Pilot Study On The Enhancement Of Ammonia Oxidizing Bacteria To The Post-denitrification Biofilter For Tertiary Treatment Of Municipal Sewage

With the rapid development of economy and urbanization, the contradiction between water supply and demand becomes more serious. Therefore, further exploit municipal sewage and realize resources recycling are of great important to the security of water supply and the sustainable utilization of environment resources. Recently, the technology of biological aerated filter (BAF) has been wildly applied in wastewater treatment. However, as the tertiary treatment unit of municipal sewage, BAF shows the characteristics of slow growth rate of nitrifying bacteria, and unstable performance of nitrogen removal. Since biological enhancement technology could achieve the goals including to rapid increase bacteria amount and improve the removal efficiency of the target pollutants by introducing the dominant microbe with special functions to systems, it is of great significance and application value to study and adopt biological enhancement technology to improve the performance of BAF for treating municipal sewage with low substrate concentration.According to the actual characteristics of the effluent of Jinan wastewater treatment plant, this paper adopted oxic/anoxic BAF process (O/A BAF) to conduct tertiary treatment of municipal sewage. The dominant ammonia oxidizing bacteria (AOB) isolated from activated sludge and the rizhosphere of Nansi lake wetland plant were employed to enhance the performance of O/A BAF. The variation characteristic of O/A BAF performance before and after enhancement, as well as the effects of operation conditions on the enhanced O/A BAF performance was studied. On the basis of paying attention to the actual engineering application, the feasibility of adopting dominant AOB to enhance the performance of nitrification and denitrification of O/A BAF was elaborated theoretically. Finally, the effluent of O/A BAF was further decolorized by ozone, and the operation parameters of ozone process were discussed. The main works of this study were as follows:1. The operation character of O/A BAF before biological enhancement was studied, which includes the method of culture and startup, and the nitrification and denitrificaiton performance of O/A BAF under the conditions of low aeration rate.(1) On the basis of aeration, liquid recirculation was added to each filter. Nitrifying biofilter was cultivated at low aeration rate condition (0.3m3/h). After 25 days, O/A BAF achieved startup. This time, the maximum nitrite accumulation rate of nitrifying biofilter reached 60%, the highest removal rate of total nitrogen of denitrifying biofilter at the dosage of 20mg/L for methanol was 30%.(2) For the influent ammonia loadings of 0.04-0.26kgNH4-N/m3·-day and organic loadings of 0.21-0.65kgCOD/m3·day, it's possible to maintain the performance of partial nitrification and denitrification of O/A BAF by operating nitrifying bio-filter at low aeration rate level. When the aeration rate was 0.4m3/h, nitrifying biofilter achieved the maximum nitrite accumulation rate of 66.9%. In this case, the corresponding dissolved oxygen concentration and ammonia removal efficiency of nitrifying biofilter was 1.5 mg/L and 37.2%, respectively.(3) Nitrifying biofilter showed the characteristics of simultaneous nitrification and denitrification (SND) at the low aeration rates (0.3-0.5m3/h). The performance of denitrifying filter on the removal of total nitrogen (TN) was mainly related with the concentration of nitrogen oxide (NOx) and the dosage of methanol. For the effluent of nitrifying biofilter at aeration rate of 0.4m3/h, as the dosage of methanol was 20mg/L, the average concentration of TN in the effluent of denitrifying biofilter was 14.1 mg/L This could meet the requirement of landscape and environmental water quality standards (GB/T 18921-2002). Despite of it, the concentration of TN in the effluent of denitrifying biofilter was unstable, it was out of limits sometimes.2. The isolation, selection, and performance study of dominant AOB(1) Four strains of dominant AOB were isolated from activated sludge and the rizhosphere of Nansi lake wetland plants, which including one strains of Arundo donax (YL-1), one strains of Herb of rice galingale (YS-2),and 2 strains of activated sludge (YH-1, YH-2). The results of Glanz staining of four dominant AOB strains all show negative. By the observation of transmission electron microscopy (TEM), it can be determined that, the strains of YL-1, YS-2, YH-1 and YH-2 was coccoid, brevibacterium, spirillum and bacillus, respectively. (2) Four dominant AOB strains all showed excellent ammonia removal performance under the conditions of high pH value (8.5) and free ammonia concentrations (18.2 mg/L). Despite of it, their performance on the removal of high ammonia loading was limited by the concentration of oxygen.3. Micro-flora constituted by the four dominant AOB strains was added to the nitrifying filter which operated at aeration rate of 0.4m3/h,, and the effects of micro-flora on the nitrification and de-nitrification of O/A BAF was studied emphasizely(1) The amount of AOB in nitrifying filter increased rapidly after the micro-flora being added.(2) The introduction of micro-flora improved ammonia removal efficiencies and nitrite accumulation rate of nitrifying biofilter at the low aeration rate of 0.4m3/h. The improvement of nitrification performance of nitrifying filter enhanced the denitrifying efficiency of O/A BAF simultaneously.(3) As the inflow rate was 2.0 m3/h, aeration rate was 0.4m3/h, and the dosage of methanol to denitrifying biofilter was 20 mg/L, corresponding to the 26.5% increase of AOB amount in nitrifying biofilter, the ammonia remove efficiency and nitrite accumulation rate of nitrifying biofilter increased by 12.1% and 13.3%, respectively, and the TN removal efficiency of the O/A BAF increased by 9.2%. The concentration of TN in the effluent of O/A BAF process was 11.9 mg/L, which could meet the requirement of landscape and environmental water quality standards (GB/T 18921-2002).4. The effects of aeration rate, methanol dosage and temperature on the nitrification and denitrification performance of enhanced O/A BAF.(1) After the biological enhancement, the ammonia remove efficiency of nitrifying biofilter improved significantly with the rise of aeration rate, while its partial nitrification performance was undermined. As aeration rate was 0.6m3/h, there was local partial nitrification occurred in nitrifying biofilter, nevertheless, as aeration rate being raised to 1.0m3/h, the accumulation of nitrite disappeared in nitrifying biofilter. The increase of aeration rate could improve not only the efficiency but also the stability of ammonia removal of nitrifying biofilter.(2) As the dosage of methanol was limit, the increase of aeration rate in nitrifying biofilter inhibit the TN removal performance of denitrifying biofilter. For the inflow rate of 2,0m3/h, as the dosage of methanol was 20 mg/L, satisfactory removal efficiencies of both ammonia and TN could be achieved by O/A BAF simultaneously when the aeration rate of nitrifying biofilter was controlled at 1.0m3/h. In this case, the concentrations of ammonia and TN in the final effluent of O/A BAF were 0.79 mg/L and 13.2 mg/L, respectively. This could meet the requirement of landscape and environmental water quality standards (GB/T 18921-2002) completely.(3) The buildup of aeration intensity changed the space distribution of AOB between attached biofilm and suspended biosolids in nitrifying biofilter, and induced much more AOB to grow on attached biofilm. The special structure and complicated food chain of attached bio-film could protect AOB from being washout by backwash or predated by predator, and ensure their stable growth rate. This is also the main reason why the stability of nitrification performance of nitrifying biofilter improved with the rise of aeration rate.(4) Biological enhancement improved the shock resistance capacity of O/A BAF to the low temperature. The operation results of winter showed that, as the inflow rate was 2.0m3/h, aeration rate was 1.0m3/h and methanol dosage was 20mg/L, for the lowest temperature conditions (water temperature 6.4-11.9℃), the concentration of ammonia and TN in the effluent of O/A BAF was 4.4 mg/L and 13.8 mg/L, respectively. These concentrations could meet the requirement of landscape and environmental water quality standards (GB/T 18921-2002).5. The decolorization effects of ozone on the effluent of O/A BAF(1) As the dosage of ozone was 2.0mg/L, and the contact time between gas and liquid was 18 min, about 10-18 folds of chroma in the final effluent of O/A BAF could be reduced to smaller than one fold. This could meet the requirement of landscape and environmental water quality standards (GB/T 18921-2002).( chroma<30 folds).(2) Ozone also showed a certain removal performance of organic substance and ammonia to the effluent of O/A BAF when carried out the decolorization.The main innovation of the study was as follows:1. Aimed at the characteristics of poor organic substrate and low C/N ratio to the secondary effluent of municipal sewage, biological enhancement technology was introduced to O/A BAF for tertiary treatment of municipal sewage. This technology resolved the problems of O/A BAF about slow growth rate of nitrifying bacteria and unstable performance of TN removal aroused from the poor substrate conditions, and ensure the final effluent of O/A BAFs meet the requirement of landscape and environmental water quality standards (GB/T 18921-2002).This work provided a new process pattern for the application of BAF technology in wastewater treatment.2. Proposed a new culture method that aeration and liquid recirculation carried out simultaneously in a single reactor. This method could not only save the extra-designed sludge tank in traditional recalculating culture method, but also resolved the problem of sludge deposition in the aeration culture method. This method provided a new technical approach to the anoxic and facultative aerobic biofiltration process for achieve rapid culture and start.3. Selected and cultivated dominant AOB to increase the activity and quantity of AOB on attached biofilm, and thus enhance the removal of total nitrogen, Elucidated the mechanism of dominant AOB to the nitrification and denitrification performance of O/A BAF.4. By compared the growth properties and space distribution character of AOB on attached bio-film and suspended bio-solids, the affecting mechanism of aeration on nitrification performance of enhanced O/A BAF was revealed from the perspective of microbiology.