A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science, School of Environment, Resources and Development

Thesis (M.Sc.) - Asian Institute of Technology, 1997

The performance of constructed wetlands in the removal of pathogenic indicators, especially the viral indicators (bacteriophages) and the bacterial indicators (fecal coliforms and fecal streptococci) was evaluated. Four laboratory-scale and one pilot-scale free-water surface (FWS) constructed wetland units were used to evaluate the kinetic coefficients of bacteriophages, fecal coliforms and fecal streptococci die-offs into the wetland beds. The emergent plants, cattails (Typha), were planted in the constructed wetland units. The experimental results indicated that the organic loading rate (OLR) of 50 kgCOD/(ha.day) and the HR.Ts of 0.5-5 days resulted in the bacteriophage removal of 57-94%, while fecal coliform and fecal streptococci removal ranged from 60 to 97%. Under these conditions, the BOD5 removal was 47-74%, while the COD and SS removal efficiencies were 33-60% and 71- 96%, respectively. TKN and Total-P removal were 25-65% and 16-34%, respectively. The removal efficiencies of bacteriophage, fecal coliform and fecal streptococci during the post-harvesting periods were found to be better than tho~e during the pre-harvesting periods because of more sunlight exposure to the wetland beds during the post-harvesting periods. With respect to the kinetic studies, the k20 of the bacteriophage were 0.13 day" 1 for the pre harvesting and post-harvesting periods. However, for the fecal coliform and fecal streptococci, the k20 was found to be 0.16 and 0.18 da/ during the pre-harvesting and post-harvesting periods, respectively.