Simultaneous Sludge Disintegration and Carbon Source Generation for Enhanced Biological Phosphorous Removal Using Ozonation

One of the major drawbacks of wastewater treatment is the amount of excess sludge produced, which depends on the type of process applied. Since the quantities of sludge produced in a typical activated sludge process are considerable, it has a strong impact on the cost of sludge treatment and final disposal. The sludge treatment and disposal from an activated sludge process can make up to 60% of the total wastewater treatment operational cost (Inchauste-Daza et al., 2011). The ozonation of the excess sludge is considered to be one of the extensively studied and successfully applied methods for sludge reduction (Chu et al., 2009; Inchauste-Daza et al., 2011). When sludge is ozonated, a new carbon source is formed and it has been reasoned that due to its new characteristics of biodegradability it may be consumed by the microorganisms such as by PAOs (bio-P organisms) in enhanced biological phosphorous removal (EBPR). However, the investigation of the use of ozonated sludge as substrate in nutrient removal is limited. Two types of experiments have been carried out-ozonation tests of activated sludge, and biological activity tests for enhanced biological phosphorous removal. The ozonation of sludge resulted in the reduction of both MLSS and MLVSS; and it is evident from the trend that the volatile fraction is disintegrated and becomes soluble making the trend of both close to parallel. It has been observed that while the amount of residual biosolids drops with ozone dose increase, the soluble fraction rises; and the mineralized fraction becomes more significant.The results with acetate (HAc) as carbon source show that during the anaerobic phase all the substrate was consumed and stored by PAOs in the first 20 minutes; the poly-P internally stored was effectively used as energy, releasing up to 3.30 mg PO4-P/g VSS at the end of the anaerobic phase. In the following stage, PAOs did not uptake all the phosphorus, and thus the specific P uptake was found to be 3.19 mg PO4-P/g VSS at the end of the tests. The results from disintegrated sludge use indicate that the ozonated sludge at various ozone doses were certainly used by PAOs during the anaerobic phase. However, not all substrates were identically used. The highest specific P-release was found to be 2.78 mg PO4-P/g VSS, with a rate of 5.52 mg PO4-P/g VSS·h, when using ozonated sludge at higher dose of 0.13 g O3/g MLSS as substrate. The results indicate that the properties of the carbon source present in the ozonated sludge are promising; the wastewater treatment plants can be integrated with sludge ozonation to significantly reduce the amount of sludge generation and external chemical (carbon source) requirement.