PM02 Remediation Techniques and Strategies
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(PM013) Modeling removal of fecal coliforms by pilot-scale constructed wetland treatment systems.

Garber, K1, Rodgers, J1, Johnson, A1, Gallagher, J1, 1 Clemson University, Clemson, SC, USA

ABSTRACT- Fecal coliforms (FC) are used by regulatory authorities to indicate impaired water quality due to fecal borne pathogens. Contamination by FC can present a significant threat to public health, and a serious limit to commercial and recreational activities, with negative ramifications for tourism. This has prompted research and development of mitigation strategies such as constructed wetland treatment systems (CWTS). Current evaluations of performance of CWTS usually involve percent removal of constituents of concern. Percent removal alone is inadequate to describe CWTS performance. Removal rate coefficients are useful for evaluating CWTS performance and contribute to understanding temporal and spatial declines of FC in CWTS. Study of influences of hydraulic retention time (HRT), season and plant species on CWTS performance involved the use of removal rate coefficients. We observed that a longer HRT did not necessarily result in greater removal of FC. Longer HRT was less efficient because it required more time and space to achieve essentially the same removal. Season influenced removal of FC, with greater efficiency in summer than in winter. For designing CWTS for FC removal, consideration must be given to declines in removal efficiencies in winter. For the plant species used in these experiments, no significant distinctions were observed in overall performance of CWTS. For the simulation models designed to predict dominant mechanisms of removal of FC in CWTS, the following mechanisms of removal were used: mortality, grazing and filtering by micro- and macroorganisms, settling and sorption to plant surfaces. The models indicate that dominant removal processes within CWTS may shift during different seasons. Overall, these models imply that in order to accurately estimate FC declines in CWTS, we must discern the dominant removal mechanisms that occur in specific CWTS.

Key words: constructed wetlands, fecal coliforms, removal performance, simulation models

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