Lessons learnt from 15 years of ICA in anaerobic digesters.

Anaerobic digestion plants are highly efficient wastewater treatment processes with inherent energy production. Despite these advantages, many industries are still reluctant to use them because of their instability confronted with changes in operating conditions. There is therefore great potential for application of instrumentation, control and automation (ICA) in the field of anaerobic digestion. This paper will discuss the requirements (in terms of on-line sensors needed, modelling efforts and mathematical complexity) but also the advantages and drawbacks of different control strategies that have been applied to AD high rate processes over the last 15 years.     

An integrated system to remote monitor and control anaerobic wastewater treatment plants through the internet.

The TELEMAC project brings new methodologies from the Information and Science Technologies field to the world of water treatment. TELEMAC offers an advanced remote management system which adapts to most of the anaerobic wastewater treatment plants that do not benefit from a local expert in wastewater treatment. The TELEMAC system takes advantage of new sensors to better monitor the process dynamics and to run automatic controllers that stabilise the treatment plant, meet the depollution requirements and provide a biogas quality suitable for cogeneration. If the automatic system detects a failure which cannot be solved automatically or locally by a technician, then an expert from the TELEMAC Control Centre is contacted via the internet and manages the problem.     

侧吹气流方向对大功率CO2激光焊缝成形的影响

激光深熔焊过程中会在熔池上方产生等离子体云，若该等离子体云过密，将降低激光入射到工件表面能量密度。在工业应用中，常采用侧吹辅助气体来减弱等离子体云的影响。本文通过试验，研究了在不同气体流量下，侧吹气体方向不同对焊接过程稳定性和焊缝成形的影响。结果发现：使用大功率CO2激光焊接AH32时。侧吹气体方向对焊缝成形有着明显的影响。从熔池和等离子体两个方面，解释了侧吹气体方向的影响机制。     

Genetic analysis of geraniol metabolism during fermentation

Geraniol produced by grape is the main precursor of terpenols which play a key role in the floral aroma of white wines. We investigated the fate of geraniol during wine fermentation by Saccharomyces cerevisiae. The volatile compounds produced during fermentation of a medium enriched with geraniol were extracted by Stir-bar sorptive extraction and analysed by GC–MS. We were able to detect and quantify geranyl acetate but also citronellyl- and neryl-acetate. The presence of these compounds partly explains the disparition of geraniol. The amounts of terpenyl esters are strain dependant. We demonstrated both by gene overexpression and gene-deletion the involvement of ATF1 enzyme but not ATF2 in the acetylation of terpenols. The affinity of ATF1 enzyme for several terpenols and for isoamyl alcohol was compared. We also demonstrated that OYE2 is the enzyme involved in geraniol to citronellol reduction. Fermenting strain deleted from OYE2 gene produces far less citronellol than wild type strain. Moreover lab strain over-expressing OYE2 allows 87% geraniol to citronellol reduction in bioconversion experiment compared to about 50% conversion with control strain.     

Combined anaerobic digestion and biological nitrogen removal for piggery wastewater treatment: a modelling approach

In order to deal with the environmental problems associated with animal production industrialization and at the same time considering energy costs increasing, a piggery wastewater treatment process consisting of combined anaerobic digestion and biological nitrogen removal by activated sludge was developed. This contribution presents a modelling framework in order to optimize this process. Modified versions of the well established ASM1 and ADM1 models have been used. The ADM1 was extended with biological denitrification. pH calculation and liquid gas-transfer were modified to take into account the effect of associated components. Finally, two interfaces (ADMtoASM and ASMtoADM) were built in order to combine both models. These interfaces set up the COD, nitrogen, alkalinity and charge fractionation between both models. However, for the mass balances between both models, some hypotheses were considered and might be evaluated.     

Monitoring and control of the biogas process based on propionate concentration using online VFA measurement.

Simple logic control algorithms were tested for automatic control of a lab-scale CSTR manure digester. Using an online VFA monitoring system, propionate concentration in the reactor was used as parameter for control of the biogas process. The propionate concentration was kept below a threshold of 10 mM by manipulating the feed flow. Other online parameters such as pH, biogas production, total VFA, and other individual VFA were also measured to examine process performance. The experimental results showed that a simple logic control can successfully prevent the reactor from overload, but with fluctuations of the propionate level due to the nature of control approach. The fluctuation of propionate concentration could be reduced, by adding a lower feed flow limit into the control algorithm to prevent undershooting of propionate response. It was found that use of the biogas production as a main control parameter, rather than propionate can give a more stable process, since propionate was very persistent and only responded very slowly to the decrease of the feed flow which lead to high fluctuation of biogas production. Propionate, however, was still an excellent parameter to indicate process stress under gradual overload and thus recommended as an alarm in the control algorithm.     

Microrheology: new methods to approach the functional properties of food

Three configurations have been developed to improve the understanding of structural element interactions in food material during deformation. The three configurations combine an inverted confocal scanning laser microscope (CSLM) and a cell that can apply to the sample a specific deformation: continuous shear, linear oscillatory shear and biaxial extension (compression).In the continuous shear and oscillatory shear configurations (OSCs), a zero-velocity plane is created in the sample by moving two plates in opposite direction, maintaining stable observation conditions of the structural behaviour under deformation. The OSC allows simultaneous application of CSLM and diffusing wave spectroscopy, a multiple light scattering technique. The third configuration (compression configuration) allows observation at a stagnation point during rheometric measurements. The configurations accept semi-liquid products (dressing, sauces, dairy products, etc.) for investigations in area such as aggregation, gelation, interactions at interface, coalescence, break-up.     

Bio-hydrogen production during acidogenic fermentation in a multistage stirred tank reactor

The objective of this study was to evaluate the production of hydrogen in a two-stage CSTR system – both reactors having the same volume – and compare its performance with a conventional one-stage process. The lab-scale two-stage and one-stage systems were operated at five pHs and five hydraulic retention time (HRTs). The maximum volumetric hydrogen productivity and yield obtained with the two-stage system were 5.8 mmol L⁻¹ h⁻¹ and 2.7 mol H₂ mol glucose⁻¹, respectively, at an HRT of 12 h and pH 5.5. Overall, the two-stage system showed, at steady state, a better performance that the one-stage system for all the evaluated pHs. However, a comparison between the one-stage system, operating at 6 h of HRT, and the first reactor of the two-stage system at the same HRT did not show any significant difference, highlighting the positive impact of having a two-stage process. The determination of the ratio between the experimental measured H₂ in the gas phase and the theoretical H₂ generated in the liquid phase (discrepancy factor) indicated that an important part of the hydrogen produced in the first reactor was transferred into the second reactor instead of being desorbed in the headspace. Therefore, the improving of hydrogen production in the two-stage system is rather attributed to the increased transfer of hydrogen from liquid to gas than an actual total hydrogen production increase.     

Oxidation resistance improvement of arc-evaporated TiN hard coatings by silicon addition

Ti-Si-N coatings were deposited on M2 steel by arc evaporation using a Ti-Si composite target in an industrial reactor. The films structure before and after heat treatment at 700 °C was characterised by XRD. In addition, two types of quantitative experiments were performed in thermobalance: oxidation rate was deduced from isothermal thermogravimetric analyses at 800 °C, while the temperature of oxidation beginning (Tc) was measured in dynamic mode. Tc was then calculated by a mathematical approximation based on the non-linear least square. The results were compared to those obtained using TiN and SiN_x standards.Depending on the deposition conditions, ternary films have been deposited with an atomic ratio Si/Ti of 0.10 and 0.15. The hardness of the films was close to 40 GPa. Only the TiN phase was detected by XRD. The mean crystal size was estimated to be in the 6-8 nm range, which suggested the nanocomposite nature of the coatings. After air oxidation at 700 °C, it was found that this crystal size was not affected by the thermal treatment, indicating a good thermal stability of the structure. Moreover, incorporation of silicon into TiN-based coatings led to a drastic decrease of their oxidation rate, together with a shift of 200 °C of Tc. The high resistance of oxidation of Ti-Si-N films at elevated temperature is attributable to the network of refractory SiN_x, which acted as a diffusion barrier for oxygen and insulated TiN nanograins from the aggressive atmosphere.