| The treatment and disposal of excess sludge have become a serious problem, whichlead the sludge reduction to a necessary. Owing to the characteristics of highefficiency and no poisonous side effect, the ozonation reduction technology based onthe lysis growth has attracted more and more attention all around the world. Becauseof the ozone’s high sterilizing ability, it can kill the bacteria by destroying the organiclong chain structure once entering the cell wall. The organic products which releasedby cytolysis can be recycled for organism metabolism, which can lead to the reductionof sludge production. In this paper, the ozone was applied to disintegrate the excesssludge in order to deeply research on some basic theoretical problems along with thepossibility as well as the efficiency of combined treatment of ozonation andacid/alkaline.The mechanism of ozonation disintegration for excess sludge reduction was studiedby continuous experiment in lab scale process, and the dissolving laws of someindexes were analyzed. During the treatment process, various parameterscharacterizing sludge were investigated. A substantial reduction in the volume ofsludge and the release of intracellular materials were observed. After ozoneconsumption of40minutes, the removal efficiencies of Total Solids(TS) and VolatileTotal Solids (VTS) increased to57.33%and72.76%respectively; Soluble ChemicalOxygen Demand (SCOD) proliferated as a consequence of extending the ozonefeeding time in the first30minutes, and rose to a final concentration of6298.32mg/Lfrom the original3501.24mg/L, demonstrating a growth rate of79.88%; a steadydecline both in30-min Settled Sludge Volume (SV30) and water content of sludgecake was observed through ozonation, which suggested that ozonation could improve both of the sedimentation and dewatering performances; the pH value also fell to5.75from the previous6.85at the end of60minutes’ oxidation treatment. Experimentproves a remarkable effect of the sludge reduction.The experiment of particle size showed that, with the increase of ozonation time, theaverage grain diameter decreased and then ascended. Given the concentration ofsoluble polysaccharide of mixed sludge liquid, it could be considered that the highmolecular components such as protein and polysaccharose would flocculate the smallparticles that produced by ozonation and finally lead to the rise of grain diameter.In order to increase the degradation rate of excess sludge, acid and alkaline wereadded to the ozonation. Several cell-lysis techniques, including30-minute ozonation,ozonation plus30-minute acid hydrolysis and ozonation plus18-hour acid hydrolysis,ozonation plus30-minute alkaline hydrolysis and ozonation plus18-hour alkalinehydrolysis, were compared by lab-scale experiment. The decrement rate of MLSSunder30-minute ozonation treatment was21.97%, and it received a concentration of28.07mg/L in soluble polysaccharide, which is7.75%more than the raw samples.Compared to30-minute ozonation, the combination of both ozonation andacid/alkaline was more effective. The treatment of ozone combined with18-houralkaline hydrolysis worked best, which had a biggest drop of MLSS of36.32%andlargest increase of soluble polysaccharide of40.81%. The particle size analysisshowed that after combination treatment of ozonation and acid/alkaline hydrolysis,the mean diameters dropped from29.33μm to24.77μm (under ozonation plus30-minute acid),20.56μm (under ozonation plus18-hour acid),22.44μm (underozonation plus30-minute alkaline) and18.26μm (under ozonation plus18-houralkaline), while30-minute ozonation only got a mean diameter of26.23μm. Themicroscope examination also showed that ozonation-acid/alkaline combinativetreatment received better results than30-minute ozonation, especially samples under alkaline hydrolysis, where flocculate structures were totally destroyed.In general, treatment combined30-minute ozonation with30-minute/18-hour alkalinehydrolysis achieved better solubilization effect of excess sludge than ozonation-acidhydrolysis combinative treatment or30-minute ozonation treatment. Moreover, thelonger feeding time of acid or alkaline hydrolysis would receive a higher sludgeremoval rate. On the other hand, ozonation/acid treatment could improve both of thesedimentation and dewatering performance. |
PDF Full Text Request