Effect of temperature, HRT, vegetation and porous media on removal efficiency of pilot-scale horizontal subsurface flow constructed wetlands

doi:10.1016/j.ecoleng.2006.06.013

Ecological Engineering

Volume 29, Issue 2, 1 February 2007, Pages 173-191

https://doi.org/10.1016/j.ecoleng.2006.06.013 Get rights and content

Abstract

In order to investigate the effect of temperature, hydraulic residence time (HRT), vegetation type and porous media material and grain size on the performance of horizontal subsurface flow (HSF) constructed wetlands treating wastewater, five pilot-scale units of dimensions 3 m in length and 0.75 m in width were operated continuously from January 2004 until January 2006 in parallel experiments. Three units contained medium gravel obtained from a quarry. The other two contained one fine gravel and one cobbles, both obtained from a river bed. The three units with medium gravel were planted one with common reeds and one with cattails, and one was kept unplanted. The other two units were planted with common reeds. Planting and porous media combinations were appropriate for comparison of the effect of vegetation and media type on the function of the system. Synthetic wastewater was introduced in the units. During the operation period, four HRTs (i.e., 6, 8, 14 and 20 days) were used, while wastewater temperatures varied from about 2.0 to 26.0 °C. The removal performance of the constructed wetland units was very good, since it reached on an average 89, 65 and 60% for BOD, TKN and ortho-phosphate (P-PO₄³⁻), respectively. All pollutant removal efficiencies showed dependence on temperature. It seems that the 8-day HRT was adequate for acceptable removal of organic matter, TKN and P-PO₄³⁻ for temperatures above 15 °C. Furthermore, based on statistical testing, cattails, finer media and media obtained from a river showed higher removal efficiencies of TKN and P-PO₄³⁻.

Section snippets

Introduction and background

The need for treatment of municipal wastewater, even for small towns, is now imperative, based on EU directive 1991/271/EEC. A good alternative for small settlements is the use of constructed wetlands (CW). The use of these systems is becoming very popular in many countries. It is necessary then to find the optimal CW design characteristics in order to maximize their removal efficiency and keep the area to a minimum. The main characteristics, affect the removal efficiency of CWs are the

Pilot-scale unit description

Various wetland models have been constructed in our open-air laboratory, a facility with a total surface area of approximately 400 m². A portion of the area is assigned to the experiments described here. Five similar pilot-scale horizontal subsurface flow constructed wetlands have been constructed and are in operation in this facility (Fig. 1). A schematic of the experimental layout is shown in Fig. 2. They are rectangular tanks made of steel, with dimensions 3 m long, 0.75 m wide and 1 m deep.

Overall performance statistics

Influent and effluent concentrations and percent removal statistics (i.e., mean value, standard deviation, minimum and maximum values) for BOD, COD, TKN, ammonia, TP and P-PO₄³⁻ are presented in Table 2. The greater removal efficiency among the various constituents for all units was for BOD and COD. The units with the greater removal efficiencies in BOD and COD were the MG-C and FG-R (about 89%). The units with the lower removal efficiency for BOD and COD were the MG-R and MG-Z (BOD mean

Conclusions

Five pilot-scale constructed wetlands operated continuously for almost two years, with hydraulic residence times of 6, 8, 14 and 20 days. The operation period of each residence time was approximately half year, in order to include the entire temperature range from the minimum to the maximum, in every experiment. During this period the constructed wetlands showed a significant removal efficiency of organic matter, which is not influenced greatly by temperature, or vegetation and porous media. It

Acknowledgements

The first author gratefully acknowledges a graduate studies scholarship from the Mpodosaki Foundation and from REVOIL S.A. Associate Professor A. Rigas helped in statistical analyses and Mr. J.N.E. Papaspyros in the experiments and water quality analyses.

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Effect of temperature, HRT, vegetation and porous media on removal efficiency of pilot-scale horizontal subsurface flow constructed wetlands

Abstract

Section snippets

Introduction and background

Pilot-scale unit description

Overall performance statistics

Conclusions

Acknowledgements

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