These systems can fulfil stringent effluent standards and guarantee low effluent concentrations, as shown by extensive surveys carried out by Molle et al. Vertical flow systems with intermittent feeding represent an important variant of subsurface flow constructed wetlands. The removal efficiencies were associated with the accumulation of solids in the upper part of the filter resulting from seven years of operation and to the operating hydraulic conditions, which are important elements in the performance of the system. Oxygen concentrations and redox potential in the effluent were evaluated, together with the effluent flow rate profiles. The shorter duration of feeding time and higher instantaneous hydraulic loading rate were associated with significantly higher chemical oxygen demand and total Kjeldahl nitrogen removal efficiencies, but with no significant differences in terms of biochemical oxygen demand (BOD) and suspended solids (SS). in Brazil, and was comprised by only the first stage and two units in parallel. The system treated raw wastewater from a population equivalent of 100 p.e. This paper analyses two scenarios in the same system, the first of a faster feeding by pump and the second of a slower feeding by siphon, both with instantaneous hydraulic loading rate values lower than the literature recommendations. The technology of vertical flow constructed wetlands – French system for treating raw wastewater depends on several hydraulic factors, one of them being the duration of the pulse feeding and the resulting instantaneous hydraulic loading rate.
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