Polyaluminium Chloride and Anionic Polyacrylamide Water Treatment Residuals as an Amendment in Soils for Phosphorus: Implications for Reuse in Stormwater Bioretention Systems

Polyaluminium chloride and anionic polyacrylamide water treatment residuals (PAC-APAM WTRs) as an amendment in three types of soils with the ratios (w/w) of 10%, 15%, and 20% were evaluated for phosphorus adsorption from aqueous solutions by batch studies. Compared with soils without PAC-APAM WTRs, the maximum adsorption capacity of phosphorus increased by 0.50 to 25.30% in silty clay soil with PAC-APAM WTRs, by 18.59 to 47.13% in loam soil with PAC-APAM WTRs, and by 38.30 to 64.35% in silty loam (loess) soil with PAC-APAM WTRs. Langmuir model gradually replaced Freundlich model for better describing the isotherm data with the increase of PAC-APAM WTRs in soils, indicating the predominant adsorption mechanism shifted from multilayer adsorption to monolayer adsorption. The better fit of pseudo-second-order model for kinetics data implied that the phosphorus adsorption was mostly irreversible which is desirable and favorable for reuse of PAC-APAM WTRs into soil-based filling media of stormwater bioretention systems. Both pH and temperature obviously impacted the phosphorus adsorption in all treatments in the range of pH 2 to 9 and 20 degrees C to 40 degrees C, respectively. FT-IR spectroscopy analysis illustrated that multiple groups participated in the adsorption reactions including -OH, organic Si-H, C = C or C = O, H-O-H, Fe(Al)-O, and Si-O-Al. This short-term study confirmed the phosphorus adsorption effects of PAC-APAM WTRs as an amendment in soils for potential engineering application in stormwater bioretention systems. Further studies are needed to evaluate phosphorus adsorption performance by soils with PAC-APAM WTRs addition in real stormwater under various flow conditions.