You are here:
Molecular Microbial Ecology of a Full-Scale Biologically Active Filter
Citation:
WHITE, C. P., D. A. LYTLE, R. DeBry, AND A. Galloway. Molecular Microbial Ecology of a Full-Scale Biologically Active Filter. Presented at AWWA WQTC Conference, Seattle, WA, November 15 - 19, 2009.
Impact/Purpose:
To inform the public.
Description:
Drinking water utilities are challenged with a variety of contamination issues both from the source water and in the distribution system. Source water issues include inorganic contaminants such as arsenic, barium, iron, and biological contaminants such as bacteria and viruses. As a result of treatment, many water utilities face distribution system issues such as disinfection by-products, biological regrowth, corrosion, and biological nitrification. Nitrification is the biological process by which ammonia is oxidized to nitrate in the presence of dissolved oxygen. Nitrite and nitrate are toxic to humans and are regulated, while ammonia is not. Furthermore, nitrite and nitrate are regulated at the entry point of the distribution system, rather than in the distribution system where nitrification occurs. Consequently, there is a need to remove elevated levels of ammonia from water. The objectives of this study were three fold: (1) to design a biologically active filter to oxidize ammonia to nitrate (2) to evaluate the impact of water quality and operation on filter effectiveness (3) to use molecular biological methods to elucidate the microbial ecology and the impact of input parameter changes on the microbial population. Two PVC columns, 6 feet high by 2.5 inches in diameter were constructed. Column one was filled to 30 inches with gravel, sand, and anthracite coal. Column two was filled to 25 inches with medium gravel with a diameter of ¼ inch. The columns were feed with dechlorinated Cincinnati tap water dosed with 0.8 mg/L NH3-N as NH4Cl and 30 μg/L As (III) as NaAsO2 to pH 8.0 ±0.1. The initial effluent flow rate was 300 ml/min, corresponding to a loading rate of 2.6 gpm/ft2 and EBCT of 12 and 11 minutes for columns 1 and 2, respectively. Columns were run in parallel throughout the course of the investigation, and backwash was conducted once the headloss reached 30 inches. Concurrent with operation, water quality was monitored; analytes included ammonia, nitrite, nitrate, alkalinity, phosphate, TOC, and 15 metal species. Clone libraries using 16S rDNA, AroA, and AmoA sequences were constructed, and results were used to construct phylogeny and elucidate ecological structure. Denaturing gradient gel electrophoresis (DGGE) was used to examine microbial population shifts in response to changes in input operating parameters. Culture dependent methods, such as HPC and total coliform counts, were also used. Results presented will include: (1) while both columns achieved greater than 90% ammonia oxidation, column 2 required a longer period to achieve full nitrification but required fewer backwashes as compared to column 1 (2) post backwash recovery of nitrifying columns was less than one hour when influent water was used as the backwash medium (3) increases in loading rate briefly destabilized ammonia oxidation (4) columns maintained high ammonia oxidation up to a loading rate of 4.6 gpm/ft2 with 1.6 mg/L NH3-N (5) thick biofilms were observed on the surface of media.
