Research On The Partial Nitrification Using The Internal-Circulation Three-Phase Bio-Fluidized Bed Reactor To Treat High Ammonia Concentration Wastewater And Molecular Biological Characteristics

Internal-circulation three-phrase bio-fluidized bed reactor has been proved a prevalent and efficient aerobic bio-reactor because it has the characteristics of high performance, high loading rate, little area occupation, infrequent sludge bulking, etc. Naturally, the biomass in this reactor has the characteristics of both attached growth and suspended growth. Due to its attached growth characteristic, nitrobacteria with long generation time can pile up in the biofilm. Therefore, under given suitable condition, internal-circulation three-phrase bio-fluidized bed will be employed as a highly efficient nitration bio-reactor.Recently, some new nitrogen removal processes absorbe people's eyes during which the process of partical nitrification have advantage of saving energy and reducing cost especially treating high ammonia-containing wastewater. In order to seek a highly efficient and lasting partial nitrification process, this paper try to combined partial nitrification theories with aerobic bio-fluidized bed reactor. The nitrification performance of the biofilm in the fluidized bed was enhanced in this research by applying the method of enhancing the start-up condition and changing the operating parameters. The feasibility of achieving partial nitrification process and the effects of different operating parameters on partial nitrification were investigated when the fluidized bed was used to treat high ammonia concentration wastewater. Based on the effects of different operating parameters on treatment efficiency using partical nitrification process the best conditions for the process of partial nitrification was determined.First of all, the quick start-up condition of reactor was investigated. It is found that short hydraulic residence time and little inoculation sludge was good for attached bacteria growing and to achieve the reactor's quick start-up.Then, according to the former experimental results, the start-up condition of high N/C and low COD concentration was applied. After the reactor start-up, the effects of ammonia nitrogen condition in influent,different operating parameters and organic matter on the nitrification performance and nitrite accumulation were investigated. Choosing mature biofilm, the nitrifying microbial distribution and the dominant bacteria in the biofilm were investigated by the technologies such as FISH, PCR and clone.Results of the influence of ammonia concentration in influent showed that average partial nitrification rate of 79% was achieved in the beginning period. However, completed nitrification occurred when sufficient DO was supplied and ammonia concentration in influent was 100mg/L, whereas, partial nitrification was achieved again and when the ammonia concentration in influent was increased from 100mg/L to 300mg/L. The nitrification process was destroyed afterwards and nitrite accumulation rate is not stable because higher free ammonia (FA) nitrogen concentration can inhibit the activity of NOB. The nitrite oxidizing bacteria can also accustome to the high concentration of FA under the condition of increasing ammonia nitrogen loading slowly. In this study, 8mg N/L FA can inhibit the activity of AOB and NOB.Results of the influence of pH, temperature and DO showed that the optimal condition of pH,temperature and DO is 7.9-8.2, 33-35℃and 2.0-3.0mg/L, respectively. The reactor was operated for 15 days under the optimal condition, nitrite accumulation rate increased from 37% to 74% with the average 81% removal of ammonia nitrogen.Results of the influence of organic matter in influent showed that the competition for oxygen of heterotrophic bacteria with nitrifying bacteria was the main reason for the decrease of nitrification performance when organic matter was added in the influent. SEM photos of nitrifying biofilm presented compact nitrifying bilfilm became loose and single bacilli became flora containing kinds of filamentous bacteria when organic matter was added in the influent.FISH results showed that the nitrifying bacteria intended to grow at the inner layer of the biofilm, whlie ammonia oxidizing bacteria intended to grow at the outside. The amount distribution of the two species of bacteria was rather equal.Nitrosococc sp.and Nitrosomonas sp., Nitrobacter sp.and Afipia sp. were the dominant species for ammonia oxdizing bacteria and nitrfying bacteria in the high ammonia concentration treatment system.