| Aerobic granular sludge technology is attractive in current biological wastewater treatment field, especially in dealing with high concentrations of toxic industrial wastewater due to its outstanding settling performance, high concentration of microorganisms, good impact resistance, microbial species diversity and simultaneous nitrification and denitrification, but how to shorten the startup time of aerobic granular sludge system is one of the difficult problems that need key breakthrough in practical industrial applications. For this reason, this project researches the feasibility of simply and quickly startup aerobic granular sludge system by external pressure method, the mechanism and physical model of sludge granulation, and treatment effect of actual high ammonia concentration fertilizer industry wastewater.The experiment applied external pressure on the activated sludge to produce artificial granules using vacuum filtration method, then, cultivated the artificial granules in SBR without the addition of other auxiliary substances. Through the comparison of granulation process and property changes of the artificial granules under different operating parameters, the results showed that: When the water content and particle size of artificial granules are respectively in the range of 69.6%~86.4% and 0.5 mm~2 mm, the lower water content, the larger particle size, the granulation effect is better; But when water content < 66.1%, particle size > 2.8 mm, the biological activity of granules significantly reduces, and the removal efficiency of pollutants becomes poor. Experiment showed that the granulation effect of artificial granules is best when water content of 69.6%, particle size of 2 mm, compared with conventional activated sludge inoculation, the artificial granules under such operating parameters can greatly shorten the startup time of aerobic granular sludge system, aerobic granules formed have large and centralized distribution of particle size, compact structure, good settling properties, and higher nitrogen removal efficiency. Its granulation time, average particle size, specific gravity, SVI value and TN removal rate are respectively 20 d, 1.68 mm, 1.048 g/cm3, 29.5 m L/g and 84.3%, while the inoculating activated sludge are 40 d, 0.46 mm, 1.024 g/cm3, 54.3 m L/g and 65.1%.The key mechanism of external pressure method accelerating the granulation is that activated sludge dehydrates rapidly under external pressure, which can promote the microbial extracellular polymeric substances(EPS) closely bridging in order to agglomerate into larger particles, thus greatly reduce the hydrophobic self coagulation and growth time of sludge. Physical model of granulation proposed in this paper could vividly describe the formation process of aerobic granular sludge under external pressure.The experimental results for treatment of actual high ammonia concentration fertilizer industrial wastewater showed that: after 45 d of acclimation, granules gradually adapted to the actual wastewater, the removal rate of COD, NH4+-N and TN reached 93.5%, 89.2% and 66.5% respectively, and the nitrite accumulation rate has been maintained at between 71%~84%, while the physical properties of the particles remained stable, indicating that aerobic granular sludge has high resistance to shock load and decontamination capability.Based on the above, this paper can achieve the purpose of starting the aerobic granular sludge system simply and quickly by external pressure method, and can obtain high treatment effect of fertilizer industrial wastewater, thus provides some scientific basis and technical support for the application of aerobic granular sludge in the actual industrial wastewater treatment. |
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