| Aerobic granulation technology has been proposed as an efficient and innovative technology in wastewater treatment. With the clear-outer shape, compact and strong microbial structure, aerobic granules have the advantages of good settling ability, high biomass retention, and the ability to withstand a high organic loading rate and resistance to inhibitory and toxic compounds. Therefore aerobic granules have been extensively investigated in numerous laboratory-scale reactors and few pilot-scale reactors in recent years for wastewaters treatment. However aerobic granulation has been strongly influenced by organic loading rate(OLR), ammonia concentration, hydraulic shear force caused by aeration, aerobic starvation and settling time. Different operational strategies could lead to different characteristics of granules, thereby affect the reactor performance. However, to date, no research has been done to compare the OLR, ammonia concentration and shear force together to verify the extent influences on physical properties and reactor performance during granules reactivation. And the impact of storage substrate and storage temperature on granules reactivation performance has been less reported. Therefore, the objective of this study is to investigate the reactivation performance of stored aerobic granules under different reactivation operational strategies and different storage conditions.The SBRs were operated using three operational strategies for reactivation a) different organic loading rate (OLR); b) different ammonia concentration; and c) different shear force (a superficial upflow air velocity). The results indicated that granules after long-term storage could be successfully recovered after 7 days operation and the excellent granules reactivation performance was closely related to the operational strategies, since inappropriate operational strategies could cause the outgrowth of filamentous bacteria and granules disintegration. Based on comprehensive comparison of reactivation performance using different operational strategies, the optimal operation strategy for granules reactivation was suggested at OLR of 0.8 KgCOD/m3·d, ammonia concentration of 15-20mg/L and a superficial upflow air velocity of 2.6cm/s. After 7 days operation under the optimal strategy, the dark brown granules (12 months storage) restored their bioactivities to previous state, in terms of COD removal efficiency(97.44%) and specific oxygen uptake rate (40.63mg-O2/g-SS h-1). The results shed light on the future practical application of stored aerobic granules as bioseed for reactor fast start-up.The storage of aerobic granules is a complicated process, which is influenced by storage temperature, storage substrate and storage time and the affective mechanism is not very clear. The results showed that the storage temperature has huge impact on the morphology and physical properties, and the storage substrate has little impact. The granules stored at 4℃for 8 months preserved the most complete structure and there was small changes on granules morphology and physical properties, which is more suitable for long-term stable storage of aerobic granules. Meanwhile granules stored at 20-26℃for 8 months had the worst stability. Aerobic granules under different storage conditions after 1 month operation all achieved good reactivation performance. The granules stored at -25℃obtained excellent settling characteristics and stable physical structure after 1 month reactivation, and the PN/PS remained stable during the operation. The reactivation performance of granules stored at 20-26℃was relatively poor and the reactivation performance of granules stored at 4℃was in between. The aerobic granules under different storage conditions could be reactivated after 10 days operation. The microbial activity(SOUR) could be fully restored and the granules could also achieve good COD,NH4+-N and PO43--P removal performance. No matter what the storage temperature or the storage substrate is, aerobic granules after long-term storage (6-12 months) could be used as bioseed for reactor fast startup. This study aimed to offer useful information for the practical application and further commercial production of aerobic granules.
|
PDF Full Text Request