Dewatering is an extremely important step in wastewater treatment process to reduce the final sludge volume in order to minimize the cost of sludge transportation and disposal. In the present study, the effect of different sludge solids content (1, 2 and 3.8%) on the dewaterability of anaerobically digested sludge using Acidithiobacillus ferrooxidans and A. thiooxidans was studied. The rate of pH reduction was higher during initial process in the sludge having low solids content, but after 48 h

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... of bioleaching, similar pH of below 3 was observed in all the treatments with different solids content. Bio-oxidation rate of Fe 2+ was initially higher in sludge with low solids content, but complete oxidation was observed within 60 h in all the three treatments. Compared to the control, specific resistance to filtration was reduced by 75, 78 and 80% in the sludge with a solids content of 1, 2 and 3.8% respectively, showing improvement in dewaterability with an increase in sludge solids content. Sludge effluent quality and sludge settling rate were also improved in treatments with higher solids content after the bioleaching process.