Skip to main content
European Commission logo print header

Improved Estimation Algorithms for Water Purification and Desalination Systems

Periodic Reporting for period 1 - PURE-WATER (Improved Estimation Algorithms for Water Purification and Desalination Systems)

Reporting period: 2019-01-01 to 2022-06-30

Sustainable access to drinking water and providing usable water supply for adequate sanitation and also for irrigation based agriculture forms one of the major challenges for the global society in the 21st century. Accordingly, finding respective solutions became part of the Sustainable Development Goals (SDG 6) formulated by the United Nations in 2015. Politics shows broad interest in view of the growing population in many arid and semi-arid regions on the one side, and the loss of fresh water resources related to global warming on the other side. The clear demand for technological approaches focusing on efficient water usage and the exploitation of alternative sources led to the emphasis of this consortium activities on waste water purification as well as seawater and brackish water desalination processes. As a crucial part of a functional water resource management system, besides water distribution itself, the information processing and monitoring of the respective water filtration and refinement procedures are subject to high requirements for accuracy, real-time standards and reliability. From a system engineering point of view, major issues with respect to the corresponding complex underlying physical principles are to gain an appropriate mathematical description of the dynamic behavior combined with an adequate parameterization and knowledge about the internal state conditions of the distributed processes via intelligent sensor data evaluation in spite of external perturbations.
Making contaminated water accessible for nutrition, sanitation or irrigation is an ancient human struggle. Several technological approaches have emerged over the years which are relevant for modern water purification and desalination tasks. The two most common solutions for separating salt or other substances from a target liquid are thermal distillation plants and membrane based filtration processes. Desalination is a significant representative for filtration techniques. Historically, evaporation facilities have been the first commercially used seawater desalination installed by the Ottomans in Jeddah (Saudi Arabia). This has been made possible in course of an increased understanding of the underlying thermodynamics. Ever since the early stage, such plants suffered from corrosion influence. During the Second World War, there was a high demand of potable water availability in arid territory which led to rising interest in condensation methods. Subsequently from the 1960s on, the commercialization of water desalination plants went on with rising pace, especially within the Arabic region a large demand and progress could be noted.
During that time, the Multistage Flash Distillation (MSF), that consists of several distillation steps of countercurrent heat exchangers flashing the water into steam over numerous stages, became popular and common. In the 1980s the Reverse Osmosis (RO) membrane technology received more attention. With higher energy efficiency this approach purifies water utilizing a high-pressure pump which overcomes the osmotic pressure and drives the respective fluid through pores separating a concentrate (solvent) from undesired solute. Both, thermal and membrane based desalination plants are established. Worldwide, RO accounts for more than 60% of the total desalination capacity nowadays. Although just a quarter of the distribution belongs to the MSF concept, it still dominates the Middle East region for historical reasons. The rest is made up of emerging approaches like the thermal Multi Effect Distillation (MED) or the promising Electro-Dialysis (ED) technology. The consortium focuses on membrane based technological solutions because of their versatility with respect to purification and desalination processes, likewise, their energy saving potential and higher feed recovery rates. Furthermore, additional water related operational concepts such as biochemical purification and pH adjustment for waste water treatment shall be included into the project scope so as to develop a comprehensive and innovative information processing scheme.
There remain several problems in the supervision and dynamical analysis of modern water purification and desalination processes. Irrespective of the significant social task behind saving secure and accessible water supplies, the following current technical challenges are emphasized by the consortium:

- Several advanced control and estimation concepts for water processes are reported in the literature which do not get applied to actual plants despite satisfactory simulation results. Accordingly, realistically implementable observer schemes (soft sensors) have to be developed with respect to reliable validation standards.

- Often, specific approximations of the underlying complex dynamical processes are made which concentrate on very specific conditions and fail to capture all significant influences. For applications with high safety requirements such as water treatment which directly or indirectly relates to nutrition, a reliable system description is indispensable. Thus, more accurate procedures should be enabled. Compositions of membrane, thermal and biochemical processes, as they occur in water purification, may then be treated in a unified way.

- In membrane based filtration facilities, fouling of membranes is a major challenge (especially RO). This may fully change the plant behavior and lead to complete plugging. Treating the phenomenon as a perturbation, a novel fault isolation concept for membranes shall be developed, combining the competences of the consortium. This includes to classify the membrane condition for identifying fouling early and to adapt the process control or to initiate adjustment actions.

- The overall efficiency of a water resources system is crucial with respect to distribution and energy consumption. A proper information processing unit integrated into the management system builds the basis of an optimal control scheme which may reduce the partially unacceptable high distribution losses and helps increase the applicability through better energy recovery, avoiding uneconomical operating costs.
Major achievements of the PURE-WATER project thus far include:

(i) Comprehensive diagnosis systems for reverse osmosis based desalination plants based on structural analysis;

(ii) Non-asymptotic state observer desgin methods for distributed reaction-diffusion systems governed by partial differential equations based on the Modulating Function Method;

(iii) Exact state observer application and adjustment to process control tasks;

(iv) Real-time capable adaptive and robust identification methods implemented by FIR filter realization of modulation kernels.
The following central outcomes of the PURE-WATER project with respect to reasearch and innovation are expected:

(1) Advanced parameter and state estimation techniques for hydrodynamic systems utilizing modulating function approaches;

(2) Accurate modelling and simulation of diffusion processes for water purification;

(3) Real-time capable observer design for distributed membrane systems;

(4) Hardware implementation of modulation based estimation algorithms for water applications;

(5) Smart sensor development for integrated information processing in context of water purification;

(6) Software and test bench validation platform of water filtration processes in an experimental environment.