Fractional analysis of arsenic in subsurface-flow constructed wetlands with different length to depth ratios

2009 ◽  
Vol 60 (7) ◽  
pp. 1771-1778 ◽  
Author(s):  
C. Singhakant ◽  
T. Koottatep ◽  
J. Satayavivad
Keyword(s):  
Constructed Wetlands ◽  
Subsurface Flow ◽  
Volume Ratio ◽  
Pilot Scale ◽  
Sequential Fractionation ◽  
Fractional Analysis ◽  
The Media ◽  
Subsurface Flow Constructed Wetlands ◽  
Dispersion Number ◽  
Iron And Manganese

Arsenic (As) removal in subsurface-flow constructed wetlands (CW) planting with vetiver grasses was experimented by comparing between two different configurations; (i) deep-bed units (dpCW) with length to depth (L:D) ratio = 2 and (ii) shallow-bed units (shCW) with L:D ratio = 8; operating at hydraulic retention time (HRT) of 6, 9, and 12 days. The tracer study of CW units revealed that no effect of L:D ratio on dispersion number could be determined, but affecting to the effective volume ratio. Based on the data obtained from the pilot-scale experiments of CW units for 117 days, it is apparent that the dpCW could achieve relatively high As removals (52.9%, 59.2%, and 72.1% at HRT of 6, 9, and 12 days, respectively). Analysis of As mass balance showed that only 0.2–0.4% of As input was uptaken by vetiver grasses whereas the major portion was retained in the CW media (38.9–77.6%). Forms of the retained As was determined by sequential fractionation which could indicate As complexation with iron and manganese on the media surface of 31–38% and As trapping into the media of 42–52% of the total. No obvious difference of As fractions in bed of between dpCW and shCW units was observable.

Reversing clogging in subsurface-flow constructed wetlands by hydrogen peroxide treatment: two case studies

2009 ◽  
Vol 59 (10) ◽  
pp. 2037-2046 ◽  
Author(s):  
Jaime Nivala ◽  
Diederik P. L. Rousseau
Keyword(s):  
Hydrogen Peroxide ◽  
Constructed Wetlands ◽  
Subsurface Flow ◽  
Pilot Scale ◽  
Hydrogen Peroxide Treatment ◽  
Negative Effect ◽  
Subsurface Flow Constructed Wetlands ◽  
Full Scale Tests ◽  
Wetland Cell

One of the most frequently encountered operational problems in subsurface-flow constructed wetlands is clogging. Traditionally, the restoration procedure is to remove the clogged gravel or sand and replace it with clean material. This method, while effective, is costly and may require sections of the facility to be taken offline for extended periods of time. Another common remediation strategy is to have a resting period for each wetland cell, although this is not an option for very small systems which often consist of only one treatment cell. Recently, a more radical approach has been tested on a number of lab-scale and pilot-scale setups which consists of an aggressive oxidation of organic matter by means of hydrogen peroxide (H2O2). Results indicate that after treatment, clogging was substantially reduced and that H2O2 did not appear to have a long-term negative effect on plants and biofilms. The outcomes of two full-scale tests are discussed in this paper.

Simulation of subsurface flow constructed wetlands - results and further research needs

2003 ◽  
Vol 48 (5) ◽  
pp. 157-166 ◽  
Author(s):  
G. Langergraber
Keyword(s):  
Constructed Wetlands ◽  
Reactive Transport ◽  
Transport Model ◽  
Subsurface Flow ◽  
Pilot Scale ◽  
Research Needs ◽  
Nitrogen And Phosphorus ◽  
Surface Water Treatment ◽  
Hydraulic Behaviour ◽  
Subsurface Flow Constructed Wetlands

Simulation of constructed wetlands has two main tasks: to obtain a better understanding of the processes in constructed wetlands, and to check and optimise existing design criteria. This paper shows simulation results for two indoor pilot-scale constructed wetlands for wastewater and surface water treatment respectively. The results presented and discussed are mainly focussed on the hydraulic behaviour of the constructed wetland systems. In addition results of reactive transport simulations with CW2D are shown. The multi-component reactive transport model CW2D (Constructed Wetlands 2 Dimensional) was developed to model transport and reactions of the main constituents of wastewater (organic matter, nitrogen, and phosphorus) in subsurface flow constructed wetlands. For the pilot-scale constructed wetlands a calibration of the flow model was possible and therefore the results of the reactive transport simulations with CW2D fit the measured data well. The further research needs regarding the simulation of subsurface flow constructed wetlands are discussed.

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