STOAT Features

STOAT™ is a wastewater treatment process modeling software for the design and optimization of wastewater treatment plants. STOAT is used worldwide for the design of new wastewater treatment facilities and in improving the performance of existing facilities. STOAT provides a completely graphical modeling environment and operates within Microsoft® Windows™. Both imperial and metric (SI) units are supported.

Unparalleled Modeling Capabilities

STOAT (Sewage Treatment Optimization and Analysis over Time) allows the wastewater engineer to dynamically model a wastewater treatment plant. STOAT includes both BOD and COD based modeling. STOAT can be used to optimize the design of a new wastewater treatment facility and in improving the performance of an existing facility to substantially reduce the capital and operational costs of the treatment plant.

With STOAT, you can construct a numerical model to simulate the performance of all or any part of a wastewater treatment facility, including sludge treatment processes, septic tank imports, and recycle streams. With STOAT, the user can build and define their own treatment facility, with no limit on complexity. STOAT can also be used with wastewater sewer collection models and river quality models, and directly interfaces to MOUSE™ and MIKE11™. Included with STOAT is a wastewater sewer collection model that allows the user to develop an integrated model of sewers, treatment facilities, and receiving waters.

A large range of processes are available to model the activated sludge process, including biological nutrient removal. For activated sludge aeration tanks, the number of stages can be specified. This allows the user to specify the mixing regime in the aeration tank. STOAT can model internal recycling of waste within the wastewater treatment plant. For example, sludge can be de-watered and the remaining sludge liquors can be returned to the head of the sewage treatment works. STOAT uses a mechanistic process model for determining BOD. All other wastewater treatment models use conversion factors along with the computed COD results to approximate BOD. No such factors are required in STOAT—it computes BOD directly.

In STOAT, the operational parameters required for defining a settling tank involve specifying the RAS (return activated sludge) and WAS (waste activated sludge) flows. The RAS can be specified as a fixed flowrate, or as a ratio of the influent flow rate. STOAT can simulate a large range of WAS pumping regimes, and can be set to automatically change the wastage rate to achieve a user-defined MLSS (mixed liquor suspended solids) setpoint in the aeration tank. This is particularly useful when designing a new wastewater treatment plant.

In addition, STOAT can be used to predict settling tank effluent quality over a range of different sludge settling properties and operational scenarios. This allows a design engineer to carry out a risk analysis on the settling tank design. After specifying the settling properties of the activated sludge by selecting a suitable SVI (sludge volume index) or by specifying each settling parameter individually, STOAT will then predict the effluent quality and status of the sludge blanket. Wastewater treatment models can be quickly developed by graphically dragging and dropping process symbols onto the plant drawing board. Double-clicking on any process symbol displays a dialog box describing the wastewater treatment processes for the selected symbol. The user simply fills out the data describing the process.

Model Calibration

Once a wastewater treatment model has been defined, STOAT can perform automated batch analysis runs on the model to examine a range of operational and calibration parameters without having to revise the model for each run. This allows model calibration to be performed overnight. STOAT includes additional automated calibration routines, which adjust the wastewater treatment model parameters so that the analysis results match actual plant observations.

STOAT provides full access to all model calibration parameters. The default calibration parameters provided within STOAT are based upon application of STOAT at over 100 wastewater treatment plants from around the world. For simulations involving wastewater plants treating domestic sewage, it is unlikely that any significant changes will need to be made to the model.
At least one influent symbol must be specified in the process diagram. For each influent, an influent profile must be specified. The influent profile describes the quality and quantity of wastewater that the treatment system will receive over the duration of the simulation.

Advanced Design Capabilities

BOSS StormSHED can automatically design pipes for a particular routing peak flow based upon minimum cover at structures, minimum and maximum invert slopes, and maximum flow velocity criteria. Any or all pipe inverts and diameters can be pre-specified, if desired. In addition, detention basins and orifice outlet structures can be automatically sized and designed for the computed and routed hydrographs.