Therefore, various methods such as thermal pre-treatment, ultrasonic pre-treatment and microwave, have been introduced to improve organic matter biodegradation, and it has been proven that thermal pre-treatment was a successful approach to make sewage sludge more amenable to AD ( Li & Noike 1992 Erdincler et al. During the AD process, hydrolysis of organic is the main rate-limiting step. Compared with traditional AD of low solid sludge, high solid AD (total solid content of feed especially about 15% (w/w)) is more interesting due to its merits such as higher loading, smaller reactor volume, and lower energy consumption ( Xu & Lancaster 2009 Dai et al. Yield stress for activated sludge was prominent, while it could be ignored for thermal treated sludge.ДЄnaerobic digestion (AD) or methanisation is one of the most widely used methods of treating sludge by converting a part of organic matter into biogas to achieve high-energy recovery and limit environmental impact. However, for thermal treated sludge, Arrhenius law was invalid. Arrhenius law was also suitable for describing the relationship between storage modulus and process temperature for activated sludge. As solid content was at range of 80вЂ“100 g/L, active energy of viscosity for both kinds of sludge were similar, indicating that physicochemical properties' change of sludge after thermal hydrolysis had little effect on viscosity sensibility. Moreover, the logistic model was certified to be accurate in describing the functionality for thermal treated sludge.

The relationship between viscosity and temperature could be expressed by Arrhenius equation for activated sludge, and it was interesting that this law was only suitable when certain solid content (80 g/L) for thermal treated sludge. Results show viscosity of activated sludge and thermal treated sludge both decreased with increasing temperature, while temperature dependence of viscosity for both types of sludge were not same at the whole study range.

In this paper, flow behavior for activated sludge and thermal treated sludge at different process temperature and various solids content were analyzed.

Viscosity of water at room temperature