| Wastewater with high levels of COD and ammonia could be produced by many ways, such as the drainage from public toilets of expressway service area, landfill leachate and the reject water from the sludge concentration tank of urban wastewater treatment plant or industrial wastewater station, etc. It has been an effective way to use biological nitrogen removal process to treate wastewater with high concentration of ammonia. In order to make full use of organic carbon in raw water as the electron donor for denitrification, a number of advanced biological nitrogen removal processes have been developed, including the widely used A/O (pre-denitrification) process. It is a research focus on biological nitrogen removal and has great significance to continue to explore new biological nitrogen removal process with high efficiency and low energy waste.The multi-stage inner-loop biological nitrogen removal process was investigated. The outer layer of plastic caecum with geotextile was placed in the reaction pool. The inner of plastic caecum with aeration was used as aerobic zone, and the outer without aeration was used as anoxic zone, consisting the multi-stage inner-loop biological nitrogen removal reactor. Besides suspended sludge in the process, there were biofilm adhering to the inner and outside of geotextile (the inner biofilm was aerobic, the outside was anoxic). Therefore, it had both active sludge and biofilm features. For the concentration difference, the action of air lift and the reflux of pump, wastewater could exchange between inner and outside (i.e. aerobic area and anoxic area) of caecum, and high TN removal efficiency could realize in the multi-stage inner-loop process.According to the volumetric ammonia loading rate of influent, the experiment was divided into four phases, used for exploring a appropriate design load. Phase 1:HRT=48h, C:N:P=1000:200:10; Phase 2:HRT=48h, C:N:P=1000:100:10; phase 3:HRT=24h, C:N:P= 1000:100:10; Phase 4:HRT=36h, C:N:P=1000:100:10. The result indicated:the volumetric loading of phase 1 and phase 3 was to high and the effect was bad; treatment effect of phase 2 was excellent, but the volumetric loading was too low; phase 4 with medium volumetric loading and good treatment was recommended. In phase 2, the concentration of COD and ammonia in influent were 890.1～1094.7mg/L and 97.0～110.3mg/L respectively. The experiment results showed that the average removal efficiency of COD and ammonia nitrogen were higher than 97.0% and 99.5% respectively while the maximum removal rate of TN was 92.1% and the average removal efficiency of TN was 88.4%.In phase 3, the concentration of COD and ammonia in influent were 747.6～988.0mg/L and 83.2～114.7mg/L respectively. The experiment results showed that the average removal efficiency of COD was 92.4% while the average removal efficiency of ammonia and TN were higher than 70% except for a few data.In phase 4, the concentration of COD and ammonia in influent were 938.7～974.4mg/L and 92.4～103.9mg/L respectively. The experiment results showed that the average removal efficiency of COD and ammonia nitrogen were 95.3% and 97.4% respectively while the average removal efficiency of TN was 84.8%.those impacts of volumetric loading rate,HRT and reflux ratio on the treatment effect were discussed tentatively. The study showed that, under experimental water quality conditions, the optimal HRT was 36h and the optimal reflux ratio was 0.75.In addition, based on the mass balance of ammonia,COD and nitrate-nitrogen, the theoretical calculation formula of TN removal rate was obtained:if the raw water quality to meet 100%; if the raw water quality to meet 100%. Besides, it was proved that the TN removal rate in this process was higher than the conventional A/O process in theory. |
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