Wpływ natlenienia złóż hydrofitowych na efektywność usuwania zanieczyszczeń

Na podstawie uzyskanych rezultatów dotyczących wpływu stężeń i jakości substancji organicznej na dopływ tlenu oraz efektywności usuwania zanieczyszczeń, sformułowano następujące wnioski: 1. Wzrost obciążenia złóż rozkładalną zawiesiną organiczną (XS) i niepodatną na rozkład biologiczny (XI) powodował obniżenie dopływu tlenu określonego na podstawie pomiarów współczynnika Dg. 2. Na podstawie zależności Dg = f(XS + XI) można określić dopuszczalne obciążenie złóż hydrofitowych substancją organiczną. W analizowanych systemach dopuszczalne obciążenie zawiesiną organiczną wynosiło dla złóż typu HF-CW ? 14,0 g/m2d zaś dla złóż typu VF-CW ? 4,0 g/m2d. 3. W złożach, w których wartości obciążeń były poniżej wartości dopuszczalnych efektywność usuwania zanieczyszczeń wynosiła średnio: 71,2% dla BZT5, 62,4% dla ChZT i 59,2% dla zawiesiny ogólnej.

In the recent years the increase of interest in the combined (hybrid) constructed wetland systems has been observed. These systems are composed of two or more filters with mixed vertical and horizontal flow of sewage. Hybrid constructed wetlands require smaller unit areas and secure higher efficiency of pollutants removal. In Poland up till now the configuration with Horizontal Flow Constructed Wetland (HF-CW) at the beginning of treatment system has been only used. Opposite configuration with Vertical Flow Constructed Wetland (VF-CW) at the beginning of biological process are applied mainly in Germany and the United Kingdom. It is proved in literature that pores clogging because of organic suspended solids limits oxygen flux to filters. Moreover oxygen demand caused by organic matter decomposition can cause anaerobic conditions to occur in soil and significantly decrease organic matter decomposition processes. Insufficient supply of oxygen to beds can cause lack of biodegradation of part of organic matter in beds and its accumulation in free spaces of the filtration material or on its surface. Process of organic matter accumulation can lead to decrease of pollutants removal effectiveness and even decreased period of beds operation. The aim of this paper is to evaluate not only organic loads applied to beds but also both the organic matter quality in the influent and accumulation in soil. Investigations were carried out in three hybrid constructed wetlands with subsurface flow of domestic sewage. These systems were composed of HF-CW and VFCW flow filters planted with reed. Analysed objects were uniform in relation to their construction (material, depth and time of operation) but they had different hydraulic loadings. Object in Wieszyno has the highest loading of both horizontal and vertical beds, equal to 40.0 and 80.0 mm/day, respectively. While loadings of HF and VF beds in Wiklino were twice lower. Quality of organic matter was estimated on the basis of its speciation according to German guideline ATV 131 (1995). Fractions of dissolved organic compounds easily degradable (SS) and non-degradable (SI) as well as organic suspension hardly degradable (XS) and non-degradable (XI) were determined. It was proved that the decomposition rate of organic matter was determined by proportions of XS and XI fractions. On the basis of the function between the diffusion coefficient and suspended organic matter Dg= f(XS+XI), it was shown that the object in Wieszyno underwent colmatation because inflow of oxygen was below the critical for sufficient supply of oxygen value of diffusion coefficient in soil (Dg). On the basis of the obtained results organic matter permissible loadings for both VF and HF beds were established. For HF beds the load is equal to 14.0 g/m2day and for VF beds it is lower than 4.0 g/m2day