Abstract
Micropowder (20–250 µm) made from ground dry waste sludge from a municipal sewage treatment plant was added in a sequencing batch reactor (R2), which was fed by synthetic wastewater with acetate as carbon source. Compared with the traditional SBR (R1), aerobic sludge granulation time was shortened 15 days in R2. Furthermore, filamentous bacteria in bulking sludge were controlled to accelerate aerobic granulation and form large granules. Correspondingly, the SVI decreased from 225 mL/g to 37 mL/g. X-ray Fluorescence (XRF) analysis demonstrated that Al and Si from the micropowder were accumulated in granules. A mechanism hypotheses for the acceleration of aerobic granulation by adding dry sludge micropowder is proposed: added micropowder acts as nuclei to induce bacterial attachment; dissolved matters from the micropowder increase abruptly the organic load for starved sludge to control overgrown filamentous bacteria as a framework for aggregation; increased friction from the movement of micropowder forces the filaments which extend outwards to shrink for shaping granules.
Highlights
Aerobic granular sludge is a promising biotechnology in wastewater treatment
In R1, a few granules occurred on day 6 (Figure 1(c)) and loose and irregular granular sludge was observed on day 30 (Figure 1(e))
The results indicated that adding the micropowder had a positive effect on the formation of aerobic granules and shortening the time of aerobic granulation
Summary
Aerobic granular sludge is a promising biotechnology in wastewater treatment. It has some advantages, including high biomass concentration, fast settling velocity and compact structure [1,2,3].The earlier work demonstrated that shortening settling time, increasing organic loading rate (OLR), extending starvation period and increasing shear force were beneficial to enhance aerobic granulation [4].Recently, rapid aerobic granulation has received more attention. Aerobic granular sludge is a promising biotechnology in wastewater treatment. It has some advantages, including high biomass concentration, fast settling velocity and compact structure [1,2,3]. Rapid aerobic granulation has received more attention. Some researchers tried to accelerate the aerobic granulation according to mechanism of “nuclei”. The nuclei hypothesis theory was first proposed by Lettinga et al [5]. This theory suggests that the formation of granules is similar to a crystallization process. Coal ash, activated carbon, calcium chloride and coagulants commonly act as nuclei for anaerobic or aerobic granulation. It was reported that divalent metal ions such as Ca2+, Mg2+
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