Risk assessment of sewage sludge granulation process using HAZOP study

Abstract

The article presents application of hazard and operability study (HAZOP) technique to identify and analyze hazards associated with the process of producing fertilizer granulates from sewage sludge. The aim was to indicate deviations from the proper performance of the system, which may occur at the operation stage of the installation for granulating sewage sludge, and, as a consequence, lead to interrupting the process. The hazards, that is, dangerous and harmful factors, which may generate dangerous events, were meticulously identified. Thanks to that, it was possible to propose preventive actions aimed at reducing risk at the stage of designing an installation. The research showed that producing fertilizer granulates from sewage sludge may generate an explosion hazard when dust and gases during the process of transportation or storage are present. Gases responsible for explosions such as NH3, H2S, CH4 are by-products of the reaction of sewage sludge with the lime, while explosive dust consists of a microcrystalline cellulose powder. A few scenarios leading to epidemiological risk are associated with the composition of badly stabilized sewage sludge. Additionally, the material corrosion resulting from wrongly selected material and aggressive environment, were also identified. The HAZOP results were used to conduct process hazard assessment, which analyzed frequency of hazards in given technology nodes and categories of their potential consequences.