1. The constant parameters obtained from
Table 2 the fitting of the linear form of the Langmuir model to the batch
Major elemental chemical composition of the aluminium-based water treatment
residual compared to other water treatment residual and potential wetland media.
Element
(mg g1)
Water treatment residual Other potential media
a b c d e f
Al 42.67 38.3–125.4 15–300 297 nd 0.065–0.084
Fe 3.336 16.3–26.1 5–66 102 nd 21.9–45.8
Ca 0.820 4.5–54.6 3–50 29 nd 12.1–34
P 0.123 0.5–4.4 0.2–4.4 3.5 nd nd
As 0.034 0.007–0.04 nd nd 0.001–0.07 nd
Pb 0.005 0.005–0.032 nd 0.04 0.03–11.69 nd
Mg 0.237 0.054–0.142 nd 8.9 nd 6.5–27.1
Mn 0.270 0.036–2.688 nd nd nd 0.39–0.846
Ti 0.099 nd nd nd nd nd
Zn 0.03 0.05–0.0017 nd 0.03 0.07–7.89 nd
*Cl- 16.1 nd nd nd nd nd
*SO4 2 8.3 nd nd nd nd nd
*SiO4 2 11.2 nd nd nd nd nd
*TOC 97.5 nd 8.5–225** nd nd nd
a This study, b DeWolfe (2006), c Makris and O’Connor (2007), d Babatunde and Zhao
(2007), e EPA (2001), f Kvarnstrom et al. (2004), *mean values obtained from Yang
et al. (2006), nd no data, **total carbon. Determination was carried out on air-dried
aluminum-based water treatment residual with particle sizes <2 mm.
60
65
70
75
80
85
90
95
100
0 24 48 72 96 120 144
Time (hours)
P removal (%)
5g/l 10g/l 15g/l 20g/l
Fig. 3. Kinetics of P removal as a function of adsorbent dosage (Al-WTR ¼ 5, 10, 15 and
20 g L1) using an initial P concentration of 5 mg L1 (error bars denote mean S.D).
A.O. Babatunde et al. / Environmental Pollution 157 (2009) 2830–2836 2833
data were used to determine the maximum P adsorption capacity of
the Al-WTR and other parameters and presented in Table 3. From
Table 3, it can be seen that the adsorption capacity decreased with
an increase in pH from 4 to 9, indicating that the adsorption process
is more favoured under acidic conditions. A decrease in the Al-WTR
adsorption maxima with increasing pH can be attributed to change
of surface potential and competitive adsorption between phosphate
and hydroxyl ions. The pH at the point of zero charge (pHpzc)
also plays an important role in the adsorption phenomenon. The
Al-WTR used in this study had a pHpzc of 8.5 (Yang et al., 2006). At
pH below the pHpzc, the surface would be positively charged.
Therefore, at low pH (with abundant positive sites), phosphate
adsorption will be facilitated by electrostatic and chemical attraction
onto the positively charged surface, but as the pH rises towards
and above the pHpzc, the surface becomes predominantly negatively
charged due to competitive adsorption of OH and phosphate
adsorption decreases. A maximum adsorption capacity of
31.9 mg P g1 was obtained at pH 4, about three times the value
obtained at pH 9. Several industrial by-products including slags,
shale, fly ash and bottom ash have been tested for their P removal
capacities. Their removal capacities evaluated from batch studies
ranged from 0.31 mg P g1 to 44.2 mg P g1 (Westholm, 2006).
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