Dual slag filters for enhanced phosphorus removal from domestic waste water: performance and mechanisms

Abstract

The phosphorus (P) removal of five combinations of dual filters consisting of blast furnace slag (BFS), argon oxygen decarburisation slag (AOD) and electric arc furnace slag (EAF) was evaluated in column experiments with domestic waste water. The columns were fed with waste water for 24 days. The column with only EAF had the best P removal performance (above 93% throughout the experiment). The speciation of the bound P was evaluated by P K-edge X-ray absorption near-edge structure (XANES) spectroscopy. In all five columns, the main P species of the slag packed in the outlet chamber was amorphous calcium phosphate (ACP). In samples from the inlet chambers, the contributions from crystalline Ca phosphates, P adsorbed on gibbsite and P adsorbed on ferrihydrite were usually much greater, suggesting a shift of P removal mechanism as the waste water travelled from the inlet to the outlet. The results provide strong evidence that P was predominantly removed by the slags through the formation of ACP. However, as the pH decreased with time due to the progressively lower dissolution of alkaline silicate minerals from the slag, the ACP was rendered unstable and hence redissolved, changing the P speciation. It is suggested that this process strongly affected the lifespan of the slag filters. Of the slags examined, EAF slag had the best P removal characteristics and BFS the worst, which probably reflected different dissolution rates of alkaline silicates in the slags.Electronic supplementary materialThe online version of this article (10.1007/s11356-017-0925-y) contains supplementary material, which is available to authorized users.

A Probabilistic Approach to Phosphorus Speciation of Soils Using P K-edge XANES Spectroscopy with Linear Combination Fitting

“…The final list of selected standards for soils, and the rationale for not including the other standards, is summarized in Table S2. In all, 15 standards were selected-of which one (the ACP standard) is only used at pH values above 7.5, as ACP is not stable below this pH value and will quickly dissolve [33]. The XANES spectra of the selected standards are shown in Figure S4.…”

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

“…Phosphorus removal from wastewater in decentralized applications (influent flowrate below 3600 L/d) is a challenge because low costs and low maintenance associated with small-scale systems are not compatible with phosphorus-removal technologies used in large scale facilities (Brunce et al 2018). Steel slag filters are attractive for domestic wastewater treatment in decentralized applications because of their high phosphorus removal efficiency, low costs and potential low maintenance needs (Zuo et al 2017). Effluent o-PO4 concentration as low as 0.1 mg P/L were observed in recent studies in which steel slag filters were fed with synthetic domestic wastewater (Blanco et al 2016), real domestic wastewater (Hussain et al 2015) or pretreated fish farm effluent (Kõiv et al 2016).…”

Determination of Phosphorus Removal Mechanism in Aerated and Unaerated Steel Slag Filter System as Secondary Treatment System for Textile Industrial Wastewater

“…The removals of phosphorus are likely to occur from the formation of calcium phosphate (Ca-P) owing to the high calcium content in steel slag. Other than that, the precipitation of hydroxyapatite (Ca5(PO4)3OH; HAP) and octacalcium phosphate (Ca8H2(PO4)6•5H2O; OCP) also contributed to phosphorus removal in steel slag filter system by the formation of white crystalline at the bottom of the filter [24]. Besides that, the removal of phosphorus by adsorption also plays and important role.…”