Simple improvement of digested sludge quality: is postaeration the key?

Postaeration, where digested sludge is introduced into aerobic conditions, is a technology that could improve the quality of sludge and sludge liquor in many ways. Although it is a fairly simple process, only few data about the effect of postaeration have been published. In this study, batch experiments have been performed first, indicating that postaeration affects the total ammonia nitrogen (TAN) and sludge dewaterability. In the removal of TAN, both stripping and biological oxidation can play an important role depending on specific condition. Then the postaeration was investigated in a semicontinuous batch reactor. In addition, the effect of postaeration on the concentration of selected micropollutants such as pharmaceuticals, EOX and AOX was studied. The hydraulic retention time (HRT) of 8, 6, 4 and 2 days and different aeration intensities were tested. The TAN removal efficiency achieved was about 40-60%, sludge dewaterability expressed by sludge cake total solids (TS) concentration after dewatering improved relatively by 5-30%. In addition, TS degradation is also taking place and therefore the reduction of the amount of final sludge to be disposed could be even higher. The biggest changes in observed parameters were recorded at the longest HRT.