A comprehensive insight into the combined effects of enzymatic and freeze thawing on the dewatering performance of activated sludge

Abstract

In this study, the effect of enzymatic (lysozyme) and physical (freeze-thaw) methods alone or in combination conditioning on the sludge dewatering performance were comparatively investigated. After the optimization of the dewatering conditions using response surface methodology (RSM), the joint conditioning achieved the water content (W) of the dewatered sludge of 52.01% at the lysozyme (LZM) dosage of 5.9 × 106 Ug−1 DS, the freezing temperature of -26.56°C and the freezing time of 5.78 h. The variance analysis further demonstrated that LZM dosage and the freezing temperature showed significant interaction. Moreover, the improved dewatering performance was mainly attributed to the destruction of the microbial cell wall and extracellular polymeric substance (EPS) structure by enzymatic conditioning, as well as the larger particle size and compact sludge floc structure due to the freeze-thaw conditioning. It followed by the bound water content of sludge decreased from 7.31 gg−1 DS to 3.84 gg−1 DS, which was beneficial for the enhancement in sludge dewaterability. Therefore, the sludge dewaterability was remarkably improved after LZM in combination with freeze-thaw conditioning.