United States
Environmental Protection
Agency
Municipal Environmental
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-84-117 Sept. 1984
Project Summary
Chlorinated Organic Compounds
in Digested, Heat-Conditioned,
and Purifax-Treated Sludges
Albert B. Pincince and Christopher J. Fournier
A study was conducted to investigate
the effects of sludge stabilization
methods on the production of priority
pollutants and chlorinated organics.
Three stabilization methods were
examined in pilot studies— the Purifax*
process, anaerobic digestion, and heat
conditioning.
Results showed that sludge processed
by the Purifax process at chlorine
dosages normally used in processing
wastewater sludges contains 2 to >14
times the total organic chlorine in raw
sludge. Both insoluble and soluble
forms of organic chlorine increase with
chlorine dosage. According to the
study, most of the chlorinated
compounds are associated with the
solid fraction of the sludge. More than
94 percent of the total organic chlorine
is insoluble, and about 97 percent of
that is associated with the cake. Using
the Tchebychev inequality, it was deter-
mined that the probability that Purifax
treatment produces the same
concentration of insoluble organic
chlorine in sludge cake as the other
stabilization processes is less than
22.5 percent (assuming a unimodal
distribution, this probability is less than
10 percent). Leachate obtained by the
EPA extraction procedure contained
less than 0.2 percent of the organic
chlorine in the sludge cake after Purifax
treatment. In analyses for priority
pollutants, less than 16 percent of the
chlorinated material was identified. A
new analytical technique using
ionization/gas chromatography/mass
*Mention of trade names or commercial products
does not constitute endorsement or recommenda-
tion for use
spectrometry gave results inconsistent
with the priority pollutant analyses.
This Project Summary was ifeve/oped
by EPA's f(^unicipal Environmental Re-
search Laboratory, Cincinnati. OH, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
In the Purifax process, chlorine gas is
added to wastewater sludge, septage, or
digester supernatant to stabilize and
condition the material before dewatering
and disposal. The chlorine dosage is high
(50,000 mg/kg of dry solids), and the
residual chlorine concentration is also
high (roughly 60 to 400 mg/L). Because
of these high concentrations, concern
has existed that the process might
produce unacceptable levels of
chlorinated organics. The objective of this
study was therefore to determine the
effects of stabilization processes on the
production of priority pollutants and
chlorinated organics. Three stabilization
methods were examined-the Purifax
process, anaerobic digestion, and heat
conditioning.
Procedures
Sources of Sludge
To allow for variability in sludges from
plants receiving different types of
wastewater, sludges were tested from
three wastewater treatment plants--
Amherst, Massachusetts, Willimantic,
Connecticut; and Pittsfield, Massachu-
setts The Amherst plant serves a
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residential area that has developed
around several college campuses. The
Willimantic plant receives flow from
some 20 industries, which constitutes
about 25 percent of the total flow for the
plant. Industrial processes include dyeing
of cotton and synthetics, production of
woolen fabrics, and poultry processing.
The Pittsfield plant receives about 5
percent of its total flow from two
industries—General Electric and the
Crane Paper Company. The General
Electric plant discharges pretreated
wastes containing phenolic compounds.
The Crane Paper Company's main dis-
charge consists of liquids from a pulp
digestion process.
Anaerobic Digestion
The feed material added to the batch
digesters included mixtures of rawsludge
and digested sludge seed in two ratios of
raw sludge to seed by volume, 25/75,
and 50/50.
Digestion temperature was maintained
at 35°C, and the digester contents were
continually mixed with digester gas. The
tests lasted 28 days. Gas production was
very low by that time, and changes in total
volatile solids were minimal. Also, the
total volatile solids in the sludge
approached the concentration in the
digester seed.
Heat Treatment
Bench-scale heat-conditioning tests
were conducted on a 1 -L autoclave. This
unit was used as a batch heat-condition-
ing system in which approximately 0.8 L
of sludge was mixed and heated for 30
min to 180°C at 970 kPa. (Full-scale heat-
conditioning units operate at 120° to
220°C and 1700 to 2000 kPa for 20 to 30
min.)
Purifax Pilot Tests
The pilot plant tests were conducted to
provide sludges with high, medium, and
low chlorine residuals (as compared with
medium residuals at full-scale Purifax
processing plants). Medium residuals
were those from 150 to 200 mg/L; high
residuals were 280 to 350 mg/L; and low
residuals were 60 to 120 mg/L.
Results
Only Purifax-treated sludges showed
substantial increases in total organic
chlorine after processing (Figure 1). In
these tests and others, the total organic
chlorine content in Purifax-treated
sludge is 2 to >14 times that in raw, heat-
conditioned, or digested sludge. The
200
700
Amherst Sludge
200
6
.0
I
a ;oo
roo
Pittsfield Sludge
Willimantic Sludge
I
to
I
<3
.0
,*5
•6
if
II
h
.
Figure 1. Effects of stabilization processes on total organic chlorine levels in sludge.
only exception is the concentration
shown for heat-conditioned sludge from
Pittsfield, which appears to be an error.
These ratios are for a chlorine residual of
about 170 mg/L (a medium residual),
which occurred after a chlorine dosage of
about 1500 mg/L. The dosage and
residual are comparable to those used at
Purifax plants.
The concentrations of soluble and
insoluble organic chlorine increase with
increased chlorine residual or chlorine
dosage. There is scatter to the data for all
four combinations, but a statistically
significant line of fit can be drawn
through the data. Coefficients of
determination (r2) range from 0.18 to
0.32. For the number of samples in each
case, the trends are significant at 1.5- to
8.1 -percent levels.
The tests showed that more than 94
percent of the total organic chlorine in all
tested sludges is insoluble. For Purifax-
treated sludge, more than 97 percent of
the organic chlorine is insoluble. Since
most of the organic chlorine is insoluble.
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nearly all of it ends up in the cake after
centrifuging. The data show that less
than 3 percent of the total organic
chlorine in processed sludge is in the
centrate. In the Purifax-treated samples,
only 1.4 percent of the chlorine was in
the centrate. And of the portion in the
cake, less than 0.2 percent was leached
by the EPA extraction procedure.
Tests were conducted to quantify and
identify chlorinated compounds present
before and after processing in sludge
from the Amherst wastewater plant (the
one serving a residential area). Test
methods included those for quantifying
organic priority pollutants and a new
analytical technique--ionization/gas
chromatography/mass spectrometry.
The tests for priority pollutants identified
only a portion of the chlorinated
compounds. For sludge samples, tests
identified less than 16 percent of the
chlorinated material in feed sludge and
less than 2.6 percent in Purifax-treated
sludge. For cake samples, tests identified
less than 0.1 percent of the residual
chlorinated compounds. Though the new
analytical technique identified com-
pounds with properties similar to those of
some chlorinated priority pollutants, the
two techniques identtfied different com-
pounds.
Purifax treatment of the Amherst
sludge produced an approximate 5-fold
increase in total chlorinated organics. It
appears that the identifiable chlorinated
organic compounds are approximately
the same before and after Purifax
processing, although proportions have
shifted. The reliability of the analytical
technique for quantifying the various
organic compounds is not sufficiently
trustworthy to permit statements about
quantitative changes in these compounds.
Confirming work is recommended, prefer-
ably with improved extractions and
analytical techniques.
The full report was submitted in
fulfillment of Contract No. 68-03-2803 by
Camp Dresser & McKee Inc. under the_ ^
sponsorship of the U.S. Environmental««,
Protection Agency.
Albert B. Pincince and Christopher J. Fournier are with Camp, Dresser & McKee,
Boston. MA €2108.
James A. Ryan is the EPA Project Officer fsee below).
The complete report, entitled "Chlorinated Organic Compounds in Digested, Heat-
Conditioned, Purifax-Treated Sludges." (Order No. PB 84-212 695; Cost:
$13.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati. OH 45268
•ft U S. GOVERNMENT PRINTING OFFICE; 1984 — 759-015/7803
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isearch
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