Rapid Formation of Aerobic Granular Sludge and Its Mechanism in a Continuous-Flow Bioreactor

Abstract

Based on the principle of self-coagulation of microorganisms, the flocculant-producing denitrifying bacterial TN-14 sludge was added to the continuous-flow reactor for treating domestic sewage. The bacterial TN-14 sludge acted as the main seed sludge to promote the rapid formation of aerobic granular sludge. The sludge morphology, sludge volume index (SVI) values, amounts of extracellular polymeric substances (EPS), and the role of calcium in the granulation process of the sludge were investigated. Results showed that brown aerobic granules with the particle size of 0.5 ~ 2.0 mm was successfully cultivated at 40 days, and its SVI decreased from 122.62 mL g initially to 46.61 mL g and remained at 44.28 ~ 60.51 mL g afterwards. The protein (PN) content in sludge EPS increased from 76.4 mg g initially to 512.3 mg g. Compared with PN, the polysaccharide (PS) content did not change much throughout the operation process of the bioreactor. Energy-dispersive spectrum (EDS) showed that Ca elements were deposited inside the granular sludge, and X-ray diffraction (XRD) showed that Ca elements existed in the granular sludge in the forms of CaCO, KCaPO, CaPO, and CaO(PO). The formation mechanism of continuous-flow aerobic granular sludge was that bacterial TN-14 sludge could promote the EPS content of sludge, and PN content of EPS increases the hydrophobicity and settling performance of the sludge. Calcium mainly exists in the granular sludge in the form of inorganic calcium phosphate, and therefore plays the role of nucleation in sludge granulation.

Continuous flow reactors for cultivating aerobic granular sludge: configuration innovation, principle and research prospect

“…Some attempts have been made to achieve high granulation with reduced H/D ratio. A successful application was a continuous‐flow bioreactor (CFBR) with a height/length ratio of 3.75 47 . In this configuration, a vertical baffle divided the reactor into two parts, a sedimentation zone and an aeration zone.…”

“…However, PS with a simple structure is easily hydrolyzed, which results in the disintegration of AGS 90 . In contrast, the PN in EPS can increase the hydrophobicity of microorganisms 31,47 . Therefore, higher PN content promotes the maintenance of granule integrity 91,92 …”

“…The content of Fe, Si, Ca, Al, and P in the influent has been significantly concentrated in the mature granules cultured in CFRs (Table 3). Although the negative charge on the surface of microbial cells causes electrostatic repulsion between them, 47 these metal ions can result in microbial cells with opposite surface charges to interact and promote granulation 6,100,101 . In addition, metal cations can combine with anions in wastewater to form inorganic precipitates, such as Ca 4 O(PO 4 ) 2 , K 2 CaP 2 O 7 , and Ca 2 P 2 O 7 47 .…”

Rapid Startup of Simultaneous Nitrogen and Phosphorus Removal (SNPR) Process and the Bacterial Community Dynamics in a GSBR

“…The inoculated aerobic granular sludge (AGS) was obtained from our previous study [22]. The sludge was yellow, and its diameter and sludge volume index were approximately 0.6~1.5 mm and 38.1 mL/g, respectively.…”

Cultivation of aerobic granular sludge in a microbial fuel cell

“…At present, the formation conditions, formation mechanism, and pollutant removal performance of AGS are mainly carried out in sequential batch reactors with large aspect ratios (H/D) [4,5]. There are few reports on the cultivation of AGS in continuous flow reactors [6]. However, in actual wastewater treatment operations, continuous-flow operation of low-to-diameter ratio reactors are needed.…”