THMOD: Improving the disinfection process using digital twins to reduce trihalomethanes

Development of a digital twin in ETAP and a supply network for the process control of chlorination and the generation of trihalomethanes.

The supply of quality drinking water requires a series of physicochemical treatments that are carried out in Water Treatment Plants (WTPs). One of the most widespread disinfection methods is chlorination, which oxidises products contained in the source water, as well as maintaining minimum levels of free residual chlorine that prevent microbial recontamination during supply. However, the chlorination process can also produce by-products which, in excess, can reduce the quality of drinking water, particularly when treating surface water due to its higher organic matter content. This is one of the phenomena that has captured attention in recent years.

One of the challenges facing water purification is the use of new, more sustainable disinfection technologies, as well as achieving the maximum benefits from chlorine use with the aim of minimising environmental impact and toxicity from disinfection by-products. The new legislative framework for drinking water supply in force (Royal Decree 3/2023) expands the current scope and raises the level of demand through more restrictive requirements regarding the number of disinfection by-product (DBP) species and their more rigorous control.

To carry out the optimisation of these processes, it is of interest to analyse in more detail the mixing, chlorine distribution and disinfection reactions that occur inside the water treatment tanks, focusing on disinfection by-products of increasing interest, such as trihalomethanes (THMs).

The main objective of the THMod project is to develop a modelling tool for ETAP and the supply network, which will reproduce the dynamics of the chlorination process focused on calculating the generation of Trihalomethanes. This will be carried out using computational fluid dynamics (CFD) simulation tools. Furthermore, water quality monitoring inside the tanks will be deepened through experimental measurements with an underwater vehicle.

Results obtained: The THMod project has successfully developed a modelling tool focused on the generation and control of Trihalomethanes (THM) in both water treatment plants (WTPs) and the supply network. Using advanced computational fluid dynamics (CFD) simulation techniques and an underwater drone to monitor tanks and carry out experimental measurements, a detailed 3D model of the chlorination tanks has been developed. Specific sub-models that reproduce THM generation and residual chlorine consumption have been implemented in the network's hydraulic model, which has allowed for the reproduction of THM generation in these tanks.

The process improvement has been evaluated in a representative urban system, selecting the municipality of Toledo to carry out the study. All of this has made it possible to diagnose the current state of the chlorination process and new operating strategies and redesigns of the supply tanks have been proposed, optimising chlorine dosing and mixing, minimising the generation of THMs and reducing energy consumption.

In summary, the THMod project has successfully developed an effective tool for the control and optimisation of the chlorination process, with the potential to be replicated in other cities at state and international levels.