Aerobic Granulation In Small-Scale Oxidation Ditch Reactor

Compared with conventional activated sludge system, with advantages of strong and compact microbial structure, improved stability and higher biomass activity and strong ability to withstand shock loading, aerobic granular sludge has become a hotspot in the field of sewage treatment in both domestic and abroad. Presently, aerobic granular sludge has been mainly successfully cultured in the sequencing batch reactors (SBR). The most of the sewage treatment plants use continuous-flow process, so it is significant to research on aerobic granulation in the continuous-flow reactor.This study cultivated the aerobic granular sludge in the integrated continuous-flow oxidation ditch system to treat real urban sewage on-site. On the basis of controlling the inlet wastewater load, aeration quantity and stirring rate, an adjustable sedimentation tank for controlling settling time made various selection pressure. The high-quality aerobic granular sludge was formed. Comparing this granular sludge with the granules from SBR, the forming process, property and pollutant treatment effect were analysed.Aerobic granular sludge in the integrated oxidation ditch operated steadily120days. The SVI was up to44mL/g and granule was mainly between0.3and0.6mm in diameter. Great removal efficiency on both NH4+-N and BOD5. The morphology of sludge in the reactor and lower effulent SS showed that adjustable sedimentation tank could control separation of granule and floe. Compared with SBR reactor, granulation occurred later, a little lower in settling velocity in the oxidation ditch reactor, SEM images showed that the surface of the sludge was consistent but not smooth structure due to a blocky structure. The results of DGGE indicated that the microorganism community of sludge in the oxidation ditch reactor was similar to the sludge in SBR, but still had some differences. The XRF and XRD results revealed that there were abundant Fe, Si and Ca in the sludge, which could play a role in promoting the rapid formation of aerobic granulation as crystal nuclei.