The Characteristics Of The A-step In AB-ASBR Process

The anaerobic granular sludge is a typical characteristic of a group of high-rate anaerobic reactor , which is represented by ASBR. The anaerobic granular sludge has porous physical structure, high porosity, it is easy to adsorption macromolecular material and has strong adsorption capacity. Using adsorption of organic pollutant on anaerobic granular sludge in the beginning and based on the theory of anaerobic microbiology and biological reaction kinetics and the experimental research, AB-ASBR process was developed. The ASBR reactor of A-step wan mainly designed to eliminate the influent organic pollutant by adsorption; the ASBR reactor of B-step broke down surplus organic pollutant in drainage of A-step to be stable, its operation mode was the same with the ordinary ASBR reactor's. The adsorptive removal happened in the A-step at first, so the operation mode and process characteristics of the ASBR reactor of A-step was surely different from the ordinary ASBR reactor's. Process characteristics of the A-step in AB-ASBR process were studied in this thesis. Granular sludge which was inoculated with return sludge from secondary sedimentation basin of urban sewage plant and was fed glucose as substrate with minerals and alkalinity, was cultivated at mesophilic conditions(35℃). After the granular sludge had formed, the substrate of it was transferred from glucose to fat dried milk, which was rich in colloidal substances. At this time, the ASBR reactor of A-step operated on "adsorption (fill)—settle—draw—regeneration" mode. The experimental study on the ASBR reactor of A-step was carried out at influent organic volumetric loading rate of 2.4gCOD/(L·d),4.8 gCOD/(L·d),6.5 gCOD/(L·d),8.1 gCOD/(L·d).The following conclusions were draw from the study: (1)The adsorption of anaerobic granular sludge is remarkable in the beginning, it achieved equilibrium within 10 minutes under different influent COD concentration, and the adsorption rate could reach 90%. (2)The influent COD concentration and sludge loading rate was significantly correlated with adsorption capacity of anaerobic granular sludge. The higher influent COD concentration or sludge loading rate, the higher adsorption capacity of granular sludge could be. (3)In the process of adsorption on anaerobic granular sludge, the membrane mass transfer was the main rate-limiting step of adsorption on anaerobic granular sludge, but was not the only rate-limiting step. (4)The pseudo-second-order reaction equation was more suitable than the pseudo-first-order reaction equation to describe adsorption kinetics of anaerobic granular sludge. (5)The regeneration was able to enhance the adsorption performance of anaerobic granular sludge. With the increase of the regeneration time of anaerobic granular sludge, adsorption capacity and adsorption rate of anaerobic granular sludge was gradually raising, too. When the regeneration period had exceeded 6 hours, adsorption capacity and adsorption rate of anaerobic granular sludge didn't increase along with the extension of the regeneration period, but was invariable basically. (6)Through the studies on four different stirring frequencies, it can be discovered that, the time for adsorption equilibrium was the least when inflow was continuous stirred. Stop stirring after that, and deposit for 20 minutes to separate liquid and solids, then drain. (7) The COD varieties during regeneration period were investigated at different volumetric loading rate. During the whole process of regenerating, the COD was decreasing before it became stable after 6 h, and the volatile fat acids concentration also decreased down to 50mg/L. (8) At different volumetric loading rate of the experiments, the pH varied in the range, which was best for anaerobic digestion. This indicated that anaerobic granular sludge had enough alkalinity during regeneration to ensure the pH of the digesting solution at the range required.