Mass transfer approach and the designing of horizontal subsurface flow constructed wetland systems treating waste stabilisation pond effluent

2018 ◽  
Vol 78 (12) ◽  
pp. 2639-2646 ◽  
Author(s):  
Anita M. Rugaika ◽  
Damian Kajunguri ◽  
Rob Van Deun ◽  
Bart Van der Bruggen ◽  
Karoli N. Njau
Keyword(s):  
Mass Transfer ◽  
Constructed Wetlands ◽  
Rate Constants ◽  
Removal Rate ◽  
Subsurface Flow ◽  
Oxygen Demand ◽  
Domestic Wastewater ◽  
Organic Load ◽  
Mass Transfer Effect ◽  
Horizontal Subsurface Flow

Abstract Pilot-scale constructed wetlands (CWs) that allowed wastewater to flow with high interstitial velocities in a controlled environment were used to evaluate the possibility of using mass transfer approach to design horizontal subsurface flow constructed wetlands (HSSF-CWs) treating waste stabilisation ponds (WSPs) effluent. Since CW design considers temperature which is irrelevant in tropics, mass transfer approach could improve the design. HSSF-CWs were operated in batch recycle mode as continuous stirred tank reactors (CSTR) at different interstitial velocities. The overall removal rate constants of chemical oxygen demand (COD) at various interstitial velocities were evaluated in mesocosms that received pretreated domestic wastewater. The mean overall removal rate constants were 0.43, 0.69, 0.74 and 0.73 d−1 corresponding to interstitial velocities of 15.43, 36, 56.57 and 72 md−1, respectively. Results showed that the interstitial velocities up to 36 md−1 represented a range where mass transfer effect was significant and, above it, insignificant to the COD removal process. Since WSPs effluent has high flow rates and low organic load, it is possible to induce high interstitial velocities in a HSSF-CW treating this effluent, without clogging and overflow. The performance of these HSSF for tertiary treatment in tropical areas could be improved by considering flow velocity when designing.

Effect of diffusional mass transfer on the performance of horizontal subsurface flow constructed wetlands in tropical climate conditions

2011 ◽  
Vol 63 (12) ◽  
pp. 3039-3045 ◽  
Author(s):  
K. N. Njau ◽  
L. Gastory ◽  
B. Eshton ◽  
J. H. Y. Katima ◽  
R. J. A. Minja ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Flow Velocity ◽  
Rate Constants ◽  
Removal Rate ◽  
Subsurface Flow ◽  
Plug Flow ◽  
Pollutant Removal ◽  
Velocity Correlation ◽  
Climate Conditions ◽  
Horizontal Subsurface Flow

The effect of mass transfer on the removal rate constants of BOD5, NH3, NO3 and TKN has been investigated in a Horizontal Subsurface Flow Constructed Wetland (HSSFCW) planted with Phragmites mauritianus. The plug flow model was assumed and the inlet and outlet concentrations were used to determine the observed removal rate constants. Mass transfer effects were studied by assessing the influence of interstitial velocity on pollutant removal rates in CW cells of different widths. The flow velocities varied between 3–46 m/d. Results indicate that the observed removal rate constants are highly influenced by the flow velocity. Correlation of dimensionless groups namely Reynolds Number (Re), Sherwood Number (Sh) and Schmidt Number (Sc) were applied and log–log plots of rate constants against velocity yielded straight lines with values β = 0.87 for BOD5, 1.88 for NH3, 1.20 for NO3 and 0.94 for TKN. The correlation matched the expected for packed beds although the constant β was higher than expected for low Reynolds numbers. These results indicate that the design values of rate constants used to size wetlands are influenced by flow velocity. This paper suggests the incorporation of mass transfer into CW design procedures in order to improve the performance of CW systems and reduce land requirements.

scholarly journals PHOSPHORUS REMOVAL FROM DOMESTIC WASTEWATER IN HORIZONTAL SUBSURFACE FLOW CONSTRUCTED WETLAND AFTER 8 YEARS OF OPERATION – A CASE STUDY

2004 ◽  
Vol 12 (4) ◽  
pp. 126-131 ◽  
Author(s):  
Agnieszka Karczmarczyk
Keyword(s):  
Sorption Capacity ◽  
Subsurface Flow ◽  
Oxygen Demand ◽  
Domestic Wastewater ◽  
Phosphorus Sorption ◽  
Fine Grained ◽  
Hydraulic Load ◽  
Horizontal Subsurface Flow ◽  
Al And Fe Oxides

Horizontal subsurface flow constructed wetlands can effectively treat high levels of biochemical oxygen demand (BOD) and suspended solids. They are also effective as phosphorus trap but usually for a short time. This phenomenon was observed in the presented case study, an example of subsurface flow reed bed filled with “improved” site soil where it was assumed that the permeability of bed would increase as a result of reed penetration. Fine grained site soil was initially effective trap for phosphorus from wastewater. However, during operation clogging of bed media proceeded and phosphorus sorption capacity used up. In general, the longevity of subsurface flow wetlands as phosphorus sinks depends on the hydraulic load, phosphorus load and the type of the media used in bed construction. To be effective as phosphorus sorbent, substrate should contain high levels of Ca, Al and Fe oxides and possess suitable sorption capacity, quick time of reaction and suitable permeability.

scholarly journals Evaluation of Ageratum conyzoides in field scale constructed wetlands (CWs) for domestic wastewater treatment

2017 ◽  
Vol 75 (10) ◽  
pp. 2268-2280 ◽  
Author(s):  
A. S. Tilak ◽  
Suhas P. Wani ◽  
A. Datta ◽  
M. D. Patil ◽  
M. Kaushal ◽  
...  
Keyword(s):  
Constructed Wetlands ◽  
Subsurface Flow ◽  
Typha Latifolia ◽  
Oxygen Demand ◽  
Domestic Wastewater ◽  
Fecal Coliforms ◽  
Pistia Stratiotes ◽  
Field Scale ◽  
Ageratum Conyzoides ◽  
Canna Indica

Ageratum conyzoides were evaluated in field scale subsurface flow constructed wetlands (CWs) to quantify its nitrogen (N) and phosphorus (P) uptake and compare with wetland plants (Pistia stratiotes, Typha latifolia and Canna indica). The two-field scale subsurface flow CWs, located in the International Crops Research Institute for Semi-Arid Tropics, received wastewater from an urban colony. The CW1 and CW2 had the same dimensions (length:10 m, width:3 m, total depth:1.5 m and sand and gravel:1 m), similar flow rates (3 m3/d), hydraulic loading rates (HLRs-10 cm/d) and hydraulic retention time (HRT-5 days) from July 2014–August 2015. The vegetation in both CWs consisted of Pistia stratiotes, Typha latifolia, Canna indica, and Ageratum conyzoides, respectively. The CW1 (% reduction with respect to concentrations) reduced total suspended solids (TSS) (68%), NH4-N (26%), NO3-N (30%), soluble reactive P (SRP) (20%), chemical oxygen demand (COD) (45%) and fecal coliforms (71%), while the CW2 (%-reduction with respect to concentrations) reduced TSS (63%), NH4-N (32%), NO3-N (26%), SRP (35%), COD (39%) and fecal coliforms (70%). Ageratum conyzoides can be used in combination with Pistia stratiotes, Typha latifolia and Canna indica to enhance removal of excessive N, P and fecal coliforms from domestic wastewater.

scholarly journals Efficiency of horizontal subsurface flow constructed wetlands cultivated with grasses of different root systems

2020 ◽  
Vol 20 (8) ◽  
pp. 3318-3329
Author(s):  
Fernanda Lamede Ferreira de Jesus ◽  
Antonio Teixeira de Matos ◽  
Mateus Pimentel de Matos
Keyword(s):  
Constructed Wetlands ◽  
Subsurface Flow ◽  
Oxygen Demand ◽  
Root Systems ◽  
Sodium Concentration ◽  
Pollutant Removal ◽  
Organic Loading Rate ◽  
Vetiver Grass ◽  
Horizontal Subsurface Flow ◽  
Subsurface Flow Constructed Wetlands

Abstract The objective of this study was to evaluate the influence of stoloniferous and fasciculated root systems, of Tifton 85 and vetiver grass respectively, on pollutant removal for primary treatment of sewage in horizontal subsurface flow constructed wetlands (HSSF-CWs). For this, three HSSF-CWs measuring 4 m × 1 m × 0.25 m, filling with gneiss gravel # 0 (D60 of 7.0 mm and 48.4% porosity) as substrate, were used. One unit was cultivated with Tifton 85 grass (HSSFT-CW), one with vetiver grass (HSSFV-CW) and one remained uncultivated (HSSFC-CW) as a control. Sewage was applied at a flow rate of 0.53–0.80 m3 d−1, corresponding to an organic loading rate of approximately 350 kg ha−1 d−1 (biochemical oxygen demand – BOD), which resulted in a hydraulic retention time of 0.6–0.9 day. The HSSFV-CW was more efficient than the HSSFC-CW in removing dissolved solids (measured as electrical conductivity) and reducing the total suspended solids (TSS), BOD5, turbidity and sodium concentration, while the HSSFT-CW was not superior in any way. The results indicate that cultivation of vetiver grass provided increased efficiency for removing pollutants from sewage when compared with Tifton 85-grass, in the HSSF-CW.

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