University of Oulu

Cainglet, A., Kujala, K., Liimatainen, M., Prokkola, H., Piippo, S., Postila, H., Ronkanen, A.-K., & Heiderscheidt, E. (2023). The influence of coagulant type on the biological treatment of sewage sludge. Science of The Total Environment, 869, 161706.

The influence of coagulant type on the biological treatment of sewage sludge

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Author: Cainglet, Annaliza1; Kujala, Katharina1; Liimatainen, Maarit2;
Organizations: 1Water, Energy and Environmental Engineering Research Unit, Faculty of Technology, 90014, University of Oulu, Finland
2Natural Resources Institute Finland (Luke), Paavo Havaksentie 3, 90570 Oulu, Finland
3Sustainable Chemistry Research Unit, Faculty of Technology, 90014, University of Oulu, Finland
4Waste and Circular Economy Department, Finnish Environment Institute (SYKE), Latokartanonkaari 11, 00790 Helsinki, Finland
5Water Resources Department, Finnish Environment Institute (SYKE), Paavo Havaksentie 3, 90570 Oulu, Finland
Format: article
Version: accepted version
Access: embargoed
Persistent link:
Language: English
Published: Elsevier, 2023
Publish Date: 2025-01-20


Anaerobic digestion (AD) and composting are commonly utilized sludge management methods however, the influence of different coagulant types on these biological processes and their stabilized biomass characteristics have not been fully explained. In this study, the effect of the coagulant used in municipal wastewater treatment on the biological stabilization of sludge was investigated. Fully controlled and monitored small-scale AD and composting bioreactors were utilized. The coagulants tested included an inorganic coagulant (IC), polyaluminium chloride (PAC), and organic coagulants, (OC) polyamine (pAmine) and chitosan (Chit). Overall, the coagulant applied showed a measurable influence on the biological stabilization of sludge. The presence of complex organics compounds from OC in the sludge biomass was found to decrease biomass biodegradability while increasing gas production. During AD, Chit-sludge achieved higher biogas production than pAmine- and PAC-sludges (13 % and 16 %, respectively, in Nm³ CH₄ t−1 VS). In composting, pAmine-sludge achieved the highest feedstock temperature (34–35 °C) and CO₂ gas emissions, followed by Chit- (33 °C) and PAC-sludges (32 °C). Generally, tot-P concentration in PAC-sludge was higher than in pAmine and Chit-sludges both before (20, 17 and 15 g/kg DM, consecutively) and after AD (23, 21 and 20.5 g/kg DM, consecutively), and during the composting (31, 29.5 and 26 g/kg DM, consecutively) process. Tot-N concentrations (g/kg DM) showed a substantial increase after AD (pAmine and PAC ca 50 % and Chit 81 %), while a decrease was observed after composting, specifically in PAC-sludge (PAC 28 %, pAmine and Chit ⁓5 %). The selection of the most suitable coagulant by wastewater treatment facilities depends on the objective of the biological stabilization process. In cases where AD is applied and biogas yield is selected as the target output, the semi-natural OC Chit was found to be the best option among the coagulants tested. Comparably, when the nutrient content of resulting biosolids (AD or composting) is more relevant, it was found that OC-produced sludge contained higher N concentrations, while IC-produced sludge contained slightly higher P concentrations.

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Series: Science of the total environment
ISSN: 0048-9697
ISSN-E: 1879-1026
ISSN-L: 0048-9697
Volume: 869
Article number: 161706
DOI: 10.1016/j.scitotenv.2023.161706
Type of Publication: A1 Journal article – refereed
Field of Science: 218 Environmental engineering
Funding: This study was part of the NutriSludge project, funded by Maa-ja vesitekniikan tuki ry, the University of Oulu and other stakeholders in Finland (Pohjois-Suomen Vesivaliokunta, Lakeuden Keskuspuhdistamo, and the Finnish Water Utilities Development Fund).
Copyright information: © 2022. This manuscript version is made available under the CC-BY-NC-ND 4.0 license