Efficient application of pretreatment for enhanced anaerobic digestion of sewage sludge

Abstract

The significant increase of sewage sludge generation from WWTP and prohibition of ocean dumping since 2012 make anaerobic digestion more important as a stabilization and reduction process. However, slow and incomplete degradation of sewage sludge induced by its rigid structure has been considered as major problems of anaerobic digestion of sewage sludge. In order to solve those problems, various pretreatment has been introduced before anaerobic digestion process. Therefore, this study was conducted to figure out effect of various pretreatment methods such as thermal, ultrasound, microwave and alkaline on sludge solubilization and its correlation with methane production. During the experiment, combined pretreatment was also carried out to check whether it has advantages against single pretreatment with same energy input. Furthermore, combining of advantages of UASB and combined pretreatment was suggested to make anaerobic digestion with sludge efficient and economic. Firstly, performance of various pretreatment methods was evaluated by measuring solubilization improvement indicating acceleration of anaerobic process and increase of methane production. In case of single pretreatment, ultrasonication showed the highest increment of solubilization among 5 different pretreatments. On the other hand, addition of more than 5 g/l of KOH seemed like waste due to no further solubilization increase. In case of combined pretreatment, 3 different combined pretreatments were employed to compare their performance. Alkaline treatment carried out as a base treatment then, thermal, ultrasound and microwave pretreatment was followed with the same operating condition at each single pretreatment. From the certain combinations, positive value named as synergistic effect or negative value caused by re-flocculation of sludge was took place. Maximum positive value around 15% was obtained from combination of alkaline with thermal pretreatment, while highest negative value occurred fr...