Management of fish farm sludge in vertical flow treatment wetlands planted with macrophytes: mesocosm experiment
Inland fish farms are significant sources of water pollution. The main objectives of this work were to: a) develop on-site methods for fish farm sludge management and treatment with modified partly hydraulically saturated vertical flow treatment wetlands (TWs); b) to determine if effective TWs’ plant species, Phragmites australis subsp. australis (invasive in North America), could be replaced with native Phragmites australis subsp. americanus. The performance of 12 on-site mesocosms (both species and unplanted mesocosms in 4 replicates) during two vegetation periods was assessed. The TWs were fed with a batch load of raw sludge, influent and effluent quality and plant development were monitored. Good sludge dewatering and percolate treatment was achieved in TWs (solids removal over 80%; COD 50-70%; TKN and TP 50-60%). As there were no significant differences in efficiency of the sub-species and unplanted mesocosms, the native Phragmites could replace the invasive in TWs. Longer lasting full-scale studies should be done to assess the influence of plants and species choice to the TW performance in order to validate the findings of this experiment.