more important factor than the O 2 level to control the denitrification process and reduce N 2 O production. ...
Constructed wetlands (CWs) are an eco-technology for wastewater treatment and are applied worldwide. Due to the regular influx of pollutants, CWs can release considerable quantities of greenhouse gases (GHGs), ammonia (NH3), and other atmospheric pollutants, such as volatile organic compounds (VOCs) and hydrogen sulfide (H2S), etc., which will aggravate global warming, degrade air quality and even threaten human health. However, there is a lack of systematic understanding of factors affecting the emission of these gases in CWs. In this study, we applied meta-analysis to quantitatively review the main influencing factors of GHG emission from CWs; meanwhile, the emissions of NH3, VOCs, and H2S were qualitatively assessed. Meta-analysis indicates that horizontal subsurface flow (HSSF) CWs emit less CH4 and N2O than free water surface flow (FWS) CWs. The addition of biochar can mitigate N2O emission compared to gravel-based CWs but has the risk of increasing CH4 emission. Polyculture CWs stimulate CH4 emission but pose no influence on N2O emission compared to monoculture CWs. The influent wastewater characteristics (e.g., C/N ratio, salinity) and environmental conditions (e.g., temperature) can also impact GHG emission. The NH3 volatilization from CWs is positively related to the influent nitrogen concentration and pH value. High plant species richness tends to reduce NH3 volatilization and plant composition showed greater effects than species richness. Though VOCs and H2S emissions from CWs do not always occur, it should be a concern when using CWs to treat wastewater containing hydrocarbon and acid. This study provides solid references for simultaneously achieving pollutant removal and reducing gaseous emission from CWs, which avoids the transformation of water pollution into air contamination.
... Commercial greenhouse operations typically use fertigation, a soil-less drip irrigation method that requires both large quantities of water and nutrients. To ensure nutrient uptake by the cultivated plants and to prevent salt accumulation, plants are over irrigated by 25% to 45% (Lévesque et al., 2009). The excess water is collected, treated and recirculated back to crop. ...
... Greenhouses producing high-demand vegetables are a fixture of modern agriculture and spent nutrient solutions will continue to be produced and require removal (Pardossi et al., 1999). However, technologies exist and need to be implemented to ameliorate the nutrient loads of greenhouses (Gruyer et al., 2013;Lévesque et al., 2009), requiring cooperation between growers and regulators to ensure the vitality of the sector while limiting pollution in the watershed. Principal component scores from highly correlated longitudinal data-sets can effectively evaluate the relationship between climatic changes and nutrient concentrations using a single statistical model that incorporates multiple rivers, analytes, years, and agricultural uses. ...
Greenhouse production of vegetables is a growing global trade. While greenhouses are typically captured under regulations aimed at farmland, they may also function as a point source of effluent. In this study, the cumulative impacts greenhouse effluents have on riverine macronutrient and trace metal concentrations were examined. Water samples were collected Bi-weekly for five years from 14 rivers in agriculturally dominated watersheds in southwestern Ontario. Nine of the watersheds contained greenhouses with their boundaries. Greenhouse influenced rivers had significantly higher concentrations of macronutrients (nitrogen, phosphorus, and potassium) and trace metals (copper, molybdenum, and zinc). Concentrations within greenhouse influenced rivers appeared to decrease over the 5-year study while concentrations within non-greenhouse influenced river concentrations remained constant. The different temporal pattern between river types was attributed to increased precipitation during the study period. Increases in precipitation diluted concentrations in greenhouse influenced rivers; however, non-influenced river runoff proportionally increased nutrient mobility and flow, stabilizing the observed concentrations of non-point sources. Understanding the dynamic nature of environmental releases of point and non-point sources of nutrients and trace metals in mixed agricultural systems using riverine water chemistry is complicated by changes in climatic conditions, highlighting the need for long-term monitoring of nutrients, river flows and weather data in assessing these agricultural sectors.
... [14] The efficiency of slow filtration has been found to be related to a complex combination of these mechanisms, with the most important process being biolog- ical. [15] Similarly, artificial wetlands have been used to effectively reduce NO − 3 , SO 2− 4 , and water-borne plant pathogens in greenhouse effluent.161718 However, a lack of land near the greenhouse facility may limit the use of artificial wetlands to treat greenhouse effluents. ...
... Continuous flow through the columns was maintained using peristaltic pumps (OmegaFlex pump, model FPU190-Dual-Case-Ct; Omega Engineering, Stamford, CT, USA) providing 247 mL per day, and the hydraulic retention time was set at 5 days. The bioreactor affluent representing an artificial greenhouse effluent [18] was made daily with 36 g L −1 calcium nitrate, 15 g L −1 potassium nitrate , 12 g L −1 potassium phosphate, 22 g L −1 magnesium sulfate, 20 g L −1 potassium sulfate, and 7 g L −1 potassium chloride, to reach 500 mg L −1 SO 2− 4 and 300 mg L −1 NO − 3 , corresponding to SO 2− 4 and NO − 3 concentrations commercially observed in a soilless tomato greenhouse effluent. The experiment used a randomized design with 3 replicates, for a total of six bioreactor units. ...
The goal of this study was to evaluate the use of passive bioreactors to reduce water-borne plant pathogens (Pythium ultimum and Fusarium oxysporum) and nutrient load (NO(-) 3 and SO(2-) 4) in greenhouse effluent. Sterilized and unsterilized passive bioreactors filled with a reactive mixture of organic carbon material were used in three replicates. After a startup period of 2 (sterilized) or 5 (unsterilized) weeks, the bioreactor units received for 14 weeks a reconstituted commercial greenhouse effluent composed of 500 mg L(-1) SO(2-) 4 and 300 mg L(-1) NO(-) 3 and were inoculated three times with P. ultimum and F. oxysporum (10(6) CFU mL(-1)). Efficacy in removing water-borne plant pathogens and nitrate reached 99.9% for both the sterilized and unsterilized bioreactors. However, efficacy in reducing the SO(2-) 4 load sharply decreased from 89% to 29% after 2 weeks of NO(-) 3-supply treatment for the unsterilized bioreactors. Although SO(2-) 4 removal efficacy for the sterilized bioreactors did not recover after 4 weeks of NO(-) 3-supply treatment, the unsterilized bioreactor nearly reached a similar level of SO(2-) 4 removal after 4 weeks of NO(-) 3-supply treatment compared with affluent loaded only with SO(2-) 4, where no competition for the carbohydrate source occurred between the denitrification process and sulfate-reducing bacteria activity. Performance differences between the sterilized and unsterilized bioreactors clearly show the predominant importance of sulfate-reducing bacteria. Consequently, when sulfate-reducing bacteria reach their optimal activity, passive bioreactors may constitute a cheap, low-maintenance method of treating greenhouse effluent to recycle wastewater and eliminate nutrient runoff, which has important environmental impacts.
... The next application of this strategy could be drip-irrigated chrysanthemums, which would reduce the requirement for overirrigation to leach salts from the potting medium [73]. Finally, applying our low-input nutrient delivery strategy to other floricultural crops may be possible. ...
Fertilizer boron (B) and molybdenum (Mo) were provided to contrasting cultivars of subirrigated pot chrysanthemums at approximately 6–100% of current industry standards in an otherwise balanced nutrient solution during vegetative growth, and then all nutrients were removed during reproductive growth. Two experiments were conducted for each nutrient in a naturally lit greenhouse using a randomized complete block split-plot design. Boron (0.313–5.00 µmol L−1) or Mo (0.031–0.500 µmol L−1) was the main plot, and cultivar was the sub-plot. Petal quilling was observed with leaf-B of 11.3–19.4 mg kg−1 dry mass (DM), whereas Mo deficiency was not observed with leaf-Mo of 1.0–3.7 mg kg−1 DM. Optimized supplies resulted in leaf tissue levels of 48.8–72.5 mg B kg−1 DM and 1.9–4.8 mg Mo kg−1 DM. Boron uptake efficiency was more important than B utilization efficiency in sustaining plant/inflorescence growth with decreasing B supply, whereas Mo uptake and utilization efficiencies appeared to have similar importance in sustaining plant/inflorescence growth with decreasing Mo supply. This research contributes to the development of a sustainable low-input nutrient delivery strategy for floricultural operations, wherein nutrient supply is interrupted during reproductive growth and optimized during vegetative growth.
... Wastewater contaminated with sulfate and nitrate generally carries an unmanageable low content of organic matter hampering denitrification and bacterial sulfate reduction due to a lack of electron donors (Park et al. 2009;Chang et al. 2016). A minimum C/N ratio of 5-3.5 with NO 3 − ranging from 20 to 400 mg/L was found suitable for complete nitrate removal (Lévesque et al. 2011;Lin et al. 2002). Also, the production of organic nitrogen, NO 2 − , NH 4 + , and S 2− must be considered during the degradation of organic substances for the simultaneous removal of sulfate and nitrate. ...
In this study, heat-pretreated sulfate-reducing bacteria (SRBs) were evaluated for simultaneous sulfate and nitrate removal in a bioelectrochemical system (BES). The effect of the applied potential of 20 mV to SRBs was evaluated at a sulfate concentration of 3 g/L and/or nitrate concentration of 0.5 g/L supplemented before heat pretreatment for sulfate and nitrate removal. The highest H2 production of 2.24 ± 0.04 mM/L in heat-pretreated culture was observed in the presence of sulfate at an applied potential of 20 mV (BHE-S). Simultaneous reduction of sulfate and nitrate was significant in BESs supplemented with either sulfate or nitrate during heat-shock pretreatment of the culture. The highest SO42− removal of 88.91 ± 0.8% was found in culture heat pretreated with NO3− and applied with 20 mV potential (BHE-N). The kinetics of heat-pretreated culture showed higher R2 and ultimate potential for H2 on the continuous application of 20 mV potential.
... Thus, the nutrient requirements over the crop cycle can be reduced by approximately 75%-87.5%. It is also of interest to optimize nutrient delivery with drip irrigation, another common method for irrigating indoor ornamentals (Lévesque et al. 2009). Unlike subirrigation, drip irrigation is scalable to any size, and a reduction in salt accumulation in the root medium obtained with a lower nutrient supply could reduce the need for over irrigation. ...
Academic scientists face an unpredictable path from plant biology research to real-life application. Fundamental studies of γ-aminobutyrate and carotenoid metabolism, control of Botrytis infection, and the uptake and distribution of mineral nutrients illustrate that most academic research in plant biology could lead to innovative solutions for food, agriculture, and the environment. The time to application depends on various factors such as the fundamental nature of the scientific questions, the development of enabling technologies, the research priorities of funding agencies, the existence of competitive research, the willingness of researchers to become engaged in commercial activities, and ultimately the insight and creativity of the researchers. Applied research is likely to be adopted more rapidly by industry than basic research, so academic scientists engaged in basic research are less likely to participate in science commercialization. It is argued that the merit of Discovery Grant applications to the Natural Sciences and Engineering Research Council (NSERC) of Canada should not evaluated for their potential impact on policy and (or) technology. Matching industry funds in Canada rarely support the search for knowledge. Therefore, NSERC Discovery Grants should fund basic research in its entirety.
... It would also be of interest to study the timing and optimization of nutrient delivery using drip irrigation, another common environmentally friendly method for irrigating indoor floricultural crops (Lévesque et al. 2009). Unlike subirrigation, drip irrigation is scalable to any size, and reducing nutrient delivery would lower the need for overirrigation. ...
Excessive fertilizer use in greenhouse floricultural operations results in low-nutrient use efficiency by plants and poses environmental risk. Here, we optimized the usage of fertilizer manganese (Mn) and iron (Fe) by modern cultivars of subirrigated pot chrysanthemum. Mn and Fe (approximately 100% to 6% of industry standards) were provided in an otherwise balanced nutrient solution during vegetative growth, and all nutrients were removed during reproductive growth. Two experiments were conducted for each nutrient in a naturally lit research greenhouse using a split-plot design with four blocks arranged randomly. Mn (5.00–0.3125 µmol L⁻¹) or Fe (10.56–0.66 µmol L⁻¹) was the main plot and cultivar (“Milton Dark Pink”, “Williamsburg Purple”, and “Olympia White”) was the subplot. The cultivars exhibited contrasting phenotypes. However, any treatment effects on plant yield and inflorescence development and quality were minor, so that Mn or Fe use efficiency increased approximately 16-fold with decreasing supply. Even though leaf Mn, zinc, and calcium levels were occasionally correlated inversely with decreasing Fe delivery, the leaf Mn (44.8–121.8 mg kg⁻¹) and Fe (68.5–121.8 mg kg⁻¹) levels were always considered acceptable. These findings contribute to the development of a low-input practice that would improve the sustainability of floricultural crop production.
... The wetland units received wastewater in an intermittent flow of 8, 6 and 8 L d −1 for CWS, CWC and CW, respectively, using multiple inlet devices controlled by timers (13 pulses per day, 8 min per pulse) to uniformly distribute the influent to each unit. The influent was uniformly distributed in each wetland unit in a batchsequential way as performed at the commercial scale (Lévesque et al., 2011). The outlet was installed at the end bottom of the wetland unit and treated waters flowed passively in an intermittent way. ...
Because of the lack of high-quality water and the potential pollution of groundwater by leached nutrients, recirculation of nutrient solutions for greenhouse production is now unavoidable. Although closed growing systems offer several advantages from an environmental standpoint, the risk of pathogen dissemination is a major concern for growers. Constructed wetlands represent an ecological and low-cost alternative method for treating agricultural wastewaters. The objective of this study was to evaluate the effectiveness of three types of constructed wetlands for removing the waterborne plant pathogens, such as Pythium ultimum and Fusarium oxysporum, that can be found in greenhouse wastewater. The experiment was conducted in a greenhouse using three types of horizontal subsurface-flow constructed wetlands in eight replicates. The wetlands were filled with pozzolana, planted with common cattail (Typha latifolia) and supplemented with sucrose or compost carbon sources or left without an external carbon source. The wetland units received reconstituted greenhouse wastewater and were inoculated five times consecutively with P. ultimum and F. oxysporum at 106 CFU mL−1. Physical, chemical and biological properties as well as environmental parameters were evaluated during 12 weeks to characterize conditions related to plant pathogen removal efficiency. Even though 99.62–99.99% efficiency for pathogen repression was observed for the constructed wetlands, the compost amendment to the wetland promoted the development of biofilm around the filter media and the production of cell-wall degrading enzymes. Depending on the source of carbon that was provided to promote microbial population growth and wetland activity, different possible modes of action for pathogen removal were predominant but resulted in very high efficiency, considering that the wetlands were inoculated with massive populations of plant pathogens that are not found at the commercial level. This study showed that constructed wetlands can constitute an efficient and safe alternative to treat and then reuse greenhouse wastewater.
Struvite (MgNH4PO4●6H2O) can be recovered from wastewaters for mitigation of phosphorus content. However, the interaction of dissolved constituents with struvite is rarely evaluated. Removal of heavy metals and organic carbon (TOC) in a greenhouse wastewater (GW) by struvite was investigated. Pre-synthesized struvite was added to GW and removal of Zn (689 μg/L), Cu (151 μg/L) and TOC (51 mg/L) monitored from 1-26d. Metal uptake in sodium nitrate solutions was used to assess competition, and the influence of other GW constituents on sorption. Struvite was also directly precipitated from GW (PPT). Recovered GW solids had 64-247 mg/kg Zn, 12-54 mg/kg Cu and 1721-8806 mg/kg TOC, with lowest loadings for PPT and highest for 26d solids. X-ray absorption spectroscopy detected polymerized Zn-phosphate, induced by dissolved phosphorus in GW, and Cu co-polymerization, initially limited by aqueous Cu-organic complexation. Sorbed Cu shifts Fourier Transform infrared-sensitive phosphate bands and changes the intensities of reflections in X-ray diffraction patterns of struvite more so than Zn. Struvite from GW is more susceptible to thermal decomposition than unreacted struvite, evolving CO(g), CO2(g), NH3(g) and H2O(g). Therefore, struvite from GW sorbs metals and organics, and can release sorbed and structural components to the aqueous and gas phases.
The environmental impacts associated with fossil energy use, in addition to water and fertilisation management continue to be major concerns for Northern greenhouse production systems. To reduce the environmental impacts of greenhouse farming under Northern climate conditions and to maintain its competitiveness, the use of renewable energy sources and suitable nutrient management are becoming essential. From this perspective, a closed-loop demarcated bed-grown organic production system that increases the efficiency of water and nutrient use and utilises waste biomass as a source of energy was developed and tested in the province of Quebec, Canada. The goal of this study was to assess the environmental impacts of this so-called sustainable organic system compared with an open conventional growing system using fossil energy. The environmental analysis was conducted with life cycle assessment methodology as defined by the ILCD handbook (2010) and the SimaPro v.7.3.2 software. The functional unit was 1,000 kg of tomatoes and 1 ha of cultivated area. The system boundary was from raw materials extraction to the farm gate. The life cycle stages considered were infrastructure, auxiliary equipment, climate control system, farm operation, fertilisers, pesticides, waste management and packaging. For both growing systems, results from the environmental assessment indicate that high energy demand was the main contributor to all impact categories. When organic farming using wood biomass as renewable energy was applied, the CO2 footprint of 1 kg of tomatoes was 0.812 kg CO2 eq kg-1, while the impact of an open conventional growing system using fossil energy was 5.788 kg CO2 eq kg-1. The fertiliser assessment of the closed-loop organic crop had a lower environmental burden on abiotic depletion (by 12 times), acidification (by 6 times), eutrophication (by 136 times) and global warming (by 10 times) compared with the fertiliser assessment of the open conventional growing system.
Abstract High phosphate content in wastewater is currently a major issue facing the North American greenhouse industry. Phosphate-sorbing material filters could provide a means of removing phosphate from wastewater prior to discharge to the environment, but characterization of economically viable materials and specific recommendations for greenhouse wastewater are not available. Batch and column experiments were used to examine the capacity of two calcium-based waste materials, basic oxygen furnace slag and a concrete waste material, to remove phosphate from greenhouse nutrient solution in varied operating conditions. Material columns operating at a hydraulic retention time (HRT) of 3 hours consistently removed >99% of influent phosphate at a concentration of 60 mg/L over repeated applications, and demonstrated high phosphate retention capacity of 8.8 and 5.1 g P/kg for slag and concrete waste, respectively. Both materials also provided some removal of the micronutrients Fe, Mn, and Zn. Increasing HRT to 24 h increased P retention capacity of slag to >10.5 g P/kg, but did not improve retention by concrete waste. Decreasing influent phosphate concentration to 20 mg/L decreased phosphate retention capacity to 1.64 g P/kg in concrete waste columns, suggesting fluctuations in greenhouse wastewater composition will affect filter performance. The pH of filter effluent was closely correlated to final P concentration, and can likely be used to monitor treatment effectiveness. This study demonstrated that calcium-based materials are promising for removal of phosphate from greenhouse wastewater, and worthy of further research on scaling up the application to a full-sized system.
Phosphate (P) contamination in nutrient-laden wastewater is currently a major topic of discussion in the North American greenhouse industry. Precipitation of P as calcium phosphate minerals using hydrated lime could provide a simple, inexpensive method for retrieval. A combination of batch experiments and chemical equilibrium modelling was used to confirm the viability of this P removal method and determine lime addition rates and pH requirements for greenhouse wastewater of varying nutrient compositions. Lime: P ratio (molar ratio of CaMg(OH)4: PO4‒P) provided a consistent parameter for estimating lime addition requirements regardless of initial P concentration, with a ratio of 1.5 providing around 99% removal of dissolved P. Optimal P removal occurred when lime addition increased the pH from 8.6 to 9.0, suggesting that pH monitoring during the P removal process could provide a simple method for ensuring consistent adherence to P removal standards. A Visual MINTEQ model, validated using experimental data, provided a means of predicting lime addition and pH requirements as influenced by changes in other parameters of the lime-wastewater system (e.g. calcium concentration, temperature, and initial wastewater pH). Hydrated lime addition did not contribute to the removal of macronutrient elements such as nitrate and ammonium, but did decrease the concentration of some micronutrients. This study provides basic guidance for greenhouse operators to use hydrated lime for phosphate removal from greenhouse wastewater.
The objectives of this study were to evaluate the risks and benefits of using artificial wetland-treated waters to irrigate tomato plants (Lycopersicom esculentum) and the potential for suppression of Pythium ultimum. The experiment was conducted in a greenhouse using tap water (control) and treated waters coining from three types of horizontal subsurface flow artificial wetlands filled with pozzolana and implanted with common cattail (Typha latifolia). Wetland units contained either a simple [artificial wetland with sucrose (AWS)] or complex [artificial wetland with compost (AWC)] carbon source or no [artificial wetland with no carbon (AW)] additional carbon source. A complete randomized split-block design comparing root sensitivity to root rot (inoculated and uninoculated plants) in main plots and four nutrient solutions [1) control, 2) treated water from AWS, 3) treated water from AWC, and 4) treated water from AW] in subplots was used in six replications. Tomato plants were inoculated with P. ultimum twice during the experimental period. The use of treated waters reduced the in vivo root Pythium population by 84% and 100% when the treated waters were from AWS and AWC, respectively. In vitro trials showed that sterilization or membrane filtration (0.2 mu m) of treated waters significantly reduced the potential for suppression of P. ultimum, suggesting that microbial activity played an important role. On the other hand, all AW-treated waters had a negative effect on root development of uninoculated young tomato plants. Root dry weights of plants irrigated with treated waters was 56% lower than in control plants, while their shoot:root ratio was two times higher for plants irrigated with treated waters. The inoculated and AWC-treated water treatments also reduced the Fv:Fm ratio of dark-adapted leaves, representing the maximum quantum efficiency of photosystem II. Organic compounds present in treated waters, expressed as total and dissolved organic compounds, may have affected tomato root development.
This review summarizes the microbial mechanisms responsible for removal of carbon, nitrogen, and sulfur compounds in treatment wetlands (TWs) and identifies, categorizes and compares various techniques, from plate count to more modern genomic methods used to elucidate these mechanisms. Removal of a particular pollutant is typically associated with a specific microbial functional group, therefore employment of design and operational methodologies that enhance the activity of that group will better optimize performance. Redox condition is a manipulable parameter that can be used to optimize growth of a targeted functional group, therefore factors influencing the TW redox condition and its influence on organic carbon removal mechanisms are emphasized. Environmental factors influencing growth and activity of N and S cycling microbes (including temperature, pH, salinity, plant species selection and availability of organic carbon and/or inhibiting substances) are discussed with particular attention to factors that might be manipulated. This information is used to offer design and operational methodologies that might enhance growth of a desirable microbial functional group and project what additional microbially-focused research is required to better optimize TW performance.
The osmotic and ionic effects of the electrical conductivity (EC) of the nutrient solution and its interactions with climatic factors and cultural practices on tomato yield and fruit quality are reviewed. Adjusting the salinity of the nutrient solution allows growers to modify water availability to the crop and hence improve fruit quality. At some point, however, increases in salinity limit marketable yield. Under high ECs, fruit size is inversely related to EC while the dry matter content of the fruit is linearly increased by the EC. The exact rate of yield decline varies with interactions between cultivars, environmental factors, composition of the nutrient solution, and crop management. According to different studies and growth conditions, salinities higher than 2.3-5.1 mS$\cdot$cm$^{-1}$ result in an undesirable yield reduction, while ECs of 3.5-9.0 mS$\cdot$cm$^{-1}$ improve tomato fruit quality. Manipulating the indoor climate such as humidity, temperature and ambient CO$_2$ level may offset the negative effect of high salinity on yield and fruit quality such as blossom-end rot. The light intensity received by the plant directly affects the quantity of photoassimilates available to the fruit, it also increases their sugar: acid ratio, and influences the transpiration rate and the water uptake by the plant, which in turn, affect the EC around the root. Increasing the EC with NaCl reduces titratable acids, potassium and nitrogen in the fruit but also increases their sodium content. NaCl enhances the sweetness of tomato fruit and improves the overall flavour intensity. Depending upon the composition of the saline solution, ion toxicities or nutritional deficiencies may arise because of a predominance of specific ion or competition effects among cations and anions. Keeping the proper nutrient levels and ratios between all the nutrients in the root environment for each growth stage of a crop should be targeted in order to achieve high yields and high quality products throughout the cropping season. Several EC and fertigation management regimes could improve fruit quality and are presented in this review. Influence de la régie de la conductivité électrique de la solution nutritive sur le rendement et la qualité de la tomate de serre. Cette revue de littérature porte sur les effets osmotiques et ioniques de la conductivité électrique (CE) de la solution nutritive et de ses liens avec les facteurs climatiques et culturaux sur le rendement et la qualité de la tomate de serre. L'ajustement de la salinité de la solution nutritive permet aux producteurs de modifier la disponibilité en eau pour la plante de façon à contrôler la qualité des fruits. Cependant, des salinités élevées affectent le rendement vendable. Sous une haute CE, le calibre des fruits est inversement relié à la CE alors que le contenu en matière sèche des fruits augmente linéairement avec la CE. Le taux de réduction du rendement varie selon les interactions entre la CE et les cultivars, les facteurs environnementaux, la composition de la solution nutritive, et la gestion de la culture. Selon différentes études et conditions de croissance des plants, une CE plus élevée que 2.3-5.1 mS$\cdot$cm$^{-1}$ entraîne une baisse de rendement alors qu'une salinité de 3.5-9.0 mS$\cdot$cm$^{-1}$ améliore la qualité des fruits. La manipulation du climat de la serre (humidité relative, température, niveau de CO$_2$ ambiant) peuvent compenser les effets négatifs engendrés par de hautes salinités sur le rendement et la qualité des fruits. L'intensité lumineuse reçue par la plante affecte directement la quantité de photoassimilats disponibles pour les fruits, accroît leur rapport sucre : acide, influence les taux de transpiration et d'absorption de l'eau par les plants, lesquels influencent la CE de la zone radiculaire. L'accroissement de la salinité par l'ajout de NaCl réduit le contenu en acides titrables, en potassium et en azote des fruits et augmente leur contenu en sodium. Le NaCl accroît la qualité gustative des fruits et la perception d'une saveur plus sucrée. Selon la composition de la solution nutritive, des déficiences ou toxicités nutritionnelles peuvent survenir suite à une prédominance d'ions spécifiques ou à une compétition parmi les cations et les anions. De façon à obtenir des rendements élevés de très grande qualité tout au long de la saison de production, un équilibre entre les éléments nutritifs de la rhizosphère doit être préservé pour chacun des stades de croissance. Cet article présente plusieurs stratégies de gestion de la CE afin d'améliorer la qualité de la tomate de serre.
Constructed wetlands are a natural alternative to technical methods of wastewater treatment. However, our understanding of the complex processes caused by the plants, microorganisms, soil matrix and substances in the wastewater, and how they all interact with each other, is still rather incomplete. In this article, a closer look will be taken at the mechanisms of both plants in constructed wetlands and the microorganisms in the root zone which come into play when they remove contaminants from wastewater. The supply of oxygen plays a crucial role in the activity and type of metabolism performed by microorganisms in the root zone. Plants' involvement in the input of oxygen into the root zone, in the uptake of nutrients and in the direct degradation of pollutants as well as the role of microorganisms are all examined in more detail. The ways in which these processes act to treat wastewater are dealt with in the following order: Technological aspects; The effect of root growth on the soil matrix; Gas transport in helophytes and the release of oxygen into the rhizosphere; The uptake of inorganic compounds by plants; The uptake of organic pollutants by plants and their metabolism; The release of carbon compounds by plants; Factors affecting the elimination of pathogenic germs.
The processes that affect removal and retention of nitrogen during wastewater treatment in constructed wetlands (CWs) are manifold and include NH(3) volatilization, nitrification, denitrification, nitrogen fixation, plant and microbial uptake, mineralization (ammonification), nitrate reduction to ammonium (nitrate-ammonification), anaerobic ammonia oxidation (ANAMMOX), fragmentation, sorption, desorption, burial, and leaching. However, only few processes ultimately remove total nitrogen from the wastewater while most processes just convert nitrogen to its various forms. Removal of total nitrogen in studied types of constructed wetlands varied between 40 and 55% with removed load ranging between 250 and 630 g N m(-2) yr(-1) depending on CWs type and inflow loading. However, the processes responsible for the removal differ in magnitude among systems. Single-stage constructed wetlands cannot achieve high removal of total nitrogen due to their inability to provide both aerobic and anaerobic conditions at the same time. Vertical flow constructed wetlands remove successfully ammonia-N but very limited denitrification takes place in these systems. On the other hand, horizontal-flow constructed wetlands provide good conditions for denitrification but the ability of these system to nitrify ammonia is very limited. Therefore, various types of constructed wetlands may be combined with each other in order to exploit the specific advantages of the individual systems. The soil phosphorus cycle is fundamentally different from the N cycle. There are no valency changes during biotic assimilation of inorganic P or during decomposition of organic P by microorganisms. Phosphorus transformations during wastewater treatment in CWs include adsorption, desorption, precipitation, dissolution, plant and microbial uptake, fragmentation, leaching, mineralization, sedimentation (peat accretion) and burial. The major phosphorus removal processes are sorption, precipitation, plant uptake (with subsequent harvest) and peat/soil accretion. However, the first three processes are saturable and soil accretion occurs only in FWS CWs. Removal of phosphorus in all types of constructed wetlands is low unless special substrates with high sorption capacity are used. Removal of total phosphorus varied between 40 and 60% in all types of constructed wetlands with removed load ranging between 45 and 75 g N m(-2) yr(-1) depending on CWs type and inflow loading. Removal of both nitrogen and phosphorus via harvesting of aboveground biomass of emergent vegetation is low but it could be substantial for lightly loaded systems (cca 100-200 g N m(-2) yr(-1) and 10-20 g P m(-2) yr(-1)). Systems with free-floating plants may achieve higher removal of nitrogen via harvesting due to multiple harvesting schedule.
Constructed wetland (CW) treatment systems are engineered systems that have been designed and constructed to utilize the natural processes involving wetland vegetation, soils, and their associated microbial assemblages to assist in treating wastewater. They are designed to take advantage of many of the same processes that occur in natural wetlands, but do so within a more controlled environment. CWs for wastewater treatment may be classified according to the flow regime into surface flow (SF or free water surface (FWS)) and subsurface flow (SSF) systems. The FWS CWs could be further categorized according to the life-form of the dominating macrophyte into systems with free-floating, floating-leaved, emergent, and submerged macrophytes. CWs with emergent macrophytes are the most commonly used FWS systems. FWS CWs are found in all continents with majority being in Europe and North America. They have been used around the world for various wastewaters including municipal and domestic sewage, wastewaters from livestock operations, industrial wastewaters including those from agroindustry and landfill leachates. During the last four decades thousands of applications have proved that FWS CWs are viable alternative to conventional treatment technologies.
During the last decade, several sustainable management practices have been proposed by researchers and extension services. For greenhouse production, three main factors should be considered to reduce environmental burdens: 1) waste management, 2) nutrient emission, and 3) fossil energy use. Organic waste represents a significant source of biomass production for protected crops. Wastes such as 4.5 t tomato leaf biomass ha -1 week -1 are usually discarded in sanitary landfills or directed to other waste management sites such as composting sites or accumulated near the production facility thus constituting a phytosanitary problem. When drainage water from producing greenhouse vegetables is not recycled, nutrient emission into the groundwater may represent a major environmental impact (up to 3000-4500 m 3 per ha of tomato wasted nutritive solution containing 4- 10 t of nutrients such as nitrogen and phosphorus). Greenhouse culture production also uses a significant quantity of fossil fuel energy, in the form of heat (10-40% of production costs), CO 2-enrichment, and fertilizers. Thus, management of significant quantities of organic solid and liquid waste produced by greenhouse crops as well as the use of renewable energy constitute a challenge that can be partly solved by more sustainable production systems. Our integrated closed-loop process recycles both solid and liquid organic waste, and converts the waste into renewable energy (CH 4), CO 2, and liquid and solid fertilizers. Organic waste products and drained water are then reintroduced into the irrigation system. This ensures minimal risks using biological processes such as anaerobic digestion and nitrifying bioreactor, artificial wetlands and passive bioreactors to reduce nutrient pollutants and sulfate content as well as risks associated to pathogens. The proposed integrated production system uses organic growing media or soil with organic fertilizers as well as liquid organic culture, and constitutes a sustainable organic production system achieving productivity levels as high as conventional growing systems.
The horizontal subsurface-flow-constructed wetlands (HSSF CWs) were initiated by Kathe Seidel in the 1960s in Germany and spread throughout Europe and other parts of the world during the 1980s and 1990s. HSSF CWs exhibit high removal of organics, suspended solids, and bacteria, while removal of nutrients is limited due to predominantly anoxic/anaerobic conditions in the filtration beds which do not allow for ammonia nitrification and low-sorption capacity for phosphorus unless special materials are used. On the other hand, vertical flow constructed wetlands which are fed intermittently provide higher oxygen transfer rate and good removal of ammonia. Various types of constructed wetlands may be combined in order to achieve higher treatment effect, especially for nitrogen.
A single solution reagent is described for the determination of phosphorus in sea water. It consists of an acidified solution of ammonium molybdate containing ascorbic acid and a small amount of antimony. This reagent reacts rapidly with phosphate ion yielding a blue-purple compound which contains antimony and phosphorus in a 1:1 atomic ratio. The complex is very stable and obeys Beer's law up to a phosphate concentration of at least 2 μg/ml.The sensitivity of the procedure is comparable with that of the stannous chloride method. The salt error is less than 1 %.
Nitrate contamination is a serious problem worldwide. By providing an ample supply of carbon and an anaerobic environment, wetlands are a valuable low technology for treating nitrate-contaminated waters with low organic carbon concentrations. Denitrification is apparently limited by the C:N ratio, with ratios >5:1 resulting in >90% nitrate removal efficiencies. The denitrification rate constant, VNO3 varies in direct proportion to carbon supply. Several novel or emerging applications of wetlands include renovation of nitrate-contaminated aquifers (a pump-and-treat strategy), denitrification of nitrified sewage effluents, and treatment of irrigation return flows. Treatment of dual sources is also discussed. In arid regions with limited supplies of high quality water, nitrate treatment wetlands may play a significant role in the development of water resources.
A full-scale integrated natural system has been used to treat high strength potato processing water for 2 years. The integrated natural system consists of free water surface and vertical flow wetlands, and a facultative storage lagoon. Influent wastewater averages 2800 mg/L COD, 150 mg/L TN and 350 mg/L TSS. Approximately 5300 m3/d of wastewater flows through the treatment system annually. The treatment objective is a 53% reduction in total nitrogen. The wastewater application permit requires an annual nitrogen load of 500 kg/ha yr on 213 hectares of land used to grow alfalfa and other fodder crops. Free water surface wetlands are used for sedimentation, mineralization of organic matter, and denitrification. Vertical flow wetlands oxidize organic matter and nitrogen. A lagoon provides storage during the winter when irrigation is not possible and functions as a facultative lagoon. Free water surface wetlands were planted with Typha latifolia and Scirpus validus in fall 1995. Wastewater application began in July of 1996. In the summer months COD removal has been greater than 95% through the free water surface wetlands and vertical flow wetlands. The removal rate decreased to about 75% in the winter. Average summer water temperatures are 18°C; average winter water temperatures are 3°C. Ammonia removal through the vertical flow wetlands averages 85% during the summer and 30–50% removal during the winter. Addition of exogenous carbon to the free water surface wetlands resulted in 95% removal of N03-N. Use of natural systems have proved to be a cost effective treatment alternative for high strength industrial wastewater.
In a laboratory study we investigated 1) the potential production of nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) and 2) the effect of nitrate (NO3−) and anaerobic N2O development on CH4 production in sediment from a recently recreated free surface water wetland (FSWW) and in soil from an adjacent meadow. We designed an experiment where production of greenhouse gases was registered at the time of maximum net development of N2O. We made additions of biodegradable carbon (glucose) and/or NO3− to sediment and soil slurries and incubated them at four temperatures (4, 13, 20, 28 °C). Gas production from both substrates was positively correlated with temperature. We also found that the sediment produced more N2O than the soil. N2O production in sediment was NO3− limited, whereas in soil carbon availability was lower and only combined additions of NO3− and glucose supported increased N2O development. CH4 production was generally low and did not differ between soil and sediment. Nor did glucose addition increase CH4 rates. The results suggest that neither soil nor sediment environment did support development of methanogenic populations. There were no clear effects of NO3− on CH4 production. However, the highest records of CH4 were found in incubations with low N2O production, which indicates that N2O might be toxic to methanogens. In summary, our study showed that transforming meadows into FSWWs implies a risk of increased N2O emissions. This does not seem to be valid for CH4. However, since N2O is almost always produced wherever NO3− is denitrified, increased N2O production in wetlands leads to reduced rates in downstream environments. Hence, we conclude that when balancing NO3− retention and global warming aspects, we find no reason to discourage future creation or restoration of wetlands.
The effect of influent loading rate on mass removal of nitrogen and phosphorus from dairy parlour wastewaters was compared in four pairs of planted (Schoenoplectus validus) and unplanted gravel-bed wetlands (each 19 m2). The wetlands were operated at nominal retention times of 7, 5.5, 3 and 2 days, with in and outflows sampled fortnightly over a 20 month period. Hydraulic flows were monitored to enable calculation of the mass flows of nutrients, and plant biomass and tissue nutrient levels sampled to evaluate plant nutrient uptake. Influent water quality varied markedly during the trial period (TN, 10–110; NH4-N, 5–70; and TP 8–18 g m−3). As theoretical wastewater retention times increased from 2 to 7 days, mean reduction of TN increased from 12 to 41% and 48 to 75% in the unplanted wetlands and planted wetlands, respectively, and TP removal increased from 12 to 36% and 37 to 74%, respectively. In the planted wetlands, mean annual removal rates of TN (0.15–1.4 g m−2 d−1) and TP (0.13–0.32 g m−2 d−1), increased gradually with mass loading rates. The unplanted wetlands showed a marked decline in TN and TP removal at high loadings. Net storage by plants in the first year of monitoring accounted for between 3 and 20% of the greater N removal and between 3 and 60% of the greater P removal in the planted wetlands.
The adsorption characteristics of various filter media and treatment efficiency of small pilot-scale constructed wetlands (CWs) were investigated in order to design optimum CWs for treating greenhouse wastewater. Calcite was the best filter medium for the adsorption of ammonium nitrogen and phosphorus under various temperature and pH conditions. However, removal efficiency of calcite for total nitrogen (T-N) removal was low due primarily to high nitrate levels. Thus, several hybrid CWs (containing calcite as filter media) consisting of combinations of vertical flow (VF) and horizontal flow (HF) beds were evaluated for improving efficiency for T-N removal. Both 2- and 3-stage combinations of the VF and HF beds were tested. The optimum hybrid CWs was demonstrated to be a 3-stage combination of horizontal flow (HF)–vertical flow (VF)–horizontal flow (HF), which provided suitable conditions for both nitrification and denitrification, which improved removal of T-N in wastewater containing nitrate. In the HF–VF–HF 3-stage hybrid CWs, the reduction in chemical oxygen demand (COD), T-N, and total phosphorus (T-P) in the effluent were 95.1, 68.4 and 94.3%, respectively. The removal of COD, T-N and T-P in 3-stage HF–VF–HF CWs was rapid in order of VF (second stage) ≫ HF (first stage) ≫ HF (third stage), VF (second stage) ≫ HF (third stage) > HF (first stage) and VF (second stage) ≫ HF (first stage) ≫ HF (third stage), respectively.
The first experiments using wetland macrophytes for wastewater treatment were carried by out by Käthe Seidel in Germany in early 1950s. The horizontal sub-surface flow constructed wetlands (HF CWs) were initiated by Seidel in the early 1960s and improved by Reinhold Kickuth under the name Root Zone Method in late 1960s and early 1970s and spread throughout Europe in 1980s and 1990s. However, cohesive soils proposed by Kickuth got clogged very quickly because of low hydraulic permeability and were replaced by more porous media such as gravel in late 1980s in the United Kingdom and this design feature is still used. In fact, the use of porous media with high hydraulic conductivity was originally proposed by Seidel. HF CWs provide high removal of organics and suspended solids but removal of nutrients is low. Removal of nitrogen is limited by anoxic/anaerobic conditions in filtration beds which do not allow for ammonia nitrification. Phosphorus removal is restricted by the use of filter materials (pea gravel, crushed rock) with low sorption capacity. Various types of constructed wetlands may be combined in order to achieve higher treatment effect, especially for nitrogen. However, hybrid systems are comprised most frequently of vertical flow (VF) and HF systems arranged in a staged manner. HF systems cannot provide nitrification because of their limited oxygen transfer capacity. VF systems, on the other hand, do provide a good conditions for nitrification but no denitrification occurs in these systems. In hybrid systems (also sometimes called combined systems) the advantages of the HF and VF systems can be combined to complement processes in each system to produce an effluent low in BOD, which is fully nitrified and partly denitrified and hence has a much lower total-N outflow concentrations.
The performance response of planted and the unplanted wetlands to simulated wastewater with different ratios of carbon to nitrogen (C/N) was studied during a 9-month period in greenhouse conditions. With different C/N ratios for influent water (C/N ratios 2.5:1, 5:1 and 10:1), average removal efficiencies for the unplanted and the planted wetlands were as follows: COD (41-52% and 59-68%), TN (24-48% and 25-62%), TP (35-64% and 59-71%) and TOC (22-37% and 16-33%). At C/N 5:1, both systems performed most efficiently for removal of COD and TP. However, high N removal efficiency only occurred when C/N ratio ranged 2.5-5. Both wetlands exhibited good capabilities of total organic carbon removal at C/N 10:1. Maybe, appropriate control of the carbon or nitrogen source concentration and C/N ratio in the influent can achieve the optimal effect of nutrients removal.
Several microcosm wetlands unplanted and planted with five macrophytes (Phragmites australis, Commelina communis, Penniserum purpureum, Ipomoea aquatica, and Pistia stratiotes) were employed to remove nitrate from groundwater at a concentration of 21-47 mg NO3-N/l. In the absence of external carbon, nitrate removal rates ranged from 0.63 to 1.26 g NO3-N/m2/day for planted wetlands. Planted wetlands exhibited significantly greater nitrate removal than unplanted wetlands (P<0.01), indicating that macrophytes are essential to efficient nitrate removal. Additionally, a wetland planted with Penniserum showed consistently higher nitrate removal than those planted with the other four macrophytes, suggesting that macrophytes present species-specific nitrate removal efficiency possibly depending on their ability to produce carbon for denitrification. Although adding external carbon to the influent improved nitrate removal, a significant fraction of the added carbon was lost via microbial oxidation in the wetlands. Planting a wetland with macrophytes with high productivity may be an economic way for removing nitrate from groundwater. According to the harvest result, 4-11% of nitrogen removed by the planted wetland was due to vegetation uptake, and 89-96% was due to denitrification.
A series of investigations was conducted to evaluate the feasibility of using constructed treatment wetlands to remove pollutants from saline wastewater. Eight emergent plants; cattail, sedge, water grass, Asia crabgrass, salt meadow cordgrass, kallar grass, vetiver grass and Amazon, were planted in experimental plots and fed with municipal wastewater that was spiked with sodium chloride (NaCl) to simulate a saline concentration of approximately 14-16 mScm-1. All macrophytes were found tolerant under the tested conditions except Amazon and vetiver grass. Nutrient assimilation of salt tolerant species was in the range of 0.006-0.061 and 0.0002-0.0024 gm-2d-1 for nitrogen and phosphorus, respectively. Treatment performances of planted units were found to be 72.4-78.9% for BOD5, 43.2-56.0% for SS, 67.4-76.5% for NH3-N and 28.9-44.9% for TP. The most satisfactory plant growth and nitrogen assimilation were found for cattail (Typha angustifolia) though the plant growth was limited, whereas Asia crabgrass (Digitaria bicornis) was superior for BOD5 removal. Both were evaluated again in a continuous flow constructed wetland system receiving saline feed processing wastewater. A high removal rate regularly occurred in long-term operating conditions. The reduction in BOD5, SS, NH3-N and TP was in the range of 44.4-67.9%, 41.4-70.4%, 18.0-65.3% and 12.2-40.5%, respectively. Asia crabgrass often provided higher removal especially for BOD5 and SS removal. Nutrient enriched wastewater promoted flourishing growth of algae and plankton in the surface flow system, which tended to reduce treatment performance.
In this study, bacterial removal efficiencies of planted and unplanted subsurface vertical flow constructed wetlands are compared. Indicator organisms such as faecal coliforms (Escherichia coli, total coliforms) and enterococci, and a number of heterotrophic bacteria (heterotrophic plate counts) have been analysed from the influent and effluent of the constructed wetlands as well as at different depths (water and substrate samples). Furthermore dry matter content and total organic carbon (TOC) have been analysed and correlated. The investigated systems show a high removal rate for indicator organisms (a log removal rate of 2.85 for HPC, 4.35 for E. coli, 4.31 for total coliforms and 4.80 for enterococci was observed). In general no significant difference in the removal efficiency of planted and unplanted vertical flow beds could be measured. Only enterococci measured in the substrate samples of the main layer of the filter could a statistically significant difference be observed.
Ministry of agriculture food and rural affairs
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Omafra. 2008. Ministry of agriculture food and rural affairs. http://www.omafra.gov.
on.ca/english/environment/hort/grhouse.htm.
Fixation of soil phosphorus
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Dean, L.A. 1949. Fixation of soil phosphorus. Adv. Agron. 1:391-411.
Les industries des cultures de serre, des gazonnières et des pépinières Ministre de l'industrie, Ottawa. Catalogue No 22-202-X
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