Sludge Particle Size Reduction Under Alkaline, Ultrasonic, Thermal, and Combined Pretreatments

Abstract

Sludge particle size reduction (PSR) via pretreatment stage has been believed to accelerate the hydrolysis of sludge anaerobic digestion and enhance the degradation of organic matters. This work aimed at investigating the evolution of PSR under individual and combined pretreatment methods, including ultrasound (US), thermal, and alkaline pretreatments. In addition, the relationship between sludge PSR and COD release in the aqueous phase was taken into detailed consideration for the first time. US pretreatment showed the most predominant role in reducing sludge particle size compared to other methods. The reduction of the volume moment mean diameter of sludge (D[4,3]) were dependent on US specific energy input (ES) (68-77 %). Moreover, the PSR was slightly improved in adiabatic conditions and applied pressure (about 10 %). Alkaline addition prior to US also further accelerated the PSR. However, the strong D[4,3] reduction observed in the early stage of the process (low ES) was insufficient to affect COD solubilisation. It is therefore necessary combine with other factors (chemical, biological parameters), not only base on PSR for process optimization.