49 ANAEROBIC GRANULES DEVELOPED FOR REDUCTIVE
DECHLORINATION OF CHLOROPHENOLS AND
CHLORINATED ETHYLENE
Wei-Min Wu, Engineer
Jeffrey Nye, Scientist
Robert F. Hickey, Senior Engineer
Lakshmi Bhatnagar, Senior Scientist
Michigan Biotechnology Institute
Lansing, Michigan 48909
INTRODUCTION
Anaerobic processes have been developed for the treatment of organic wastes and wastewaters for
many years. It has also been demonstrated that anaerobic bacteria can perform reductive dechlorination of toxic chlorinated organic compounds including polychlorinated biphenyls (PCBs), tetrachlo-
roethylene (PCE) and chlorinated benzenes.1,6 These compounds are aerobically recalcitrant but can
be reductively dechlorinated to less chlorinated compounds, allowing for further mineralization to
C02 by aerobic organisms. In addition, some chlorinated aromatic compounds such as chlorophenols
and chlorobenzoates can be mineralized to CH4 and C02 under anaerobic conditions.
Anaerobic granules are self-immobilized microbial consortia which form a matrix structure with
diameters ranging from 0.1 to 5.0 mm. This granular structure helps protect the anaerobic bacteria
from unfavorable environmental conditions such as changes in pH and exposure to oxygen. It also
provides favorable conditions for syntrophic metabolism of substrates and cogrowth of different
microbial species. Anaerobic granules have a much higher cell-density than suspended-growth cultures and, therefore, have a high metabolic activity per unit volume. The prevalent organisms in
granules are, generally, methanogens, syntrophic acetogens, and hydrolytic-fermentative bacteria.2
Sulfate-reducing bacteria may also be present.3 The anaerobic granules developed on organic wastewaters which do not contain chlorinated organic compounds normally do not have significant
dechlorinating activity. However, anaerobic granules with special dechlorinating activities can be
developed by using microbial consortia which are able to form granular structure together with
additional dechlorinating organisms.
Anaerobic granular sludges have been developed for the treatment of various chlorinated compounds including pentachlorophenol (PCP), PCE and PCBs at Michigan Biotechnology Institute. In
this communication, we will describe the performance of anaerobic granules developed for the
dechlorination of PCP and PCE.
BACKGROUND
Reductive Dechlorination and Mineralization of PCP
Pentachlorophenol (PCP) is a biocide that was widely used in the United States, mainly for the
preservation of wood and wood products. Along with other chlorophenols, PCP has been listed as a
priority pollutant by the U.S. Environmental Protection Agency.4 PCP can be completely mineralized
to methane and C02 by anaerobic microorganisms.5 Sequential reductive dechlorination of PCP
occurs prior to complete mineralization in digested sludges, sediments and soils.1,5"12 Phenol can be
further degraded to methane and C02 by anaerobic organisms. The metabolic pathways of reductive
dechlorination of PCP were identified by several individual batch experiments and yielded a complex
pathway based on intermediate chlorophenols observed.5,6,11"14 The sequential dechlorination of
PCP could take place at any position, i.e., ortho, meta or para, and result in formation of various
chlorophenols with a lesser number of chlorine substituents. Eventually, these intermediate chlorophenols could be completely dechlorinated to phenol and subsequently mineralized to CH4 and
48th Purdue Industrial Waste Conference Proceedings, 1993 Lewis Publishers, Chelsea, Michigan 48118. Printed in
U.S.A.