Effects of Hydraulic Retention and Inorganic Carbon During Municipal Wastewater Treatment Using a Microalgal Bacterial Consortium

Thiruchchelvam, T; Johir, M; Krishna, KCB; Sathasivan, A

Effects of Hydraulic Retention and Inorganic Carbon During Municipal Wastewater Treatment Using a Microalgal Bacterial Consortium

Thiruchchelvam, T Johir, M

Krishna, KCB Sathasivan, A

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Publisher:: MDPI
Publication Type:: Journal Article
Citation:: WATER, 2026, 18, (1)
Issue Date:: 2026-12-24

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Field	Value	Language
dc.contributor.author	Thiruchchelvam, T
dc.contributor.author	Johir, M https://orcid.org/0000-0001-6222-6943
dc.contributor.author	Krishna, KCB
dc.contributor.author	Sathasivan, A
dc.date.accessioned	2026-06-09T02:31:28Z
dc.date.available	2026-06-09T02:31:28Z
dc.date.issued	2026-12-24
dc.identifier.citation	WATER, 2026, 18, (1)
dc.identifier.issn	2073-4441
dc.identifier.issn	2073-4441
dc.identifier.uri	http://hdl.handle.net/10453/195264
dc.description.abstract	Municipal wastewater (MWW) was treated using a microalgal–bacterial consortium without mechanical aeration. An inoculum for the reactor was prepared by acclimatizing Chlorella vulgaris to MWW and supplementing with a small amount of activated sludge. The hydraulic retention time (HRT) and solids retention time (SRT) were progressively reduced from 6.67 to 1.17 d and from 10 to 6.67 d, respectively, to test the process robustness under realistic MWW operation. The COD removal efficiency was 88% at 0.23 kg-COD/m3/d. Mass balance suggested the major nitrogen and phosphorus removal mechanism as assimilation. A high percentage (80%) of oxidized nitrogen indicated an efficient nitrification at all HRTs. Inorganic carbon (IC) balance calculation explained the observed IC dynamics. The chlorophyll a-to-mixed liquor volatile suspended solids (MLVSS) ratio and percentage of nitrite responded to IC limitation and supplementation. The mixed liquor exhibited excellent settleability (sludge volume index: 42 mL/g) with dense algal–bacterial flocs. An increased organic loading rate, however, reduced daytime dissolved oxygen, suggesting limitation under non-aerated conditions. These findings demonstrate the potential of microalgal–bacterial systems to achieve efficient COD removal and nitrification at realistic HRTs without aeration while emphasizing the importance of IC management.
dc.language	English
dc.publisher	MDPI
dc.relation.ispartof	WATER
dc.relation.isbasedon	10.3390/w18010057
dc.rights	info:eu-repo/semantics/openAccess
dc.title	Effects of Hydraulic Retention and Inorganic Carbon During Municipal Wastewater Treatment Using a Microalgal Bacterial Consortium
dc.type	Journal Article
utslib.citation.volume	18
pubs.organisational-group	University of Technology Sydney
pubs.organisational-group	University of Technology Sydney/Faculty of Engineering and Information Technology
pubs.organisational-group	University of Technology Sydney/Faculty of Engineering and Information Technology/School of Civil and Environmental Engineering
pubs.organisational-group	University of Technology Sydney/UTS Groups
pubs.organisational-group	University of Technology Sydney/UTS Groups/Centre for Technology in Water and Wastewater (CTWW)
utslib.copyright.status	open_access	*
pubs.consider-herdc	false
dc.rights.license	This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0). To view a copy of this license, visit https://creativecommons.org/licenses/by/4.0/
dc.date.updated	2026-06-09T02:31:26Z
pubs.issue	1
pubs.publication-status	Published
pubs.volume	18
utslib.citation.issue	1

Abstract:

Municipal wastewater (MWW) was treated using a microalgal–bacterial consortium without mechanical aeration. An inoculum for the reactor was prepared by acclimatizing Chlorella vulgaris to MWW and supplementing with a small amount of activated sludge. The hydraulic retention time (HRT) and solids retention time (SRT) were progressively reduced from 6.67 to 1.17 d and from 10 to 6.67 d, respectively, to test the process robustness under realistic MWW operation. The COD removal efficiency was 88% at 0.23 kg-COD/m3/d. Mass balance suggested the major nitrogen and phosphorus removal mechanism as assimilation. A high percentage (80%) of oxidized nitrogen indicated an efficient nitrification at all HRTs. Inorganic carbon (IC) balance calculation explained the observed IC dynamics. The chlorophyll a-to-mixed liquor volatile suspended solids (MLVSS) ratio and percentage of nitrite responded to IC limitation and supplementation. The mixed liquor exhibited excellent settleability (sludge volume index: 42 mL/g) with dense algal–bacterial flocs. An increased organic loading rate, however, reduced daytime dissolved oxygen, suggesting limitation under non-aerated conditions. These findings demonstrate the potential of microalgal–bacterial systems to achieve efficient COD removal and nitrification at realistic HRTs without aeration while emphasizing the importance of IC management.

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http://hdl.handle.net/10453/195264