Exploration of sulfate reducing sludge granulation with real domestic sulfate-laden wastewater

Abstract

Extending sulfate reducing sludge granulation to real sulfate-laden wastewater was trialed in this study. Two types of reactors, namely sulfate reducing upflow sludge blanket (SRUSB) reactor and continuous stirred tank reactor (CSTR), were used for granulation. Sulfate-reducing granules were observed after 5 months' operation of stepwise hydraulic retention time (HRT) shortening, recirculation cycle adjustment, and air scouring in the SRUSB reactor. Comparatively, granular sludge was achieved in the CSTR after 6 months of cultivation with an average size of 220 μm. With the process of granulation, the HRTs of the two types of reactors were reduced to 2.2 and 2.8 h, respectively for the SRUSB and CSTR reactors. The abundance of sulfate-reducing bacteria (SRB) related genera reached 29.3 and 45% in the SRUSB and CSTR reactors, respectively. Incomplete organic oxidizing SRB were dominant in the CSTR and SRUSB is predominated by complete organic oxidizing SRB, which facilitated a higher organic loading rate. Considering the operating merits, the CSTR is preferable as a pretreatment unit (e.g., for acidification), while the SRUSB reactor can be used for maximum organics removal or sulfide production. Due to the high suspended solids in the influent, full granulation was not achieved by using real sulfate-laden wastewater, and fine particles accumulation in the reactor was also a concern particularly for the long-term operation.