Technical Report on a Microbial Ecology Approach to Fecal Coliform Problems at Field’s Point Wastewater Treatment Facility, Providence, RI under jurisdiction of Narragansett Bay Commission

Perry Sheffield

From 1995-1998, Field’s Point Wastewater Treatment Facility (FPWWTF), under the Narragansett Bay Commission (NBC), has experienced seasonal problems with effluent fecal coliform bacteria exceedances. Decreased chlorine efficiency is hypothesized to be the primary source of this problem caused by physico-chemical characteristic changes in the wastewater that reduce the toxic ability of the chlorine. Bound legally by both fecal coliform level and chlorine residual limits for their final effluent, NBC has particular interest in both understanding the cause and potential predictors of this problem and has already done some research to investigate physical, chemical and operational factors presumed associated with the problem. This study takes a microbial ecology approach focusing specifically on the mixed liquor microscopic populations (diversity, density, dominance, and specific groups of protozoa, mesofauna, and bacteria) and associated ecological parameters (flow, rainfall, air temperature, MLDO, and chlorine dose). Regression analysis is used to compare the trends of these variables from 1995-1998 to effluent fecal coliform levels. Rainfall on the day of exceedances, organism dominance, and specific groups, flagellates, free swimming ciliates, and Nocardia show the strongest relationships to the quality of effluent measured by fecal coliform level. Multiple regression analyses are used for these and a few less strongly correlated variables (air temperature, minimum and total flow, mixed liquor dissoved oxygen, and rotifers). These analyses show the possibility of modeling the mixed liquor microbial system as the relationships between other parameters and fecal coliform levels come to be better understood and can be incorporated. Suggestions for operational control include closer monitoring of the relevant parameters identified in this study. Suggestions for further research include more thorough microscopic analysis of the mixed liquor and measurement of range and rate of some physico-chemical parameters already identified.