Wastewater treatment relies on careful integration of environmental engineering with microbial ecology. This would seem to be particularly the case when attempting to enhance survivability of organisms introduced from outside the main-stream reactor, i.e. bioaugmentation. Molecular biology tools were utilised in this study to assist in understanding the mechanisms of successful bioaugmentation. Molecular fingerprinting showed that side-stream reactor configuration strongly influenced ammonia-oxidising bacteria (AOB) community structure. In both lab-scale and full-scale systems, AOB communities in the side-stream and main-stream were very similar. The experimental systems revealed that a PFR side-stream produced greater diversity of AOB than a CSTR side-stream in a PFR main-stream system, whereas the full-scale side-stream resulted in essentially an AOB monoculture. Phylogenetic analysis revealed less diversity than molecular fingerprinting perhaps due to biases in the cloning/transformation procedure.
Step feed biological nitrogen removal, (BNR), is the cornerstone of New York City DEP's Nitrogen Control Plan. Aeration tank thirteen, (AT-13), was designed specifically as a step feed BNR facility. AT-13 was operated at slightly above its design flow of 25 MGD and its nitrogen removal capacity evaluated for the winter and summer months of 2000/2001. The evaluation consisted of characterization of the primary settling tank, (PST) and final settling tank (FST) effluents for COD, SS, VSS, total and soluble TKN, ammonia, nitrite and nitrate, pH, and alkalinity, and multiple in-situ experiments to determine the nitrification and denitrification rates. The total nitrogen concentration in the PST effluent was 21.1 mg/L of which 25% was organic nitrogen, 74 % ammonia nitrogen, and 2% was combined nitrate-nitrite nitrogen. The average concentration of total COD was 158 mg/L of which 35% was soluble and 16% was readily biodegradable COD. Process control was enhanced using an on line SS analyzer provided by Royce Instrument Corporation, New Orleans, LA (Royce 7011A Analyzer & 73A sensor) and continuous monitoring of the RAS and WAS flow rates. The SRT averaged between 13 and 16 days during the evaluation period. PST effluent splits between the four passes and the relative volumes of the anoxic zones were varied to effect greater nitrogen removal. Total nitrogen removal for AT-13 averaged between 49% and 62% between the winter and summer periods, respectively, without addition of supplemental alkalinity or an external source of organic carbon. Approximately 8% of the nitrogen was assimilated in the waste sludge. It appeared that significant amount of denitrification took place in the oxic zone, sludge blanket in the FSTs and RAS flow. A quantitative determination of the relative amount of denitrification in each zone was performed.Step feed BNR is a viable process that can remove significant amounts of nitrogen while taking full advantage of the alkalinity and organic carbon available in the wastewater. For the wastewater treated the ratio of total COD to TKN was 8.1 and alkalinity to TKN was 4.5. Nitrogen removal in AT-13 was limited by the denitrification capacity rather than the nitrification rate.
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