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Effects of hydraulic retention time on aerobic granulation and granule growth kinetics at steady state with a fast start-up strategy

Effects of hydraulic retention time on aerobic granulation and granule growth kinetics at steady state with a fast start-up strategy
Effects of hydraulic retention time on aerobic granulation and granule growth kinetics at steady state with a fast start-up strategy
A hydraulic retention time (HRT) of 4, 6, and 8 h was employed, respectively, in three reactors to study the effects of HRT on granulation with a newly developed fast granulation strategy, i.e., a strategy by combining strong hydraulic selection pressure with high organic loading rate (OLR). Granules with clear boundary appeared within 24 h after reactor start-up and all reactors reached a pseudo steady state after 6-day operation. A 4-h HRT resulted in a relatively higher increasing rate in terms of granule size during granule development period, i.e., 208 ?m day?1, and the bigger granule size and the higher sludge volume index at the pseudo steady state. For HRT of 6 or 8 h, no obvious difference was observed. However, it was found that HRT influenced sludge retention time (SRT) and kinetics significantly. A HRT changing from 4 to 8 h led to an increased SRT from 3 to 21 days, a decreased observed specific biomass growth rate (? obs) and an decreased observed biomass yield (Y obs) of stable granules from 0.37 to 0.062 days?1, and 0.177 to 0.055 g MLVSS g?1 COD, respectively. Both ? obs and Y obs had a linear relationship with the reciprocal of HRT. In addition, the great difference of microbial community between seed sludge, sludge retained in the reactors, and sludge washed out indicated a strong microbial selection for fast granulation within 24 h. However, during the granule development period from day 1 to 6, no more microbial selection was observed except an adjustment of microbial community. Little influence of HRT on microbial population in granular sludge indicated a minor role of HRT played for granulation with the fast start-up strategy adopted in this study. The results demonstrated that hydraulic selection pressure for granulation was mainly from short settling time, which led to strong microbial selection during the granulation period. Meanwhile, although HRT did not affect granulation with the fast start-up strategy, it played an important role on sludge retention time and excess sludge production. Therefore, HRT should be carefully optimized to balance benefits and shortfalls it brings to aerobic granular sludge system.
aerobic granule, hydraulic selection pressure, cycle time, fast start-up, sequential batch reactor (SBR), settling time, microbial selection
0175-7598
469-477
Liu, Yongqiang
75adc6f8-aa83-484e-9e87-6c8442e344fa
Zhang, Xing
e92abcc2-6163-40b0-9b53-0a61bdf864d7
Zhang, Rui
71b0b627-7bd4-47c6-9f31-1f07ff8b52ab
Liu, Wen-Tso
fccdee24-dda4-4d44-b373-a575d59801cc
Tay, Joo-Hwa Tay
f5859228-c6f1-44c9-8c05-96f54b0ac7d0
Liu, Yongqiang
75adc6f8-aa83-484e-9e87-6c8442e344fa
Zhang, Xing
e92abcc2-6163-40b0-9b53-0a61bdf864d7
Zhang, Rui
71b0b627-7bd4-47c6-9f31-1f07ff8b52ab
Liu, Wen-Tso
fccdee24-dda4-4d44-b373-a575d59801cc
Tay, Joo-Hwa Tay
f5859228-c6f1-44c9-8c05-96f54b0ac7d0

Liu, Yongqiang, Zhang, Xing, Zhang, Rui, Liu, Wen-Tso and Tay, Joo-Hwa Tay (2016) Effects of hydraulic retention time on aerobic granulation and granule growth kinetics at steady state with a fast start-up strategy. Applied Microbiology and Biotechnology, 100 (1), 469-477. (doi:10.1007/s00253-015-6993-3). (PMID:26403920)

Record type: Article

Abstract

A hydraulic retention time (HRT) of 4, 6, and 8 h was employed, respectively, in three reactors to study the effects of HRT on granulation with a newly developed fast granulation strategy, i.e., a strategy by combining strong hydraulic selection pressure with high organic loading rate (OLR). Granules with clear boundary appeared within 24 h after reactor start-up and all reactors reached a pseudo steady state after 6-day operation. A 4-h HRT resulted in a relatively higher increasing rate in terms of granule size during granule development period, i.e., 208 ?m day?1, and the bigger granule size and the higher sludge volume index at the pseudo steady state. For HRT of 6 or 8 h, no obvious difference was observed. However, it was found that HRT influenced sludge retention time (SRT) and kinetics significantly. A HRT changing from 4 to 8 h led to an increased SRT from 3 to 21 days, a decreased observed specific biomass growth rate (? obs) and an decreased observed biomass yield (Y obs) of stable granules from 0.37 to 0.062 days?1, and 0.177 to 0.055 g MLVSS g?1 COD, respectively. Both ? obs and Y obs had a linear relationship with the reciprocal of HRT. In addition, the great difference of microbial community between seed sludge, sludge retained in the reactors, and sludge washed out indicated a strong microbial selection for fast granulation within 24 h. However, during the granule development period from day 1 to 6, no more microbial selection was observed except an adjustment of microbial community. Little influence of HRT on microbial population in granular sludge indicated a minor role of HRT played for granulation with the fast start-up strategy adopted in this study. The results demonstrated that hydraulic selection pressure for granulation was mainly from short settling time, which led to strong microbial selection during the granulation period. Meanwhile, although HRT did not affect granulation with the fast start-up strategy, it played an important role on sludge retention time and excess sludge production. Therefore, HRT should be carefully optimized to balance benefits and shortfalls it brings to aerobic granular sludge system.

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More information

e-pub ahead of print date: 25 September 2015
Published date: March 2016
Keywords: aerobic granule, hydraulic selection pressure, cycle time, fast start-up, sequential batch reactor (SBR), settling time, microbial selection
Organisations: Water & Environmental Engineering Group

Identifiers

Local EPrints ID: 382255
URI: https://eprints.soton.ac.uk/id/eprint/382255
ISSN: 0175-7598
PURE UUID: b08d0b20-f9b9-49fe-9bb8-662e49708401

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Date deposited: 02 Oct 2015 15:23
Last modified: 15 Jul 2019 21:03

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