Artificial aeration to increase pollutant removal efficiency of constructed wetlands in cold climate (original) (raw)
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Journal of Environmental Engineering and Science, 2007
We studied the contribution of artificial aeration, loading rate, and macrophyte species on pollutant removal in horizontal subsurface flow constructed wetlands (HSSFCWs) treating reconstituted trout farm wastewater. Twelve 1 m 2 mesocosms located in a controlled greenhouse environment were used to test two species of macrophytes (Phragmites australis, Typha angustifolia), three loading rates (30, 60, and 90 L·m −2 ·d −1 ), and presence or absence of artificial aeration at the intermediate loading rate. There was no effect of any variable (macrophytes, loading, aeration) on total suspended solids (TSS) or chemical oxygen demand (COD) removal. Artificial aeration improved nitrogen removal while higher loading rates diminished removal of nitrogen and phosphorus. Macrophytes improved nitrogen and phosphorus removal, but this effect varied depending on loading rates and presence or absence of artificial aeration. We found no differences between Phragmites and Typha for treatment of trout fish farm wastewater. Under summer conditions, our results suggest that artificial aeration could be used to improve nitrogen removal by HSSFCWs.
Performance Variations of Cod and Nitrogen Removal by Vegetated Submerged Bed Wetlands
Journal of the American Water Resources Association, 2002
Vegetated submerged bed wetlands can supplement treatment of onsite wastewater systems. This study evaluated vegetation, media, and seasonal impacts on system performance in six meso scale rock plant filters with and without narrow leaf cattails (Typha augustifolia). Daily chemical oxygen demand (COD) reductions in planted cells averaged 85 percent and weekly total nitrogen (TN) reductions averaged 50 percent. Planted cells had 17 percent greater COD reduction and 76 percent greater TN reduction than unplanted cells, both significant differences. Media type affected COD reduction, particularly in unplanted cells. COD treatment in planted cells was highest for fine crushed limestone (87±13 percent) and least variable for coarse river gravel (85±11 percent). No significant difference in TN reduction was observed for different media types (48 to 51 percent range). Seasonal influences on treatment included a significant decrease during late fall and early spring and a significant increase with temperature. After a step increase in organic loading, treatment efficiency decreased sharply but returned to prior levels after an adaptation period of about one month. Planted cells not only exhibited higher treatment efficiency but also had a retarded organic matter breakthrough, appearing after three to seven times the period for a bromide tracer. This supports a hypothesis that retardation of contaminant movement through the treatment cells results in enhanced removal. These results support the use of rock plant filters, but demonstrate the need to account for performance variations in system design.
Nutrient Removal in Wetlands During Intermittent Artificial Aeration
Environmental Engineering Science, 2008
In a pilot-scale study, the contribution of intermittent artificial aeration to nitrogen and phosphorus removal in three (i.e., aeration in the middle of the substrate, aeration at the bottom of the substrate, nonaerated substrate) subsurface vertical-flow constructed wetlands planted with Typha latifolia L. (cattail) was tested with eutrophic river water in Tianjin (China). In contrast with the nonaerated wetland, aeration enhanced ammonia-nitrogen, total nitrogen, soluble reactive phosphorus, and total phosphorus removal: 10.1, 4.7, 10.2, and 8.8% for aeration in the middle, and 25.1, 10.0, 7.7, and 7.4% for aeration at the bottom of the substrate, respectively. Analysis of above-ground plant biomass indicated that intermittent aeration restrains the increase in biomass, but stimulates assimilation of nitrogen and phosphorus into stems and leaves. Additional total nitrogen removal of 116 kg N/ha and 126 kg N/ha by harvested above-ground T latifolia biomass for intermittent artificial aeration in the middle and at the bottom of the wetland substrate, respectively, was observed. Outflow water quality of aerated subsurface vertical-flow wetlands was better than the one in the nonaerated wetlands during the whole period of the test run. Artificial aeration improved nitrogen and phosphorus removal, especially during the very hot month of August.
Seasonal Variation of Nutrient Removal in a Full-Scale Artificial Aerated Hybrid Constructed Wetland
Water, 2016
To improve nutrient removal, a full-scale hybrid constructed wetland (CW) consisting of pre-treatment units, vertical-baffled flow wetlands (VBFWs), and horizontal subsurface flow wetlands (HSFWs) was installed in August 2014 to treat sewage wastewater. Artificial aeration (AA) was applied continuously in the VBFW stage to improve the aerobic condition in the hybrid CW. Water samples were collected and analyzed twice a month between the period of August 2015 and July 2016. The results suggest that this new hybrid CW can achieve a satisfactory reduction of chemical oxygen demand (COD), ammonium nitrogen (NH 4 +-N), total nitrogen (TN), and total phosphorus (TP) with average removal rates of 85% ± 10% (35% ± 19 g/m 2 per day), 76% ± 18% (7% ± 2 g/m 2 per day), 65% ± 13% (8% ± 2 g/m 2 per day), and 65% ± 21% (1 g/m 2 per day), respectively. AA significantly improved the aerobic condition throughout the experimental period, and the positive influence of AA on nitrogen removal was found to be higher during summer that during winter. A significant positive correlation between water temperature and nutrient removal (p < 0.01) was observed in the system. Overall, this study demonstrates the application of AA in a full-scale hybrid CW with satisfactory nutrient removal rates. The hybrid CW system with artificial aeration can serve as a reference for future applications areas where land availability is limited.
Water Science and Technology, 2003
Freshwater fish farm effluents have low nutrient concentrations but high flow rates, resulting in a pollutant load, especially phosphorus (P), causing eutrophication. The feasibility was tested of a treatment combining, within a single constructed wetland, the contribution of macrophytes for reducing organic matter and nitrogen (N), with the high efficiency of steel slag and limestone for P removal. Twenty subsurface flow (SSF) basins of 280 L with different combinations of plants (Phragmites communis or Typha latifolia) and substrates (steel slag, limestone, gravel, peat) were fed with a reconstituted fish farm effluent in a greenhouse experiment. Pollutant removal was generally very good under all treatments. N and organic matter removal were correlated with plant biomass while P removal was better in substrates with steel slag and limestone. However, the high pH of the P-adsorbing substrate was detrimental to plant growth so that no combination of plants and substrates could maxi...
Water Environment Research
9 Subsurface flow (SSF) constructed wetland (CW) treatment performance with 10 respect to organics (COD) and nitrogen (ammonium and nitrate) removal from domestic 11 (septic tank) wastewater (WW) is evaluated as affected by the presence of plants, 12 different substrate "rock" having a range of cation exchange capacities (CEC), laboratory 13 versus field conditions and use of synthetic as compared to actual wastewater. This first 14 paper considers the effects of plants on CW treatment in the field, while subsequent 15 papers consider the effects of synthetic versus actual WW and substrate in the laboratory 16 and field on treatment. 17 Each CW system was comprised of two beds (2.6 m long by 0.28 m wide and 18 deep filled with ~18 mm crushed lava rock) separated by an aeration tank connected in 19 series. The lava rock had a porosity of ~47% and a CEC of 4 meq/100gm. One pair of 20 CW systems was planted with cattails in May 2008, while an adjacent pair of systems 21 remained unplanted. Collected septic tank or synthesized WW was allowed to gravity 22 feed each CW system and effluent samples were regularly collected and tested for COD 23 and nitrogen species during four different time periods spanning November 2008 through 24 June 2009. These effluent concentrations were tested for statistical differences at the 25 95% level during individual time periods as well as the 6-month period as a whole. 26 Overall organic removal from domestic WW was 78.8% and 76.1% in the planted 27 and unplanted CW systems, respectively, while ammonium removal was 94.5% and 28 90.2%, respectively. Similarly, organic removal from the synthetic WW of equivalent 29 strength was 88.8% and 90.1% for planted and unplanted CW systems, respectively, 30 while ammonium removal was 96.9% and 97.3%, respectively. 31 32
Transactions of the ASAE
The submerged-flow (SF) wetland concept offers high organics and solids removal at relatively low cost for construction, operation, and maintenance. In this comparative study, vegetated and non-vegetated SF wetlands were investigated for their ability to treat primary lagoon effluent. The experimental design was comprised of three vegetated and three non-vegetated SF wetland beds (3 m Ü 1 m Ü 0.5 m) operated in a semi-continuous-flow mode, which were fed every 12 hours with a design 5-day residence time. The wetlands were packed with 19-mm diameter trap rock and planted with bulrush (Scirpus validus). The BOD 5 and TSS removals throughout the two-year monitoring period were high (up to 98%) for both vegetated and non-vegetated wetlands and tended to follow seasonal variations. Vegetation slightly enhanced the reduction of biodegradable organic matter and suspended solids within the SF environment, although this enhancement was statistically insignificant (P > 0.05). The annual average mass removal for ammonia nitrogen in vegetated wetland beds was 3.3 kg ha-1 d-1 (up to 95%). The nitrification process in vegetated wetland beds was significantly more pronounced (P < 0.05) than non-vegetated beds. The lack of measurable dissolved oxygen in the non-vegetated wetlands likely restricted the nitrification process. The dissolved phosphorus reduction varied from month to month depending on seasonal variations of plant growth, ranging from 27% to 100% in vegetated wetland beds and from no removal to 66% in non-vegetated beds. The removal of dissolved phosphorus in vegetated beds was significantly higher than in non-vegetated wetland beds (P < 0.05). Based on the results of this study, vegetation significantly contributed to the reduction of nutrients, specifically ammonia nitrogen and dissolved phosphorus, from SF wetlands, but not for BOD 5 and TSS.
Water Air and Soil Pollution, 2009
Seven experimental pilot-scale subsurface vertical-flow constructed wetlands were designed to assess the effect of plants [Typha latifolia L. (cattail)], intermittent artificial aeration and the use of polyhedron hollow polypropylene balls (PHPB) as part of the wetland substrate on nutrient removal from eutrophic Jinhe River water in Tianjin, China. During the entire running period, observations indicated that plants played a negligible role in chemical oxygen demand (COD) removal but significantly enhanced ammonia–nitrogen (NH4–N), nitrate–nitrogen (NO3–N) total nitrogen (TN), soluble reactive phosphorus (SRP) and total phosphorus (TP) removal. The introduction of intermittent artificial aeration and the presence of PHPB could both improve COD, NH4–N, TN, SRP and TP removal. Furthermore, aerated wetlands containing PHPB performed best; the following improvements were noted: 10.38 g COD/m2 day, 1.34 g NH4–N/m2 day, 1.04 g TN/m2 day, 0.07 g SRP/m2 day and 0.07 g TP/m2 day removal, if compared to non-aerated wetlands without PHPB being presented.
Nutrient removal in vertical subsurface flow constructed wetlands treating eutrophic river water
International Journal of Environmental Analytical Chemistry, 2011
Four planted (Typha latifolia L.) pilot-scale vertical subsurface flow constructed wetlands were constructed to purify the eutrophic water of the Jinhe River in Tianjin (China) and to determine the feasibility of constructing a full-scale system in the future. The effects of intermittent artificial aeration and the use of polyhedron hollow polypropylene balls (PHPB) as part of the wetland substrate on the nutrient removal potential were also evaluated. During the entire running period, supplementary aeration enhanced the chemical oxygen demand, ammonia-nitrogen, total nitrogen, soluble reactive phosphorus and total phosphorus first order mean removal constants by 0.28 m/d, 3.05 m/d, 0.92 m/d, 0.74 m/d and 0.60 m/d, respectively, but reduced the nitrate-nitrogen removal constant by 1.72 m/d in contrast to non-aerated wetlands. A significantly positive contribution of PHPB to nutrient removal was obtained. The combination of artificial aeration and PHPB resulted in the augmentation of the first order mean removal constants by 0.29 m/d, 3.12 m/d, 1.15 m/d, 0.65 m/d and 0.54 m/d for chemical oxygen demand, ammonia-nitrogen, total nitrogen, soluble reactive phosphorus and total phosphorus, respectively. Findings from a brief cost-benefit analysis suggest that both artificial aeration and the presence of PHPB would result in enhanced nutrient removal that is cost efficient for future projects, particularly if electricity costs are low.
Removal of nutrients in various types of constructed wetlands
Science of The Total Environment, 2007
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.