Dried aerobic granules for fast startup of aerobic granular sludge reactors: Reactivation and performance

Abstract

Drying and storing of aerobic granules present a promising solution to the long startup period required for the cultivation of aerobic granular sludge. This work investigated the influence of drying of aerobic granules on the degradation of organic substances and nutrients removal after reactivation. Mature aerobic granules were dehydrated, air-dried, and inoculated to a different reactor after one-day storage. The reactor was operated for two months to examine the effect of the drying process on the performance of the reactivated granules in terms of organics and nutrients removal, settling properties, and structural stability. The reactor was fed with a synthetic substrate at OLR of 3 g COD/L.day. Results indicated that the stored and dried granules were rapidly reactivated achieving COD removal efficiency and ammonia nitrogen removal of over 90% after one day and was maintained until the end of the experiment. The granules were able to restore the original performance after reactivation with specific removal rates of 1.2 g sCOD/g MLSS.day, 39.5 mg NH3-N/g MLSS.day, and 7.4 mg PO4-P/g MLSS.day in terms of COD, ammonia, and phosphorus, respectively which is comparable to that of the granule cultivating reactor with specific removal rates for COD, ammonia, and phosphorus of 0.7 g sCOD/g MLSS.day, 34.1 mg NH3-N/g MLSS.day, and 3.9 mg PO4-P/g MLSS.day. The reactivated granules showed excellent settleability, as indicated by SVI30 below 60 mL/g, and granulation percentage of over 90%. These results demonstrated the practical potential of drying of aerobic granules for the fast startup of granular sludge reactors. Further testing is required to determine the dried granule shelf life and the survival of important strains responsible for organics and nutrients removal.