High nitrite concentration in the secondary effluent is a common cause of unexpectedly high chlorine demand for disinfection and can have a significant negative effect. To account for this the chemical disinfection model in GPS-XTM 8.1 is updated with the reaction of nitrite with free chlorine to produce nitrate. This new empirical model also considers the effect of ammonia concentration on the extent of the chlorine-nitrite reaction.
Dechlorination is commonly used in conjunction with chlorination. GPS-XTM 8.1 includes a new integrated dechlorination model, complete with four different dechlorination chemical dosage options. Additionally, the new model considers the effects of both the chlorination and dechlorination chemicals on pH when the GPS-XTM pH estimator is enabled.
The calibration of the underlying Mantis2 biological model has been updated with changes to the phosphorus accumulating organisms (PAOs) storage and growth equations, as well as updates to the hydrolysis of very slowly biodegradable materials. These changes have also been correspondingly implemented in the Mantis2S and Mantis3 models as well.
For situations where the simulation of the primary clarifiers can be simplified, we have added a new empirical model for the primary clarifiers that allows component-by-component removal efficiencies. This allows for easy setup and calibration of models where the focus will be on the biological treatment, without having to spend time adjusting settling parameters.
In the plug-flow high-purity oxygen (HPO) model, we have upgraded the output display variables to include a full set of oxygen mass transfer variables for all mass transfer to/from each liquid reactor and headspace, providing a simple way to visualize the flow of oxygen through the entire system.
A new unit process for flocculation of particles is now available in the Water Treatment library add-on module in GPS-XTM 8.1. The flocculation is modelled as a function of mixing power, floc formation, breakage kinetics and includes the options for polymer dosage.