Experiences with a top layer of gravel to enhance the performance of vertical flow constructed wetlands at cold temperatures (original) (raw)
Related papers
Influence of surface layer on hydrology and biology of gravel bed vertical flow constructed wetlands
Water science and technology : a journal of the International Association on Water Pollution Research, 2005
In France, gravel vertical flow constructed wetlands (gVFCWs) were adapted to treat raw wastewater, which led to important accumulations of matter in filters (organic and mineral). To prevent clogging, large gravel sizes were employed (O 2-6 mm). The aim of this paper was to present the influences of matter accumulation on the hydraulic and biological behaviour of the system. A one-year survey of accumulated matter content and potential respiration activities was completed in three gVFCWs (operating for 3, 4 and 8 years). Cores were sampled into filters. Results showed a vertical stratification of accumulated matter and respiration rates. Dry accumulated matter quantities ranged from 20 kg m(-2) (3 and 4 years operating) to 80 kg m(-2) in the oldest plant (8 years). Potential respiration was larger in the oldest plant (75g O2m(-2)h(-1)) than in the most recent one (15g O2m(-2)h(-1)). Accumulated matter seemed to play a role both on the water retention (enhancing initial percolation ...
Chemical Engineering Journal, 2012
Ten pilot-scale, cylindrical, vertical flow constructed wetlands (area 0.57 m 2) were constructed and operated continuously for three years in parallel experiments, treating synthetic wastewater, simulating the first treatment stage of full-scale systems. The wetland units were planted with two plant species (i.e., common reeds and cattails), had different porous media material composition (i.e., carbonate, igneous, zeolite and bauxite) and three different total substrate thicknesses and gradations. Three loading/resting schedules were used. Water quality samples were collected at the inlet and the outlet of each unit, and were analyzed in the laboratory for the determination of various pollutants. The VFCW units were quite efficient in organic matter (BOD 5 and COD) and nitrogen (TKN and NH 4 +-N) removal, with mean removal efficiencies exceeding 78% and 58%, respectively. Mean phosphorus (TP and OP) removal was lower (37%). The units were found to provide significant pollutant removal under high organic loads, up to 200 g COD/m 2 d. The presence of reeds and aeration tubes was found to improve the performance, while plant species did not affect efficiency. The use of special materials, aiming at enhancing the adsorption of different constituents, did not improve the wetland efficiency, probably due to limited contact time between material and wastewater, and is not recommended.
To foster the practical development of the constructed wetlands used for water quality enhancement in Turkey, 2 vertical subsurface flow pilot-scale constructed wetlands were implemented on the METU campus, Ankara, Turkey. Both of the wetlands were planted with Phragmites australis and operated identically at a flowrate of 3 m3.d 1 and a hydraulic loading rate (HLR) of 0.100 m.d 1, intermittently. The main objective of the research was to quantify the eect of dierent substrates (gravel and blast furnace granulated slag) on the nutrient removal performance of the constructed wetlands in the prevailing climate of Ankara. According to the monitoring study (July 2002-January 2003), concentration based average removal eciencies for the slag and gravel reed beds were as follows: TSS (64% and 62%), COD (49% and 40%), NH+ 4 -N (88% and 58%), TN (41% and 44%), TP (63% and 9%) and PO3 4 -P (60% and 4%). In general, the treatment performance of the slag system was better than that of the grave...
Linnaeus Eco-Tech, 2019
The efficiency of pollution removal from municipal sewage in two vertical flow constructed wetlands consisting of gravel filters with surface area 4 x 5 m, depth 60 cm, covered by reed was evaluated over a period of two years. The flow of wastewater was about 50 mm per day. Wastewater underwent only mechanical treatment before reed bed B, but reed bed A was supplied with wastewater after biological treatment with activated sludge. Sewage was sampled before and after filtration every IO days. Measurements were made of sewage supply and discharge, precipitation and wastewater temperatures. The main indicator of efficiency was the elimination of suspended solids, carbon, nitrogen and phosphorus from the wastewater during filtration. The elimination of the pollution load was 2-25 g per square meter per day for the BOD 5 and 0-3.5 g per square meter per day for total nitrogen. Rates of pollution removal were between 2 and 4 times as high in bed B as in bed A. The rate ofBOD 5 removal and the coefficient k for BOD5 were strongly dependent on temperature for reed bed B; less so far for bed A. The difference between summer and winter indicates that the surface area of constructed wetland B should be 3 times bigger during winter to obtain the summer rate ofBOD 5 pollution removal in the climatic conditions ofNorth Poland (54a° N).
Seasonal assessment of experimental vertical-flow constructed wetlands treating domestic wastewater
Bioresource Technology, 2013
The aim of this work was to compare the impact of different design (aggregate size) and operational (contact time, empty time and chemical oxygen demand (COD) loading) variables on the long-term and seasonal performance of vertical-flow constructed wetland filters operated in tidal flow mode. Compliance was achieved regarding ammonia-nitrogen, nitrate-nitrogen and suspended solids (SS), and non-compliance concerning biochemical oxygen demand (BOD) and ortho-phosphatephosphorus. The filter with the highest COD loading performed the best regarding outflow COD concentration. Higher COD inflow concentrations had a significantly positive impact on the treatment performance for COD, ortho-phosphate-phosphorus and SS. The wetland with the largest aggregate size had the lowest mean nitrate-nitrogen outflow concentration. However, the results were similar regardless of aggregate size and resting time for most variables. Clear seasonal outflow concentration trends (low in summer) were recorded for COD, ammonia-nitrogen and nitrate-nitrogen. No filter clogging was observed.
Water Research, 2013
The aim of this study was to evaluate the effect of different horizontal constructed wetland (CW) design parameters on solids distribution, loss of hydraulic conductivity over time and hydraulic behaviour, in order to assess clogging processes in wetlands. For this purpose, an experimental plant with eight CWs was built at mesocosm scale. Each CW presented a different design characteristic, and the most common CW configurations were all represented: free water surface flow (FWS) with different effluent pipe locations, FWS with floating macrophytes and subsurface flow (SSF), and the presence of plants and specific species (Typha angustifolia and Phragmites australis) was also considered. The loss of the hydraulic conductivity of gravel was greatly influenced by the presence of plants and organic load (representing a loss of 20% and c.a. 10% in planted wetlands and an overloaded system, respectively). Cattail seems to have a greater effect on the development of clogging since its below-ground biomass weighed twice as much as that of common reed. Hydraulic behaviour was greatly influenced by the presence of a gravel matrix and the outlet pipe position. In strict SSF CW, the water was forced to cross the gravel and tended to flow diagonally from the top inlet to the bottom outlet (where the inlet and outlet pipes were located). However, when FWS was considered, water preferentially flowed above the gravel, thus losing half the effective volume of the system. Only the presence of plants seemed to help the water flow partially within the gravel matrix.
Performance of Subsurface Vertical Flow Constructed Wetlands Receiving Municipal Wastewater
The efficiency of pollution removal from municipal sewage in two vertical flow con-structed wetlands consisting of gravel filters with a surface area of 4 ð 5 m, depth 60 cm, planted with reed (Phragmites) was assessed over a period of about two years. The flow of wastewater was 50 mm per day. Wastewater underwent only primary treat-ment before application to reed bed B, but reed bed A was supplied with wastewater after mechanical and biological treatment. Measurements were taken of sewage sup-ply and discharge, precipitation and wastewater temperatures. The main indicator of efficiency was the elimination of suspended solids, BOD 5 , nitrogen and phosphorus from the wastewater during treatment. The elimination of the pollution load was 2–25 g O 2 per square meter per day for the BOD 5 and 0–3.5 g per square meter per day for so-called "total nitrogen". Rates of pollution removal were between 2 and 4 times as high in bed B (after primary treatment) as in bed A (after biolo...
Twenty years experience with constructed wetland systems in Denmark – what did we learn
Full scale constructed wetland systems for wastewater treatment have been in operation in Denmark since 1983, mainly for the treatment of domestic sewage from small villages. The systems are constructed as soil-based horizontal subsurface flow systems but, because of low soil hydraulic conductivity, surface runoff is evident in most of the systems. Two decades of experience show that soil-based systems are generally efficient in removing suspended solids and BOD, but the removal of nitrogen and phosphorus is lower (typically 30-50%) and the systems do not nitrify ammonium. Contrary to earlier claims, the reeds do not increase the hydraulic conductivity of cohesive soils as much as necessary to secure sub-surface flow. Operation needs of soil-based reed beds are low and normally restricted to emptying of the sedimentation tank, cleaning of the distribution system and mowing of the grass around the system. The dead plant material and accumulated litter on the surface of the systems improve performance after the initial years. A significant number of systems have been shut down or extended with other technologies in order to meet new effluent standards, particularly demands for nitrification. New constructed wetland systems are either compact vertical flow systems which provide good nitrification, willow systems with no discharge or restored wetland systems for nitrate removal. If efficient removal of phosphorus is required, this is achieved by chemical precipitation in the sedimentation tank.
Turkish Journal of Engineering and Environmental Sciences, 2004
To foster the practical development of the constructed wetlands used for water quality enhancement in Turkey, 2 vertical subsurface flow pilot-scale constructed wetlands were implemented on the METU campus, Ankara, Turkey. Both of the wetlands were planted with Phragmites australis and operated identically at a flowrate of 3 m 3 .d −1 and a hydraulic loading rate (HLR) of 0.100 m.d −1 , intermittently. The main objective of the research was to quantify the effect of different substrates (gravel and blast furnace granulated slag) on the nutrient removal performance of the constructed wetlands in the prevailing climate of Ankara. According to the monitoring study (July 2002-January 2003), concentration based average removal efficiencies for the slag and gravel reed beds were as follows: TSS (64% and 62%), COD (49% and 40%), NH + 4-N (88% and 58%), TN (41% and 44%), TP (63% and 9%) and PO 3− 4-P (60% and 4%). In general, the treatment performance of the slag system was better than that of the gravel system.
Design considerations for constructed wetlands in dry and hot countries
2013
If treated wastewater should be reused water losses have to be avoided. This can be achieved by i) Selection of more efficient plants to minimise evapotranspiration losses, and or ii) Smaller footprints of the treatment system to avoid evaporation. • When treated wastewater should be reused the treatment efficiency should match the quality needed for the specific reuse purpose limiting the treatment performances to the really needed ones. Segregation of wastewater and separate treatment of greywater can help in obtaining a higher amount of effluent with the proper quality available for the reuse. • Vertical flow beds might be preferred to horizontal flow beds in order to minimize evapotranspiration losses due to their intrinsic shorter Hydraulic Retention Time in comparison to the other CW typologies; depending on the required effluent quality and reuse aim, VF beds can be filled with coarser sand, up to the smallest gravel available on site, in order to reduce the retention time (a...