| The unidirectional migration process of phosphorus from land to waterbody could lead to eutrophication of surface water like rivers, lakes and oceans. As the standard of wastewater discharge becoming stricter, phosphorus removal has become one of research focus in the field of wastewater treatment. Enhanced biological phosphorus removal(EBPR) is a cost-effective biological wastewater treatment technology, in which phosphorus accumulating organisms(PAOs) release phosphate under anaerobic condition and take up phosphate excessively under aerobic condition. Phosphorus is eventually removed through dischrging excess sludge. As the intermediate product of nitrogen removal, nitrite widely exists in municipal wastewater treatment plants performing biological nutrient removal(BNR). The latest metagenomic analysis of sludge subjected to EBPR found that no nar gene encoding respiratory nitrate reductase was identified in the Candidatus Accumulibacter whether it could utilize nitrate as electron acceptor, even though the genes responsible for nitrite reduction to nitrogen were detected. Additionly, nitrite and its protonated product-free nitrous acid(FNA) was found to inhibit the anabolic and catabolic process of PAOs. As a result, there is no agreement whether nitrite could be effectively utilized as electron acceptor as nitrate and oxygen. In this paper, three sequencing batch reactors were operated alternating anaerobic/oxic(An/O) and anaerobic/ Anaerobic/oxic(An/Ax/O) from started up period to a long run with O2, nitrate and nitrite as electron acceptor, respectively. Phosphorus uptake performance and its denitrification ability of different EBPR system were investigated. The variation of phosphorus uptake properties of the sludge acclimated to one ecletron acceptor for a long-term was also discussed.As an alternating An/O SBR was started up to perform EBPR and reached a steady state, the sludge was devided evenly and put into three reactors named R1(An/O), R2(An/Ax/O)and R3(An/the Ax/O), in which O2, nitrate and nitrite was used as electron acceptor,respectively. It was observed that R1 had the highest phosphorus removal performance and its phosphorus removal efficiency was above 94.87%. R2 took the second place. The averages phosphorus removal efficiency of R2 was 83.65%. However, the average phosphorus removal efficiency of R3 during stable stare was only 65.88% and the phosphorus uptake performance of this system deteriorated rapidly. By comparing the three systems, it was found that the specific phosphorus release rate of R1(7.67±0.62 mg/(gVSS·h)) was larger than that of R3(5.13±0.58 mg/(gVSS·h)) and R2(4.51±0.48 mg/(gVSS·h)). The specific phosphorus uptake rate of R1(8.29±0.62mg/(gVSS·h)) was found to be higher than that of R2(2.40± 0.20 mg/(gVSS·h)) and R3(2.21± 0.32 mg/(gVSS·h)). Besides, the denitrification ability of the sludge in the three EBPR, it was found that R1 could use only nitrate as electron acceptor for phosphorus uptake with low efficiency. As for nitrite, secondary phosphorus release was observed after nitrite addition. In R2, both nitrate and nitrite could be used as electron acceptor for phosphorus uptake phenomenon and the performance of nitrate system was superior to the system with nitrite. Nevertheless, R3 system showed an opposite result to R2 during the steaty operation. Based on the study mentioned above, the operating condition of the reactors was changed to determine the optimized operational performance of each system with different electron acceptor.Under the condition of low temperature(13~16℃), an alternating An/O SBR(R1) was started up and operated to investigate the phosphorus uptake property and its denitrification capability of the sludge under different DO concentrations.The results showed that under the condition of low temperature, the EBPR system could be started up successfully in the short-term(<6d). Low temperature had little impact on COD and phosphorus removal performance. DO concentration, however, could affect the stable operation of the EBPR. The system showed a high phosphorus removal performance when DO level in 2~1mg/L and 0.2~0.1mg/L(micro aerobis condition) and the removal efficiency was 99.8%~93.5% and 93.5%~91.0%, respectively. Interestingly, the phosphorus removal performance of the system deteriorated when DO level was in the range of 0.8~0.5 mg/L. In addition, the sludge was abled to use nitrate as electron acceptor in phosphorus uptake process with alow efficiency. Secondary phosphorus release was also observed after nitrite addition.Moreover, long-term operation under low DO favored sludge settling.Under the temperature of 21~23℃, an alternating An/Ax/O SBR(R2) was started up and operated to investigate the phosphorus uptake property and its denitrification capability of the sludge with long-term dosing NO3- as electron acceptor.The research showed that NO3--N concentration(<15mg/L) had no influence in the degradation of COD and NH4+-N.The total nitrogen loss rates were higher than 70%. Adding 5mg/L NO3--N to the system, due to insufficient of electron acceptor, the phosphorus removal performance deteriorated rapidly. Improved the dosing amount to 10mg/L, after nearly 30 days of recovery, the phosphorus removal rate up to 96.37%, the effluent phosphorus concentration was lower than 0.5mg/L. Further improved dosing quantity to 15mg/L, the accumulation NOx--N in system made phosphorus removal rate dropped to 60%. Before and after added the NO3- domestication, the system priority to nitrate as electron acceptor, the anoxic phosphorus uptake capacity of nitrate type and nitrite type are improved.And after domestication nitrate and nitrite type anoxic phosphorus uptake capacity was increased by 2.64 and 2.45 times, respectively, suggesting long-term dosing NO3--N was advantageous to enriching denitrifying polyphosphate accumulating organisms utilizing nitrate as electron acceptor. Moreover, the system with NO3- long-term acclimation favored sludge settling.Under the condition of 21~23℃, an alternating An/O SBR(R3) was started up, and employed to investigate the long-term inhibitory effect of FNA on aerobic phosphorus uptake performance and variation of phosphorus uptake properties of the sludge by adding nitrite.An aerobic EBPR system under long-term inhibitory effect of FNA was employed to investigate the aerobic phosphorus uptake performance and variation of phosphorus uptake properties of the sludge by adding nitrite. The results showed that FNA had no impact on phosphate release and uptake capacities of the sludge. The specific phosphate release/uptake rates, however, was found to be higher. As FNA concentration was lower than 0.53×10-3mg HNO2-N/L, phosphorus removal efficiency of the system was higher than 96.9%. Increasing FNA concentration to 0.99×10-3mgHNO2-N/L, 1.46×10-3mgHNO2-N/L and 1.94×10-3mg HNO2-N/L, phosphorus removal performance deteriorated rapidly. After 50, 12 and 30 days, phosphorus removal efficiency was recovered to 64.42%, 67.33% and 44.14%, respectively, which implied the deterioration of phosphorus removal performance caused by FNA inhibition could be recovered and long-term acclimation could shorten the recovery process. Notably, increasing nitrite consumption appeared during aerobic phase with the concentration of FNA when FNA less than 1.46×10-3mgHNO2-N/L. It was also observed that the phosphorus uptake properties of the sludge varied after long-term inhibition. Nitrate and nitrite type anoxic phosphorus uptake capacity was increased by 3.35 and 3.86 times, respectively, suggesting long-term dosing FNA was advantageous to enriching denitrifying polyphosphate accumulating organisms utilizing nitrite as electron acceptor. Moreover, long-term acclimation favored sludge settling. |
PDF Full Text Request