| IC reactor treating citric acid wastewater can form anaerobic granular sludge with good performance, this paper studied experimentally on the characteristics, the formation and preservation of anaerobic granular sludge, and it was applied to the re-start process of the IC reactor.Anaerobic granular sludge was with black color, regular elliptical or spherical shape, clear boundary, smooth surface, and many gaps within it which was the channel matrix and gas transmission; 58.74% of the anaerobic granular sludge with particle diameters in the range from 0.93mm to 1.7mm was the main body of IC reactor for the treatment of the organism; The average settling velocity of particles was 92.3m/h, the water content, VSS content, the ash content of anaerobic granular sludge were 93.82%,5.01%,1.17%, respectively, and the VSS/TSS ratio was 0.81, which showed that the anaerobic granular sludge consisted of a large number of microorganisms; Particles contain a small amount of K, Ca, Mg and Fe and other metal elements, Ca content up to about 66.05mg/gTSS which affected the process of sludge particles.Conservation of granules test the formation of anaerobic granular sludge was similar to the crystallization process. The wastewater contained massive amounts of Ca2+ in terms of CaCO3, which gathered in the center of the anaerobic granular sludge to provide a support framework for the particles. The microorganisms would grow around the CaCO3. In addition, the bridge and adsorption of Ca2+ in the particles can accelerate the formation of sludge particles and form good anaerobic granular sludge.Conservation of granules test show that the maximum specific methane production rate of anaerobic granular sludge (umax) was affected by different temperature for storage, after preservation for 30d,60d and 90d at 25℃, the umax fell to 223.5mlCH4/(gVSS·d),164.4mlCH4/(gVSS·d) and 93.7mlCH4/(gVSS·d) from 287.3mlCH4/(gVSS·d), respectively, and after preservation for same time at 5℃, the umax fell to 266.4mlCH4/(gVSS·d),172.9mlCH4/(gVSS-d) and 145.1mlCH4/(gVSS·d), respectively, the decrease was more prominent in the former than in the latter, the reason was that the microbial particles still maintain a certain activity with the residual nutrients were decomposed at 25℃, but at 5℃, the basic particles within the micro-organisms to enter "sleep" state, it temporarily inhibit anaerobic the activity of granular sludge to save the process to avoid being in the activity of large losses and even permanent loss of activity, Low-temperature preservation of anaerobic granular sludge can keep the activity and integrity, So that it can play the most effect with continue to use when time and space changed greatly.The anaerobic granular sludge which keep more than three months were selected as seed sludge, and it was applied to the re-start process of the IC reactor, when the biomass of inoculants was 15.3kgVSS/m3, the influent pH, temperature were within the range of 5.5-6.5,39～41℃, respectively, and the HRT, hydraulic loading and initial volume load were 18h,1.09m3/(m2·h),2.61kgCOD/(m3·d), respectively, by first raising the organic loading and then the quantity of influent was enhanced step by step, at the start-up initial stage, the COD removal efficiency of IC reactor reached 70%, which indicating that the activity of anaerobic granular sludge recovered well, besides, sludge granulation rate experienced from slow to fast growth process, and finally stabilized at about 70%; After the successful start-up of IC reactor, the maximum volume load can reach 17.76kgCOD/(m3·d), the removals of COD generally ranged from 82% to 87%, and the COD concentration in the effluent was less than 700mg/L, VFA was lower than 300mg/L, and ALK was not less than 1500mg/L.Substrate degradation models of high load and extract processing of IC reactor were deduced respectively in the state of complete mixture and plug flow. The model of IC reactor used for the citric acid wastewater treatment was confirmed as follows; the substrate degradation rate has a positive correlation with the sludge concentration at high load area, hydraulic retention time and the quantity of cycle. The optimization of reactor structure and the culture of the anaerobic granular sludge were effective ways to enhance the efficiency of the substrate degradation of IC reactor.
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