The performances of vertical flow experimental wetlands have been shown to be very efficient (Breen and Chick, 1989; Breen, 1990; Rogers et al., 1991). However the reported systems have potentially important operational and environmental differences or advantages when compared to the operational formats and conditions of full scale systems. For example the reported systems have been operated under glasshouse conditions, were batch loaded and the plants in the systems had never been harvested.

This study evaluates the influence of batch versus continuous loading at several retention times (and consequently loading rates) and a range of operational conditions (glasshouse versus ambient versus harvested). Statistically significant differences were found between the various treatments but these differences tended to be small in most operational contexts. For example percentage load reduction for TP under glasshouse versus ambient versus harvested conditions was 97.5, 95.7 and 91.9% respectively. Similarly the TP load reduction performance of continuously operated systems was between 98.1-98.9% and 99.2-96.3% depending on loading rate.

However results from the loading method trial also indicate that operational format and retention time could have a significant influence on the performance, design and operation of full-scale systems. For example the performance of continuously loaded systems at a 2.5d retention time was always worse than continuously loaded systems at a 5d retention time or batch loaded systems at either 2.5 or 5d retention times.

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