A method to determine residence time distribution (RTD) of municipal sewage sludge in a continuous contact dryer with agitation has been developed. Experiments were conducted using a pulse injection of chloride sodium and by sampling and analysing the electrical conductivity of sludge leachate offline. Experiments were performed with the same operating conditions in triplicate but with a sampling interval at the wastewater treatment plant of several weeks. Accuracy and reproducibility of the method was quantified with an averaged mean residence time of 160 ± 7 min. The RTD curves shows sludge flow behavior is intermediate between a plug flow and a perfectly mixed flow. This is due to presence of paddles which induces axial dispersion on the flow.
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