The effect of operational parameters on the fate of tetracycline resistant bacteria in biological wastewater treatment plants.

摘要

The main focus of this research is to study the fate of antibiotic resistant organisms in biological treatment processes as a function of operation and antibiotic presence. Data generated as a part of this study are expected to elucidate key relationships between common process variables and survival of antibiotic resistance. Based on the literature review and general knowledge about biological wastewater treatment plants, the effects of antibiotic presence (tetracycline), wastewater feed pattern, organic loading rate, and growth rate change on the fate of antibiotic resistant organisms have been chosen to be the focus of this study.; A laboratory study was conducted to examine the influence of key operating conditions on the fate of tetracycline resistant organisms in the activated sludge processes. Four lab-scale sequencing batch reactors (SBRs) were operated to simulate the activated sludge process in three phases.; To evaluate two hypotheses (the effects of antibiotic presence and wastewater feed pattern simultaneously), four lab-scale biological suspended growth sequencing batch reactors (SBRs) were employed. To address the issue of how influent tetracycline concentration influences tetracycline resistant organism survival, two of the reactors were operated with antibiotic added to the influent wastewater (A types) and two served as controls with no antibiotic added (B types). To test the feed pattern influence on tetracycline resistant organism survival, each subset of two SBRs (based on antibiotic addition) was further subdivided by the rate of influent addition. For two reactors, influent was added nearly instantaneously (over a two minute period) simulating a pulse load, called "slug". The other two reactors had influent added slowly and continuously over the appropriate feed cycle time and were considered to more closely mimic a continuously fed reactor, called "cont". In Phase I, the overall growth rate was fixed in all reactors by controlling the mean cell residence time (MCRT) at 10 days. A hydraulic residence time (as defined by volume/flowrate) of 24 hrs was applied during Phase 1 experiments.; To evaluate the effects of a higher organic loading rate, the hydraulic detention time in Phase 2 studies was decreased to 7.4 hrs which increased the organic loading rate by over three-fold. All other conditions, including sampling, from Phase 1 were maintained. To evaluate the importance of growth rate, SBRs were operated in Phase 3 at a MCRT of 3 days and a hydraulic residence time of 7.4 hrs. These data were compared to that collected in Phase 2 to evaluate the effect of growth rate changes. (Abstract shortened by UMI.)