Tracer studies indicated that the experimental TRHs were significantly lower than the theoretical ones, particularly for the vertical flow with gravel. Though the vertical flow with lapilli performed better than the one with gravel, the hybrids showed quite similar removals.
Planting or varying the hydraulic loading rate introduced little differences between the vertical flows or the hybrids. Average removals for the gravel-based hybrid constructed wetland were 86 % for BOD, 80 % for COD, 88 % for ammonia-N, 96 % for SS and turbidity, 24 % for phosphate-P, and 99.5 % for faecal coliforms and 99.7 % for faecal enterococci. Thus, it can be concluded that hybrid constructed wetlands proved to be robust configurations for wastewater treatment in the Canary Islands.