PATHOGEN INDICATOR ORGANISM REMOVAL IN SUBSURFACE FLOW CONSTRUCTED WETLANDS

Constructed wetlands (CW) have been shown to remove or transform wastewater constituents efficiently and economically, under a variety of treatment conditions. This paper presents research performed at the University of Nebraska that documents the performance of a horizontal subsurface flow CW systems in the removal of pathogenic related organisms under variable loading and operating conditions. The two CW systems evaluated in this research project are located near Lincoln, Nebraska. The first (Firethorn) is located in a small suburban housing community, and the second (Rogers Farm) at a single-family dwelling. Although both facilities were extensively monitored, only pathogen (Salmonella spp.) and pathogen indicator (fecal coliform) data are presented in this paper.Firethorn demonstrated effective removal of fecal coliforms with 96.8% removal in the wetland cell and 98% by the wetland system. Rogers Farm fecal coliform had an average removal of 99.3%. Isolation of Salmonella spp. was not successful. However, a reduction of other isolated bacteria was observed. Summer periods resulted in fecal coliform reductions of 97%, 94%, 98.2%, and 97.6%, with an average of 96.7%. Winter removals were 97.7%, 98.9%, 90.9%, and 98%, for each period, with a 99% average removal rate. If the initial start-up period is excluded, the summer removal rate increases to 98.5%. No clear difference in removal efficiency was observed with a change in temperature at either Firethorn or Rogers Farm. Maintenance concerns at Firethorn began in the summer of 1998. Surface eruptions and pooling due to clogging were prevalent, but did not affect the removal efficiency of fecal coliform. The threat of clogging was partially attributed to a solids loading which was higher than recommended values.