| Aerobic granular sludge has strong resistance to high-strength wastewater, shock loadings and toxicity due to the dense and strong microbial structure, excellent settleability and high biomass retention. In recent years, applications of granules for wastewater treatment have received considerable attention. However, chemical oxygen demandand nitrogen ratio (COD/N) is an variable parameter in the area of wastewater treatment. For some high strengh ammonia wastewater, the COD/N ratio is very low, e.g., landfill leachate, sludge digestion liquid, etc.. A low COD/N ratio may change the physic-chemical characters and microbial populations in aerobic granules, which is an important reason for the disintegration of granular sludge. In this study, the aerobic granules were cultivated at COD/N ratio of 400/100 by using floceulent sludge as inoculating sludge. In addition, the effect of influent ammonia concentration on the performance of aerobic granules and microbial structures were studied. The long-term stability of the aerobic granular sludge was investigated as well. The results are as flows:1. Aerobic granular sludge was successfully cultivated under low COD/N (400/100) condition. During 140 days’cultivation, MLSS reached 4.94 g/L in reactor A and 5.36 g/L in reactor B, respectively, and SVI30/SVI5 maintained as 1. Aerobic granular sludge exhibited good performance with an COD removal efficiency of above 90%, ammonium removal efficiency close to 100%.2. The nitrifying Characteristics and physic characters of the aerobic granular sludge were not affected under the condition of COD/N ratio of 400/200. Decrease the influent COD/N ratio to 400/200, biomass concentration in the reactor A increased rapidly after a short adaptation phase,. During around 110-day’s operation, the MLSS increased to 11.38 g/L. At the same time, SVI30/SVI5 maintained as 1. The reactor exhibited good performance with 98% ammonia removal efficiency. With the further increase of the load from 400/200 to 600/300, the physical characteristics of aerobic granular sludge did not change much, but the ammonia removal efficiency was deteriorated. In detail, MLSS maintained above 9.82 g/L and the value of SVI30 was around 50 mL/g. However the removal efficiency of ammonium decreased gradually to 34.88% at the end of the experiment. The possible reason for the decline of ammonium removal efficiency may be the the inner renew of the granular sludge and the effect of low temperature.3. DGGE results at different COD/N ratios show that, heterotrophic bacteria which have the ability to remove nitrogen and maintain structural stability was the most dominant microorganism in the granular sludge.. However, the results of FISH experiments were found there is nitrifying bacteria exist in aerobic granular sludge, which distributed in the particles inside, nearly 50-100 um from the granular sludge surface.4. Aerobic granular sludge formed under low COD/N conditions has good self-healing ability. During the operation period, the aerobic granules disintegrated first and then recovered by themselves. However, this disintegration has little effect on the ammonium removal efficiency. Although the biomass concentration and settleability declined during the process of disintegration, they increased with the recovery of the system. In the process of system recovery, isolate Sphingomonas sp was found dominant in the granular sludge. |
PDF Full Text Request