Inhibiting NOB under alternating starvation by operating the PN1/PN2 system
In order to inhibit the growth and reproduction of nitrite oxidizing bacteria(NOB),a sequence batch reactor(SBR)(consisting of four groups of reactors R1～R4)was used to run the PN1/PN2 system,in which an alternating starvation/recovery strategy with an alternating 3 day period was used for 70 day operation.The dissolved oxygen concentrations in the starvation phase were set to(1±0.5),(2±0.5),(3±0.5)and(4±0.5)mg/L,respectively,and the selection of alternating cycles and effects of dissolved oxygen conditions on the activity,sludge concentration,particle size and extracellular polymer(EPS)of functional bacteria during the starvation period were evaluated to define the stable operation of the nitrification.The results show that,compared with ammonia oxidizing bacteria(AOB),NOB was more sensitive to starvation,the activity decay rate was higher,and the activity recovery rate of AOB was higher than that of NOB in the first days of the recovery period,so the 3 day alternating cycle could effectively inhibit NOB and retain AOB activity.The nitrous accumulation rate(NAR)of the four groups of reactors reached 73.36％,84.43％,91.21％and 95.97％,respectively,followed by sludge reduction,but the sludge concentration of R1～R3 could remain stable after a period of adaptation,while R4 showed a downward trend.The alternating starvation/recovery strategy allowed the system to gradually eliminate flocs with poor sedimentation performance,while the sludge with good sedimentation performance remained in the reactor,and the sludge particle sizes in the four reactors on the 70th day reached 190.69,197.56,207.69 and 153.56μm,respectively.Environmental changes stimulated microorganisms to secrete more EPS,so the EPS content of the sludge in the four groups of reactors increased at varying amplitudes.Evidently,the alternating starvation/recovery strategy can stimulate beneficial changes in sludge to achieve effective NOB inhibition and stable NO2-N accumulation.
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