REMOVAL OF AQUEOUS MERCURY AND PHOSPHATE BY GEL-ENTRAPPED CHLORELLA IN PACKED-BED REACTORS

The removal of mercury from aqueous solution by packed-bed reactors (P BRs) containing Chlorella emersonii (CCAP 211/8A) entrapped in alginat e and agarose gels was studied. Reactors were constructed from chromat ography columns packed with 200 gel particles 4-6 mm in diameter. The effects of variation in cell stocking density, influent mercury concen tration, and medium flow rate on mercury removal were investigated. Ph osphate uptake activity was abo evaluated to give an indication of cel l viability. Accumulation of mercury by gel-entrapped Chlorella in pac ked-bed reactors was found to be only a small percentage (typically 5- 20%) of that supplied to such reactors, whereas losses due to volatili zation were more extensive (typically 40-90%). Levels of volatilizatio n could be reduced by using agarose rather than alginate as the immobi lization matrix. Variation in cell stocking density and flow rate enab led optimization of mercury accumulation, but levels of accumulation w ere always much lower than those reported in previous batch culture st udies (i.e., 40-50%). Operation of reactors in a recycle mode resulted in no increase in metal bioaccumulation by the immobilized cell parti cles, but did increase mercury loss through volatilization. Extensive volatilization thus remains a major hindrance to the stable removal of mercury from aqueous effluents by gel-entrapped Chlorella, and modifi ed/alternative systems worthy of further investigation are suggested.