Steel slag filter design criteria for phosphorus removal from wastewater in decentralized applications

Abstract

The objective of this project was to develop a novel phosphorus removal system using steel slag filters applicable in decentralized applications and to propose design criteria about maintenance needs. Slag exhaustion functions were measured on 2-3 mm, 3-5 mm, 5-10 mm and 16-23 mm slag. Three steel slag columns with particle size of 2-3 mm, 3-5 mm and 5-10 mm were fed with the effluent of an aerated lagoon during 589 days. A barrel reactor test was fed during 365 days with the effluent of an attached growth aerated biological reactor. The o-PO concentration at the effluent of the 2-3 mm and 3-5 mm columns and barrel reactor test was between 0.04 and 0.3 mg P/L. Particulate phosphorus, however, was removed by about 50%. The P-Hydroslag model implemented in PHREEQC was successfully calibrated with data from the column test, and validated with data from the barrel reactor test. The calibrated model was used to simulate long-term operation of a slag barrel reactor with two parallel streams of five replaceable steel slag barrels, with total hydraulic retention time of voids of 15 h. The system longevity was strongly influenced by the influent alkalinity. The simulated longevity was 7 years with an influent alkalinity of 50 mg CaCO/L and 2 years with an influent of 210 mg CaCO/L. The alkalinity of the steel slag filter influent was influenced by the type of aquifer supplying drinking water, the presence of nitrification activity and by the CO concentration in the enriched air of the upstream biological process. Simulated scenarios with partial barrel replacement (e. g. barrels 1 and 2 out of 5 replaced at frequency of 0.5, 1, 1.5, 2, 2.5, 3, 3.5 or 4 years) increased the system longevity up to 14 years while slightly increasing the number of barrels needed.

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

“…The recirculation flow was set at 25%, 50% and 75% with respect to the influent flowrate, for days 0 to 100, 100 to 250 and 250 to 275, respectively. The steel slag filter was saturated with a porosity of approximately 40% based on previous experiments with the same media [9]. The steel slag filter was fed by continuous pumping.…”

“…Slag filters are economical, passive and efficient for phosphorus removal, which makes them appealing for decentralized treatment. Steel slag filters have been used for phosphorus removal in several pilot applications: secondary treatment of domestic wastewater [7] or dairy farm effluent [8], tertiary treatment of domestic wastewater [9], stormwater management [10] and lake remediation [11]. The main operational challenges for steel slag filters are exhaustion and clogging, which require the occasional replacement of media [9], and the need for an additional treatment step for effluent neutralization.…”

“…Steel slag filters have been used for phosphorus removal in several pilot applications: secondary treatment of domestic wastewater [7] or dairy farm effluent [8], tertiary treatment of domestic wastewater [9], stormwater management [10] and lake remediation [11]. The main operational challenges for steel slag filters are exhaustion and clogging, which require the occasional replacement of media [9], and the need for an additional treatment step for effluent neutralization. Steel slag filters achieve a high phosphorus removal efficiency with reported total phosphorus (TP) at the effluent of wastewater treatment systems below 1 mg P/L [6,9,11,12].…”

“…The main operational challenges for steel slag filters are exhaustion and clogging, which require the occasional replacement of media [9], and the need for an additional treatment step for effluent neutralization. Steel slag filters achieve a high phosphorus removal efficiency with reported total phosphorus (TP) at the effluent of wastewater treatment systems below 1 mg P/L [6,9,11,12].…”

Geochemical Characterization of Iron and Steel Slag and Its Potential to Remove Phosphate and Neutralize Acid

“…Previous studies have documented the effectiveness of ferrous slag as a sorbent to remove nutrients and trace elements from solution to control unwanted anthropogenic emissions, as summarized by Piatak et al [1]. Numerous studies have documented the effectiveness of using steelmaking slag to remove phosphorus (P) from wastewaters and agricultural runoff [3][4][5][6][7][8][9][10][11][12][13][14][15]. Ferrous slag has also been shown to be an effective acid-neutralizing agent with applications in the treatment of acid-mine drainage from coal and base-metal operations [16][17][18][19][20][21][22].…”