The Mantis2 model in GPS-X is a comprehensive bio-chemical whole plant model that allows user to analyze different wastewater treatment plant configurations for biological BOD, nitrogen and phosphorous removal, resource recovery (biogas, struvite) and side stream treatment using the deammonification process.

Some major features of the model includes:

  • A single set of state variables for both the liquid (Activated sludge) and solid (Anaerobic digestion) processes
  • Two step nitrification and denitrification processes
  • Methylotrophic denitrification on external substrate like Methanol
  • ANAMMOX (Anaerobic ammonium oxidation) process
  • Precipitation of common precipitates of Al, Fe, Ca, Mg and PO4 in the liquid and sludge streams
  • pH estimation in both the liquid and solid streams and
  • Elemental mass balance for COD, C, N and P and other inorganic components like Ca, Mg, and K.

The model uses a set of 48 state variables (21 soluble + 27 particulate) and 56 biological, chemical and physical reactions. Algebraic equations for estimating pH and alkalinity are implemented in the model. The chemical precipitation reactions of precipitation of CaCO3, MgHPO4, CaPO4, AlPO4, FePO4 and struvite are also included in the model.



The ASM library is based on the the Classical Activated Sludge Models developed by the International Association on Water Pollution Research and Control task group. Development of these models by the task group began in 1983 as it was becoming accepted in the industry that mathematical modelling could be a beneficial tool in the design and understanding of the treatment capability of a wastewater treatment plant.

This library was developed for a single-sludge system with carbon oxidation, nitrification, and denitrification occuring. The model contains X state variables.


This ADM1 library is based on the Anaerobic Digestion Model no. 1 from IWA Task Group.

This library contains 32 state variables which are used in multiple biochemical and physico-chemical processes. The biochemical reactions result from intra or extracellular enzymes that transform the biologically active organic material, while the physico-chemical reactions describe ion association/dissociation and gas-liquid transfer. The ADM1 model does not include precipitation.

Mantis3 - Model for Greenhouse Gas and Carbon Footprint Estimation

The Mantis3 model for estimation of GHG and carbon footprint is an extension of Mantis2 model. The Mantis3 model extends the biological model to include N2O production during denitrification. The four-step denitrification scheme used by Hiatt and Grady (2008) is used to estimate N2O production during heterotrophic denitrification. Some modifications in the model are introduced to reduce the number of model parameters and to make it compatible with the existing structure of Mantis2 model. The model also includes biological processes to estimate N2O production during autotrophic nitrification. The model for autotrophic N2O production was adapted from the model structures proposed by Mampaey et al. (2011) and Ni et al. (2012).

The Mantis3 model uses classifies carbon emissions in three categories of Scope-1, Scope-2 and Scope-3 according to IPCC (2006). The emission in each scope are estimated based on the process emissions, emissions due to energy consumption and emissions due to consumables. The model also considers emission offsets based on non-fossil carbon, carbon capture and heat recovery options at the wastewater treatment plant.

The Mantis3 model is a powerful tool for process engineer to optimize wastewater treatment process design and operation in the light of minimizing the carbon footprint of the plant.

Mantis3 Flow Chart

MantisIW - Industrial Library

The Industrial Library provides a dynamic-mechanistic model based on chemical oxygen demand (COD), nitrogen, phosphorus, and sulfur balances that include biological and physical transformation processes. The model combines the ASM1 biological model (Henze et al., 1987) with a revised categorization of the influent COD, the modeling of sulfur compounds and toxics, and new biological and physical transformation processes.

In Industrial Library, the influent soluble biodegradable COD fractions (readily biodegradable soluble COD and inert soluble COD) are replaced with the following COD fractions:

  • Aromatic compounds
    • Short-chain (e.g. Benzene and Toluene)
    • Long-chain (e.g. Naphthalene)
  • Aliphatic compounds
    • Short-chain (e.g. hexane to decane, olefins)
    • Long-chain (hydrocarbons with more than 10 carbons)
  • Halogenated solvents (e.g. chloroform)
  • Toxic or inhibitory organic compounds (e.g. phenols)
  • Mixed organics (all other organic biodegradable COD including alcohols and organic acids)

The COD categorization is developed by considering the biodegradability and volatility of different organic compounds. Consideration was also given to the classes of compounds that are normally tracked in industrial WWTPs.

Each COD fraction has a portion that is non-biodegradable. The non-biodegradable fractions have been determined using published biodegradability studies and the ToxChem modeling package. Inhibition is modeled using the Haldane (1930) equation. As in ASM1, COD fractions are provided for biodegradable particulate COD and the inert particulate COD. The following physical and biological processes are included in Industrial library:

  • Biological oxidation of each COD fraction (separate kinetics for each category)
  • Adsorption of each COD fraction onto biomass (separate kinetics for each category)
  • Volatilization of each COD fraction (separate kinetics for each category)
  • Hydrolysis of particulate COD and long-chain organics
  • Biological inhibition caused by toxic compounds
  • Ammonification of organic nitrogen to ammonia
  • Nitrification of ammonia
  • Biological oxidation of reduced sulfur compounds
  • Decay of each biomass type

The industrial library is a useful tool to model the fate of some of the common hydrocarbon compounds in petrochemical industry.

MantisPW - Process Water Library

The Process Water Library focuses on simulating the process water treatment systems which require modelling the inorganic interactions among different inorganic compounds in process water. The library allows the user to model the performance of commonly found unit processes in water treatment system. The list of the available unit processes includes different sources of raw water (river, lake, ground, municipal, brackish and sea), chemical dosing objects (acid feed, alkali feed, nutrients, flocculants and polymers), equalization tank, sedimentation basin, bioreactor, neutralization tank, lime softening, dissolved air floatation, cation exchange, anion exchange, Reverse Osmosis, decarbonation, evaporator, cooling tower, boiler and others.

The model includes the inorganic soluble compounds like Mg, Ca, K, Cl, HCO3, Cl2, Cu, Fe(II), F, HSO3, Mn, Na, SO4, S, Zn, SiO2, PO4, NH3, NO3, NO2, and inorganic precipitates of Ca, Mg, Fe and silica. The model also allows modeling biological degradation of organic compounds, nitrification and denitrification. The model uses equilibrium chemistry and ionic balance equations to predict the pH in different streams of water in the plant. For every stream, important operational parameters like alkalinity, hardness, Langelier stability index (LSI), Ryznar stability index (RSI), Puckorius stability index (PS), Ionic strength, conductivity, resistivity, osmotic pressure, Turbidity and Color are calculated.

The Water Process Library is valuable tool to process water engineers, who are involved in water treatment process design, plant operation, trouble-shooting and optimization.


The MantisSeS model simulates the biological removal of selenium oxyanions (SeO42− and SeO32-) present in FGD blowdown, coal-mining and agricultural drainage wastewater. The selenium reducing bacteria use electron donors of acetate, methanol, propionate and soluble readily degradable substrate to reduce selenate and selenite to elemental selenium. The model considers the effect of electron acceptor O2, NO2- and NO3-, SO42- gradient on the growth process of selenium reducing bacteria.

The model also includes sulfate reduction by including processes for growth of propionate, hydrogen, acetate and methanol utilizing sulfate reducing bacteria. The production of hydrogen sulfide and metal precipitation reactions are also included in the model. The model has been successfully used to model the Suez's ABMET technology.


The MantisCHC model simulates the removal of chlorinated hydrocarbons (CHCs) by biological, chemical and physical processes in ground water treatment plants.

The model focuses on the following key CHCs :

  • Tetrachloroethene (PCE) family: Tetrachloroethene (PCE), trichloroethene (TCE), dichloroethene (DCE), vinyl chloride (VC)
  • Tetrachloroethane (PCA) family: Tetrachloroethane (PCA), trichloroethane (TCA), dichloroethane (DCA), chloroethane (MCA)
  • Carbon Tetrachloride (CCl4) family: Carbon tetrachloride (CCl4), chloroform (CHCl3), dichloromethane (CH2Cl2), chloromethane (CH3Cl)

Some of the key bio-chemical transformation processes included in the model are as listed below:

  • CHCs
    • Reductive dehalogenation (i.e. biological removal of chlorine atoms) using hydrogen as an electron donor and an inorganic carbon source for cell synthesis
    • Aerobic growth (on species with less than 3 chlorine atoms)
  • VFAs
    • Fermentation of butyrate and other higher order VFAs to acetate
    • Aerobic growth on butyrate and other higher order VFAs (aerobic growth on acetate already in model)
  • Nitrates
    • Aerobic growth on butyrate and other higher order VFAs (aerobic growth on acetate already in model)
  • Sulphur Species
    • Anaerobic sulphate reduction using acetate, butyrate, or hydrogen
    • Aerobic sulphide oxidation (existing equations modified)
    • Calculation of unionized H2S inhibition on anaerobic reactions
  • Iron Species
    • Anaerobic Fe(III) reduction using acetate, butyrate, or hydrogen
    • Aerobic oxidation of Fe(II) to Fe(III)
    • Iron sulphide precipitation
  • Aromatic Species (e.g. Benzene, phenol)
    • Aerobic growth
  • All Species
    • Sorption
    • Stripping and volatilisation (only in liquid and liquid/air interface; not within biofilm)
    • Diffusion
    • Stripping and volatilisation (only in liquid and liquid/air interface; not within biofilm)