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A constructed wetland system to improve the effluent quality from an oxidation ditch
Ruud Kampf 1, Sylvia Toet 2, Michiel Schreijer 1, Richard van Logtestijn 2 and Jos Verhoeven 2
1 Waterboard Uitwaterende Sluizen, Lingerzijde 41, 1135 an, Edam, The Netherlands.
2 Department of Plant Ecology and Evolutionary Biology, Utrecht University - Sorbonnelaan 16, 3584 ca, The Netherlands.
Figures and results
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| This figure gives an example of the influence of solar energy (red curve) on the oxygen in the presettling basin (black line) and at the end of the aquatic plant section of one of the ditches (blue). The differences between sunny and (partly) cloudy days are obvious | |
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| The "solar oxygen production" was stable over longer periods. But when the surface became covered by Lemna and floating macro-algae the production came to a halt. But the "machine" came into action again, shortly after the removal of the floating cover | |
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| Two of the ditches have had the same retention time - just over two
days -over the whole research period from 1995 until 1998. Most of the time E.Coli numbers were reduced from around 800/ml to an average of 10 /ml at the end of the ditches in summer. Surprisingly the reed or cat tail compartments contributed most to the E.Coli removal. The HRT of two days was too short for a stable disinfection time in winter. |
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The next figures show the seasons 1997/1998:ur red = spring, blue = summer, green = autumn, purple = winter red= ple = reew |
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| The ammonia removal is strongly dependent on the hydraulic retention time. The effect was most clear at higher ammonium levels of the STP-effluent in winter time. | |
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| Nitrate levels showed the effects of HRT and season clearly. In all seasons at longer HRT led two low nitrate levels in the effluent of the wetland. | |
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| The fate of phosphate in the wetland system is rather confusing. In spring and summer we found a P-release, while in autumn and winter a P-removal occurred. Monitoring over a longer period is needed the fate of P at longer HRT's. To remove P at shorter HRT's in an Everstekoog type wetland chemical precipitation in either the STP or in the constructed wetland is more reliant. |
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| The turbidity puzzled us at first. The longer the retention time the higher the turbidity. It pointed out that it was caused by the growth of biomass in the system. In the STP organics from the wastewater is transferred in sludge biomass and soluble minerals. Those minerals cause a prosperous growth of "higher organisms" in the wetland. |
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| The most profound influence of the HRT is shown by the E.Coli numbers. Usually, except in winter, a HRT of 4 days is enough to reach around 1 E.Coli per ml. |
