Résumé
The aim of this study was to determine the kinetics of fouling and their influence on the performance of a thermal treatment process used for sanitisation of pig slurry. Two temperatures (55 degrees C and 80 degrees C) were investigated. One trial was carried out at 55 degrees C and 80 degrees C in which the slurry was not re-circulated and one trial at 80 degrees C in which 100% or 50% of the slurry was re-circulated Fouling of the heat exchangers was assessed by on-line monitoring of the drop in pressure, changes in treatment temperature, heat transfer coefficients, heat recycling rate, and energy consumption. Similar energy consumption of around 38 kWh m(-3) of effluent was observed at the two temperatures. The operating periods prior to excessive fouling or blockage were 18 days at 55 degrees C and four days at 80 degrees C. Recycling treated manure to obtain 50% dilution of the raw feed increased the viable operating period to 14 days at 80 degrees C but doubled energy consumption. At 55 degrees C, the significant drop in the target temperature (>7 degrees C) with fouling severely jeopardised the process. The nature of the decline in performance suggests that the main fouling mechanisms were bio-fouling at 55 degrees C and organic/mineral deposits at 80 degrees C. Recycling treated manure enabled the operating period to be extended but increased the total cost of heating. One hundred percent recycling showed that the fouling potential of the manure was largely eliminated after one thermal treatment, suggesting a pretreatment may be advantageous. (C) 2013 Elsevier Ltd. All rights reserved.