| Petrochemical, pharmacal and tanning processes can produce large amount of high concentration ammonia wastewaters which is beyond 1000 mg/L, and in some specific units of processes, the concentration is even beyond 10000 mg/L. Untreated high-ammonia wastewater will have significant impact on receiving water bodies when discharged directly. Biological nitrification-denitrification technique has been applied widely because of its high efficiency, high stability and low cost. However, both nitrifying microorganisms, ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB), are autotrophic microorganisms, which are slow growth and sensitive to environmental factors. In practical industrial high-ammonia wastewaters, there also contain large amount of saline ions (Cl-, Na+, etc.) and a certain concentration range of COD, which will inhibit the activity of nitrifying functional bacteria, and further the nitrification process. Thus, abovementioned problems are emergence and urgent to be solved for treating high-ammonia wastewater.Membrane bioreactor (MBR) is a new wastewater treatment technology which combines membrane separation and biological wastewater treatment, offering many advantages including high concentraion of activated sludge, good effluent quality and high degree of automation, has been a hot spot in the field of wastewater treatment.MBR was applied to research the biological nitrification process of high-ammonia wastewater treatment process. Moreover, high-throughput sequencing technology and polymerase chain reaction (PCR)-molecular clone biotechnology were combined to research microbial community structures in MBR, and explicated the dynamic shift of functional bacteria. The main research contents and results are as follows.(1) The effect of different salinity level on the start-up process of MBR with low concentration ammonia nitrogen (30 mg/L) was investigated. The results showed that, 10000 mg/L (1%) NaCl inhibited the activity of AOB, ammonia-oxidizing rate reduced 87%, and the minimum anomia removal efficiency was only 33.7%. The NaCl stress resulted in the increase of soluble microbial product (SMP), and accelerated membrane fouling rate. Cluster analyses showed that the microbial community structure changed significantly in MBR under NaCl stress.(2) The mechanisms and effects of ammonia loads rate on MBR operation and microbial community were investigated. The results showed that, MBR could treat the highest concentration ammonia wastewater at 3000 mg/L with ammonia load at 5.14 kgNH4+-N/m3-d, and the average ammonia removal efficiency reached 93%. When influent concentration increased from 500 mg/L to 1000 mg/L, the nitrification process in MBR was inhibited in a long period. Specifically, the salinity, which increased with increasing ammonia load, inhibited the activity of AOB, resulting in the accumulation of ammonia. The accumulating free ammonia (FA)was beyond the beginning inhibitory level of AOB, which in further inhibited the activity of AOB and nitrification process. Moreover, ammonia loads significantly changed microbial community, especially at 1.71 kgNH4+-N/m3·d. With the increasing ammonia load, AOB could accumulate in the MBR, and under influent ammonia concentration of 1500 mg/L, the ralative abundance of AOB could be 14.82%, which was 54 times than the lowest abundance sample.(3) The mechanisms and effects of salinity on high ammonia loads MBR operation and microbial community were investigated. The results showed that, when influent ammonia concentration at 1000 mg/L with ammonia load at 1.71 kgNH4+-N/m3·d, the MBR could be resistant to 40000 mg/L NaCl (4%, w/w), and under this stress, the ammonia removal efficiency could be beyond 99.5%. When NaCl was increased to 7%, the MBR broke down rapidly and could not recover under 4% NaCl stress. Both of the increasing ammonia load and salinity could change the microbial community structures. The increasing ammonia load could reduce the diversity of microbial community, while increasing salinity could enhance the diversity of microbial community. Under high salinity stress, the abundances of Methyloversatilis, Maribacter increased significantly. After cultivation under high salinity stress, AOB had great saline tolerant capability and the relative of abundance of AOB increased to 15.07% at 222nd day, which was 25.5 times and 8.2 times than that in the lowest sample and seed sample, respectively.(4) The mechanisms and effects of C/N on high ammonia loads MBR operation and microbial community were investigated. The results showed that the increasing C/N could reduce the ammonia-oxidizing rate of sludge, and the stabilization of MBR mainly depended on the increase of sludge concentration.The increasing of influent COD concentration promoted the production of humic acids type SMP, When C/N reached to 1, the membrane fouling rate was increasing and the running time of membrane module was reduced. The relative abundances of AOB and NOB decreased with increasing C/N, which decreased 86.54% and 90.17% respectively from C/N at 0 to 2.(5) The effect of environmental factors on functional bacteria and microbial community structures were investigated by PCR-molecular clone biotechnologies and high throughput sequencing. The results showed that, AOB was mainly belonged to Nitrosomonas genus in the MBR, and the environmental factors could change the specific species of AOB in Nitrosomonas genus. Nitrosomonas oligotropha was responsible for ammonia removal under low ammonia load rate condition, and Nitrosomonas europaea mainly worked under high ammonia concentration condition, while Nitrosomonas marina played a decisive role in ammonia removal under high-saline and high-ammonia load rate condition. Canonical Correlation Analysis (CCA) indicated that COD, sodium ion and ammonia in influent could significantly change the microbial community structures, and meanwhile, microbial community also had effect on COD removal and membrane fouling rates. Based on the microbial community structure, the total 19 samples were divided into 5 groups, and environmental factors of each group had individual characteristics, indicating that microorganisms could be specific community under special environmental stress, and the similar environmental stress could also induce the similar microbial community structures. |
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