Study On CAST Process For Wastewater Of High Concentration COD And Ammonia

CAST(Cyclic Activated Sludge Technology) process is a new technics, which is based on SBR(Sequencing Batch Reactor) technology and biological selection principle. As it could offer high efficiency process condition for Simultaneous Nitrification and Denitrification (SND) to remove nitrogen, it does not only have good ability to remove organism and nitrogen, but also has a feature of short flow, high efficiency, space saver and so on. Experiments and research have been carried out on CAST technics.Compared with traditional method for ammonium removal,SND could reduce energy consumption and construction cost,making the process of the technics easier,and the device is prone to integrating. Simultaneous Nitrification and Denitrification (SND) has become a popular topic in the field of biological nitrogen removal nowadays.Through the static experiments, best Hydraulic Retain Time (HRT) that is 6 hour has been found, and the whole cyclic time is 8 hour.Basing on the static experiments, parallel experiments have been carried out by changing the main influence factors including C/N, MLSS and DO. Furthermore, three factors, three levels orthogonal test have been designed.With the orthogonal test results, experiments toilet wastewater have been carried out which simulate the real wastewater quality. The experiments prove that when COD concentration is between 800 to 1200mg/L, ammonia concentration between 85 to 120 mg/L which is the same as the system cubage burden between 0.086 and 0.12 kgNH3-N/(m3·d), the removal rate of ammonia reaches up to 80%, and nitrite and nitrate get low accumulation. The average removal rate of total nitrogen stable on 75%, which shows SND removal nitrogen have good effect in CAST process.When SND occurs, the alkalinity generated by denitrification can simultaneously compensate the decrease of the period, which will buffer the decreasing of alkalinity in the system. At the same time, the character of sludge sedimentation has been analyzed, and the experiment shows that SVI maintains between 85 and 158 ml/g, which shows CAST process can overcome sludge expansion.On the base of analysis, this thesis point out two assumptions that have been existed in CAST process. The first one is that, in the pulse influent style, as the intensity of influent is little, it could avoid the restraint to nitrate rate from the high COD. After the ammonia is oxidized, the pulse influent could offer organism for denitrification. The second one is biological selection. When floccule bacterium becomes superiority, it absorbs amount of organisim, and storage of organisim is also used to denitrification.This paper has done a benefit research on simultaneous nitrification and denitrification (SND) used to treat high concentration COD and ammonia wastewater, and established a foundation on the application in decentralization point source pollution for CAST technics. Basing on the experiments, this dissertation enriches the mechanism research of CAST process.