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Suspended solids mean cells residence time (MCRT) and temperature are two key parameters for designing Integrated Fixed Film Activated Sludge (IFAS) wastewater treatment processes, as an alternative for achieving year-round nitrification. It has been demonstrated from both full-scale and bench-scale studies that IFAS can accomplish year-round nitrogen removal and denitrification in aerobic zones in winter when operated with suspended growth MCRTs less than the critical MCRT for nitrifiers, thus avoiding increasing reactor or clarifier volumes. The objective of this study was to investigate the performances of IFAS systems that were operated at relative high MCRT compared to nitrifier washout MCRT and low temperature for biological nutrient removal. The comparison between two IFAS systems with Accuweb media in both the anoxic and aerobic zones, and a conventional three zone biological nutrient nemoval (BNR) system was conducted at 10[degrees]C with a 10 day MCRT using the UCT/VIP configuration for both systems and feeding with Blacksburg domestic wastewater. Influent flow was split 50% to the first anaerobic reactor and 50% to the first anoxic reactor to enhance denitrification in one of IFAS systems and the conventional BNR control system whereas 100% of the influent flow was fed to the first anaerobic reactor in the other IFAS system. The data from this investigation indicated that the performances of the control and IFAS systems were insignificantly different under the experimental operating conditions for both biological nitrogen and biological phosphorus removal except for IFAS with integrated fixed film media in the anoxic zone and when 50% of the influent was added directly to the first anoxic reactor. DOI: 10.1061/(ASCE)0733-9372(2005)131:11(1550) CE Database subject headings: Activated sludge; Biofilm; Phosphorus; Nitrogen; Temperature effects; Wastewater management.

The Integrated Fixed Film Activated Sludge (IFAS) wastewater treatment systems are activated sludge biological nutrient removal processes that have been enhanced by the addition of biofilm support media into the aerobic zone of the system to obtain year round nitrification in activated sludge systems that otherwise could not support it. The objective of this study was to develop a computer package called 'IFAS' that allows steady-state simulation of IFAS wastewater treatment processes based on the International Association Water Quality general model for activated sludge and empirical equations for chemical oxygen demand (COD) uptake and nitrification on integrated fixed film developed at Virginia Tech. The current version of the IFAS program supports only sponge-type media; however, the model could be modified for other media if the appropriate equations and required parameters values are known. Data obtained from IFAS sponge media pilot scale plants treating a weak municipal wastewater supplemented by sodium acetate, urea, sodium bicarbonate, and potassium phosphates and operated at different aerobic mean cells residence times were used to evaluate the model with parameter values for nitrification and COD uptake rates developed in batch studies. The model-generated ammonia and soluble COD profiles were insignificantly different statistically from the experimental data. The IFAS model satisfactorily predicts carbonaceous removal and nitrification, and has the potential to be a useful tool for scientists and engineers seeking to design and optimize either IFAS or conventional biological nutrient removal activated sludge systems. DOI: 10.1061/(ASCE)0733-9372(2005)131:11(1540) CE Database subject headings: Computer programming; Activated sludge; Biofilm; Nitrogen; Mathematical models; Wastewater management.

An 11-month trickling filter pilot study was conducted at a synthetic fiber manufacturing facility. COD removals increased linearly as organic loading increased from 2.53-4.90 kg TCOD/[m.sup.3]/d (158-306 lb TCOD/1,000 [ft.sup.3]/d) and then reached a constant maximum from 4.90-5.78 kg TCOD/[m.sup.3]/d (306-361 lb TCOD/1,000 [ft.sup.3]/d). Hydraulic loadings did not significantly affect removals over a broad range of 27.1-70.6 [m.sup.3]/[m.sup.2]/d (666-1,733 gpd/[ft.sup.2]). Four design models were evaluated for their ability to model the data. Two models, including the Modified Velz equation, incorporated hydraulic loading as the major independent variable, while the other two equations were based on organic loading. The design equations based on organic loading modeled the data much more accurately. For the two organic loading models evaluated, a Monod-like, pseudo-mixed order model gave slightly superior results to the first order model. In addition, significant stabilization of influent total suspended solids (TSS) was observed. The implications for industrial pretreatment design of trickling filters, as opposed to traditional methodologies developed largely from municipal treatment data, are discussed.