Integration of Ozonation and Activated Sludge Process for Sludge Reduction in Tannery Effluent Treatment

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Addis Ababa University


In tannery wastewater treatment plants, sludge comprising of primary and secondary sludge is generated. If the concentration of Cr (III) exceeds 5000 mg/kg, then it is considered as hazardous wastes and this sludge has to be disposed in hazardous waste landfill site as per existing statutory requirements in India. Further, for disposal of wastes into hazardous landfill, the amount of organics concentration in the sludge shall not exceed 20% and if so, then these wastes are not permitted to be disposed in hazardous wastes landfill. Currently, lime and fly ash are added to the wastes to reduce the concentration of organics. Hence, there is urgent need for treatment methods to reduce of organic content in sludge before disposal into hazardous landfill. In this study, attempt was made to reduce the volatile solids generated from secondary biological sludge using advanced oxidation process (AOP) i.e., ozonation. Lab scale aerobic process using sequential batch reactor (SBR) for treatment of tannery wastewater and ozonation of excess sludge generated from SBR were carried out with 24 hrs cycling time. SBR was operated with primary treated tannery wastewater and excess sludge generated was ozonated and returned back to SBR reactor. The performance of sequential batch reactor (SBR) operated with tannery wastewater alone as control and another SBR operated with tannery effluent along with ozonated excess bio-sludge were studied and compared. It was observed that 15 minutes is the optimum ozonation time for oxidation of excess sludge from SBR treating primary treated tannery waste water as influent and the optimum ozone dose respective to optimum ozonation time is found to be 0.168g-O3/g-MLSS. It was observed that COD in the final effluent was reduced to total and soluble COD concentrations in the range of 548.2mg/l and 379.2mg/l for control SBR and 537.581mg/l and 376.049 mg/l for SBR with ozonated sludge respectively at total cycling time of 24 h. In terms of overall sludge reduction, 35.1% reduction of the excess sludge could be achieved by ozone treatment at 0.168 g-O3/g-MLSS.



Chemical Engineering