Abstract:
The research focuses on formation and stability of aerobic granular sludge in lab scale sequential batch reactor (SBR) treating municipal wastewater with increment in VER and wane in settling time taken as the main selection pressure for bacteria and protozoa growth. In the 1st strategy, the granules sludge from the Nerada® was inoculated in the SBR at 20% VER and 5 min settling time, which led to the breakdown of the granules until the 27th day. Rejuvenation of the granules started after 27th day, such that most of the aerobic granule came under the diameter range of 200-300 μm, on the 39th day. The COD and ammonium were removed up to 88% and 99% correspondingly in the 2nd phase. The collapse of the reactor happened after day 48 i.e. in 3rd phase owed to the loss of the biomass concentration. In the 2nd strategy, the reactor was started with activated sludge at 20% VER and 15 min settling time. Granules were first observed at the end of the 2nd phase i.e. on 39th day with utmost granules lies in the diameter range between 50-100 μm. The diameter range was amplified to 100-150 μm and 200-250 μm with the augmentation in the VER to 30% in the 3rd phase. The average COD and ammonium reduction was 91% and 99% respectively. By the microscopic analysis, it was pragmatic that sessile ciliate protozoa play an imperative role in the development of the aerobic granule. The presence of the attached growth ciliate protozoa (Epistylsis spp. and Zoothamnium spp.) and large swimming protozoa (Nemotodes, Cephalodella Elegans, Rotaria spp.) was acknowledged as the indicator for the good granule sludge formation and with less TSS and COD concentration in the effluent.
