SAFETY IN BIOSOLIDS DRYING-PELLETIZING PLANTS, THEORY AND BEST PRAC TICE

Drying and pelletizing of biosolids is a relatively recent process only applied extensively since the beginning of the nineties. Almost all biosolids drying processes on the market are derived from other industrial applications. Unfortunately a large majority of the systems do not take all the characteristics of sewage sludge into account, in particular the related safety risks.The first part of the paper presents an overview of the relevant standards, regulations and guidelines in this field such as the new guideline for the design and operation of biosolids drying plants issued by the UK Health & Safety Executive (HSE) and the NFPA 654 standard. In addition to the drying process itself, the transport, handling and storage of dried biosolids is addressed.The second part of the paper reviews the practical measures that can be taken to prevent or limit the safety risks in a biosolids drying plant and to bring the plant in compliance with the applicable regulations. This is done by means of a case study in which a systematic analysis of the relevant risk factors identified in the first part is carried out for a Seghers Tray Dryer-Pelletizer system.