Epsilon Archive for Student Projects

Abstract

Aluminium sulphate (Al2(SO4)3) is usually added during the drinking water treatment process
in order to precipitate organic and inorganic material, resulting in aluminium-based drinking
water treatment residual sludge (WTR). Since 2003 Swedish law no longer permits WTR to
be deposited in lakes, and there is an interest to explore the possibility to utilize WTR as soil
amendment. The aim of this study was to examine the effects of WTR application on crop
growth and concentrations of macronutrients and trace elements (including micronutrients and
potential toxic elements). A greenhouse pot experiment was conducted with three soils; a clay
loam rich in phosphorous (P), a loamy sand rich in P, and a silty loam with a low soil P
concentration, and two crop species Italian ryegrass (Lolium multiflorum Lam. cv. Fredrik)
and spring barley (Hordeum vulgare L., cv. Barbro) mainly used as livestock feed. Addition of
WTR at a rate of 30 tons (t) ha-1 revealed significantly higher yields (6.3 t ha-1) of Italian
ryegrass harvested twice, compared with a control without WTR addition (4.1 t ha-1) for a clay
loam. The corresponding value for a loamy sand was 7.0 t ha-1 with WTR compared with 4.1 t
ha-1 for the control. For the third soil studied, a silty loam, yield was only marginally higher
with WTR addition. Significantly higher yields were also found after application of 15 t ha-1
WRT to these soils. .In contrast, spring barley showed no significant increase in yield after
WTR application on any of the three soil types. Concentrations of copper (Cu) were
significantly higher in Italian ryegrass grown with WTR application (mean 9.3 mg kg-1)
compared with the control (7.2 mg kg-1). Both Italian ryegrass and spring barley grown on a
clay loam took up a significant amount of sulphur (S) from the WTR-amended soils compared
with the same soil with no amendment. On a clay loam with high soil concentrations of Cu
(25 mg kg-1), Cu offtake with Italian ryegrass was 0.049 kg ha-1. Molybdenum (Mo), and zinc
(Zn) may have been limiting for the growth of Italian ryegrass and spring barley, since their
concentrations in plants were significantly higher (28 mg kg-1 Mo and 32 mg kg-1 Zn) without
WTR application than at the higher load (30 ton ha-1) of WTR applied (9 mg kg-1 Mo and 30
mg kg-1 Zn). Concentrations of the trace elements Ni, Mo, Cu, Zn were below the limit
considered toxic to ruminants. However, the latter has only been poorly investigated.
Drinking water treatment residuals could be applied to soils like the clay loam and loamy sand
studied here as soil amendments when growing crops such as Italian ryegrass and spring
barley. For the silty loam, no positive effects or negative effects were apparent.