A full-scale activated sludge plant was modified for high-rate BNR operation at minimal cost. Three different processes (A/0+, A2/0+ and UCT) were studied at BSRTs varying from 4 to 14 days and HRTs of 2 to 6 hours. Onset of BPR was almost immediate without addition of special seed. Good phosphorus removal was obtained with all three processes except for periods of extremely high influent flows or high nitrate recycle to the anaerobic zone. However, because of high process phosphorus loadings resulting from high influent concentrations and sludge processing recycles, effluent TP concentrations were typically in excess of 2 mg/L. Nitrogen removal was excellent when nitrification could be maintained and nitrate recycle was sufficiently high. All processes yielded excellent nitrogen removals during warm weather, but complete nitrification could not be maintained during winter conditions. Implementation of a statewide phosphate detergent ban resulted in a 40 per cent decrease in the influent wastewater concentrations. Following the ban, the UCT process was shown to be capable of consistently meeting the Virginia nutrient discharge standards of 10 mg/L TN and 2 mg/L TP during the growing season.

Anaerobic stabilization (AnS) is denned as difference between actual and theoretical oxygen use in activated sludge systems with anaerobic selectors. AnSrelated oxygen savings translate into po tentially lower aeration power costs. A comprehensive electron balance approach was developed for more accurate determination of AnS, along with procedures forzyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA in-situ oxygen uptake rate (OUR) measurement and analysis of dissolved gases by vacuum stripping.Labscale anaerobic/oxic (A/O) and anaerobic/anoxic/oxic (A2/ O) systems operated under various conditions yielded AnS values of 1555% of the theoretical oxygen requirement. Hydrogen and methane production together explained less than 1% of AnS, except when the A/ O feed was supplemented with formate, in which case methane pro duction explained about 19% of AnS. Stripping of reduced volatiles ex plained less than 1% of AnS in both systems. Kinetic limitations of the chemical oxygen demand (COD) test were not found to be significant in explaining AnS, but thermodynamic limitations were identified as potentially capable of explaining a significant fraction of AnS. Mecha nisms are hypothesized that can partially explain AnS based on the results of this study. Water Environ. Res., 66, 161 (1994).

No abstract

Wastewater treatment process models, as they have evolved in recent years, may broadly be classified as stoichiometric models and kinetic models. Stoichiometric models are typically simple tools that primarily maintain an inventory of flow and pollutant quantities entering and leaving individual unit processes and describe process transformations mainly in terms of empirical stoichiometric parameters. The models must also quantitatively account for effects of process and non-process recycles within the facility. The simple platform, however, limits the capability of the stoichiometric models to adequately describe the complex kinetics of physical-chemical and/or biological transformations that occur within each unit process. Sophisticated kinetic models are available that provide modules for accurate, rigorous simulation of individual unit processes, but are cumbersome and inefficient for use in tracking facility-wide mass balances. This paper describes a new modeling technique that combines the simplicity and comprehensive mass balance capability of a spreadsheet based "refined stoichiometric" model developed by CH2M HILL (Pro 2 D) with the accuracy of a sophisticated kinetic model (GPS-X by Hydromantis). The use of this technique in facilitating comprehensive facility process design is demonstrated. The demonstration shows how rigorous mass balance including recycles and rigorous process kinetics can be simultaneously accomplished and automated through the use of Dynamic Data Exchange (DDE) capability.

Driven by continuing rapid growth, potential site space constraints, and pressures to reduce cost, Clean Water Services (formerly Unified Sewerage Agency of Washington County, Oregon) decided to evaluate the performance of the step feed activated sludge process on a demonstration basis at its Rock Creek Advanced Wastewater Treatment Facility. Construction and startup of a new 1.7 million gallon three-pass step feed demonstration aeration basin was completed in June 2001. Performance of the step feed basin was compared with that of an existing plug flow aeration basin of identical size.Testing was conducted in two modes. Mode 1 involved demonstration of comparable SRT and performance with higher loadings to step feed, while Mode 2 involved higher step feed SRT and comparable performance under similar loading conditions.Testing results demonstrate that the step feed process may be flexibly used to either achieve higher capacity (flow) at comparable sludge ages, or to achieve a higher level of treatment (higher sludge age) at comparable flows, while maintaining comparable solids loading rates to the secondary clarifiers. The results also show that the step feed system achieved a better and more reliable effluent quality as measured in this case by lower effluent ammonia-N concentrations. Results of this testing support the recommendation for future plant-wide conversion from plug flow to step feed at the Rock Creek facility.