Phosphorus Retention Mechanisms of a Water Treatment Residual

Abstract

Water treatment residuals (WTRs) are a by-product of municipal drinking water treatment plants and can have the capacity to adsorb tremendous amounts of P. Understanding the WTR phosphorus adsorption process is important for discerning the mechanism and tenacity of P retention. We studied P adsorbing mechanism(s) of an aluminum-based [Al2(SO4)3 x 14H2O] WTR from Englewood, CO. In a laboratory study, we shook mixtures of P-loaded WTR for 1 to 211 d followed by solution pH analysis, and solution Ca, Al, and P analysis via inductively coupled plasma atomic emission spectroscopy. After shaking periods, we also examined the solids fraction by X-ray diffraction (XRD) and electron microprobe analysis using wavelength dispersive spectroscopy (EMPA-WDS). The shaking results indicated an increase in pH from 7.2 to 8.2, an increase in desorbed Ca and Al concentrations, and a decrease in desorbed P concentration. The pH and desorbed Ca concentration increases suggested that CaCO3 controlled Ca solubility. Increased desorbed Al concentration may have been due to Al(OH)4 formation. Decreased P content, in conjunction with the pH increase, was consistent with calcium phosphate formation or precipitation. The system appeared to be undersaturated with respect to dicalcium phosphate (DCP; CaHPO4) and supersaturated with respect to octacalcium phosphate [OCP; Ca4H(PO4)3 x 2.5H2O]. The Ca and Al increases, as well as OCP formation, were supported by MINTEQA2 modeling. The XRD and EMPA-WDS results for all shaking times, however, suggested surface P chemisorption as an amorphous Al-P mineral phase.

Two strategies for improving animal farm wastewater treatment in reed beds

“…It can be explained that the abundance of aluminium ions in the sludge facilitated P removal from wastewater through ligand exchange. This is in agreement with the suggestions of Ippolito et al (2003) which state that P retention by water treatment plant residual may be due to chemisorption, as P may be initially adsorbed as an outer sphere complex or found in the diffuse ion swarm near the individual sludge particles.…”

Selenium adsorption to aluminum-based water treatment residuals

“…Because of their amorphous nature, WTRs have a large surface area (up to 105 m 2 g À1 ) [4] and are highly reactive. They have the proven ability to adsorb tremendous quantities of P [5,6] and have been shown to adsorb other oxyanions such as As(V), As(III), and ClO À 4 [7,8]. Water treatment residuals may also adsorb selenium species although this phenomenon and the bonding mechanisms have yet to be documented.…”

Effectiveness of a drinking-water treatment sludge in removing different phosphorus species from aqueous solution

“…Different masses of alum sludge ranging between 0.1g to 0.5 g and 100 ml of P suspension were hours [8,11], 48 hours [10], 6 days [12] and up to 80 days [4] with initial P concentration ranged from 5.0 to 3,500 mg P/L were reported in similar studies. Then the samples were removed from the shaker and filtered using a 0.45 Millipore membrane filter to separate the solids from the liquid.…”

“…Other recent studies explore the phosphorus adsorption ability of DWTS (especially aluminium based DWTS) and its use in other applications [6][7][8][9][10]. Ippolito et al [11] reported a high phosphorus-binding capacity of approximately 12.5 g P/kg DWTS while Dayton and Basta [12] claimed a capacity ranging from 10.4 to 37.0 g P/kg DWTS by examining 18 DWTSs in the U.S.…”