Optimization of Artificial Wetland Design for Removal of Indicator Microorganisms and Pathogenic Protozoa

Abstract

The enhancement of water quality by artificial wetland systems is increasingly being employed throughout the world. Three wetlands were studied in Tucson, AZ to evaluate their individual performance in the removal of indicator bacteria (coliforms), coliphage, and enteric pathogens (Giardia and Cryptosporidium). A duckweed-covered pond, a multi-species subsurface flow (SSF) and a multi-species surface flow (SF) wetland were studied. Removal of the larger microorganisms, Giardia and Cryptosporidium, was the greatest in the duckweed pond at 98 and 89 percent, respectively. The lowest removal occurred in the SF wetland, 73 percent for Giardia and 58 percent removal for Cryptosporidium. In contrast, the greatest removal of coliphage, total and fecal coliforms occurred in the SSF wetland, 95, 99, and 98 percent respectively, whereas the pond had the lowest removals (40, 62, and 61 percent, respectively). Sedimentation may be the primary removal mechanism within the duckweed pond since the removal was related to size, removal of the largest organisms being the greatest. However, the smaller microorganisms were removed more efficiently in the SSF wetland, which may be related to the large surface area available for adsorption and filtration. This study suggests that in order to achieve the highest treatment level of secondary unchlorinated wastewater, a combination of aquatic ponds and subsurface flow wetlands may be necessary.

Propagation of Human Enteropathogens in Constructed Horizontal Wetlands Used for Tertiary Wastewater Treatment

“…The observed wastewater concentrations of Cryptosporidium oocysts and Giardia cysts (Table 1) confirm previous reports (23,28,31,32,40). However, the results of the present study are in some contrast to existing data on pathogen removal efficiencies (10,23,24,28,31,32,39,40). Horizontal SSF engineered wetlands have been shown to remove Cryptosporidium oocysts and Giardia cysts from wastewater with efficiencies of 64.2 and 87.8% (39); 100 and 100% (31), 99.9% (24), 44.3 and 98.6% (28), 1.5-to 2.5-log and 1.5-to 2.5-log removal (40), and 98.9 and 97.6% (32), respectively.…”

“…The wetland concept has become an attractive wastewater treatment alternative to conventional tertiary treatment processes for (i) municipal wastewater, (ii) on-site domestic wastewater treatment, and (iii) concentrated animal feeding operations (24). In wetlands, human-pathogenic microorganisms are physically removed and biodegraded by sedimentation (2,23), filtration and evapotranspiration-driven attachment to plant roots (10,43), natural die-off (28), UV radiation, straining and sorption by biofilm (31), and protozoan predation (37). It is thought that the performance of subsurface flow (SSF) wetlands in removing human pathogens is superior to that of secondary wastewater treatment, i.e., conventional sewage sludge activation (40).…”

“…It is commonly assumed that human pathogens identified in wetland effluents originate from the wastewater (39). However, this was never proven because studies of human pathogens in wetlands (10,23,28,31,32,39,40) did not utilize molecular epidemiology techniques to differentiate pathogen species or assess their viability.…”

Management reducesE. coliin irrigated pasture runoff

“…Predicted E. coli concentrations in pasture tailwater above and below the wetland as (A) tailwater runoff rate increases (time since first runoff 3 hours, days since grazing 7 days); (B) days rested from cattle grazing prior to irrigation increases (time since first runoff 3 hours, tailwater runoff rate 1 cfs); (C) time since tailwater runoff begins during an irrigation event (days since grazing 7 days, tailwater runoff rate 1 cfs). s livestock wastewater (Gerba et al 1999;Hill 2003;Quinonez-Diaz et al 2001).…”

Tratamiento biológico de aguas residuales: Principios, modelación y diseño

“…Es probable que la eficiencia de sedimentación sea mejor en humedales construidos a causa de la presencia de plantas y la resuspensión es también menos probable. Los sistemas híbridos que incorporan los estanques con plantas acuáticas y de flujo subsuperficial pueden producir resultados para la eliminación de parásitos superior a la de los estanques con tiempos de retención similares (Kadlec y Knight, 1996;Gerba et al, 1999.). Tabla 8.11 Indicadores y reducción de patógenos por parte de un biorreactor de membrana, lodos activados filtrados por arena y sistema de tratamiento anaerobio de lecho de lodos de flujo ascendente (Ottoson et al, 2006 Debido a la presencia de animales (mamíferos pequeños, aves), que excretan bacterias fecales, la eliminación de bacterias indicadoras (es decir, coliformes fecales) suele ser muy variable, especialmente si se utilizan efluentes desinfectados de los lodos activados (Kadlec y Knight, 1996).…”