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 mgl(-1), for VFA and SCOD, respectively. The particle size was reduced from 65.5 to 9.3 microm after 15 min of disintegration with the simultaneous release of proteins (1550 mgl(-1)) and carbohydrates (307 mgl(-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 (>or=10 min or >or=9000 kJkg(-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.

There is a need to investigate processes that enable sludge re-use while enhancing sewage treatment efficiency. Mechanically disintegrated thickened surplus activated sludge (SAS) and fermented primary sludge were compared for their capacity to produce a carbon source suitable for BNR by completing nutrient removal predictive tests. Mechanically disintegration of SAS using a deflaker enhanced volatile fatty acids (VFAs) content from 92 to 374 mg l(-1) (4.1-fold increase). In comparison, primary sludge fermentation increased the VFAs content from 3.5 g l(-1) to a final concentration of 8.7 g l(-1) (2.5-fold increase). The carbon source obtained from disintegration and fermentation treatments improved phosphate (PO(4)-P) release and denitrification by up to 0.04 mg NO(3)-Ng(-1)VSS min(-1) and 0.031 mg PO(4)-Pg(-1)VSS min(-1), respectively, in comparison to acetate (0.023 mg NO(3)-Ng(-1)VSS min(-1)and 0.010 mg PO(4)-Pg(-1)VSS min(-1)). Overall, both types of sludge were suitable for BNR but disintegrated SAS displayed lower carbon to nutrient ratios of 8 for SCOD:PO(4)-P and 9 for SCOD:NO(3)-N. On the other hand, SAS increased the concentration of PO(4)-P in the settled sewage by a further 0.97 g PO(4)-P kg(-1)SCOD indicating its potential negative impact towards nutrient recycling in the BNR process.

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The primary driver for efficient biological nutrient removal (BNR) in activated sludge treatment is the sufficient supply of soluble carbon. Several methods have been proposed to increase available carbon sources and enhance BNR. This study examines the effect of ultrasonic equipment and mechanical disintegration technologies on surplus activated sludge (SAS), to release additional soluble chemical oxygen demand (SCOD) and volatile fattty acids (VFA), as a carbon food source for BNR. A laboratory sonicator with a maximum power of 550W, a 3KW SONIX radial horn and a deflaker declared to be used in the paper industry were investigated. All caused significant release of SCOD, up to 48 fold. The maximum concentration of VFA reached (from 0-1 mg 1(-1)), was 530 mg 1(-1). To assess the likely impact to BNR, batch (21) anaerobic lab tests examining the use of disintegrated sludge on phosphorus and nitrogen removal were completed. Phosphorus removal was estimated by observing the phosphate release under anaerobic conditions and up to 460% more release was observed relative to controls. In addition, denitrification rates were improved by over 106%. Ultrasonic and mechanical disintegration technologies have been shown to release soluble carbon for BNR, with subsequent laboratory nitrogen and phosphorus removal efficiencies observed to be comparable to acetate.