Disintegration of waste activated sludge via Thermo-Chemical Pre-Treatment.

Abstract

The rate limiting step in the digestion of the waste active sludge is hydrolysis the stage. Thermal pre-treatment and chemical sludge disintegration methods can be used to shorten the biochemical hydrolysis process and increase the digester capacity. In this study, the disintegration of waste activated sludge via thermal pre-treatment, chemical oxidation using potassium permanganate and thermo-chemical disintegration method (which is a simultaneous combination of thermal pre-treatment and chemical oxidation) was investigated. Optimizations of these methods were carried out depend on the increases in chemical oxidation demand, carbohydrate and protein concentrations in the dissolved phase. In addition, biochemical methan production tests were performed under the optimized conditions in order to determine the influences of these methods on biogas production. On the other hand, the change in dewaterability of waste sludge was investigated by parameters of turbidity and capillary suction time (CST). As a result, the optimum temperature for thermal pre-treatment is 100 °C and the optimum concentration for chemical oxidation with KMnO4 is 1000 mg l-1 ; the optimum conditions for the thermochemical pre-treatment method were determined to be a concentration of 250 mg l -1 potassium permanganate and a temperature of 100 °C. In these conditions, the thermo-chemical pre-treatment was found to increase biogas production by 38% and methane production by 34% compared to anaerobic digestion of the raw (unpre-treated) sludge. As a result, thermo-chemical pre-treatment has been found to solubilize the sludge more efficiently and to improve the anaerobic digestion of sludge even at lower chemical doses compared to chemical oxidation method.