A control for optimizing the advanced oxidation processes—Case of a catalytic ozonation reactor
Introduction
An advanced oxidation process (AOP) in wastewater treatment is a technology based on a chemical treatment (Metcalf & Eddy, Inc., 2002). This treatment involves the introduction of reagents, ozone or hydrogen peroxide for instance, which leads to the development of hydroxyl radicals to oxidize organic pollutants (Gogate and Pandit, 2004, Oller et al., 2011). There are a large number of applications such as domestic and industrial wastewater effluents, sludge and membrane concentrates. Nevertheless, the main problem, which hinders a wide AOP industrial development, is the high operating cost due to an open-loop implementation. In such an implementation, the inlet reagent is introduced in excess in order to respect discharge standards. A closed-loop AOP control could easily reduce reagents consumption, and hence the operating costs.
The first problem with the AOP control is the online measurement of contaminant concentration or contamination abatement, the output signal to be controlled. An artificial neural network approach was developed to predict the Chemical Oxygen Demand (COD) removal in Hamzaoui et al. (2011). A biosensor based on gas phase monitoring was designed to measure the hydrogen peroxide concentrations in Modrzejewska, Guwy, Dinsdale, and Hawkes (2007). It is worth to mention also a specific continuous monitoring of hydrogen peroxide formed in situ was proposed by Oh, Kim, Kang, Oh, and Kang (2005), or a model-free learning control to deal with the chemical characteristic variations with time is given by Syafiie, Tadeo, Martinez, and Alvarez (2011).
However, even today, many wastewater treatment companies hesitate to invest in such a measurement equipment to implement AOP in a closed-loop control. They prefer to keep open-loop processes and their excessive consumption.
In this paper, the goal is to consider a single application to quantify the potential reagent savings with a closed-loop implementation (Abouzlam, 2014). Thus, we hope to convince industry to invest and to give AOP technologies a better place in wastewater treatment (Oller et al., 2011).
The considered wastewater treatment pilot is based on the catalytic ozonation, an innovative AOP (Legube and Karpel Vel Leitner, 1999, Luck et al., 1997, Pontlevoy et al., 2003). The pollutant to be removed is the paranitrophenol which presents the advantage to have a concentration measurable via its absorbance near the visible spectrum (around 340 nm). With this application, the goal is to reduce the oxygen consumption by minimizing the ozone overproduction with a closed-loop control.
For the same application, an internal model control application is described in Abouzlam et al. (2012a). In Abouzlam et al. (2013), an optimal control (H2) strategy was adopted. In the present paper, we address the problem of disturbance attenuation through the synthesis. This attenuation is achieved by the inclusion of weighting transfer functions. A closed-loop simulation with a nonlinear model of the pilot is developed to test different weighting transfer tunings in order to assist the user for the selection of an efficient controller. The set-point tracking is achieved by PI controllers. And a closed-loop stability analysis is dedicated to this new controller structure.
The paper is organized as follows. Section 2 describes the catalytic ozonation pilot. The problem is formulated in Section 3. Section 4 presents preliminary studies on the catalytic ozonation pilot. Section 5 describes the control implementation, and Section 6 a stability analysis. The experimental results are given in Section 7.
Section snippets
Catalytic ozonation pilot
In an ozonation process, the reagent is the ozone gas O3. This process involves both direct and indirect reactions: the selective and slow direct reaction of ozone with pollutants and the less selective but faster reaction involving hydroxyl radicals (Hoigné & Bader, 1976). The AOP techniques with ozone promote hydroxyl radicals production.
The use of a catalyst in catalytic ozonation allows an efficient combination between direct and indirect reactions. The first work on the ozone activation by
Problem statement
In general, the AOP plants run in open loop. In order to deal with the variability of the influent to be treated, an industrial process is often oversized by more than 20% which increases the investment cost. Regarding operating costs, losses are very important. In fact, the reagent flow is fixed to face the worst case, the maximum pollutant concentration, even if, for most of the time, the concentration is much lower. Therefore a collaboration between the automatic control community and the
Operating point choice
To find a nominal operating point, an open-loop experimental test has been performed. The considered experimental conditions are given in Table 1. The treated effluent flow is constant and the pH is not controlled (pH=2.6 in steady state).
A step signal has been applied to the ozone generator power input of the catalytic ozonation pilot. We deduce from this test that the normal range of the ozone generator power P input is , and it allows the desired paranitrophenol abatement
control
The control loop is applied around an operating point corresponding to an absorbance of 0.5. In the real time application, an initialization phase is applied to the pilot where it runs in an open-loop configuration in order to reach the desired operating point. The closed-loop configuration is applied when the absorbance reaches the value of 0.5.
Closed-loop stability analysis
In the previous section, we do not consider the estimated time delays of models (1). The aim of this section is precisely to investigate the stability of the closed-loop system in the presence of input delay.
The numerical problem encountered in the controller design in the presence of delays is the result of a huge amount of decision variables that makes the LMI solver to run out of memory. We have adapted the work of Kim (2011) to the multiple delay case with a bound constraint. In our
control results
The presented test is divided into four parts:
- •
In the first part, the pilot operates in open loop with a power P=160 W during the first 97 min to allow an operating point of an absorbance of around 0.5 to be attained.
- •
In the second part, , the proposed control scheme is applied. The inlet absorbance Absinlet is maintained at its initial value 1.5.
- •
In the third part, , in order to test the positive disturbance rejection, the inlet absorbance Absinlet is increased to
Conclusion
The main objective of this work is to prove the gain of a closed-loop implementation for the advanced oxidation processes. Indeed, since the industrial plants are implemented in open loop, they are often oversized in order to deal with the variability of the influent to be treated (an investment cost). Regarding operating costs, the inlet reagent is introduced in excess in order to meet discharge standards which results in very important losses.
In this paper, experimental results obtained with
References (37)
- et al.
An optimal control of a wastewater treatment reactor by catalytic ozonation
Control Engineering Practice
(2013) - et al.
Weighting function selection in the design process
Control Engineering Practice
(1996) - et al.
A regularity result for the singular values of a transfer matrix and a quadratically convergent algorithm for computing its -norm
Systems & Control Letters
(1990) - et al.
A review of imperative technologies for wastewater treatment. IOxidation technologies at ambient conditions
Advances in Environmental Research
(2004) - et al.
Optimal performance of COD removal during aqueous treatment of alazine and gesaprim commercial herbicides by direct and inverse neural network
Desalination
(2011) - et al.
The role of hydroxyl radical reactions in ozonation processes in aqueous solutions
Water Research
(1976) Note on stability of linear systems with time delay
Automatica
(2011)- et al.
Catalytic ozonationA promising advanced oxidation technology for water treatment
Catalysis Today
(1999) - et al.
Destruction of pollutants in industrial rinse waters by advanced oxidation processes
Water Science and Technology
(1997) - et al.
Measurement of hydrogen peroxide in an advanced oxidation process using an automated biosensor
Water Research
(2007)
Combination of advanced oxidation processes and biological treatments for wastewater decontamination—A review
Science of the Total Environment
Model-free control based on reinforcement learning for a wastewater treatment problem
Applied Soft Computing
Ozonation catalytique du phénol et de ses produits d'ozonation
Environmental Technology Letters
Nonsmooth synthesis
IEEE Transactions on Automatic Control
Cited by (6)
From static output feedback to structured robust static output feedback: A survey
2016, Annual Reviews in ControlCitation Excerpt :For all these reasons, and the fact that the solvers are available to users, these tools have gained very rapidly a large reputation and are intensively used on applications. See Abouzlam et al. (2015); Falcoz et al. (2015); Frechard and Knittel (2013); Lhachemi, Saussié, and Zhu (2015); Puyou and Ezerzere (2012) and Rezac and Hurak (2013) to cite just a few in different application fields. The main drawback of these methods is that these cannot cope with robustness issues, at least not in the same guaranteed way as the Lyapunov based methods.
Cost-effective catalytic materials for AOP treatment units
2019, Handbook of Environmental Chemistryℋ<inf>∞</inf> tuning technique for PMSM cascade PI control structure
2017, Proceedings - 6th IEEE International Conference on Control System, Computing and Engineering, ICCSCE 2016Study the activity of titanium dioxide nanoparticle using orange G dye
2016, Malaysian Journal of SciencePreparation of Azo dye and study of the photo activity of zinc oxide
2016, Journal of Chemical and Pharmaceutical SciencesPrepared coupled ZnO-Co<inf>2</inf>O<inf>3</inf> then study the photocatalytic activities using crystal violet dye
2016, Journal of Chemical and Pharmaceutical Sciences