Physicochemical properties related to long-term phosphorus retention by drinking-water treatment residuals.
Drinking-water treatment residuals (WTRs) are nonhazardous materials that can be obtained free-of-charge from drinking-water treatment plants to reduce soluble phosphorus (P) concentrations in poorly P sorbing soils. Phosphorus sorption capacities of WTRs can vary 1-2 orders of magnitude, on the basis of short-term equilibration times (up to 7 d), but studies dealing with long-term (weeks to months) P retention by WTRs are lacking. Properties that most affect long-term P sorption capacities are pertinent to the efficacy of WTRs as amendments to stabilize P in soils. This research addressed the long-term (up to 80 d) P sorption/desorption characteristics and kinetics for seven WTRs, including the influence of specific surface area (SSA), porosity, and total C content on the overall magnitude of P sorption by seven WTRs. The data confirm a strong but variable affinity for P by WTRs. Aluminum-based WTRs tended to have higher P sorption capacity than Fe-based WTRs. Phosphorus sorption with time was biphasic in nature for most samples and best fit to a second-order rate model. The P sorption rate dependency was strongly correlated with a hysteretic P desorption, consistent with kinetic limitations on P desorption from micropores. Oxalate-extractable Al + Fe concentrations of the WTRs did not effectively explain long-term (80 d) P sorption capacities of the WTRs. Micropore (CO2-based) SSAs were greater than BET-N2 SSAs for most WTRs, except those with the lowest (<80 g kg(-1)) total C content. There was a significant negative linear correlation between the total C content and the CO2/N2 SSA ratio. The data suggest that C in WTRs increases microporosity, but reduces P sorption per unit pore volume or surface area. Hence, variability in C content confounds direct relations among SSA, porosity, and P sorption. Total C, N2-based SSA, and CO2-based SSAs explained 82% of the variability in the long-term P sorption capacities of the WTRs. Prediction of long-term P sorption capacities for different WTRs may be achieved by taking into account the three proposed variables.
Makris
Konstantinos C
KC
Environmental Geochemistry Laboratory, Department of Earth and Environmental Science, University of Texas, San Antonio, 6900 North Loop 1604, San Antonio, Texas 78249-0663, USA. Konstantinos.Makris@utsa.edu
Harris
Willie G
WG
O'Connor
George A
GA
Obreza
Thomas A
TA
Elliott
Herschel A
HA
D000327:Adsorption; D000535:Aluminum / Q000032:analysis / Q000737:chemistry; D002244:Carbon / Q000032:analysis; D002245:Carbon Dioxide / Q000737:chemistry; D007501:Iron / Q000032:analysis / Q000737:chemistry; D007700:Kinetics; D009584:Nitrogen / Q000737:chemistry; D010070:Oxalates / Q000737:chemistry; D010758:Phosphorus / Q000032:analysis* / Q000737:chemistry; D016062:Porosity; D013696:Temperature; D014865:Waste Disposal, Fluid / Q000379:methods*; D014873:Water Pollutants / Q000032:analysis*; D018508:Water Purification / Q000379:methods*; D014881:Water Supply
D010070:Oxalates; D014873:Water Pollutants; D002245:Carbon Dioxide; D010758:Phosphorus; D002244:Carbon; D000535:Aluminum; D007501:Iron; D009584:Nitrogen