Reduction of Fecal Indicator Bacteria Counts in an Ecologically-Engineered Acid Mine Drainage and Municipal Wastewater Passive Co-Treatment System

Abstract

Passive co-treatment of municipal wastewater and synthetic acid mine drainage in a laboratory-scale, four-stage continuous flow reactor system was examined for changes in fecal indicator bacteria counts. Synthetic acid mine drainage was mixed at a 1:2 ratio with raw municipal wastewater from the City of Norman, Oklahoma and introduced to the system. The municipal wastewater contained varying concentrations of total coliforms (TC), fecal coliforms (FC), E. coli (EC), and fecal streptococci (FS). Initial concentrations ranged from 6-13, 0.6-6, 3-5, and 0.1-0.7 million cfu/100 mL, for TC, FC, EC, and FS, respectively. During the 6.6-day system residence time, a 100% reduction of all indicator bacteria was observed. However, indicator bacteria exhibited evidence of sublethal injury with slower colony formation rates on standard growth media. Extending standard incubation periods resulted in higher concentrations of all indicator bacteria in each treatment stage, except the final stage where only EC and TC counts increased. Although this co-treatment regime effectively reduced indicator bacteria concentrations, much remains unknown about the potential for sub-lethal injury to indicator bacteria and its impact on the viability of cotreatment for pathogen removal.