University of Oulu

Elisangela Heiderscheidt, Tiina Leiviskä, Evaluating the influence of pH adjustment on chemical purification efficiency and the suitability of industrial by-products as alkaline agents, Journal of Environmental Management, Volume 213, 2018, Pages 180-188, ISSN 0301-4797, https://doi.org/10.1016/j.jenvman.2018.02.067

Evaluating the influence of pH adjustment on chemical purification efficiency and the suitability of industrial by-products as alkaline agents

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Author: Heiderscheidt, Elisangela1; Leiviskä, Tiina2
Organizations: 1Water Resources and Environmental Engineering, Faculty of Technology, University of Oulu, 90014, Oulu, Finland
2Chemical Process Engineering, Faculty of Technology, University of Oulu, 90014, Oulu, Finland
Format: article
Version: accepted version
Access: embargoed
Persistent link: http://urn.fi/urn:nbn:fi-fe2019112143505
Language: English
Published: Elsevier, 2018
Publish Date: 2020-02-27
Description:

Abstract

Metal salts of iron are currently used in several treatment facilities purifying peat extraction runoff water. Although chemical purification is considered best available technology for the treatment of this natural humic water, fluctuations in purification efficiency occur with low pH (3–4) and high metal concentration found in treated waters. The need for pH neutralisation increases the costs and overall environmental impacts related to chemical purification. The use of industrial by-products can decrease costs while supporting the sustainable use of natural resources and the principle of a circular economy. This study investigated the suitability of a range of calcium-based alkaline products (including by-products of the paper, cement and mineral industries) for neutralisation of chemically treated runoff water. The influence of the time of pH adjustment relative to time of coagulant addition (before coagulant, after but within coagulation, during flocculation and after sedimentation) on purification efficiency was evaluated. The hypotheses that the physical form of the coagulant was a relevant factor affecting purification was also assessed. The best performing pH-adjusting products were cement kiln dust (CaO and SiO₂) and Mahtikalkki (Ca(OH)₂, CaCO₃ and CaO), by-products of the cement and paper industry, respectively. Time of pH adjustment in relation to time of coagulation addition had a significant influence on purification efficiency, especially when solid coagulant was used. Adjustment of pH at 30 s before coagulant dosing resulted in a negative effect on treatment results. Based on results obtained, suitable points of pH adjustment are during the flocculation stage or at the outlet of sedimentation, particularly if solid coagulants are used.

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Series: Journal of environmental management
ISSN: 0301-4797
ISSN-E: 1095-8630
ISSN-L: 0301-4797
Volume: 213
Pages: 180 - 188
DOI: 10.1016/j.jenvman.2018.02.067
OADOI: https://oadoi.org/10.1016/j.jenvman.2018.02.067
Type of Publication: A1 Journal article – refereed
Field of Science: 218 Environmental engineering
215 Chemical engineering
Subjects:
Funding: This research was supported by i) Maa-ja Vesitekniikan tuki r.y, ii) Water Resources and Environmental Engineering, University of Oulu, iii) Finnish Environment Institute (SYKE) and iv) Chemical Process Engineering, University of Oulu.
Copyright information: © 2018 Elsevier Ltd. All rights reserved.