| In biology N and P removal system, organics(COD/BOD) not only act as electron donor but also carrier in the form of rich-phosphorus sludge by assimilation. Therefore, organics come to be an important carbon-resource to guaranty the efficiency of N and P removal. In the low carbon-resource sewage treatment system, it is a problem to enhance the utilization efficiency of organics.According to the traditional biology N and P removal theory, the carbon consumptions during N and P removal are analysis. It is concluded that the carbon consume to removal unit N is 6.1 times of that to removal unit P, and change the way of P removal will benefit to develop a low carbon-resource sewage treatment technology. Base on the analysis of the N and P removal technologies, it was found that the low DO strategy could reduce the invalid oxide; Denitrifying phosphorus removal bacteria could eliminate the carbon competition and SRT contradiction between the PAOs and DPAOs; Carbon source conversion of the excess sludge could make-up the carbon lack of system. Meantime, the sidestream phosphorus removal technology could eliminate the dependence of phosphorus removal effect on the amount of excess sludge. Base on the above analysis, a low carbon consumption sewage disposal system consist of denitrifying phosphorus removal, the sidestream phosphorus removal technology, low DO strategy and carbon source conversion of the excess sludge was design and studied. The main contents include: characteristics of denitrifying phosphorus removal with low carbon source sewage, carbon source conversion characteristics of excess sludge, and the influence of DO on the phosphorus and nitrogen removal effect. The phosphorus and nitrogen removal efficiency of LCS-SDS. It can obtained some consultation that:1) The study on the feature of denitrifying phosphorus removal with low-carbon source sewage shown that: LCS-SDS could take full use of the PHB in P-release sludge and the residual NO3--N of last period, enhance the denitrifying phosphorus removal. It could reduce the NO3--N in subsequent anaerobic phase, the phosphorus concentration were 5.8mg/L and 1.1 mg/L in the end of anaerobic and aerobic which meat that there were a clear phenomenon of anaerobic P-release and aerobic P-uptake. This thermodynamic analysis of denitrifying phosphorus removal by microcalorimetry shows that when acetic acid was the carbon source, heats liberated in the denitrifying phosphorus removal system was 2 times the heat of traditional phosphorus removal system. It illustrated that the majority of the carbon source of sewage in DPR were released as heat which led to the lower sludge yield of denitrifying phosphorus removal bacteria under anaerobic/anoxic compared to that of PAOs under anaerobic/aerobic. Further study showed that the denitrifying phosphorus removal system has higher anoxic release heat, less energy for phosphorus absorption, lower anaerobic synthesis of PHB with too low or too high of SRT of the system, the optimal SRT was 32 d. But, the optimal SRT was 20d~25d from the perspective of nitrogen and phosphorus removal efficiency. Therefore, denitrifying phosphorus bacteria could not be effectively enriched in the biology phosphorus removal system with excluding excess sludge, especially when the influent was lack of carbon source. SRT contradiction between the PAOs and DPAOs would become more prominent.2) The affect factors test showed that the NO3--N concentration experiment shows that the efficiency of denitrifying phosphorus removal mainly depend on the NO3--N concentration in anoxic phase and the PHB in the cell. Prolonged anoxic could not improve the effect of denitrifying phosphorus removal. The experiment also found that the SRT has no significant effect on denitrifying phosphorus removal, too low or too high of SRT of the system will reduce the removal efficiency.3) According to the DO influence test that the optimal DO of LCS-SDS system was 0.21mg/L, the COD, NH4+-N, TN, TP in effluent could achieve a stable standard under this condition, wherein the NH4+-N average concentration was only 0.3mg/L and the removal rate reached 98.6%, which meat that the nitrification would not be inhibited significantly. Further experiment showed that DO would impact on the diversity of nitrogen removal ways, the denitrifying phosphorus removal in anoxic phase would disappear when the DO was 0.1mg/L. There was maximum carbon source utilization when DO was 0.21mg/L, the carbon source consumption of SND accounted for 58% of total carbon source consumption in aerobic phase, much larger than the other two. When the average aerobic DO concentration was 0.21 mg/L, there were three denitrifying ways, denitrifying phosphorus removal(15%), anoxic denitrifying(70%) and SND(15%), it was optimal condition for the N and P removal. It could reduce the carbon source consumption about 27.4 mg/L during the N and P removal process compared to the ERP-SBR.4) A batch experiment results showed that inoculating anaerobic fermentable sludge could improve the production of VFAs though it has no apparent effect on excess sludge reduction. VS degradation rate is proportional to the ratio of excess sludge dose. The system had high VFAs concentration which could reach 600mg/L and VFAs conversion about 24% with 60%-80% of excess sludge dose ratio at fermentation 5d or 25 d. The optimal excess sludge dose range was 4.0-5.5 g/d while the sludge loading rate(Nfs) was 0.048-0.053 g excess sludge /(g MLSS?d) under the operation mode of succession dose. The VFAs conversion rate was high(6.5%) after the system was stable. Moreover, the VFAs concentration and VFAs/COD ratio were 430mg/L and 40%, respectively that were both high than other sludge dose level. It was optimal condition for the operation mode of succession dose.5) The phosphorus release pool still got stable phosphorus release effect when the carbon source fermented(SCOD and VFAs were 1690mg/L and 295mg/L, respectively) from excess sludge was used as carbon source for phosphorus release, the average phosphorus release amount reached 42.0 mg/L. In addition, it would not affect the diversity of denitrifying ways and improve the denitrifying phosphorus removal in pre-anoxic compared to the system that used Na Ac as carbon source for phosphorus release. It would not impact on the N and P removal efficiency significantly, although the carbon source fermented from excess sludge would increase the N and P concentration in the supernatant in phosphorus release pool. It was feasible that used fermentation supernatant from excess sludge as carbon source.6) The LCS-SDS system was running well when the average C/N(BOD/TN) and C/P(BOD/TP) ratio was 2.6 and 14.3, respectively, the DO concentration in aerobic phase was 0.21 mg/L, SRT was 40 d and sludge circulation ratio was 10%, the quality of effluent could achieve the A standard in《Discharge standard of pollutants for municipal wastewater treatment plant》 stability. Further analysis showed that the phosphorus removal efficiency could meet the requirements of effluent with 8% sludge circulation ratio.7)The PCR- DGGE technique analysis indicates that the LCS- SDS systems was helpful to the reproductive growth of DPAOs, but would inhibit the growth of PAOs(Acinetobacter sp.) and GAOs(Rhizobiales bacterium). According to the calculation of Biolog analysis, the functional diversity index showed that the biodiversity of system did not change while the main dominant bacteria shifted compared to the inoculation sludge, this is similar to the results of PCR- DGGE. It illustrated that the LCS-SDS system could enhance the ability of denitrifying phosphorus removal and have a diversity ways of N and P removal. Three denitrifying phosphorus strains were isolated from the LCS-SDS, and were identified as Klebsiella pneumoniae strains13#,Ralstonia pickettii strain15#,Acinetobacter junii strain17#, respectively. The 13# was considered as the efficient DPAOs for treating low carbon source sewage. Furthermore, 13# and 15# were capable of denitrification under aerobic condition. |
PDF Full Text Request