A reevaluation of the toxicity of coal conversion process waters.

Abstract

The acute toxicity to Daphnia magna of both untreated and treated process waters from a hydrocarbonization (HCZ) coal conversion process was evaluated recently by PARKHURST et al. (1979). Phenol, ammonia, and the three cresol isomers displayed additive toxicity in the untreated HCZ effluent. However, the treated HCZ effluent, in which concentrations of ammonia, phenol, and the cresols were reduced by biological oxidation, was much less toxic than might have been predicted from the concentrations of the individual components. At the LC50 dilution for the treated HCZ effluent, the concentration of total ammonia present was more than three times the LC50 value for D. maqna. This indicated a less-than-additive ammonia toxicity ~dT-6~--antagonistic interactions among ammonia and the other constituents. The less-than-additive ammonia toxicity was calculated from total ammonia concentrations and was attributed by PARKHURST et al. to a lower pH in the treated HCZ effluent than in a separate ammonia toxicity bioassay. But total ammonia includes both un-ionized ammonia (NH3) and ionized ammonia (NH4 +) in a pH- and temperature-dependent equilibrium. Un-ionized NH 3 is toxic to many aquatic organisms while NH4 + is relatively nontoxic (MCKEE and WOLF 1963). Therefore, if D__ L. magna are indeed more sensitive to NH 3 than to NH4 +, PARKHURST et al. incorrectly calculated the contribution of ammonia to the HCZ effluent toxicities by using total ammonia rather than un-ionized ammonia concentrations. Their interpretations of the importance of ammonia in these HCZ effluents may, therefore, be misleading and are reevaluated in the present report. The purposes of this paper are (1) to clarify the role of ammonia in the toxicity of complex coal conversion wastewaters, (2) to reevaluate the toxic contribution of ammonia in the treated HCZ effluent, and (3) to compare these results with literature reports for other coal conversion effluents (DEGRAEVE et al. 1980, HERBERT 1962). For the U.S. Department of Energy's Hanna-3 underground coal gasification (UCG) condenser water, DEGRAEVE et al. evaluated the interaction of phenol and ammonia in the toxicity of this process water to aquatic biota. Similarly, HERBERT determined the toxic contributions of phenol and ammonia in spent coal distillation process liquors to rainbow trout.