Envlron. Scl. Technol, 1889, 27, 1434- 1439
Chlorophenol Toxicity Removal and Monitoring in Aerobic Treatment: Recovery from Process Upsets Palvi M. Makinen,t Thomas J. Theno,* John F. Ferguson,? Jerry E. Ongerth,* and Jaakko A. Puhakka'lt
Department of Civil Engineering and Department of Environmental Health, University of Washington, Seattle, Washington 98195 Bioremediation of simulated groundwater containing 2,4,6trichlorophenol (TCP),2,3,4,6-tetrachlorophenol (TeCP), and pentachlorophenol (PCP) was studied in a laboratoryscale aerobic fluidized-bed reactor. Chlorophenols were the sole source of carbon and energy in the enrichment culture. At a hydraulic retention time of 5 h and chlorophenol loading rate of 445 mg L-l d-l, stable chlorophenol removal of over 99.7 % and adsorbable organic halogen removal of 99.4% were maintained with the mean inorganic chloride release (IC1) of 94 % . Oxygen consumption tests also indicated chlorophenol mineralization. Specific oxygen consumption decreased in the order: TCP > TeCP > PCP. Endogenous oxygen uptake rates varied from 3.4 to 4.7 mg oxygen (g of VSS)-l h-l, corresponding to biomass decay rates of 0.06-0.08 d-l. Net biomass yield in the process was 0.03 mg of VSS/mg of CP removed or 0.09 mg of VSS/mg of TOC removed. The effect of interruptions in oxygen supply on process performance and recovery was studied by monitoring chlorophenol concentrations and the impact of deteriorating effluent quality on Photobacterium phosphoreum (Microtox test). During steady reactor operation, the Microtox assay showed no effluent toxicity. The Microtox assay provided a reliable indication of chlorophenol degradation effectiveness. Process upsets were consistently accompanied by increases in effluent PCP concentration. Such conditions were detected sensitively and reliably by the Microtox assay.
Introduction Chlorophenols are introduced into the environment as products of chemical manufacture, through use as biocides, or as unintentional byproducts of, for example, pulp bleaching, water disinfection, or waste incineration. In addition, chlorophenols may be formed in the environment as chemical and biological breakdown products of other chlorinated xenobiotics such as chlorophenoxy herbicides ( I ) . Due to their toxicity, tendency to bioaccumulate, and persistence in the environment, chlorophenol contamination of soil and water is of concern, and remediation is warranted. Biodegradability of chlorophenols is wellknown (e.g., refs 2 and 3), and therefore, bioremediation is an attractive alternative for both in situ and liquid treatment applications. The sensitivity of bacteria toward chlorophenols varies, depending on the chlorophenol congener as well as the bacterial species (4). For example, PCP, is an uncoupler of oxidative phosphorylation (5). Thus, biological treatment processesfor these contaminants need to be carefully designed and monitored to prevent toxic effects on microbes responsible for degradation. A sensitive, rapid t Department f
of Civil Engineering. Department of Environmental Health.
1434 Environ. Sci. Technol., Vol. 27, No. 7, 1993
response monitoring test is needed to serve as an early indicator of bacterial toxicity and process failure. A variety of short-term biological screening tests have been developed to assess the toxicity of a substance to biological treatment. These include the use of mixed flora or specific test species for measurement of growth, respiration, viability, or bioluminescence (6-9). Aerobic fluidized-bed treatment of synthetic chlorophenol solutions ( 1 0 , I I )and chlorophenol contaminated groundwater (12)by an enriched mixed culture has been described previously. In this study, we characterized the growth of this enrichment culture and the stoichiometry of chlorophenol conversions. The response of the chlorophenol degradation process to upsets was also determined. The Microtox acute toxicity assay, in which luminescent bacteria were exposed to the treatment effluent, was successfully used to monitor chlorophenol degradation performance.
Experimental Section Reactor. Experiments were performed using a glass fluidized-bed reactor with pure oxygen aeration. The reactor dimensions were as follows: liquid volume 300 mL, height 360 mm, and inner diameter 48 mm. The fluidized-bed volume was held at 150 mL. The reactor was continuously fed and had an internal recycle. The recycle flow was adjusted to maintain the media volume expansion at 50 % ,resulting in a recycle ratio ranging from 500 to 1000. Silica-based biomass support material (50 g) with surface area of 1.3 m2/g and mean pore diameter of 6.5 hm (Celite R633, Manville, CO) was used for biomass attachment and retention. Dissolved oxygen (DO) in the reactor liquid was maintained at over 5 mg/L. Reactor temperature varied between 20 and 28 "C. Detailed description of the reactor design has been reported earlier (10, 11). Biomass. The source for enrichment was unacclimated activated sludge from a pilot-scale reactor treating simulated municipal sewage, seeded originally from a municipal sewage treatment plant, Tampere, Finland. Chlorophenol-degrading biomass was enriched and maintained using mono- and dichlorophenol(13) as the sole source of carbon and energy for 1year, and then actual TCP, TeCP, and PCP contaminated groundwater (Klirkola, Finland) at 44-55 mg/L of feed chlorophenol concentration (12)for 1.5 years prior to use as reactor inoculum in this study. Experimental Design. The process operating parameters, including loading rates and hydraulic retention times (HRT), were based on the fluidized-bed volume occupied by microorganisms. Growth on the reactor walls above the fluidized-bed and in the reactor tubings was removed, and, therefore, these volumes were excluded from the reaction volume. The reactor was inoculated with the chlorophenol degrading enrichment (80 mg of VSS in 2 g of carrier). 0013-936X/93/0927-1434$04.00/0
0 1993 American Chemical Society
Table I. Reactor Performance During Steady Operation.
compd
N
effluent content % remaining % released mean SD mean SD
TCP TeCP PCP AOX IC1
10 10
