In this study, two lab-scale UASB reactors were established to testify S-0 recovery efficiency, and one of which (M-UASB) was improved from the previous T-UASB by shortening reactor height once S-2 over oxidation was observed. After the height was shortened from 60 to 30 cm, S-0 recovery rate was improved from 7.4% to 78.8%, and while, complete removal of acetate, nitrate and S-2 was simultaneously maintained. Meanwhile, bacterial community distribution was homogenous throughout the reactor, with denitrifying sulfide oxidization bacteria predominant, such as Thauera and Azoarcus spp., indicating the optimized condition for S-0 recovery. The effective control of working height/volume in reactors plays important roles for the efficient regulation of S-0 recovery during DSR process. (C) 2015 Elsevier Ltd. All rights reserved.