Study On Function And Character Of Nitrifying Bacteria In Sewage Treatment Processes

In this paper, DGGE and Real-Time PCR methods are designed and optimized for study of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) communities in wastewater treatment process. Two kinds of methods can be used for analysis of communities' structure and population size for AOB and NOB, respectively. The nested PCR method and the primers based on 16SrDNA of Nitrospira and Nitrobacter groups are applied in DGGE experiment. Quantitative determination for cells density of Nitrobacter group is also developed in this paper. The results prove the availability of the upper methods in analysis of samples from wastewater treatment system. Certain region of special bacterial 16SrDNA can be successfully amplified for biodiversity and quantitative study in sludge and biofilm samples.The upper methods are utilized in study of several newly developed wastewater treatment process including aerobic granular sludge reactor, two-stage biofilter and integrated AmOn reactor, in which simultaneous nitrification and denitrification (SND) are all found.In the study of aerobic granular sludge, it can be successfully cultured in 40-60 days using the anaerobic granular sludge as seed sludge. The cultured aerobic granular sludge has the mean size of 1.9-2.3mm. Under the influent condition of synthetic and real wastewater, we study the influence of start-up process, carbon/nitrogen ratio, cycle length, operational temperature and air flow level on contaminations removal performance. Besides these, we also study the dissolved oxygen (DO) restriction in start-up process and compare the removal performance of aerobic granular sludge to that of activated sludge. The results show that SND performance is affected by upper operational conditions in different levels. The optimal conditions in this study including C/N=5/1-7/1, cycle length=4h, DO level=1.2-0.5mg/L, the higher(35℃ in this study) temperature also increase the SND performance. Under the optimal operational conditions, the removal rates of COD_Cr, NH₄⁺-N and TN are 75%, 76%, and 58%, respectively. Compared with traditional sludge, granular sludge has better SND performance because of the special structure and characters. A certainly high ammonia or DO restriction in start-up process can lead to stable nitrite accumulation, and denitrification can be achieved via nitrite. The adjustment of primary operational conditions should have relatively complex impact on nitrifying bacterial community structure and population size. Nitrosomonas genus is the dominant AOB in aerobic granular sludge, and Nitrospira group takes the dominant position in NOB community. Population size of Nitrobacter is an order less than that of Nitrospira. And in the adjustment of operational conditions, AOB and Nitrospira groups show obvious change, while Nitrobacter group can keep relatively stable.In the study of two-stage biofilter, SND can be achieved by DO restriction in first stage biofilter. The C/N ratio and air flow are studied in experiment with the influent of synthetic wastewater. The removal rates of CODEr, NH₄⁺-N and TN are 79%, 91%, and 76% under optimal C/N=5/1 and DO=1.6-0.8mg/L(in the first stage), respectively. Special nitrifying bacteria communities are revealed in two stages and obvious change can be found when DO level is higher than 1.6mg/L. In the first stage, AOB and NOB communities can keep stable within certain C/N region. The Nitrobacter group also shows higher stability than Nitrospira.In the study of AmOn process, we focus on the impact of packing ratio on primary contaminations removal and nitrifying bacteria community. The result shows that Nitrosomonas and Nitrospira groups are dominant bacteria AOB and NOB, respaectively. The change of packing ratio obviously affect dominant species in nitrifying bacteria community, and the Nitrospira seem to be more sensitive for the variety of packing ratio than AOB and Nitrobacter.We investigate the short-term and long-term impact of three metal ions Mn²⁺,Cu²⁺,Cr⁶⁺ on nitrification and nitrifying bacteria community in activated sludge, granular sludge and biofilm, respectively. Results reveal that different bio-solid has different sensitivity for short-term and long-term impact of upper three metal ions, it is found that activated sludge＞granular sludge＞biofilm, which means biofilm can reduce inhibition of metal ions in certain level. The biofilm and granular sludge have faster recovery than activated sludge after 24-hour inhibition of three metal ions. Different metal ions also show inhibition at different level, and it is found Cr⁶⁺＞Cu²⁺＞Mn²⁺ in this study. After long-term culture of Mn²⁺, inhibition level became to be weak. while heavier inhibition is found after long-term culture of Cu²⁺ and Cr⁶⁺. The biodiversity and population size of nitrifying bacteria community gradually decrease in the culture of high concentration of metal ions, and it is more obvious in activated sludge than in biofilm and granular sludge.To study the correlation between classical Monod model and characters of nitrifying bacteria, different kinds of samples collected from sewage treatment processes are investigated. Three constants of ammonia-oxidizing and nitrite-oxidizing processes are measured, including maxium specific substrate utilization rate, half-velocity constant and inhibition conatant of FA (Free Ammonia). In molecular microbial analysis, the dominant species and population size of AOB and NOB are investigated. Results prove the high positive correlation between maxium specific substrate utilization rate and cells density of functional bacteria for ammonia and nitrite oxidizing process even in complex environmental samples such as sludge and biofilm. It is revealed that dominant species affect the half-velocity constant and inhibition conatant of FA too, which indicates the certain inner relation between nitrifying bacteria community structure and two kinds of constants.