What is GPS-X?
Wastewater Process Libraries
Technical Specifications
Detailed Specifications



  • Runs on PCs (Windows 95, 98, or NT 4.0), and Workstations (Solaris).
  • Mature and proven, first release in 1991.
  • Large library of models (500+).
  • Distributed and used worldwide.
  • Detailed documentation (printed and on-line).


  • User Guide: Detailed description of interface features.
  • Technical Reference: Detailed description of all libraries and models.
  • Tutorial: 10 step-by-step lessons for beginners.
  • Installation Guide: Easy installation notes for all supported platforms.
  • Entry Level: For use of GPS-X with pre- configured layouts.
  • Advanced Control Module: Quickly and easily implement MATLAB-designed controllers into GPS-X.
  • All documentation is directly accessible from the software (in Adobe Acrobat PDF format).

Maintenance and Development

  • Excellent user support: Phone, FAX, e-mail, dedicated support personnel, in most cases same day answer. Web page ( for company and product information, model parameter database, demos and much more.
  • Continuous effort, new releases every 6-9 months.

Basic Simulator Features

  • Steady state AND dynamic simulation software.
  • Powerful graphical user interface for laying out plant schematics.
  • Allows simulation of time varying process characteristics.
  • Modular, only pay for modules you need.
  • Unit conversion allows easy changing between metric and imperial units of your choice.
  • Powerful numerical methods including 8 integration routines, 2 steady-state routines, iterative flow-loop (recycle) solving and optimization.
  • Steady state solver (crucial for steady-state models and fast initialization).
  • "Point-and-Click" Help function, that provides context-sensitive information.
  • Completely interactive, allowing fast feedback and analysis of results, saves time compared to using "batch" (run and observe) simulators.
  • Simulates plants of unlimited size, from bench and pilot scale to the largest plants in the world.
  • Flexible data input and graphical output features (graphs, data files, DDE, etc.).
  • Communicates with spreadsheet programs (e.g. Microsoft Excel).
  • All forms are populated with default values from scientific literature.
  • Reads and uses real plant data as simulation inputs or for comparison to simulation results.
  • Simplified graphical user interface for operators (Scenario Manager module).
  • Automatic process consistency check and warnings.
  • Capable of supporting different languages.
  • Y2K compliant.

Advanced Simulator Features

  • Many advanced modules available to simplify modeling tasks.
  • Frequent design tasks (e.g. aeration, equipment sizing) can be standardized.
  • Sensitivity analysis module.
  • Optimization module for calibrating models and optimizing processes.
  • Dynamic Parameter Estimator module for fitting dynamic models to time varying plant data.
  • Respirogram Evaluator module for extracting biological model parameters.
  • Handles flow-through, alternating, batch, fixed film, and anaerobic processes.
  • Customizable (user can change models and interface forms, can add new models).
  • Uses fastest possible, layout specific compiled code.
  • On-line automated real-time operation capability.
  • Can be connected to SCADA systems.
  • Automatic calibration, advanced sensor fault detection, process fault detection, automated forecasting available.
  • Contains built-in routines for On-Off, P, PI, PID, and lead-lag feedforward control simulation.
  • Built in PID controller tuning facility.
  • Dynamically links to Matlab for design and simulation of advanced model based control systems.
  • Together with Matlab, can be used to design and test advanced controllers.

Currently Available Unit Operations

  • Influent
    • Composition: Based on BOD, COD, industrial, or real plant data. Diurnal, sinusoidal, or constant load.
    • Flow: Constant, diurnal, sinusoidal, or real plant data patterns (including storm flows).
    • Hauled septage influent for batch loading.
  • Splitters, 2 to 5 streams
    • Constant, real flow based, flow proportional or time-based splitting.
  • Combiners, 2 to 5 streams
    • Wastage or bypass pumping or weir overflow, with built in, customizable controller.
  • Pumping Station (Wet Well)
    • Fixed or variable level, pumping control built in.
  • Equalization Tank
    • In-line or off-line equalization, both fixed and variable volume.
    • Chemical P removal, simulates effluent P and chemical sludge generation, chemical dosage controller available, any chemical (alum, ferric, ferrous, etc.) can be used.
  • Grit Chamber
  • Activated Sludge Tanks
    • CSTR: Five standard biological models (basic and temperature dependent versions of ASM1, ASM2, and ASM3, general model, reduced order model and VNP) available in five different variations. High rate and long SRT processes, DO control. Can be used as contact tank.
    • Plug-flow tank: Simulates standard plug-flow tank, any nitrification-denitrification and biological P removal process (A/O, Bardenpho, VIP, Step Bio-P, etc.), oxidation ditch, deep shaft process. Unlimited number of stages (passes) and internal recycles combinations. Any number of aerobic, anoxic and anaerobic zones combinations. Step feeding, contact stabilization, mechanical or diffused aeration, DO control, tapered aeration.
    • Dual inlet plug-flow tank: Same as plug-flow tank, with additional influent (e.g. methanol addition) into anoxic tanks.
  • Sequencing Batch Reactor (SBR)
    • Unlimited cycle setup, unlimited number of parallel SBR's, DO control, time or volume based cycle control, floating or fixed level decanter, MLSS or SRT control, can be used to build more complex alternating processes (Biodenitro, etc.). Bio-kinetics and settling simulated, chemical reactions during settling can be simulated (N2 bubbles).
  • Trickling Filter
    • BOD and nitrogen removal, including bio-kinetics, diffusion and film thickness (solids detachment, attachment), stone or plastic media.
  • Biological Aerated Filter (BAF)
    • Upflow BAF, filter, standby, backwash, flush cycles, automatic loading controller, simulates single or multiple BAF units, BOD and nitrifying stages.
  • Rotating Biological Contactor (RBC)
    • Unlimited number of stages, BOD or nitrifying film, biofilm mass.
    • Submerged Biological Contactor (SBC): Similar to RBC, with variable or constant airflow.
  • Deep Shaft
    • The deepshaft process consisting of downcomer, riser, and a headtank with pressure effects is simulated.
  • Dissolved Air Flotation (DAF)
    • For waste activated sludge thickening. Float solids concentration, supernatant and subnatant quality is simulated.
  • Anaerobic Digester
    • One or two-stage sludge digestion, meso or thermophilic temperature regime, VFA generation, biogas (methane and CO2) generation, digested sludge and supernatant quantity and quality.
  • Dewatering
    • Belt press, centrifuge or other mechanical dewatering equipment simulation, dewatered solids and filtrate water concentrations (e.g. ASCE model).
  • Primary Settlers
    • Circular and rectangular, unlimited number of layers, 1-D models for fast simulation, 2-D models (may require Computational Fluid Dynamics package) for detailed flow pattern simulation, reactive models for ammonium and VFA generation, can be used as pre-fermenter. Underflow pump control.
  • Final Clarifiers
    • Circular and rectangular, unlimited number of layers, 1-D models for fast simulation, 2-D models (may require CFD package) for detailed flow pattern simulation, reactive models for denitrification in sludge blanket or P release, underflow and wastage pump control. Sludge blanket, effect of bulking sludge, different SVI or SSVI can be simulated.
  • Aerobic Digester
    • Aerobic digester model based on the extension of ASM1 for higher than 30 d SRT systems.
  • Thickener
    • A 1-D flux based thickener model using the double exponential settling velocity equation.
  • Sand Filter
    • Single or multi-media filter material packing, filter and backwash cycle, effluent and backwash quantity and quality simulated. If detailed simulation of the sand filter operation is not required; a simple continuous filter to predict effluent and backwash quality is also available.
  • Disinfection
    • Chlorination, exponential bacteria kill model.
  • Black Box
    • 18 predefined transfer functions for empirical modeling, user customizable.
  • Tools
    • Signal tracking and alarm, pH model, Sampler, flow or time based composite samples, PID controller, feedforward-feedback controllers, On-Off controller, multivariable controller, low-pass filter.

Process Models

  • Biological Models
    • ASM1: Activated Sludge model #1, international standard for Carbon-Nitrogen removal.
    • AMS2: Activated Sludge Model #2, international standard for phosphorus removal.
    • ASM2d: Latest version of the IAWQ Task Group ASM2 model for bio-P removal.
    • ASM3: The newest Carbon-Nitrogen model from the IAWQ Task Group.
    • Mantis: Temperature dependent version of the ASM1. The mantis model contains a modification to accurately describe aerobic denitrification.
    • General/NewGeneral: ASM1 extended to bio-P removal (Dold models published in 1991 and 1997).
    • Filament: Gujer's filament model for prediction of low aerobic bulking.
    • VNP: Simplified bio-P model.
    • Reduced: Simplified carbon-nitrogen model for control engineering applications.
  • Settling Models
    • Double exponential (extended Vesilind or Takács model).
  • Influent Models
    • BOD-based: Input BOD, TSS, TKN and stoichiometry.
    • States: input basic variables.
    • ASM2: Input COD, TSS, TKN and fractions of basic variables.
  • Fixed Film Models
    • ASM1: Activated Sludge model #1, international standard for Carbon-Nitrogen removal.
    • AMS2: Activated Sludge Model #2, international standard for phosphorus removal.
    • Mantis: Temperature dependent version of the ASM1.
  • Anaerobic Model
    • Andrews-Barnett basic two-stage anaerobic model. VSS destruction, VFA generation, CH4 and CO2 generation, pH, ammonium toxicity.
  • Filtration Model
    • Iwasaki-Horner suspended solids capture model.
  • Miscellaneous
    • Empirical models for grit removal, dewatering, disinfection, filtration, and black box.

Available Libraries

Libraries are sets of basic variables used as a basis to group compatible models. Basic variables - many basic components in wastewater treatment models, e.g. soluble and particulate substrate, DO, ammonia, nitrite and nitrate, heterotrophic, phosphorus accumulating and nitrifier population. The various libraries in GPS-X have a different number of basic variables, up to 29 in CN2IP (see below). All libraries contain 15 composite variables such as filtered, particulate and total BOD5, COD and TKN, non-volatile, VSS, TSS (MLSS, RAS, etc.) which are composites of basic variables. Even if a model is defined in terms of COD, it still calculates BOD and all the above composite variables in all streams and tanks in the plant at all times. Available libraries (6) in GPS-X:

  • CN: Carbon-Nitrogen removal library (12 basic, 15 composite variables). Simulates BOD and COD removal, nitrification, and denitrification for all processes available.
  • CNP: Carbon-Nitrogen-Phosphorus removal library (17 basic, 15 composite variables). Simulates BOD and COD removal, nitrification, denitrification, biological and chemical phosphorus removal for all processes available.
  • CN2: Advanced Carbon-Nitrogen removal library (19 basic, 15 composite variables). Simulates same processes as CN but in more detail: nitrite-nitrate separately, VFA's, alkalinity.
  • IP: Industrial Pollutant removal library (22 basic, 15 composite variables). Contains all of CN library, in addition can be used to develop models for specific (industrial) components like phenol, etc.
  • CN2IP: Advanced Industrial Pollutant removal library (29 basic, 15 composite variables). Similar to IP library, except it contain all of CN2 instead of CN, and only 10 additional industrial components.
  • OPEN: Open library (15 basic variables). For model development outside the wastewater field (e.g. production process models).

Graphical Interface Features

  • Engineering: design interface for building new plant models.
  • Simplified: Operator interface for Operator training and day-to-day operation.
  • Large drawing board.
  • Graphs: x-y, scrolling x-y, digital, histogram, 3D histogram surface, and gray-scale surface.
  • Graphical input controls:
    • Slider - interactive continuous input device.
    • Incremental - interactive discontinuous (step-wise) input device.
    • On-off - on-off button (start-stop).
    • Analyzer - sensitivity analysis of parameter.
    • Optimizer - optimization of parameter.
    • Fileinput - read in real plant data.
  • Input forms (editable by user):
    • Physical parameters - tank sizes, temperature, etc.
    • Operational parameters - aeration, pumping, etc.
    • Mass transfer - diffusion and solids exchange constants.
    • Stoichiometric - yields composition, etc.
    • Kinetic - kinetic rate constants, etc.
    • Settling - settling coefficients, SVI, clarification.
  • Display forms (in all streams and tanks, editable by user):
    • Flows.
    • Basic variables (library dependent).
    • Composite variables.
    • Internal process rates.
    • Physical variables (volume, etc).
    • Clarifier variables (sludge blanket, solids profile, etc.).
    • Miscellaneous, model dependent forms.

Minimum System Requirements

  • PC: 90 MHz Intel Pentium PC with Microsoft Windows 95, 98, or NT 4.0, 32 MB RAM, 175 MB of free hard disk space, Super VGA graphics, and a CD-ROM drive.
  • UNIX: Solaris 2.x. Systems require 32 MB of hard disk space, color graphics, and a CD-ROM drive.