Improvement of sewage sludge dewaterability by bioleaching in a continuous plug flow bioreactor: optimization of process parameters

A novel process for sewage sludge bioleaching by mixed Thiobacilli (Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans) using a 12-stage, 180 L working volume continuous plug-flow bioreactor, is presented. The objective of the present study was to assess the impact of some parameters on the sludge dewaterability and to improve the sludge dewaterability by optimization of these parameters. The parameters examined were sludge moisture content, nutrients dosage, aeration rate, and the number of reactors. The order of the influence of these factors on sludge dewaterability was found to be sludge moisture content > nutrients dosage > aeration rate > number of reactors. The optimized conditions were: sludge moisture content, 98.0%, nutrients dosage, 9 g/L, aeration rate, 8 m(3)/h, and 10 reactors. Confirmation experiments conducted under optimum conditions demonstrate the sludge dewaterability to be remarkably improved. After 2 days of bioleaching, the moisture of bioleached sludge cake was reduced to below 60%.