Research On Cultivation And Steady-State Operation Of Aerobic Granules

Aerobic granulation technology has become attractive in wastewater treatment, which is a new and promising approach to overcome the principal weaknesses of the activated sludge process. A brief review showed that aerobic granulation is not a function of microbiological groups but that of reactor operating conditions and factors, e.g. loading rate, settling time, aerobic starvation, shear force, divalent metal ions and so on. However, to date, the influences of above factors on aerobic granulation are not clear, and little information could be found currently available on the effect of starvation time and aeration intensity in steady-state aerobic granular system. Thus, the main aim of this study was focused on cultivation and stablely operation of aerobic granules in SBR, and it conclude four parts:(1) The affect of different metal ions on culture and properties of aerobic granules; (2) Aerobic granules developed with different granulation-enhancement strategies; (3) The steady-state operation of aerobic granules under different starvation time; (4) The steady-state operation of aerobic granules under different aeration intensity.The sludge with Ca had a faster granulation process compared with Mg, and the mature granules with Ca showed better physical characteristics. However, the mature granules with Mg had the higher production yield of polysaccharides and proteins, and aerobic granules with Mg experienced a faster substrate biodegradation. The PCR-DGGE analysis revealed that T Mg addition led to higher microbial diversity in mature granules. Thereby, it can be concluded that Ca had an important effect on physical properties of aerobic granules, while Mg played a key role on biological properties during the sludge granulation.The SBRs were operated by using four operational strategies could successfully enhance aerobic granulation, but showed a different role in the process. Rapid granulation process was observed by using short settling time, and the granules developed by that had better settleability, higher extracellular polymeric substance and longer storage stability than other reactors. Extended starvation period and high shear force resulted in longer granulation period and the granules with higher integrity and smaller size. Aerobic granules by controlled loading rate resulted in the granules with larger size and higher K value. Addition of calcium helped the settleability and physical strength of granules.In the steady-state sludge granular system, the starvation time and aeration intensity were not the key conditions. The steady-state aerobic granules with low aeration intensity and shorter starvation time could keep sludge granulation and stable operating, but different aeration intensity and starvation time showed an obviously effect on the characteristics of aerobic granules. Thus, the balance between advantages and disadvantages by using them should be considered.The steady-state sludge granules system had the similar COD removal rate under different starvation time. In aerobic granules with shorter starvation time, the production yield of extracellular polymeric substance was reduced, and the ratio of polysaccharides to proteins had an increased trend. However, the flocs would showed an overgrowth under a longer starvation time, thereby decreased the settling ability and physical characteristics of the granules. The kinetic behaviors of mature aerobic granules showed that the maximum specific COD removal rates of granular sludge was at a similar level under different aeration rate, but the granules in shorter starvation time had higher observed biomass yield and apparent half rate constant.Comparing with low aeration intensity, aerobic granules under high aeration intensity showed better physical characteristics and settling ability, but a smaller granule size. Meanwhile, due to the lower aeration rate, the production yield of extracellular polymeric substance and the ratio of polysaccharides to proteins in aerobic granules were reduced. In addition, kinetic behaviors of mature aerobic granules showed that the maximum specific removal rates and apparent half rate constant of granular sludge were at a similar level under different aeration rate, but the granules in lower aeration rate had higher biomass yield.