MS in Engineering Science (M.S.E.S.)
Degree Granting Department
Sarina J. Ergas, Ph.D.
Kebreab Ghebremichael, Ph.D.
Valerie Harwood, Ph.D.
E. coli, Onsite wastewater treatment systems, Reuse, Nutrients, Septic system, Adsorption
The sustainability of water resources is an international and national concern. With increased human activity, water distribution on a global, regional, and local scale has been negatively impacted. Managing water resources also includes managing wastewater. A promising solution to the issues of water scarcity and distribution in the environment is the reuse of wastewater. Wastewater is produced from various sources (domestic, industrial, and commercial); however, if this water is able to be reused closer to the source of generation it could positively impact water distribution. In the United States, approximately 25% of domestic wastewater is treated in onsite wastewater treatment systems OWTS (mainly septic tanks and drainfields). However, septic systems are not efficient at removing nitrogen and pathogens, making them a risk to public health and the environment.
In recent years, advanced onsite wastewater treatment systems have been developed to reduce contaminants into the environment. These systems are effective at removing contaminants but often require many mechanical parts and have high energy requirements. These additional components require homeowners to perform more maintenance on advanced OWTS than conventional systems or pay for maintenance to be performed. Passive Nitrogen Reduction Systems (PNRS) are being developed that provide high levels of nutrient removal while keeping maintenance requirements and costs low for the homeowner. (PNRS) use two-stage packed bed bioreactors to remove nitrogen from wastewater via nitrification (Stage I) and denitrification (Stage II). Our laboratory has developed a two-stage bench scale PNRS that uses ion exchange (IX) materials, clinoptilolite and scrap tire chips, to enhance the removal of nitrogen from wastewater by buffering transient loads to the biological processes. Pathogens can be present in domestic wastewater and if untreated can be released to groundwater and open water bodies endangering the health of the public. PNRS have the potential to reduce pathogenic microorganism released into the environment, however; the reduction of pathogens in PNRS that include IX media had not previously been studied.
In this research, E. coli was used as a fecal indicator bacteria (FIB) because of its simplicity and national and worldwide acceptance. In our study, the performance of a PNRS with and without IX media was evaluated. Hourly studies were performed to determine the removal efficiency of E. coli from the system under varying hydraulic loading rates. Biofilm detachment experiments were conducted to measure E. coli adsorption and growth patterns within the column reactors. Batch adsorption experiments were completed to determine the effect of different types of media with and without IX material on E. coli growth over extended time periods.
E. coli enumeration data from the hourly experiments demonstrated that there was a 0.84 log reduction of E. coli throughout the PNRS from the septic tank effluent to the final effluent released from the system. The evening and afternoon periods showed a higher reduction of E. coli compared with the morning period. Removal efficiencies were greater in the first stage of treatment (nitrification) as compared to the second stage treatment (denitrification). However, these variances did not result in significant differences in overall E. coli removal efficiency. Adsorbed E. coli were evenly distributed in the column containing IX media, while a decrease in adsorbed E. coli with depth was observed in the column without IX media. Batch adsorption studies revealed that when E. coli are present in wastewater solution with media, E. coli are initially adsorbed but can grow in the system after 6-12 hours. This growth indicates that other FIB should also be used to determine the fate of pathogens in PNRS. Based on all E. coli enumeration experiments, the PNRS developed reduce E. coli by almost 85%; however, this reduction is not adequate to meet onsite water reclamation regulations. Further studies are needed to develop tertiary treatment for pathogen reduction and wastewater reuse.
Scholar Commons Citation
Henderson, Michelle B., "The Fate of Fecal Indicator Bacteria in Passive Nitrogen Reduction Systems" (2017). USF Tampa Graduate Theses and Dissertations.