Comparative Studies of Vegetated and Nonvegetated Submergedflow Wetlands Treating Primary Lagoon Effluent

The submergedflow (SF) wetland concept offers high organics and solids removal at relatively low cost forconstruction, operation, and maintenance. In this comparative study, vegetated and nonvegetated SF wetlands wereinvestigated for their ability to treat primary lagoon effluent. The experimental design was comprised of three vegetated andthree nonvegetated SF wetland beds (3 m 1 m 0.5 m) operated in a semicontinuousflow mode, which were fed every12 hours with a design 5day residence time. The wetlands were packed with 19mm diameter trap rock and planted withbulrush (Scirpus validus). The BOD5 and TSS removals throughout the twoyear monitoring period were high (up to 98%)for both vegetated and nonvegetated wetlands and tended to follow seasonal variations. Vegetation slightly enhanced thereduction of biodegradable organic matter and suspended solids within the SF environment, although this enhancement wasstatistically insignificant (P > 0.05). The annual average mass removal for ammonia nitrogen in vegetated wetland beds was3.3 kg ha1 d1 (up to 95%). The nitrification process in vegetated wetland beds was significantly more pronounced (P < 0.05)than nonvegetated beds. The lack of measurable dissolved oxygen in the nonvegetated wetlands likely restricted thenitrification process. The dissolved phosphorus reduction varied from month to month depending on seasonal variations ofplant growth, ranging from 27% to 100% in vegetated wetland beds and from no removal to 66% in nonvegetated beds. Theremoval of dissolved phosphorus in vegetated beds was significantly higher than in nonvegetated wetland beds (P < 0.05).Based on the results of this study, vegetation significantly contributed to the reduction of nutrients, specifically ammonianitrogen and dissolved phosphorus, from SF wetlands, but not for BOD5 and TSS.