Rheological Characteristics Of The Activated Sludge In A Multi-habitat Membrane Bioreactor

Membrane bioreactor was a new-style and highly effective wastewater treatment system which was an. organic combination of activated sludge biological process and membrane separation technology. And this system had advantages including good water quality, high organic loading, less output of excess sludge, etc. The starting point of this research was building a multi-habitat membrane bioreactor (MHMBR), attempting to achieve a environment of the coexistence of multi-habitat. The multi-habitat membrane bioreactor not only had the advantages of traditional MBR, but also had a variety of habitats of oxic environment, anoxic-anaerobic environment and transition environment between the oxic environment and anoxic-anaerobic environment. Thus the richer microbial community diversity was, the stronger system’s stability and ability to remove pollution were. Then the reactor could possess good performance with smaller footprint and less power consumption.In this test, a self-designed multi-habitat membrane bioreactor was used as experimental device, this experimentation used a programmable logic controller (PLC) to control the inflow and outflow of MHMBR system automatically. The reactor was continuously operated for 105 days without discharging any sludge, which generated a large range of the sludge concentration from the initial 3200 mg·L-1 to the final 12500 mg·L-1. Three dissolved oxygen meters were installed in oxic (O) zone, anoixc (A) zone and transition (T) zone for the track in real time during the operation. The monitoring results showed that the DO of A area was less than 0.2 mg·L-1. This meant that the coexistence of oxic condition and anoxic condition, the MHMBR was built successfully.In the experimentation, routine quality indices were measured everyday, and the results showed that the COD removal ratio exceeded 90%. As time goes on, the removal rate of NH4+-N increased and the largest removal rate could be over 99.9%. However, the removal rate of TP did not rise but lower, this was because the assimilation of TP was limited. The content of EPS was measured which was combined with transfer membrane pressure (TMP) to analysis the membrane fouling. The results showed that the change trend of TMP were showed two periodic law which were the early stage of the slow growth and the late stage of accelerated increasing during the entire operation. The dynamic and limiting viscosities of the sludge samples as well as the viscosity of supernatant were measured simultaneously at ambient temperature during the whole operation. It was revealed that a decrease of the sludge viscosity existed with the increasing of the shear rate, which lived up to a shear-thinning property and an obvious non-Newtonian fluid’s characteristics. The limiting viscosity was positively related to the concentration of MLSS and EPS. Furthermore, the rheological model was also studied and the results showed that the rheological properties was accorded well with the Bingham model under lower sludge concentrations (<8000 mg·L-1); On the other hand, under a higher sludge concentration (>8000 mg·L-1), it’s better agreement with the Ostwald de Vaele model.