Lee et al. (2013) evaluated the effect of eggshell waste, combined
with a nitrogen, phosphorous and potassium fertilizer, on Cd and
Pb immobilisation in a neutral agricultural soil nearby abandoned
mines. Their study concluded that 80 days after incorporating 5%
(w/w) eggshell into soil, Cd and Pb concentrations extracted with
acetic acid were reduced up to 68 and 93%, respectively. In addition,
Ahmad et al. (2012) found that by adding 5% (w/w) of eggshell to a
neutral military shooting range soil, the Pb concentration extracted
with acetic acid was reduced by 68%, mainly due to pH increase
with further lead immobilisation via formation of Pb-hydroxide or
lanarkite. On the other hand, Ok et al. (2011) reported a reduction of
only 24.6% for Pb extracted with acetic acid, by also using 5% (w/w)
of eggshell, in a moderately acid soil.
Nevertheless, according to the European legal framework, ES is
classified as an animal by-product not intended for human consumption
(Regulation (EC) Nº 1069/2009 of the European Parliament
and the Council). Thus, the application of ES to soil may
require a prior thermal treatment to reduce the spreading risk of
pathogens into the environment and human health.
Co-composting is one of the ES treatment options that besides
promoting eggshell waste sanitation, can also deliver a tailored
compost rich in calcium carbonate. This product can enhance soil
remediation due to the presence of: i) stabilized/humified organic
matter that may promote soil metal immobilisation mainly through
adsorption reactions (Park et al., 2011) and ii) CaCO3 that may
precipitate heavy metals from soil solution. But to the best of the
authors' knowledge, the effect of eggshell rich organic compost on
heavy metal immobilisation in soil has not been addressed.
Accordingly, this study aims to evaluate the feasibility of using a
compost (CES) obtained from composting industrial eggshell with
other organic wastes, as a soil amendment for immobilisation of Pb
and Zn in acidic contaminated mining soil. For comparison, a
mature compost without eggshell (CWES) and natural eggshell (ES)
were also tested. The effects of such amendments on soil properties
were investigated at three levels: i) environmental availability and
speciation of Pb and Zn in soil, by using chemical extraction procedures,
ii) toxicity reduction of amended soil by performing bioassays
and iii) evaluation of CO2 emission from soil, after the
addition of such a carbonate rich amendment'.