Effects of intermittent loading on nitrogen removal in horizontal subsurface flow wetlands.
Removal of CBOD(5) and nitrogen from septic tank effluent was evaluated in four horizontal subsurface flow (HSSF) wetlands. An intermittently loaded cell was compared to a continuously loaded control cell, with both treatments receiving the same weekly volume. The intermittent cell was rapidly drained and "rested" for 24-hr, then refilled in steps, twice weekly. Two media with different particle sizes but similar porosities were also compared. The two media, light weight expanded shale and gravel, were both continuously loaded. As hypothesized, the wetland cell that was intermittently loaded had higher dissolved oxygen, greater ammonia removal, and greater nitrate production than the continuously loaded cells. Areal NH(3)-N removal for the intermittently loaded cell was 0.90 g m(-2) d(-1) compared to 0.47 g m(-2) d(-1) for the control. Ammonia removal was also higher in continuously loaded gravel cells than in cells with expanded shale. Ammonia-N removal was an order of magnitude lower in a similar SSF wetland that had been in operation for 3 years. However, CBOD(5), total suspended solids, and total nitrogen did not vary substantially among the treatments.
Center for Reservoir and Aquatic Systems Research, Baylor University, Waco, TX 76798, USA. maggie_forbes@baylor.edu
Margaret G
MG
Forbes
Joe C
JC
Yelderman
Tina
T
Potterton
Robert D
RD
Doyle
D057919:Biological Oxygen Demand Analysis; D003252:Construction Materials; D005374:Filtration / Q000379:methods; D057446:Hydrodynamics; D009584:Nitrogen / Q000032:analysis / Q000302:isolation & purification*; D010316:Particle Size; D016062:Porosity; D013781:Texas; D014865:Waste Disposal, Fluid / Q000379:methods*; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000302:isolation & purification*; D018508:Water Purification / Q000379:methods*; D053833:Wetlands
D014874:Water Pollutants, Chemical; D009584:Nitrogen