Jérôme Harmand

Analysis of fouling mechanisms in anaerobic membrane bioreactors.

In this paper, we investigate the fouling mechanisms responsible for MF and UF membrane flux decline in Anaerobic Membrane Bioreactors (AnMBR). We have used the fouling mechanism models proposed by Hermia (1982), namely pore constriction, cake formation, complete blocking and intermediate blocking. Based on an optimization approach and using experimental data extracted from the literature, we propose a systematic procedure for identifying the most likely fouling mechanism in play. Short-term as well as long-term experiments are considered and discussed. It was found that short-term experiments are usually characterized by two fouling phases during which the same fouling mechanism or two different mechanisms affect the process. In contrast, in long-term experiments involving cleaning cycles, membrane fouling appears to be better ascribed to one phase only. The impact of abiotic parameters on membrane fouling mechanisms is reviewed and discussed in the light of these results. Finally, it is shown that the mechanism most responsible for membrane fouling in an AnMBR is cake formation. This main result will be useful for the future development of simple integrated models for optimization and control.

Software sensors for highly uncertain WWTPs: a new approach based on interval observers

This paper presents the practical implementation of a new robust interval observer on a 1 m3 continuous fixed bed anaerobic reactor used for the treatment of industrial wine distillery wastewater. This interval observer is able to generate guaranteed intervals for the unmeasured variables (i.e. acidogenic and methanogenic bacteria, alkalinity and chemical oxygen demand) from few on-line measurements (i.e. input liquid flow rate, CO2 gaseous flow rate, volatile fatty acids and total inorganic carbon). The main advantage of this approach is its independance with respect to disturbances and uncertainty in the initial conditions, in the kinetics and, last but not least, in the process inputs.

Set-point regulation of an anaerobic digestion process with bounded output feedback

This work addresses the robust output feedback tracking problem for a biological wastewater treatment process in the presence of input constraints and limited knowledge on the process parameters. The considered process is an anaerobic up-flow fixed bed biological reactor within a semi-industrial scale pilot plant for the treatment of industrial wine distillery wastewater. A mathematical model describing the dynamic behavior of the biological process is considered and nonlinear control techniques are used to design a bounded output feedback control law. Local asymptotic stability and local set-point tracking of the resulting closed-loop system is proved when the dilution rate is selected as the manipulated variable and the output methane gas flow-rate as the measured and controlled variable. Finally, the implementation of the nonlinear output feedback control law is described and experimental results are reported. It is observed that the proposed controller yields set-point regulation, rejects disturbances and preserves stability despite uncertainty on the kinetic parameters.

Robust regulation of a class of partially observed nonlinear continuous bioreactors

We propose a design of robust dynamic output feedback for the global partial stabilization of a class of continuous stirred bioreactors. Our approachis robust withrespect to exogenous disturbances and functional uncertainties of the kinetics, considered as bounded unknown inputs. The method is based on a design of dynamic guaranteed bounds on the unmeasured variables, conditioned to past measurements and given bounds on the initial condition. This approach is suitable to systems which are not detectable for unknown inputs. The flexibility in the design of the parameters allows the consideration of saturation constraints on the control variable. # 2002 Elsevier Science Ltd. All rights reserved.

Further Results on Stabilization of Periodic Trajectories for a Chemostat With Two Species

We discuss an important class of problems involving the tracking of prescribed trajectories in the chemostat model. We provide new tracking results for chemostats with two species and one limiting substrate, based on Lyapunov function methods. In particular, we use a linear feedback control of the dilution rate and an appropriate time-varying substrate input concentration to produce a locally exponentially stable oscillatory behavior. This means that all trajectories for the nutrient and corresponding species concentrations in the closed loop chemostat that stay near the oscillatory reference trajectory are attracted to the reference trajectory exponentially fast. We also obtain a globally stable oscillatory reference trajectory for the species concentrations, using a nonlinear feedback control depending on the dilution rate and the substrate input concentration. This guarantees that all trajectories for the closed loop chemostat dynamics are attracted to the reference trajectory. Finally, we construct an explicit Lyapunov function for the corresponding global error dynamics. We demonstrate the efficacy of our method in a simulation.

Biogeography of soil microbial communities: a review and a description of the ongoing french national initiative

Microbial biogeography is the study of the distribution of microbial diversity on large scales of space and time. This science aims at understanding biodiversity regulation and its link with ecosystem biological functioning, goods and services such as maintenance of productivity, of soil and atmospheric quality, and of soil health. Although the initial concept dates from the early 20th century (Beijerinck (1913) De infusies en de ontdekking der backterien, in: Jaarboek van de Knoniklijke Akademie van Wetenschappen, Muller, Amsterdam), only recently have an increasing number of studies have investigated the biogeographical patterns of soil microbial diversity. A such delay is due to the constraints of the microbial models, the need to develop relevant molecular and bioinformatic tools to assess microbial diversity, and the non-availability of an adequate sampling strategy. Consequently, the conclusions from microbial ecology studies have rarely been generally applicable and even the fundamental power-laws differ because the taxa-area relationship and the influence of global and distal parameters on the spatial distribution of microbial communities have not been examined. In this article we define and discuss the scientific, technical and operational limits and outcomes resulting from soil microbial biogeography together with the technical and logistical feasibility. The main results are that microbial communities are not stochastically distributed on a wide scale and that biogeographical patterns are more influenced by local parameters such as soil type and land use than by distal ones, e.g. climate and geomorphology, contrary to plants and animals. We then present the European soil biological survey network, focusing on the French national initiative and the „ECOMIC-RMQS” project. The objective of the ECOMIC-RMQS project is to characterise the density and diversity of bacterial communities in all soils in the RMQS library in order to assess, for the first time, not only microbial biogeography across the whole of France but also the impact of land use on soil biodiversity (Réseau de Mesures de la Qualité des Sols = French Soil Quality Monitoring Network, 2200 soils covering all the French territory with a systematic grid of sampling). The scientific, technical and logistical outputs are examined with a view to the future prospects needed to develop this scientific domain and its applications in sustainable land use.

On-line estimation of unmeasured inputs for anaerobic wastewater treatment processes

Abstract This paper deals with the design of an unknown input observer for anaerobic wastewater treatment plants. A key problem in bioprocessing systems is the absence, in some cases, of reliable on-line measurements for real-time monitoring applications. The objective is to develop on-line estimation of unmeasured input (i.e. unknown input) for anaerobic processes defined as unknown input affine nonlinear systems. Based on a nonlinear state space model, the design approach is to find an observable subsystem insensitive to unmeasured inputs according to the linear theory. This subsystem is used to estimate, from available on-line measurements, the state and the unmeasured inputs. This study focuses on the on-line estimation of unmeasured inputs over a wide range of simulation and a practical experimentation on a pilot plant: an anaerobic fixed bed reactor.

Integrated Fault Detection and Isolation: Application to a Winery's Wastewater Treatment Plant

In this paper, an integrated object-oriented fuzzy logic fault detection and isolation (FDI) module for a biological wastewater treatment process is presented. The defined FDI strategy and the software implementation are detailed. Using experimental results obtained with a one cubic meter fixed bed reactor for the anaerobic digestion of industrial wine distillery vinasses, examples of material and biological failures are presented together with the corresponding fault signals generated by the FDI module.

Nonparametric identification and adaptive control of an anaerobic fluidized bed digester

Abstract In this paper, a new adaptive and robust control algorithm that is able to successfully deal with unpredictable internal changes (unmodeled dynamics) and external disturbances (changes in input) of the processes in an anaerobic digestion bioreactor is presented. The adaptive controller is based on a nonparametric statistical approach of the process identification. The regulation is done by optimally adapting the input liquid flow rate of the wastewater to designated changes in the output flow rate of the biogas (methane and carbon dioxide) resulting from the biological reaction. The fundamental advantage of this approach is its freedom from any a priori modeling assumptions about uncertain dynamic components. Experimental results, obtained using a pilot-scale 150 l fluidized bed reactor for the treatment of industrial wine distillery liquid wastes, demonstrates the usefulness of this approach in controlling biological processes.

Brief paper: Output tracking of continuous bioreactors through recirculation and by-pass

In this paper, we propose to regulate the output of an auto-catalytic bioprocess (a biological process associated with a growth of a micro-organism) by means of a recirculation loop and by-pass. We give conditions on the volume of the reactor and the kinetic function for which it is possible to stabilize the output concentration under a constant or disturbed unmeasured input flow. Furthermore, we obtain convergence of the output variable in finite time with a Lipschitz continuous feedback.