The utility of alkaline phosphatase in the precipitation
of heavy metals such as Ni
2+, Cd
2+, Cr
3+/6+, and
Co
2+ (from single-ion solutions as well as tannery and
electroplating industrial effluents) under alkaline pH was
studied with respect to bacterial alkaline phosphatase
(enzyme from
Escherichia coli
C90) and calf intestinal
alkaline phosphatase using ascorbic acid 2-phosphate, a
natural substrate. Kinetic characteristics of both the
enzymes at different regimes of pH 8–11 were studied to
find the potential of the enzymes to remain active at certain
environmental conditions. Maximum enzymatic activity
was recorded at pH 9.5 and 10 for bacterial alkaline
phosphatase and calf intestinal alkaline phosphatase,
respectively. The precipitation of metal ions from singleion
solutions by bacterial alkaline phosphatase and calf
intestinal alkaline phosphatase occurred in the order:
Cd
2+ > Ni
2+ > Co
2+ > Cr
3+ > Cr
6+ and Co
2+ > Cd
2+ >
Ni
2+ > Cr
6+ > Cr
3+, respectively. The percentage of
precipitation of Cr
6+ from tannery effluent (initial concentration
560 ppm) by bacterial alkaline phosphatase was
found to be 15.57 % at 300 min while it was 71.47 % by
calf intestinal alkaline phosphatase within 120 min. Bacterial
alkaline phosphatase was found to be more efficient
than calf intestinal alkaline phosphatase in removing Cd
2+
from electroplating effluents from an initial concentration
of 734 ppm, and the percentage of precipitation by the
enzymes was 94.6 and 66 %, respectively. This work
demonstrates a promising eco-friendly approach for a
sustainable environment, as ascorbic acid 2-phosphate is a
naturally occurring and biodegradable substrate.
