Sludge stabilization using ozonation: a pre-treatment method for composting waste activated sludge

The effects of ozonation have been studied as a pre-treatment of waste activated sludge (WAS) on duration of the composting process. This study was aimed to evaluate the comparison of two pre-treatment processes on degradation of the WAS and particularly on the duration of pre-treated sludge composting. The ozone was injected by two different doses to make semi-stabilized sludge (0.006 g O-3/gTSS) and completely stabilized sludge (0.041 g O-3/gTSS). Three mixtures were composted in 150 L three reactors using the raw (CRS), semi-stabilized (CSS) completely stabilized sludge (CCS). The organic matter evolution was assessed by characteristic of the total organic carbon, total Kjeldahl nitrogen, total phosphorous, volatile solid and total coliforms during composting. The results show that CCS reactor reached a considerable enhancement in quality of compost which could be a consequence of higher organic matter mineralization during the process of composting compared with the other two reactors. The results show that ozonation as an oxidative pre-treatment could solubilize the organic matters and could increase the biodegradability of WAS which led to rapid mineralization rate of organic matter during composting.