Mechanical sludge disintegration for the production of carbon source for biological nutrient removal

The primary driver for a successful biological nutrient removal is the availability of suitable carbon source, mainly in the form of volatile fatty acids (VFA). Several methods have been examined to increase the amount of VFAs in wastewater. This study investigates the mechanism of mechanical disintegration of thickened surplus activated sludge by a deflaker technology for the production of organic matter. This equipment was able to increase the soluble carbon in terms of VFA and soluble chemical oxygen demand (SCOD) with the maximum concentration to be around 850 and 6530 mg l−1, for VFA and SCOD, respectively. The particle size was reduced from 65.5 to 9.3 μm after 15 min of disintegration with the simultaneous release of proteins (1550 mg l−1) and carbohydrates (307 mg l−1) indicating floc disruption and breakage. High performance size exclusion chromatography investigated the disintegrated sludge and confirmed that the deflaker was able to destroy the flocs releasing polymeric substances that are typically found outside of cells. When long disintegration times were applied (⩾10 min or ⩾9000 kJ kg−1 TS of specific energy) smaller molecular size materials were released to the liquid phase, which are considered to be found inside the cells indicating cell lysis.