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Open AccessFeature PaperArticle

Phosphorus Removal and Carbon Dioxide Capture in a Pilot Conventional Septic System Upgraded with a Sidestream Steel Slag Filter

1
Department of Civil, Geological and Mining Engineering, Polytechnique Montréal, Montréal, QC H3C 3A7, Canada
2
Department of Chemical Engineering, McGill University, 3610 University Street, Montréal, QC H3A 0C5, Canada
3
Bionest, 55, 12th Street, P.O. Box 10070, Shawinigan, QC G9T 5K7, Canada
*
Author to whom correspondence should be addressed.
Water 2020, 12(1), 275; https://doi.org/10.3390/w12010275
Received: 31 October 2019 / Revised: 9 January 2020 / Accepted: 14 January 2020 / Published: 17 January 2020
The objective of this work was to demonstrate the removal of the phosphorus and carbon dioxide capture potential of a conventional septic system upgraded with a sidestream steel slag filter used in recirculation mode. A pilot scale sidestream experiment was conducted with two septic tank and drainfield systems, one with and one without a sidestream slag filter. The experimental system was fed with real domestic wastewater. Recirculation ratios of 25%, 50% and 75% were tested. Limestone soils and non-calcareous soils were used as drainfield media. The tested system achieved a satisfactory compromise between phosphorus removal and pH at the effluent of the septic tank, thus eliminating the need for a neutralization step. The phosphorus removal efficiency observed in the second compartment of the septic tank was 30% in the slag filter upgraded system, compared to −3% in the control system. The slag filter reached a phosphorus retention of 105 mg/kg. The drainfield of non-calcareous soils achieved very high phosphorus removal in both control and upgraded systems. In the drainfield of limestone soil, the slag filtration reduced the groundwater phosphorus contamination load by up to 75%. The removal of chemical oxygen demand of the drainfields was not affected by the pH rise induced by the slag filter. Phosphorus removal in the septic tank with a slag filter was attributed to either sorption on newly precipitated calcium carbonate, or the precipitation of phosphate minerals, or both. Recirculation ratio design criteria were proposed based on simulations. Simulations showed that the steel slag filter partly inhibited the biological production of carbon dioxide in the septic tank. The influent alkalinity strongly influenced the recirculation ratio needed to raise the pH in the septic tank. The recirculation mode allowed clogging mitigation compared to a mainstream configuration, because an important part of chemical precipitation occurred in the septic tank. The control septic tank produced carbon dioxide, whereas the slag filter-upgraded septic tank was a carbon dioxide sink. View Full-Text
Keywords: hydroxyapatite; calcite; onsite wastewater treatment; PHREEQC; precipitation; groundwater contamination; septic tank; drainfield; reactive filter hydroxyapatite; calcite; onsite wastewater treatment; PHREEQC; precipitation; groundwater contamination; septic tank; drainfield; reactive filter
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MDPI and ACS Style

Claveau-Mallet, D.; Seltani, H.; Comeau, Y. Phosphorus Removal and Carbon Dioxide Capture in a Pilot Conventional Septic System Upgraded with a Sidestream Steel Slag Filter. Water 2020, 12, 275.

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