As environmental awareness increases, it will become increasingly difficult to discharge pollutants to the environment without treatment. New and improved technologies can only be based on a knowledge of a large number of factors for each situation. These can be divided into: legislative requirements, environmental impacts, economics, and technical feasibility. Meeting all these criteria will often mean that no single technology will be sufficient to completely alleviate the problem. Hence, a combination of technologies can often be employed. Industrial wastewater, which is often very difficult to treat by conventional treatment, and the large volumes of sludge produced by the wastewater industry have opened up the potential for wet oxidation, which could be very effective in destroying many hazardous organic wastes, and also very effective in reducing the volume of sludge to be disposed of. The decant liquor from WO is often very concentrated and contains low molecular weight organic compounds, mostly acetic acid, but which could be treated to some degree by a biological treatment process. The Wet Oxidation (WO) process is recommended for the oxidation of organic effluent with a solids concentration of between 1% to 25% but which are too toxic to be biologically treated or too diluted to be incinerated. This research project was a continuation of a previous study by Luduvice (1992) and, when possible, most of his recommendations were investigated, including the use of pure oxygen instead of air in the reactor, the biotreatability of the heat liquor and an evaluation of the chemical characteristics of the liquor. It was not, however, possible to develop a continuous Wet Oxidation process capable of operating at both subcritical and supercritical conditions. This thesis describes the ability of wet oxidation to treat different organic wastewaters and sludges under conditions which included the stoichiometric requirement of oxygen being provided and with further biological treatment being given to the decant liquor. The organic wastewater and sludges tested were from different origins and characteristics, including paracetamol wastewater, detergent wastewater, from industries plus raw primary sludge and activated sludge from a biological wastewater treatment plant. Tests were carried out at temperatures varying between 1600 C and 3000 C at retention times of 10, 15, 30 and 60 minutes in a 3.78 1 stainless steel reactor. Temperature proved to be the most significant parameter, followed by retention time and oxygen overpressure. A considerable reduction in sludge volume and organic content was obtained in most runs, which in general produced an effluent liquor with a high oxygen demand and relatively stable residual solids. The residual WO solids, when dried were found to be capable of removing colour from a textile-dye wastewater, implying that dried WO sludge may have adsorption properties similar to that of activated carbon. Simplified empirical equations were developed from the experimental data. The equations adequately described the transformation pattern of the organic and inorganic components of the activated sludge in a WO environment. The empirical equations further demonstrate a direct relationship between the influent VTS and the transformed organic and inorganic components in the liquor after WO. The purpose of this study was also to demonstrate the feasibility of reducing the strength of heat treatment liquors to that approximating domestic wastewater. A range of aerobic and anaerobic biological treatment systems was investigated. Aerobic biological processes proved to be very effective and robust in COD and BCOD removal compared to the anaerobic biological processes.

L’industrie, quel que soit son domaine d’activité, produit une quantité importante d’effluents chargés, couramment appelés coproduits. La gestion et le traitement de ces eaux usées sont aujourd’hui strictement encadrés car leurs propriétés physiques et leurs compositions chimiques interdisent leurs rejets directs vers le milieu naturel. Cependant, la présence en forte concentration de certains éléments valorisables tels que les sels minéraux ou des composés organiques dans certains de ces effluents, leurs confèrent alors de nouvelles propriétés qui trouvent échos dans diverses applications (fertilisation des sols, alimentation animale, méthanisation, co-compostage, etc.). Le carbone étant le constituant majoritaire de tout combustible, une valorisation thermique par combustion en chaudière biomasse des effluents organiques semble être une alternative envisageable. L’objet de cette thèse est l’étude de cette voie de valorisation énergétique et de la faisabilité de cette application. Du fait de leur état liquide, les effluents seuls sont de mauvais combustibles comparés aux biomasses standards (plaquettes forestières, paille, etc.). Les travaux de recherche se concentrent donc sur l’étude et la caractérisation de biomasses en tant que support d’imprégnation, puis sur la formulation d’un co-combustible homogène imprégné d’un effluent organique industriel. Les biomasses sont en effet connues dans la littérature pour avoir des propriétés d’adsorption et d’absorption intéressantes. Une étude paramétrique à l’échelle du laboratoire a été menée afin de quantifier la capacité d’imprégnation et la sélectivité de différents types de biomasse vis-à-vis de l’effluent choisi. Le but était également de déterminer les paramètres qui influençaient l’imprégnation afin de modéliser les phénomènes. Suite à cela, des essais à l’échelle pilote sur une installation de combustion de 40 kW ont été effectués en vue de vérifier la conformité des combustibles imprégnés en termes d’émissions à la cheminée et dans l’optique de préparer le changement d’échelle pour une potentielle application industrielle. / Important amounts of organic effluents, also called wastewaters or byproducts, are produced whatever the type of industry which is considered. Nowadays, the wastewaters management and treatment are strictly controlled since the physical properties and the chemical composition of these byproducts disallow the direct reject through natural media. However, the presence of some specific compounds confers to effluents new advantages and opens the door to several applications (such as soil fertilization, cattle feed, methanization, co-composting, etc.). Carbon being the main component of every fuel, the thermal valorization of these organic effluents by combustion in a standard biomass boiler seems to be possible. The study of this recovery method and its feasibility are the subjects of the thesis here. Due to their liquid state, effluents alone cannot be considered as fuels compared to standard biomass (woodchips, straw, etc.). Therefore research works are focused on study and characterization of biomasses as impregnation base, then formulation of fuels impregnated with an industrial organic effluent. Indeed, the adsorptive and absorptive properties of biomasses are well-known in the literature. A parametric study at laboratory scale was carried out in order to quantify the impregnation capacity of different types of biomass regarding the effluent. The main goal was also to highlight the parameters which influence the impregnation in order to modeling the phenomenon. Then impregnation and combustion tests were performed at pilot scale using a biomass boiler of 40 kW to ensure the conformity of impregnated fuels in terms of stack emissions. This part of the work was conducted with the perspective of preparing the process scale-up for a potential industrial utilization.

The fate of the carbon and nitrogen in dairy farm effluent (DFE) applied onto soil was investigated through laboratory experiments and field lysimeter studies. They resulted in the development and testing of a complex carbon (C) and nitrogen (N) simulation model (CaNS-Eff) of the soil-plant-microbial system. To minimise the risk of contamination of surface waters, regulatory authorities in New Zealand promote irrigation onto land as the preferred treatment method for DFE. The allowable annual loading rates for DFE, as defined in statutory regional plans are based on annual N balance calculations, comparing N inputs to outputs from the farming system. Little information is available, however, to assess the effects that these loading rates have on the receiving environment. It is this need, to understand the fate of land-applied DFE and develop a tool to describe the process, that is addressed in this research. The microbially mediated net N mineralisation from DFE takes a central role in the turnover of DFE, as the total N in DFE is dominated by organic N. In a laboratory experiment, where DFE was applied at the standard farm loading rate of 68 kg N ha⁻¹, the net C mineralisation from the DFE was finished 13 days after application and represented 30% of the applied C, with no net N mineralisation being measured by Day 113. The soluble fraction of DFE appeared to have a microbial availability similar to that of glucose. The low and gradually changing respiration rate measured from DFE indicated a semi-continuous substrate supply to the microbial biomass, reflecting the complex nature and broad range of C compounds in DFE. The repeated application of DFE will gradually enhance the mineralisable fraction of the total soil organic N and in the long term increase net N mineralisation. To address the lack of data on the fate of faecal-N in DFE, a ¹⁵N-labelled faecal component of DFE was applied under two different water treatments onto intact soil cores with pasture growing on them. At the end of 255 days, approximately 2% of the applied faecal ¹⁵N had been leached, 11 % was in plant material, 11 % was still as effluent on the surface, and 40% remained in the soil (39% as organic N). Unmeasured gaseous losses and physical losses from the soil surface of the cores supposedly account for the remaining ¹⁵N (approximately 36%). Separate analysis of the total and ammonium nitrogen contents and ¹⁵N enrichments of the DFE and filtered sub-samples (0.5 mm, 0.2µm) showed that the faecal-N fraction was not labelled homogeneously. Due to this heterogeneity, which was exacerbated by the filtration of DFE on the soil surface, it was difficult to calculate the turnover of the total faecal-N fraction based on ¹⁵N results. By making a simplifying assumption about the enrichment of the ¹⁵N in the DFE that infiltrated the soil, the contribution from DFE-N to all plant available N fractions including soil inorganic N was estimated to have been approximately 11 % of the applied DFE-N. An initial two-year study investigating the feasibility of manipulating soil water conditions through controlled drainage to enhance denitrification from irrigated DFE was extended a further two years for this thesis project. The resulting four-year data set provided the opportunity to evaluate the sustainability of DFE application onto land, an extended data set against which to test the adequacy of CaNS-Eff, and to identify the key processes in the fate of DFE irrigated onto soil under field conditions. In the final year of DFE irrigation, 1554 kg N ha⁻¹ of DFE-N was applied onto the lysimeters, with the main removal mechanism being pasture uptake (700 kg N ha⁻¹ yr⁻¹ removed). An average of 193 kg N ha⁻¹ yr⁻¹ was leached, with 80% of this being organic N. The nitrate leaching decreased with increasing soil moisture conditions through controlled drainage. At the high DFE loading rate used, the total soil C and N, pH and the microbial biomass increased at different rates over the four years. The long-term sustainability of the application of DFE can only be maintained when the supply of inorganic N is matched by the demand of the pasture. The complex simulation model (CaNS-Eff) of the soil-plant-microbial system was developed to describe the transport and transformations of C and N components in effluents applied onto the soil. The model addresses the shortcomings in existing models and simulates the transport, adsorption and filtration of both dissolved and particulate components of an effluent. The soil matrix is divided into mobile and immobile flow domains with convective flow of solutes occurring in the mobile fraction only. Diffusion is considered to occur between the micropore and mesopore domains both between and within a soil layer, allowing dissolved material to move into the immobile zone. To select an appropriate sub-model to simulate the water fluxes within CaNS-Eff, the measured drainage volumes and water table heights from the lysimeters were compared to simulated values over four years. Two different modelling approaches were compared, a simpler water balance model, DRAINMOD, and a solution to Richards' equation, SWIM. Both models provided excellent estimation of the total amount of drainage and water table height. The greatest errors in drainage volume were associated with rain events over the summer and autumn, when antecedent soil conditions were driest. When soil water and interlayer fluxes are required at small time steps such as during infiltration under DFE-irrigation, SWIM's more mechanistic approach offered more flexibility and consequently was the sub-model selected to use within CaNS-Eff. Measured bromide leaching from the lysimeters showed that on average 18% of the bromide from an irrigation event bypassed the soil matrix and was leached in the initial drainage event. This bypass mechanism accounted for the high amount of organic N leached under DFE-irrigation onto these soils and a description of this bypass process needed to be included in CaNS-Eff. Between 80 and 90% of the N and C leached from the lysimeters was particulate (> 0.2 µm in size), demonstrating the need to describe transport of particulate material in CaNS-Eff. The filtration behaviour of four soil horizons was measured by characterising the size of C material in a DFE, applying this DFE onto intact soil cores, and collecting and analyzing the resulting leachate using the same size characterisation. After two water flushes, an average of 34% of the applied DFE-C was leached through the top 0-50 mm soil cores, with a corresponding amount of 27% being leached from the 50-150 mm soil cores. Most of the C leaching occurred during the initial DFE application onto the soil. To simulate the transport and leaching of particulate C, a sub-model was developed and parameterised that describes the movement of the effluent in terms of filtering and trapping the C within a soil horizon and then washing it out with subsequent flow events. The microbial availability of the various organic fractions within the soil system are described in CaNS-Eff by availability spectra of multiple first-order decay functions. The simulation of microbial dynamics is based on actual consumption of available C for three microbial biomass populations: heterotrophs, nitrifiers and denitrifiers. The respiration level of a population is controlled by the amount of C that is available to that population. This respiration rate can vary between low level maintenance requirements, when very little substrate is available, and higher levels when excess substrate is available to an actively growing population. The plant component is described as both above and below-ground fractions of a rye grass-clover pasture. The parameter set used in CaNS-Eff to simulate the fate of DFE irrigated onto the conventionally drained lysimeter treatments over three years with a subsequent 10 months non-irrigation period was derived from own laboratory studies, field measurements, experimental literature data and published model studies. As no systematic calibration exercise was undertaken to optimise these parameters, the parameter set should be considered as "initial best estimates" and not as a calibrated data set on which a full validation of CaNS-Eff could be based. Over the 42 months of simulation, the cumulative drainage from CaNS-Eff for the conventionally drained DFE lysimeter was always within the 95% CI of the measured value. On the basis of individual drainage bulking periods, CaNS-Eff was able to explain 92% of the variation in the measured drainage volumes. On an event basis the accuracy of the simulated water filled pore space (WFPS) was better than that of the drainage volume, with an average of 70% of the simulated WFPS values being within the 95% CI for the soil layers investigated, compared to 44% for the drainage volumes. Overall the hydrological component of CaNS-Eff, which is based on the SWIM model, could be considered as satisfactory for the purposes of predicting the soil water status and drainage volume from the conventionally drained lysimeter treatment for this study. The simulated cumulative nitrate leaching of 4.7 g NO₃-N m⁻² over the 42 months of lysimeter operation was in good agreement to the measured amount of 3.0 (± 2.7) g NO₃-N m⁻². Similarly, the total simulated ammonium leaching of 2.7g NH₄- N m⁻² was very close to the measured amount of 2.5 (± 1.35) g NH₄- N m⁻² , however the dynamics were not as close to the measured values as with the nitrate leaching. The simulated amount of organic N leached was approximately double that measured, and most of the difference originated from the simulated de-adsorption of the dissolved fraction of organic N during the l0-month period after the final DFE irrigation. The 305 g C m⁻² of simulated particulate C leached was close to the measured amount of 224 g C m⁻² over the 31 months of simulation. The dissolved C fraction was substantially over-predicted. There was good agreement in the non-adsorbed and particulate fractions of the leached C and N in DFE. However, the isothermic behaviour of the adsorbed pools indicated that a non-reversible component needed to be introduced or that the dynamics of the de-adsorption needed to be improved. Taking into account that the parameters were not calibrated but only "initial best estimates", the agreement in the dynamics and the absolute amounts between the measured and simulated values of leached C and N demonstrated that CaNS-Eff contains an adequate description of the leaching processes following DFE irrigation onto the soil. The simulated pasture N production was in reasonable agreement with the measured data. The simulated dynamics and amounts of microbial biomass in the topsoil layers were in good agreement with the measured data. This is an important result as the soil microbial biomass is the key transformation station for organic materials. Excepting the topsoil layer, the simulated total C and N dynamics were close to the measured values. The model predicted an accumulation of C and N in the topsoil layer as expected, but not measured. Although no measurements were available to compare the dynamics and amounts of the soil NO₃-N and NH₄-N, the simulated values appear realistic for an effluent treatment site and are consistent with measured pasture data. Considering the large amount of total N and C applied onto the lysimeters over the 42 months of operation (4 t ha⁻¹ of N and 42 t ha⁻¹0f C), the various forms of C and N in dissolved and particulate DFE as well as in returned pasture, and that the parameters used in the test have not been calibrated, the simulated values from CaNS-Eff compared satisfactorily to the measured data.