| A novel micro-pressure swirl bioreactor, named as MPR, was designed for domestic wastewater treatment. MPR has a newly internal structure to form a swirl by aerating at the right bottom, and conveniently to prolong the bubble residence time and then to improve the dissolved oxygen transfer efficiency. Driving by the swirl, an external aerobic zone and a core anoxic zone were created to intensify the nitrification-denitrification process in MPR. Therefore, a series of experiments, such as the swirl’s fow velocity isoclines, the aeration’s energy-saving, the denitrification process and so on, were carried on to treat high-concentration organic wastewater and domestic wastewater at room termperature or psychrophilic condition. The results were presented as followed:(1)To study the effect of the swirl in MPR, the flow velocity, the dissolved oxygen concentration and the sludge density were also investigated by using an electronic velocity meter and the particle tracing algorithm. The result showes that the flow velocity increased from the core(below 3 mm/s) to the outside(reached 36 mm/s) and the dissolved oxygen concentration possessed a similar core-outside increase at the range of 0.05-2.02 mg/L. while the sludge density decreased from the inner and got a high difference of 400 mg/L.(2) Under the sequence batch process, domestic wastewater was treated by MPR comparing with a conventional stirred-tank reactor(named as SBR). The results show that higher denitrification efficiency and orgainic matter removal rate was observed in MPR. Espercially, in a running cycle, up to 90 % of organic matter was removed in 4.5 hours in MPR, while required 6 hours in SBR. So MPR has the advantage to simultaneous remove organic matter and total nitrogen and to shorten aeration time for the energy-saving.(3) The shock resistance of wastewater water on MPR was further investigated. It can be found that higher than 91 % of organic matter removal rate was emerged in MPR, and the COD of the effluent was in the range of 24.9-99.7 mg/L while at 713.5-2979.1 mg/L in the influent(equaivalent to the organic load between 0.4 and 1.8 kgCODCr/(m3·d)). At the process, the total nitrogen removal rate was higher to 92.45 % and the total nitrogen concentration was lower to 14.3 mg/L in the effluent while at 106.3-215.1 mg/L in the influent. This indicated that MPR has well shock resistance and fine denitrification effect under high organic load.(4) A 120-days contiuous treatment experiment of domestic wastewater in MPR was also studied at room temperature. It’s clear that stable treatment efficency of wastewater was obtained in MPR and the COD of effluent was not high than 50.2 mg/L(meet the class one of the national discharging standard), althought the COD reached 556.2 mg/L in the influent.(5) A same continuous experiment was also performed at psychrophilic condition. It’s interesting that MPR started successfully at 15 oC and displayed a well ammonia oxidation effect and organic matter removal efficiency. The COD of the effluent was under 43.3 mg/L, while it remained at 60.2-450.1 mg/L in the influent(equivalent to the organic load at the range of 0.18-1.24 kgCODCr/(m3·d)). By using a gently cool down culture method, many anoxic biomass profirated at anoxic zone of MPR to enhance the denitrification of nitrate, and then the total nitrogen concentration in effluent was decreased below 15 mg/L when operated at 3-9 oC. Using start-up of MPR at 15 oC as reference, the restart-up at 5 oC was completely successful after stopping 16 days by the power lack. Moreover, the restart-up enhance the denitrification process to acquire an outstanding total nitrogen removal rate of 76.2 % besides to get a high organic matter removal. At ultralow temperature of 3 oC, MPR also presented a stable operating condition and the removal rate of the organic matter and the total nitrogen reached 94.1 % and 85 % respectively, although adding with exogenous nitrate.(6) Microflora in MPR running at psychrophilic was anlysized by the PCR-DGGE fingerprint atlas technique. The results show that bacterium in active sludge was sensitive to the temperature difference. Many mesophilic bacteria were expired to decrease the MLSS, while psychrophilic microorganism greadually proliferated and got the predominal position in active sludge to metabolize organic matter and ammonia. In addition, MPR has a special plate to create a swirl under the side aeration. As described above, the swirl also generated an external aerobic zone to culture heterotrophic bacteria for ammonia oxidation, and an internal anoxic zone to grow facultative bacteria for denitrification. Therefore, numerous anoxic biomasses well proficated in MPR and then enhanced the nitrate reduction. However, the restart-up of MPR at 5 oC obviously accelerated the anoxic biomass profiliration, which indicated the incubation of anoxic active sludge benefiting the detrification process at the start-up stage. |
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