THE NEW AND IMPROVED BASTE MODEL FOR ESTIMATING ODORS AND VOC EMISSIONS

The air quality regulatory environment for Publicly Owned Treatment Works (POTWs) is continually changing. In addition, POTWs are becoming increasingly conscious of odor control issues in an effort to be good neighbors in their communities. The Bay Area Sewage Treatment Emissions (BASTE) model is a benchmarking tool for estimating emissions of volatile organic compounds (VOCs) and other compounds from liquid wastewater processes. This paper will describe the process undertaken by the Bay Area Air Issues and Regulations (AIR) Committee to update the BASTE model to make it a more powerful and user-friendly tool to estimate odors and VOC emissions.The BASTE model, originally developed in 1990, is a computational model that estimates pathway losses (volatilization, sorption, biodegradation) from wastewater for “strings” of processes that constitute treatment trains. It allows analyses of complex treatment configurations including split flows, liquid streams, quiescent surfaces, drops, weirs, packed media, aerated processes, biological processes, and covered processes. The BASTE model has been widely used by municipal wastewater treatment agencies in the San Francisco Bay Area and beyond, and it is accepted by regulatory agencies including the Bay Area Air Quality Management District and the USEPA as an emissions estimation method.Upgrades to BASTE were undertaken in 1991, 1992 and 1994. Though the BASTE 3.02 version developed in 1994 was a powerful tool, in the eight years subsequent to its development, it was never updated to reflect changing technology or changes in POTW needs. In 2002, it became apparent that the model's format was severely outdated and its capabilities needed to be expanded to accommodate new desired uses.The AIR Committee decided to significantly revise the model to improve emissions estimates and to make it compatible with today's technology. Two categories of upgrades were made-- model usability and capability. Usability upgrades focused on technology improvements and data management, enabling the user to work in a familiar Windows-based environment. Upgrading from the current DOS-based environment to Windows also allowed for the creation of an on-line help file, enabling the user to rapidly search for additional information pertaining to both model behavior and necessary input values.Capability upgrades concentrated on expanding the uses of the model, allowing for estimation of additional compounds, accounting for wastewater processes not previously modeled, and improving estimation algorithms. These upgrades included formalizing the model's estimation of odors.In addition to making the model considerably more efficient and understandable, these upgrades have many practical benefits to the POTW community.The model is considerably easier to update if process or equipment changes are made or if additional data is made available. Some air regulators already require updated emissions inventories to be submitted annually, and these requirements are likely to spread. It is therefore important to have an easy-to-use tool to update these inventories.With a simpler interface, owners can modify and run the model themselves, without hiring consultants.Improved interface and export capability make it feasible to run multiple scenarios to make predictions about emissions as plant modifications are considered.Additional algorithms allow for more accurate modeling of the variety of wastewater systems.New capability to evaluate emissions of potential odor causing compounds and evaluate viable control technologies can assist agencies in considering odor control options.The BASTE upgrade project was initiated in November 2002. The first step was to prioritize improvements based on cost and relative importance to AIR Committee members, and programming began subsequent to prioritization. Upgrades will be completed in Fall 2003, with copies of the model available for use by wastewater agencies in the Spring 2004.