PHOSPHORUS ADSORPTION AND DESORPTION CHARACTERISTICS OF CONSTRUCTED WETLAND GRAVELS AND STEELWORKS BY-PRODUCTS

Laboratory phosphorus (P) adsorption and desorption experiments were c onducted on 9 substrata to evaluate their potential to remove P from s ewage effluent. The substrata comprised 2 gravels used in constructed wetlands, Hawkesbury sandstone, and 6 steelworks by-products: granulat ed blast furnace slag, blast furnace slag, steel slag, fly ash, bottom ash, and coal wash. The studies involved ion-exchange experiments and calculation of Langmuir and Freundlich adsorption isotherms and colum n adsorption/desorption trials. The ability to adsorb P was then corre lated to the physico-chemical attributes including X-ray fluorescence analyses of each substratum. High P adsorption capacities (>380 mg/kg) were shown for granulated blast furnace slag, blast furnace slag, and steel slag, as well as fly ash. All steelworks by-products had adsorp tion capacities greater than the constructed wetland gravels and Hawke sbury sandstone. The P adsorption capacities of the substrata were sig nificantly correlated with Ca (r(2) = 0.9206), Mg (r(2) = 0.8681), pH (r(2) = 0.7009), S (r(2) = 0.6696), and Si (r(2) = 0.6438) when fly as h was omitted from the analyses. Further research is recommended to ev aluate the sustainability of using slags for P removal (as well as oth er contaminants present in wastewater), using full-scale constructed w etlands. Research should include an evaluation of any likely environme ntal impacts using leachability and toxicity studies.