Treatment of mercury in wastewater from condensate tank of petrochemical industry by activated carbon adsorption

Abstract

In this research the mercury adsorption from petrochemical industry by activated carbon was studied. The purpose of this study was to investigate mercury method to reduce the concentration of mercury in wastewater to 5 µg/L, according to the industrial effluent standard from Pollution Control Department, Thailand. Three activated carbons which were NORIT GAC 1240, CGC-12, and MERSORB ®LW were tested. NORIT GAC 1240 and CGC-12 were ordinary activated carbon, but MERSORB ®LW was an activated carbon impregnated with sulfur which was specific to mercury. Factors of mercury adsorption and design criteria were required for application in the real treatment unit. Adsorption tests were divided into two parts which were batch and column adsorption tests. The first part was batch test, pH, equilibrium time, and amount of activated carbon were studied so as to plot isotherm and select the suitable adsorbent and optimum conditions. In the continuous test, empty bed contact time was investigated to determine the design criteria for real application. Results from batch test showed that adsorption reached an equilibrium within 12 hours, NORIT GAC 1240 was the most appropriate adsorbent at pH 2, and it was unfavorable adsorption. Freundlich isotherm cannot be explained a mechanism of mercury adsorption directly, because other substances which were more concentrated than mercury can compete and interrupt the adsorption process. In continuous test, 2 hour empty bed contact time (EBCT) was set at the same as in the mercury treatment unit of the plant. Results indicated that NORIT GAC 1240 had a maximum adsorption capacity 111.3 µg/g which was closed to the calculation from adsorption isotherm. The outcomes specified that NORIT 1240 was highly selective to mercury. At breakthrough point, ratio of treated wastewater to amount of activated carbon was 372.7. When this design was applied in the real adsorption column which had inlet wastewater 8 m³/day, the process can operate 30.7 days and cost of the treatment was 300 Baht/ m³ wastewater.