Jean-Henry Ferrasse

State-of-the-art: rheological characterisation of wastewater treatment sludge

Since wastewater treatment has been a subject of interest, non-Newtonian flows, such as sludge flows, have been widely studied in the literature, most of the time from a rheological point of view. It is well known that the hydrodynamic behaviour of sludge flows is of prime importance to optimise process parameters of wastewater plants on one hand, as well as those of excess sludge retreating processes on the other hand. The present study is devoted to a synthesis of articles dealing with the rheological characterisation of biological wastewater treatment plant sludges (activated or concentrated ones) and some other concentrated suspensions such as microorganism ones. Attention is notably given to the rheological methods used and to rheological equations and behaviours observed in the different articles. Correlation proposed by some authors linking rheological properties to physico-chemical parameters of suspensions, or to some operating parameters of a process involving the use of sewage sludges are also given in this literature review.

Investigation of Copper Speciation in Pig Slurry by a Multitechnique Approach

It is now well-known that copper (Cu) can accumulate on the surface of soils upon which pig slurry has been applied. This is due to the high quantity of Cu in pig slurry resulting from its use as a growth promoter in animal feeds. The mobility and bioavailability of Cu from pig slurry spreading can be better predicted by determining the speciation of this element in addition to its total concentration. The aim of this study was to present a multitechnique approach to investigate Cu speciation in pig slurry. First, size fractionation and chemical characterization of each size fraction were performed to complement results obtained in raw samples. Micro X-ray fluorescence spectroscopy (μXRF) highlighted the colocalization of Cu and sulfur (S). Finally, X-ray absorption near-edge structure spectroscopy (XANES) showed that Cu speciation in raw pig slurry and size fractions could be described by Cu(2)S and that its oxidation state is Cu(I). In addition, geochemical calculation demonstrated that chalcocite (Cu(2)S) was the major Cu species present under pig slurry lagoon physical-chemical conditions. This Cu speciation in pig slurry may be the main reason for the observed Cu accumulation at the soil surface.

Anaerobic biofilm reactors for dark fermentative hydrogen production from wastewater: A review

Dark fermentation is a bioprocess driven by anaerobic bacteria that can produce hydrogen (H2) from organic waste and wastewater. This review analyses a relevant number of recent studies that have investigated dark fermentative H2 production from wastewater using two different types of anaerobic biofilm reactors: anaerobic packed bed reactor (APBR) and anaerobic fluidized bed reactor (AFBR). The effect of various parameters, including temperature, pH, carrier material, inoculum pretreatment, hydraulic retention time, substrate type and concentration, on reactor performances was investigated by a critical discussion of the results published in the literature. Also, this review presents an in-depth study on the influence of the main operating parameters on the metabolic pathways. The aim of this review is to provide to researchers and practitioners in the field of H2 production key elements for the best operation of the reactors. Finally, some perspectives and technical challenges to improve H2 production were proposed.

Thermodynamic and kinetic study of phenol degradation by a non-catalytic wet air oxidation process

This work is dedicated to an accurate evaluation of thermodynamic and kinetics aspects of phenol degradation using wet air oxidation process. Phenol is a well known polluting molecule and therefore it is important having data of its behaviour during this process. A view cell is used for the experimental study, with an internal volume of 150 mL, able to reach pressures up to 30 MPa and temperatures up to 350°C. Concerning the thermodynamic phase equilibria, experimental and modelling results are obtained for different binary systems (water/nitrogen, water/air) and ternary system (water/nitrogen/phenol). The best model is the Predictive Soave Redlich Kwong one. This information is necessary to predict the composition of the gas phase during the process. It is also important for an implementation in a process simulation. The second part is dedicated to kinetics evaluation of the degradation of phenol. Different compounds have been detected using GC coupled with a MS. A kinetic scheme is deduced, taking into account the evolution of phenol, hydroquinones, catechol, resorcinol and acetic acid. The kinetic parameters are calculated for this scheme. These data are important to evaluate the evolution of the concentration of the different polluting molecules during the process. A simplified kinetic scheme, which can be easily implemented in a process simulation, is also determined for the direct degradation of phenol into H(2)O and CO(2). The Arrhenius law data obtained for the phenol disappearance are the following: k=1.8×10(6)±3.9×10(5)M(-1)s(-1) (pre-exponential factor) and E(a)=77±8 kJ mol(-1) (activation energy).

Fermentative hydrogen production in an up-flow anaerobic biofilm reactor inoculated with a co-culture of Clostridium acetobutylicum and Desulfovibrio vulgaris

Dark fermentation systems often show low H2 yields and unstable H2 production, as the result of the variability of microbial dynamics and metabolic pathways. Recent batch investigations have demonstrated that an artificial consortium of two anaerobic bacteria, Clostridium acetobutylicum and Desulfovibrio vulgaris Hildenborough, may redirect metabolic fluxes and improve H2 yields. This study aimed at evaluating the scale-up from batch to continuous H2 production in an up-flow anaerobic packed-bed reactor (APBR) continuously fed with a glucose-medium. The effects of various parameters, including void hydraulic retention time (HRTv), pH, and alkalinity, on H2 production performances and metabolic pathways were investigated. The results demonstrated that a stable H2 production was reached after 3-4days of operation. H2 production rates increased significantly with decreasing HRTv from 4 to 2h. Instead, H2 yields remained almost stable despite the change in HRTv, indicating that the decrease in HRTv did not affect the global metabolism.

Interpreting hydrodynamic behaviour by the model of stirred tanks in series with exchanged zones: preliminary study in lab-scale trickling filters

In trickling filters for wastewater treatment, hydrodynamic behaviour is affected by the growth of biofilm on the porous medium. Therefore, modelling hydrodynamic behaviour is necessary and efficient to predict the biodegradation of pollutants. In this study, laboratory-scale trickling filters were filled with two different porous media (glass beads and plastic rings) and were fed by a synthetic substrate in batch mode. Total organic carbon (TOC) of the effluent was measured and retention time distribution (RTD) was determined by injecting NaCl. Results showed that medium had no significant effect on TOC removal rate (around 80% and 60% respectively for batch time of seven and two days). However, regarding the hydrodynamic behaviour, the effective volume ratio and hydraulic efficiency in the glass beads bed increased remarkably from 28% and 18% to 80% and 70%, respectively, with the reduction of dispersion coefficient (from 4.55 to 1.53). Moreover, the short batch time accelerated this change. Conversely, no variation of hydrodynamic behaviour in plastic rings bed was evident. Along with the feeding of synthetic substrate, biofilm concentration ranged from 1.5 to 10.1 g/L in the glass beads reactor and it achieved around 2.8 g/L in the plastic rings reactor. Hydrodynamic modelling indicated that the model of stirred tanks in series with exchanged zones fitted the experimental results well. These gave values of mobile and immobile volumes of 51 mL and 17 mL, respectively, in the glass beads filter and 25 mL and 15 mL, respectively, in the plastic rings filter.

Hydrothermal Steel Slag Valorization—Part II: Hydrogen and Nano-Magnetite Production

The effect of acidic conditions (in a pH range of 3 to 6) and temperature on the kinetics of the hydrothermal oxidation of ferrous iron contained in BOF steel slag has been tested in the 150 – 350°C range for acid acetic concentrations from 0 to 4M. Reaction progress was monitored with the amount of produced H2. Higher temperature and lower pH are found to enhance the hydrothermal oxidation kinetics of the slag. These two parameters are believed to increase iron dissolution rate which has already been identified as the rate limiting step of the hydrothermal oxidation of pure FeO. An activation energy of 28  4 kJ/mole is found for the hydrothermal oxidation of the steel slag which compares very well with that of pure FeO under similar conditions. In the case of the slag run in water at 300°C for 70.5 hours, magnetite product has been separated magnetically and characterized. Particles were found to fall in three size ranges: 10 – 30 nm, 100 – 300 nm and 1 – 10 µm. The smallest fraction (10 – 30 nm) is comparable to the 10 – 20 nm size range that is achieved when nanomagnetite are synthesized by co-precipitation methods. Obviously, the production of nanomagnetite enhances the economic interest of the hydrothermal processing of steel slags, which has already proven its capacity to produce high-purity H2.

Hydrothermal Valorization of Steel Slags—Part I: Coupled H2 Production and CO2 Mineral Sequestration

A new process route for the valorization of BOF steel slags combining H2 production and CO2 mineral sequestration is investigated at 300°C (HT) under hydrothermal conditions. A BOF steel slag stored several weeks outdoor on the production site was used as starting material. To serve as a reference, room temperature (RT) carbonation of the same BOF steel slag has been monitored with in situ Raman spectroscopy and by measuring pH and PCO2 on a time-resolved basis. CO2 uptake under RT and HT are, respectively, 243 and 327 kg CO2/t of fresh steel slag, which add up with the 63 kg of atmospheric CO2 per ton already uptaken by the starting steel slag on the storage site. The CO2 gained by the sample at HT is bounded to the carbonation of brownmillerite. H2 yield decreased by about 30% in comparison to the same experiment performed without added CO2, due to sequestration of ferrous iron in a Mg-rich siderite phase. Ferric iron, initially present in brownmillerite, is partitioned between an Fe-rich clay mineral of saponite type and metastable hematite. Saponite is likely stabilized by the presence of Al, whereas hematite may represent a metastable product of brown-millerite carbonation. Mg-rich wustite is involved in at least two competing reactions, i.e., oxidation into magnetite and carbonation into siderite. Results of both water-slag and water-CO2-slag experiments after 72 h are consistent with a kinetics enhancement of the former reaction when a CO2 partial pressure imposes a pH between 5 and 6. Three possible valorization routes, (1) RT carbonation prior to hydrothermal oxidation, (2) RT carbonation after hydrothermal treatment, and (3) combined HT carbonation and oxidation are discussed in light of the present results and literature data.

Energy Optimisation of Wet Air Oxidation Process Based on the Preliminary Study on Liquid-Vapour Equilibrium

Wet air oxidation process is used to treat wastewater with high chemical oxygen demand. Temperatures up to 350°C and pressures up to 30 MPa, are operated to develop a non-catalytic process. In the literature, there is some data about the phase equilibrium of water-air system but on larger domains and not accurate enough in our range. To study the process, it is necessary to complete the data with adapted pressures, temperatures and compositions. An experimental set-up has been developed to realise equilibrium measurements as well as trials on waste degradation. It consists of a stirred reactor of 150 mL equipped with two sapphire windows (diameter 4.1 cm) allowing a total visualization of the reactive chamber. The results of experiments give the volume occupied by the liquid and the gas phases, for a combination of temperature, pressure and global composition. Measurements are realised to establish dew curves for water-air, water-nitrogen and water-waste-nitrogen systems. Nitrogen has the same behaviour as oxygen and can replace it in mixtures for the phases equilibrium studies with the waste to avoid any reaction. The presence of the waste, in the concentrations studied, has no significant influence on the equilibrium points. Those data serve to model the liquid-vapour equilibrium in the appropriate domain first with an ideal model and then with equation of state Soave-Redlich-Kwong and appropriate mixing rules. Those equilibrium models are then included in commercial engineering software to simulate WAO processes. With the objective to develop a process energetically optimised, the second part of this work is dedicated to perform energy balances for each component and for the whole process