Abstract
Constructed wetlands have become a popular treatment alternative, in Europe and USA, mostly for handling municipal wastewaters of small communities. Although treatment of stormwater, combined sewer overflows and wastewaters of different origins such as acid-mine drainage, or agricultural runoff, have also been reported. These treatment systems are complex assemblage of water, substrate, plants, litter (primarily fallen plant material), invertebrates (mostly insects larvae and worms) and an array of microorganisms (most importantly bacteria). The pollutants in such systems are removed through a combination of physical, chemical and biological processes, including sedimentation, precipitation, adsorption to soil particles, assimilation by plant tissue and microbial transformations. A number of intermittently loaded vertical-flow treatment systems have been constructed in several places of Central-North Europe (especially in Germany and in UK), mainly for the wastewater management of smal ...
Constructed wetlands have become a popular treatment alternative, in Europe and USA, mostly for handling municipal wastewaters of small communities. Although treatment of stormwater, combined sewer overflows and wastewaters of different origins such as acid-mine drainage, or agricultural runoff, have also been reported. These treatment systems are complex assemblage of water, substrate, plants, litter (primarily fallen plant material), invertebrates (mostly insects larvae and worms) and an array of microorganisms (most importantly bacteria). The pollutants in such systems are removed through a combination of physical, chemical and biological processes, including sedimentation, precipitation, adsorption to soil particles, assimilation by plant tissue and microbial transformations. A number of intermittently loaded vertical-flow treatment systems have been constructed in several places of Central-North Europe (especially in Germany and in UK), mainly for the wastewater management of small or remote villages and their performance is considered as very sufficient. However, due to the complexity of these systems relatively little information has been reported so far regarding the effect of specific operational parameters, as well as this respective mechanisms of this treatment method and the localized climatic conditions. For this reason the objective of the present dissertation was: (a) to examine with the performance of laboratory experiments the soil part of the systems, using artificial or real wastewater corresponding to wastestreams of different origins (e.g. dilute untreated domestic sewage, secondary treated domestic sewage, Combined Sewer Overflow and storm water runoff) and (b) to examine the effects of operating conditions and the particular Greek climatic conditions on the performance of semi-pilot vertical flow constructed wetlands, planted with P.australis and receiving synthetic wastewater simulating medium strength domestic sewage. The laboratory experiments were conducted in Plexiglas columns. The total height of the columns was 2 m, and the internal diameter was 19 cm. The sand layer was 90 cm height, while the gravel layer that was placed on top and bottom of the sand layer, in order to enhance the flow uniformity, was 5 cm height (each). The columns were fed in a batch sequence in order to allow the proper intermittent aeration of the soil bed. Every 72 hours (for a three month period) 8.5 L of the respective wastewater were applied batch wise to the columns from the top and drained (by gravity) from the bottom (that is that the entire wastewater volume was applied at once). The performance of these sand filters was evaluated in respect to the removal of TSS, COD and nutrients. The observations during the testing period revealed significant reductions of TSS, when existing in the influent; the mean removal efficiency of this parameter was 82% in the case of dilute wastewater examination. The addition of inoculum in the feed produced better results, in terms of COD removal. The mean COD removal efficiency was 50% of the uninoculated column, but increased to 70% for the case of inoculated columns. Significant amounts of PO4-P were also removed; the mean removal efficiencies of this parameter were ranging between 85 to 95%. Only in the case when dilute wastewater was examined, the mean removal efficiency was lower (50%).
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