| Aerobic granular sludge (AGS) has many advantages, being considered to be one of the most promising biological treatment technologies in further. However, the instability and the single form of reactor configuration (most are SBR) of AGS greatly limited the development and application of this technology. And that’s why AGS technology has not yet realized engineering application. Based on rapid cultivation of AGS, this research investigated the performances to pollutants removal and granules’ stability maintenance feeding with real wastewater in sequencing batch reactor (SBR) and continuous flow reactor respectively. The works carried out and results obtained are as follows.(1) Rapid cultivation of AGS. Aerobic granulation was successfully realized in a pilot scale SBR in 18 days, with strategy based on selection pressure method, implementation of anaerobic biological selector and inoculation of mature aerobic granules (25%, w/w) during cultivation. The cultivation method could effectively avoid the transition of disintegrating firstly then reaggregating of inoculated aerobic granules, while inoculated granules could directly serve as crystal nucleus and carriers for new granules, which greatly shorten the granulation time. By inoculating part of mature aerobic granules and maintaining high hydraulic selection pressure, the double column cyclic aerobic granular sludge reactor (CAGSR) successfully realized aerobic granulation in 18 days. By controlling the baffle depth, HRT and aeration rate, powerful hydraulic selection pressure could be created in double column CAGSR. Owing to the unique design of three-phase separator, sludge with different characteristic (diameter, settling velocity, etc) were continuously selected. Also, inoculated mature aerobic granules (30%, w/w) could serve as carriers and crystal nucleus, therefore reducing the granulation time. The inoculated granules experienced the transition of disintegration at first before reunion, but small granules were more easily to adapt to continuous flow environment. Observed from microstructure of cultivated granules, there were abundant microbial communities intricately intertwined each other, the unique structure provided skeletons for other microbial, which also accelerated the formation of aerobic granules.(2) Application of AGS for real wastewater treatment in SBR. Gradually increase the proportion of municipal sludge deep dewatering filtrate (MSDDF) in the influent, stable AGS with good nitrification and denitrification ability was successfully domesticated after 84 days in a bench scale SBR. Obviously accumulation of nitrate was monitored during the middle of the domestication, leading to the obvious decrease of TN removal rate. Then, solid sodium acetate was added in order to promote denitrification performance of aerobic granules. It was found that when the amount of sodium acetate increased from 2 g to 6 g (the corresponding COD was 152-456 mg/L), TN removal rate increased from 82% to 97%. Thus, efficient organic pollutants removal, simultaneous denitrification and phosphorus removal were realized in a single bioreactor. Gradually increasing the volume of solvent recovery raffinate (0-10.84 L) in influent, AGS with good organic removal ability was domesticated after 48 days in a pilot SBR, and COD removal rate kept above 95%. Although C/N ratio was gradually increased during the domestication, but AGS maintained its structure, and no apparent disintegration was observed during the domestication. The results indicated that AGS could maintain stability as fed with low C/N ratio and high C/N ratio real wastewater, and good removal effect of pollutants could be achieved.(3) Tolerance to organic loading rate (OLR) by AGS in a double column CAGSR. Gradually increasing the operational OLR, it was found that aerobic granules could maintain stability when OLR^15 kg/m3-d in double column CAGR. Stable aerobic granules were obtained in the first 65 days, having good removal effect on the pollutants. However, granules gradually disintegrated when OLR increased to 18 kg/m3·d. Physichemical properties of the granules deteriorated rapidly in 10 days, and pollutant removal rate dropped dramatically, which ultimately evolved to collapse of the system. With the increase of OLR, obvious pollutants gradients were monitored in double column CAGSR, which provided larger mass transfer driving force for biochemical reaction and effectively inhibted overgrowth of filamentous bacteria. However, anaerobic core gradually formed by a large number of dead bacteria with the increase of particle size under high OLRs. The anaerobic core resulted in the decrease of granules’ intensity and EPS production, which eventually led to the disintegration of the granules and the collapse of the system.(4) Application of AGS for the treatment of MSDDF in three columns CAGSR. Through gradual increase of the proportion of MSDDF in the influent, stable aerobic granules with good nitrification ability were domesticated after 72 days, and removal rate of amounia nitrogen was increased fom 75.13% to 99.59%. Although wastewater quality of MSDDF changed for three times, the granules maintained their integrity during the domestication. As specific growth rate of nitrifying bacteria was much lower than heterotrophic bacteria, thus, the enrichment of nitrifying bacteria would lower specific growth rate of the whole sludge, it was easier to maintain dynamic equilibrium between granulation and disintegration. The results indicated that AGS had good ability to resist wastewater quality mutations, and enrichment of nitrifying bacteria could effectively maintain the stability of AGS in a continous flow reactor. |
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