- Disposal of sewage sludge, which contaminated with heavy metals, to agricultural area
for consideration about suitable vegetable species and heavy metal contaminated in the
soil. Effects of two sewage sludge application rates (1,600 and 3,200 kg/rai) on growth
and heavy metals (Pb, Cd, Ni, Cu, Mn and Fe) accumulation in four vegetables (Chinese
Kale, Lettuce, Edible Rape and Kang-Kong) included heavy metals residual in the soil were
studied. Field experiment was carried out in an agricultural area at Pathum Thani Province
by using experimental design 2 x 4 factorial incompletely randomize. The results showed
that applied sewage sludge 1,600 and 3,200 kg/rai gave Chinese Kale and Kang-Kong products
equal to add fertilizer (25-7-7) 96 kg/rai. Only Edible Rape at the sewage sludge
application rate 3,200 kg/rai gave production significantly higher than added fertilizer.
On the other hand, added fertilizer gave Lettuce products higher than applied sewage
sludge 1,600 kg/rai. Sewage sludge application at both rate had no effect on accumulation
of heavy metals in Chinese Kale and Edible Rape difference among treatments but there were
resulted in increased Cu and Fe accumulation in the root system of Lettuce. Applied sewage
sludge 3,200 kg/rai enabled the increasing of Zn accumulation in the shoot system of
Lettuce and in the root system of Kang-Kong. All of heavy metals accumulated in four
vegetables in this experiment were in the range that generally accumulated in plant
tissue. The heavy metals content in the vegetables were within acceptable daily intake
(ADI) of FAO/WHO. Residue effect of heavy metals after applied sewage sludge were (1) non
significant difference among treatments on Pb, Cd, Cu and Fe contents in the soil (2)
increased both Ni content in the soil that grew Edible Rape and Zn content in the soil
that grew four vegetables. Moreover, Zn residual in the soil was increased following the
increasing rate of sewage sludge application. However heavy metals residual in the soil
were in the acceptable range for the agricultural soil.
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