Wanpen Wirojanagud, Netnapid Tantemsapya, and Puek Tantriratna

pp. 45 - 53

Abstract

Precipitation of heavy metals in synthetic and actual wastewater with lime mud (solid waste generated
from the pulp and paper production process) was experimented using Jar-tests. Separate synthetic wastewater samples were prepared for each of the following heavy metals: lead (1,433.7 mgPb²⁺/L), chromium
(506.7 mgCr³⁺/L), cadmium (1,095 mgCd²⁺/L) and mercury (9.37 mgHg²⁺/L). The actual wastewater was
tanning wastewater containing 74.49 mgCr³⁺/L and COD wastewater containing 683 mgHg²⁺/L. Adjustments
of pH in the acidic range, pH 2-7, were made for each type of synthetic wastewater except for the Hg synthetic
wastewater. The optimum conditions obtained from the tests of the synthetic wastewater were used for the
actual wastewater samples. Precipitation of heavy metals with lime mud was effective as indicated by the
removal efficiency as high as 90% up for Pb, Cd and Hg and 100% for Cr. However, the removal efficiency
for the Hg-COD wastewater was only 67%. The precipitating pH was in the range of 10 up, which is the common pH range for metal carbonate precipitation. The optimum dosage of lime mud for Pb, Cr, Cd and
Hg synthetic wastewater was 0.4-1.0 g/L, 2.0-4.0 g/L, 1.6-2.0g/L and 0.8 g/L, respectively. While the optimum
dosage of lime mud for precipitating chromium in tanning wastewater was 3.8 g/L and 3.6 g/L for precipitating mercury in COD wastewater.