Performance and Morphological Changes in Aerobic Sludge Biomass Under Stressed Condition Imposed with Copper(II) in Feed

Abstract

The published literature indicates inadequate assessment of imposed stresses on activated sludge morphology. This work aims to study the aerobic sludge biomass morphology under imposed stress and its impact on overall performance. The aerobic sludge biomass was grown up to MLSS concentration of 3800 mg/L on lactogen feed in a batch reactor of 7 L capacity. 400 mL of the aerobic sludge biomass was transferred into two 1-L capacity batch reactors CO1 and R1. These reactors were operated with fill, react, settle and withdraw modes with time period of 5, 1390, 30 and 15 min, respectively, for one complete cycle time of 24 h. The control reactor CO1 was fed with lactogen giving an initial COD level of 1100 mg/L while other stressed reactor R1 was also fed with lactogen along with 5 mg/L of Cu(II). The presence of Cu(II) in feed started to show adverse impact on stressed reactor R1 performance after 10th d of operation as effluent COD started to show increasing trends compared to control reactor CO1. On 15th d of operation, high effluent COD for reactor R1 (1050 mg/L) was observed compared to that of control reactor (85 mg/L). The settling velocity and SVI of aerobic sludge biomass from stressed reactor R1 improved due to adverse impact of Cu(II) but at the cost of high effluent COD. The microscopic and FESEM observations indicated the absence of filamentous micro-organisms in stressed reactor R1 compared to the controlled reactor on 15th d of operation, thereby showing drastic changes in morphology of aerobic sludge biomass due to the presence of Cu(II) in its feed.