Effect of peracetic acid disintegration on the acceleration of hydrolysis process

Excess sludge is difficult to be processed and it is hydrolytically degraded under both anaerobic and aerobic conditions, since a high proportion of the sludge comprise living micro-organisms. The key phenomenon that occurs during the process of disintegration of sewage sludge is destruction of cell walls in micro-organisms caused by physical, chemical or biological factors. Consequently, sludge is fragmented and some intracellular components are released into the surrounding liquid. In order to determine the best parameters of acid disintegration of excess sludge, the study examined the effectiveness of oxidizing treatment with peracetic acid. STERIDIAL W 15 solution, which is a mixture of PAA (15%), hydrogen peroxide (10%), acetic acid (36%) and water (39%) was used in the study. Pre-treatment in the ambient temperature prior to the period of 1 and 24 h was conducted. The doses of peracetic acid of 0.1-5 mL of STERIDIAL/L of excess sludge were used (as for the organic dry matter content corresponds to the about 0.01-0.66 mL of STERIDIAL/g dm(org).). The volatile fatty acid and COD levels obtained after acid pre-treatment of excess sludge were corrected by taking into account the value of those parameters originating during the PAA hydrolysis in the water surrounding. For non-pre-treatment and undergoing chemical modifications of the sludge, the organic dry matter content was 7.56 g/dm(3). In the case of non-pre-treatment sludge, the value of volatile fatty acids 51 mg CH3COOH/L was recorded. During the chemical disintegration lasting 24 h, volatile fatty acids content of 171 mg CH3COOH/L and 5734 mg CH3COOH/L was obtained, respectively, for the low dose i.e. 0.1 mL of STERIDIAL/L of sludge and the highest dose i.e. 5mL of STERIDIAL/L of sludge. The value of chemical oxygen demand (COD) for non-pre-treatment and chemically conditioned sludge after using the above doses amounted, respectively, to 102, 222 and 5432 mg O-2/L. The content of volatile fatty acids correlated with the observed level of COD.