Evaluation de l'impact environnemental du au SO2 et bio épuration de gaz charges en méthyle éthyle cétone.

Abstract

The sulfuric acid plant within the phosphate fertilizer complex located 3 kins awa> from the town ot Annaba is the largest source of SO: in the vicinity of the city besides other industrial processes and emissions from domestic sources and motor vehicles. A computer simulation using a Gaussian diffusion model was carried out to estimate downwind short term and long term SO: concentrations. The available statistical data from the meteorological station of Annaba were used for this simulation. Results indicate that in the absence of background pollution, air quality standards are exceeded in the short term as well as under unfavourable weather conditions Furthermore, the annual average pH within rainfall as well as SO: dry and wet deposition have been evaluated for the year 1995. The annual average pH of falling raindrops was computed for all precipitation events coinciding with the plume during the period of study Estimation of SO: wet deposition has been carried out using a model of transient absorption of a gas by a water droplet On the basis of this study, results show that dry deposition contributes more than 99,99 % of the total sulphur deposition in the Annaba area. Moreover, despite the fact that conversion of SO; to H:SO.t is not expected to occur during the course of SO; precipitation scavenging, aqueous phase dissociation reactions within the falling raindrops lead to pi I values comprised between 4,2 and 4,7. Following this preliminary evaluation of the environmental impact of the plant by way of an original modelling method, the issue of air pollution control constitutes the second part of this work Among the various possibilities of pollution control, waste gas biotreatment is an interesting option. Our efforts were oriented towards the purification of air contaminated by methyl ethyl ketone (MEK). The objective of the second pan of the work is to test a novel, essentially gas-phase reactor ( a modular, segmented glass tubular fixed-film column) and to characterise its mass transfer characteristics in the course of MEK degradation by a mixed aerobic biomass under non axeme conditions. Emphasis was placed on the characterisation and on the development of conceptual explanations of the phenomena occurring during the removal of the pollutant under both steady state and transient operating conditions. Selected kinetic and operational aspects of the aerobic treatment of vapours of MEK have been investigated. The maximum elimination capacity of the dry tubular (DTB) was 4,8 kg m, ’ d !. The study of the biofilm behaviour on the bioreactor walls through reproducible cy cles of detachment-recolomzaiion indicated the influence of the biofilm thickness on the system performances. The maxima! degradation activity was obtained with a thin biofilm and was not increased as the biofilm grew in thickness. MEK degradation provoked the acidification of the biofilm which in turns favoured the proliferation of two fungi capable of degrading MEK, namely, ( Icotnchum cundiJum and ]-'u\anum uxysporum. The present results suggest that both MEK diffusion within the biofilm and the affinity of the microorganisms towards he substrate are the controlling factors of the process. A substantial performance improvement of such a process necessarily results from a comprehensive knowledge of both the mass transfer and microbiological aspects