Formation and characterisation of aerobic sludge aggregates in a lab-scale activated sludge system
Sludge aggregates were developed under ambient conditions in the aeration tank of a lab-scale activated sludge system. Different strategies were employed to accelerate the aggregation process viz.: i) initiating aggregation with large-dense flocs; ii) supplementing sewage with food-waste leachate containing readily biodegradable substrates; iii) periodic aerobic starvation; iv) addition of support materials to nucleate aggregate formation. Four identical reactors were set-up, each with a different support material viz.: R1: control; R2: unburnt carbon from bagasse flyash; R3: commercial activated carbon; R4: zeolite 4A. Optical and scanning electron microscopy, supported by particle size measurement by sieving indicated the development of aggregates with mean diameter of 0.5 mm in all the four reactors after 90 days of continuous operation. The aggregates showed improved physical properties (high cell-surface hydrophobicity, high integrity coefficient, low sludge volume index, high settling velocity) and chemical properties (high extracellular polymeric substances or EPS content). The process resulted in an average of 72% to 76% COD reduction with a biomass concentration of 8 to 9 g/L in the reactor. Interestingly, introduction of the support materials into the aeration tank did not enhance the aggregation process. improved income generation and a better quality of life.