Kennith E. Foster

Fate of indicator microorganisms, Giardia and Cryptosporidium in subsurface flow constructed wetlands

Limited information is available on the ability of subsurface flow wetlands to remove enteric pathogens. Two multi-species wetlands, one receiving secondary sewage effluent and the other potable (disinfected) groundwater were studied from February 1995 to August 1996, at the Pima County Constructed Ecosystems Research Facility in Tucson, Arizona. Each wetland had a retention time of approximately 4 days. The objectives of this study were (1) to evaluate the ability of multi-species subsurface wetlands to physically remove Giardia cysts; Cryptosporidium oocysts, total and fecal coliforms, and coliphages; and (2) to determine the likely impact of local wildlife on the occurrence of these indicators and pathogens. In the wetland receiving secondary sewage effluent, total coliforms were reduced by an average of 98.8% and fecal coliforms by 98.2%. Coliphage were reduced by an average of 95.2%. Both Giardia cysts and Cryptosporidium oocysts were reduced by an average of 87.8 and 64.2%, respectively. In the wetland receiving disinfected groundwater, an average of 1.3 x 10(2) total coliforms/100 mL and 22.3 fecal coliforms/100 mL were most likely contributed by both flora and fauna. No parasites or coliphages were detected.

Multi-species plant systems for wastewater quality improvements and habitat enhancement

The use of macrophytic plants for the treatment of municipal wastewater is growing rapidly. The Constructed Ecosystems Research Facility (CERF) is a joint project of the Pima County Wastewater Management Department and The University of Arizona9s Office of Arid Lands Studies. The facility consists of five 30-mil-hyperlon-lined raceways measuring 61 m long, 8.2 m wide, and 1.4 m deep and one slightly larger raceway. Research has been and is being conducted with aquatic plants such as water hyacinth ( Eichhornia crassipes ), duckweed ( Lemna spp.), giant reed ( Arundo donax ), bulrush ( Scirpus olneyi ), black willow ( Salix nigra ), and cottonwood ( Populus fremontii ). Composite water samplers are used to collect refrigerated samples from incoming secondary wastewater from Pima County9s Sewage Treatment Facility and from the effluent leaving each raceway. Water samples have been analyzed for parameters such as pH, BOD 5 , and total nitrogen. Microbiological studies have concentrated on the removal of indicator coliform bacteria, as well as Giardia , Cryptosporidium and viruses from the wastewater. Data from the water quality studies indicate that these constructed ecosystems reduce BOD 5 consistently to below the 10 mg/L BOD 5 tertiary standard, remove nitrogen as well as decrease the concentration of pathogens significantly.