Environmental Engineering Reference
In-Depth Information
Considerations on Compost Application
Biosolids and biosolid composts are likely to increase in many countries,
so there is an urgent need for sustainable ways for their disposal. In this short-
term study, EXCH-Cd and INOR-Cd were closely related to soil pH.
Application of biosolids compost alone did not substantially modify the
availability of Cd in Cd contaminated soils, possibly because soil pH was not
modified. The application of mature compost plus lime significantly reduced
Cd soluble/exchangeable fractions, with a proportional increase in the organic
and, to a lesser extent, inorganic-bound fractions. However, some uncertainty
may raise about Cd becoming more bioavailable with time through
mineralization or soil acidification. The long-term efficacy of this amendment
requires careful examination.
C
ONCLUSION
Remediation of Cd-contaminates soils can be achieved by adding
phosphate compounds or biosolids compost. Both amendments can enhance
Cd immobilization by redistribution of Cd to less available fractions.Phosphate
addition was found to decrease Cd availability, although the mechanisms of
Cd fixation is not fully known. Alternatively, the addition of alkaline biosolid
compost decreased the concentration of the soluble and exchangeable Cd
fraction, and increased the concentration of organic and, to a lesser extent,
inorganic-bound Cd fractions.
The environmental factor more likely to have the largest effect on Cd
availability is soil acidification. Consequently, if
in situ
remediation materials
exert their effect through changes in soil pH, then reacidification of soil would
return Cd to the original toxic level. Therefore, there may be a need to manage
soil pH in perpetuity if toxicity is to be avoided. Nevertheless, one of the
major inherent problems associated with these immobilization techniques is
that, although Cd becomes less bioavailable, total Cd concentration in soils
remains unchanged. In the long-term the immobilized element may become
more mobile and bioavailable through natural weathering processes.
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