Does batch operation enhance oxidation in subsurface constructed wetlands?
Two side-by-side experimental sub-surface flow systems allowed direct comparison of wetland performance under batch and continuous-flow operation. One system consisted of microcosm "columns" operated in 20-day batch mode while the second consisted of continuous-flow "cells" operated at a five-day residence time. Both systems treated identical synthetic domestic wastewater for two years and then treated identical synthetic mine-impacted water for one year. Each system had replicates planted with Typha latifolia, Scirpus acutus and unplanted controls. Temperature was cycled annually between 4 to 24 degrees C. Results indicated that plant species, season, and mode of operation interacted strongly in controlling dynamics of COD, nitrogen species, phosphate, sulfate, and redox potentials. In batch-loaded columns, between-species differences in oxidation and COD removal were large in winter, during plant dormancy, but absent in summer; COD removal, sulfate concentration, and redox potentials were closely correlated, suggesting that variation in root-zone oxygenation due to seasonal plant growth patterns and temperature-dependent plant and microbial respiration may explain observed differences. In the continuous-flow cells, species and seasonal differences were minimal or non-existent, indicating that under continuous-flow operation plants either did not influence root zone oxidation or that this influence had no effect on wetland performance for COD and nutrient removal or sulfate reduction.
Stein
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OR
Department of Civil Engineering and Center for Biofilm Engineering, Montana State University, Bozeman, MT 59717, USA. ottos@ce.montana.edu
Hook
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Biederman
J A
JA
Allen
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Borden
D J
DJ
D017753:Ecosystem; D005160:Facility Design and Construction; D010084:Oxidation-Reduction; D010100:Oxygen / Q000032:analysis / Q000737:chemistry*; D013696:Temperature; D014865:Waste Disposal, Fluid / Q000379:methods*; D014872:Water Movements; D018508:Water Purification / Q000379:methods*
D010100:Oxygen