Unflued gas heaters have been popular as primary heating sources in Australian homes for many years due to their ease of installation and energy efficiency, with approximately 600,000 now installed in housing and schools. However, with concerns over potential health impacts to occupants, manufacturers have reduced the nitrogen dioxide emissions from unflued gas heaters in Australia over recent years. They have done so with a target level for nitrogen dioxide in indoor air of 300 p.p.b. This is somewhat higher than the ambient air (and WHO) guideline of 110 p.p.b. Several studies of child respiratory health show an impact of unflued gas combustion products. A full characterization of the combustion products is needed under conditions that simulate heater operation in practice-this study was undertaken to provide such characterization. Key findings are that the focus needs to be on total gas emissions (not just nitrogen dioxide), and that heater installation can be very sensitive to small faults which lead to very high levels of toxic pollutants. These findings have influenced current government proposals for emission limits for these heaters.

Assessment of the level of DO control necessary to meet nutrient removal performance targets and contain energy costs is critical in large wastewater treatment plants. An additional challenge for high rate, step feed BNR processes are the changing DO demands, due to both the diurnal variation and the process' step feed pattern. A comprehensive evaluation using dynamic process simulation showed that a high degree of DO control automation would not materially enhance process performance. By balancing control system complexity with process performance, it was found that utilizing a simplified control strategy with DO control provided to each pass would provide an optimal balance between O&M requirements and process performance. In case of DO control system failure, a preset dry weather diurnal air flow pattern would allow for adequate control with minimal impacts on performance. The process analysis showed that a greater reduction in effluent nitrogen levels, and reduced reliance on the DO control system would be obtained by modifying the process operating mode to allow for separate nitrification of high ammonia in-plant recycles. A probabilistic analysis of the effluent nitrogen levels under both operating modes is ongoing.

As a result of the increasingly stricter limits on effluent Total Nitrogen (TN) discharges into the East River, the Bowery Bay Wastewater Treatment Plant (WWTP) recently completed upgrades to Biological Nutrient Removal (BNR) to treat wastewater from combined sewers in June 2012. Operation of the BNR process requires optimal primary effluent (PE) flow distribution, or percentage of flow split, to each of the four passes of the step feed secondary treatment system.InfoWorks CS was used to model the treatment hydraulic profiles, and to provide optimal and preventative gate settings for dry weather conditions. Gate settings for wet weather operating conditions were provided as well to ensure that a strategy to protect the nitrifying biomass from washout at elevated flows, while simultaneously preventing early secondary bypass, was available. This memorandum summarizes the background, objectives, approach, results and conclusions.

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The Long Island Sound Study (LISS), a partnership between the United States Environmental Protection Agency, New York, and Connecticut, was formed by Congress to address water quality concerns related to eutrophication and hypoxia. Nitrogen was identified as the causal agent for the observed water quality problems, and a set of phased Nitrogen removal targets were implemented to reduce discharges to the Sound by more than 50 % over a 15-year period of time. Over the course of those 15 years, the nitrogen reductions will 'step-down' so that a phased adaptive management approach is taken to achieve the long-term nitrogen removal goals, with a 23% reduction from 1990 levels after 5 years (16 mg/L TN based on 2005 flow), a 44% reduction after 10 years (12 mg/L TN based on 2005 flow) and the full 50% reduction in 15 years (8.5 mg/L TN based on 2005 flow).The New York City Department of Environmental Protection (NYCDEP) has four wastewater pollution control plants (WPCPs) that discharge to the Upper East River, and ultimately, Long Island Sound: Hunts Point, Tallman Island, Bowery Bay, and Wards Island, with a combined secondary treatment capacity of over 700 mgd.Step-Feed Biological Nutrient Removal (BNR) was identified as the most feasible technology for implementation at the large scale WPCPs to achieve the necessary Nitrogen removal. To assist in the development of BNR designs and the management of these simultaneous upgrades, the Department formed the Advanced Wastewater Treatment (AWT) Team, to provide design and program management expertise. The AWT Team has assisted NYCDEP in meeting Consent Order milestones, development of BNR facility plans, production of site specific BNR design guidelines, review of BNR design drawings and specifications, and the development of programmatic guidance for design engineers at each of the four WPCPs. BNR guidance was developed by the NYCDEP and AWT Team (NYC/AWT) to ensure that a common approach was followed by the large number of consulting firms, as well as the Department itself, over the duration of the project. Major elements of the BNR upgrades detailed in the guidance include: ♦ Aeration System Upgrades -Provides new blowers and an enhanced process air distribution system to ensure better nitrification ♦ Upgrades to Aeration Tanks -Baffle walls to separate oxic and anoxic zones to allow nitrification/denitrification to occur with flexibility of zone, 1/6, 1/3, etc. down each pass ♦ Froth Control Systems -Reduces the population of foam-producing bacteria 2294 WEFTEC®.07 ♦ Alkalinity Addition Systems -Provides alkalinity required for nitrification and pH maintenance ♦ Return Activated Sludge Upgrades -Allows Aeration Tanks to carry a higher solids inventory ♦ Separate Centrate Treatment -Provides a dedicated aeration volume to nitrify ammonia-rich centrate ♦ Improved Flow Splitting and Control -To optimize Nitrogen removal ♦ Carbon Addition -Provides additional carbon in the form of methanol to assist in denitrification Guidance provided specific details on many other aspec...