Table of Contents
Summary
Recent publications
and technical presentations claim:
"...Biological
tests show TCF EFFLUENTS LESS TOXIC.."1
"Our tests
show...the TCF methods at our mills produce the least toxic effluents..."1
"the TCF
effluents in all the tests have shown lower TEF values compared to
the ECF effluent.... The only difference between ECFand TCF production
is the bleaching process..."2
Critical analysis of
the data and methodology used to make these claims show they are misleading
and incorrect. The data used to make these claims are insufficient and
the comparison methodology is flawed for the following reasons:
- The observations
were not consistent. Neither primary treated whole mill effluent
produced using an ECF bleaching sequence nor primary
treated whole mill effluent produced using a TCF bleaching
sequence exerted a toxic response for three of the five biological
tests used;
- The comparison
cannot account for confounding factors, such as the contribution
of toxic substances from other sources within the mill, because the
biological tests were performed on whole mill effluent;
- Bleaching
effluents are not compared. Rather whole mill effluents were tested,
therefore biological responses due to changes in bleaching practice
cannot be assessed with certainty;
- Toxicity comparisons
use Toxicity Emission Factor (TEF). This is not a valid
methodology for comparing non-toxic effluents. It was designed
to normalize toxic effluents only, and is meaningless when no toxicity
is observed; and
- Biological tests
of other pulp mill bleaching effluents produced from both ECF
and TCF processes have shown no significant difference in toxicity
in other investigations.
Further levels of investigations
of the environmental impact of pulp mills are best conducted by analysis
of receiving ecosystems exposed to realistic concentrations of individual
mill effluents. Until results of model ecosystem studies or analyses of
the receiving ecosystem are peer reviewed, validated and published, conclusions
regarding which mill has the least adverse impacts on the environment
are premature. Furthermore, claims of reductions in toxicity of bleaching
processes should be based on toxicity measurements of bleaching effluents
only.
In the final analysis,
the risk that a particular mill presents to the environment is dependent
on the processes used in the mill as well as the performance of those
processes (i.e., spill control, degree of recovery, type of effluent
treatment, etc.)
Background
A recent publication1
used laboratory biological test results, summarized in Figure
1, to suggest that primary treated whole mill effluents from a mill
operating with a "Totally Chlorine-Free" (TCF) bleaching sequence may
be relatively less toxic than effluent from the same milloperating with
an "Elemental Chlorine-Free" (ECF) bleaching sequence. (Data for another
mill operating with a "Chlorine" (Cl) process is also presented.) The
data compares the relative toxicity of primary treated whole mill effluent
when operating with the ECF bleaching process to effluent from the same
mill operating with the TCF bleaching process.
The TCF pulping
and bleaching process incorporates extended cooking, oxygen delignification,
chelation (EDTA) treatment and hydrogen peroxide. The ECF pulping and
bleaching sequence incorporates extended cooking, oxygen delignification,
chlorine dioxide in the first stage of bleaching followed by oxygen
reinforced alkaline extraction, and two chlorine dioxide brightening
stages with an intermediate extraction stage. It is important to note
that the analyses are of primary treated whole mill effluent.
The mill does not have secondary biological treatment.
The relative toxicity
compares Toxicity Emission Factor (TEF).
TEF = (100/V)
x F
V = Effluent
concentration, (% by volume) at "EC50," "LOEC," etc.
F = Effluent flow, (m3/ADt)
From this equation
it follows that if the effluent is not toxic, i.e., EC50 > 100% by volume,
then all that can be said about the TEF value is that it is less than
the effluent flow rate, F.
TEF was designed
to normalize the toxicity of effluents with respect to effluent flow
rates. However, when V > 100%, the expression is meaningless. A non-toxic
effluent is non-toxic regardless of flow rate.
Toxicity Emission
Factor Comparison and Analysis
Another publication2,
presents similar data and is reproduced in Figures 2,
3, 4,
5, 6.
The figures compare the Toxicity Emission Factor for a variety of biological
tests. These figures are designed to show that when operating with the
TCF bleaching sequence, the TEF for the primary treated whole mill effluent
is consistently lower than when the mill is operating with the ECF sequence.
Presenting the
data in this manner creates the impression that the effluent from the
mill when operating with the TCF bleaching process is "less toxic."
However, for non-toxic effluents, all the charts identify is difference
in effluent flow rate, which is not a valid indicator of any environmental
impact.
Such charts are
thus meaningless when the effluents tested are non-toxic as in three
of the five biological tests: Ceriodaphnia Reproduction (Figure 2); Ceriodaphnia Acute
Toxicity (Figure 4);
and Selenastrum Growth Inhibition (Figure
5.)
Using such a methodology,
it cannot be said that one effluent is less toxic than another. The
only conclusion from Figures 2,
4 and 5
is that the specific effluent volume when the mill was operating with
the TCF bleaching sequence was less than when it was operating with
the ECF bleaching sequence, a fact that may be totally unrelated to
the bleaching process used and is environmentally irrelevant, at least
with respect to toxicity. To suggest otherwise is misleading.
Figures 3
and 6 do show toxic responses from
effluents produced when the mill was operating with the TCF and ECF
bleaching sequence. A more detailed discussion follows in later sections.
Biological Effect
Concentration Comparison and Analysis
While the TEF approach
for comparing effluents is technically invalid here, the effluents can
be compared by examining the effluent concentration required to produce
the biological effect examined in each separate test. Using the published2
Toxicity Emission Factor data and the specific effluent volume data,
the originally measured effect concentrations can be back calculated.
Table 1
Biological
Test and Mill Production Data
(Ref. Lövblad, R and Malmström. 1994 International Non-Chlorine
Bleaching Conference.) |
| Case |
Production
ADt/d |
Flow
m3/t |
Flow
1000 m3/d
(Calculated) |
TEF
(Reported) |
Effect
Conc., %
(Calculated) |
Test |
ECF-1
ECF-1
ECF-2
ECF-3
ECF-3
TCF-1
TCF-2
TCF-2
TCF-3
TCF-3 |
800
800
900
800
800
880
930
930
980
980 |
111
111
95
133
133
95
93
93
89
89 |
89
89
86
106
106
84
86
86
87
87 |
152
<111
173
<133
<133
<95
106
103
<89
<89 |
73
100
55
100
100
100
88
90
100
100 |
Microtox
Selenastrum
Zebra Repro
Cerio Repro
Cerio Acute
Selenastrum
Microtox
Zebra Repro
Cerio Repro
Cerio Acute |
When the mill was operating using the TCF or the ECF bleaching sequence,
100% effluent concentration exerted no toxic or observable effects for:
1) Selenastrum Growth Inhibition (Fig.
7); 2) Ceriodaphnia Reproduction (Fig.
8); and 3) Ceriodaphnia Acute Toxicity (Fig.
9.) This indicates that both processes, in this pulp mill, produce
non-toxic primary treated whole mill effluent.
The biological
tests did show differences between the effluents for Microtox and Zebra
fish reproduction, with lower effect concentrations for the ECF case
(Figs. 10 & 11)
and therefore greater TEF values (Figs. 3
& 6 .)
Therefore any discussion
of differences in "toxicity" should be restricted to effect concentrations
for Microtox and Zebra fish reproduction.
Zebra Fish Reproduction
Toxicity Comparison and Analysis
The Zebra fish
reproduction test results in Figure
11 show the primary treated whole mill effluent, when the
mill was operating with a TCF bleaching sequence, did not have an observable
effect until the effluent concentration was 90%. On the other hand,
when the mill was operating with an ECF bleaching sequence, an observable
effect occurred at lower concentration, 55%. At face value, these results
suggest that whole mill effluent identified as ECF-2 was more toxic
to Zebra fish eggs/fry than whole mill effluent identified as TCF-2.
However, in another
publication, based on mill experience, comparing softwood bleaching
effluents using ECF and TCF sequences, results do not show
that ECF bleaching effluent is more toxic to Zebra fish than TCF bleaching
effluent. For example, the following figure, prepared from published
data3 shows ECF and TCF biological tests
performed on bleaching effluent only. This more accurately depicts
the impact of the bleaching process.
Observations from
this data set are:
- There is no significant
difference between bleaching effluents produced with an ECF
bleaching sequence or a TCF bleaching sequence on Zebra fish acute
toxicity, egg hatching or larvae survival.
- The effluent
from the last washing filter, (brown stock decker), prior to bleaching,
is much more toxic in all tests compared to bleaching effluent. This
would indicate that a small change in washing losses, can make a significant
change to toxicity test results performed with whole mill effluents.
This further calls into question the TCF versus ECF comparisons by
Lövblad et al., as carryover of washing filter effluent to the
bleach plant could be a confounding effect.
The importance of Figure
12 is that it compares bleaching effluents, not primary treated
whole mill effluents. The influence of effluent from other pulp mill sources
on toxicity, i.e., wash filters, is avoided. In addition, the data shows
the importance of efficient washing and recovery of black liquor.
Perhaps most importantly, as the authors stated:
"... It also
implies that toxic substances released/emitted as a result of Pulp production
need not originate in the bleach plant... "3
Finally, since
the previously discussed data analysis1,2
was for primary treated whole mill effluent, which included all effluent
sources, it is not possible to conclude with certainty that the differences
seen in the Zebra fish reproduction effect concentrations or the Microtox
data are due solely or even in part to a difference in bleaching technology.
The differences observed could be from other sources, such as increased
washing losses,even though the reported COD discharges were essentially
the same2.
Therefore, based
on the data provided and:
- by only analyzing
primary treated whole final mill effluent;
- by not accounting
for other possible sources of toxic substances; and
- by not testing
bleaching effluents
the claims that:
"... Biological
tests show TCF EFFLUENTS LESS TOXIC... "1
"... Our
tests show ... the TCF methods at our mills produce the least toxic
effluents... "1
"... the
TCF effluents in all the tests have shown lower TEF values compared
to the ECF effluent.... The only difference between ECF and TCF production
is the bleaching process ..."2
are not supported by
the data.
Conclusions
Critical analysis
of the data and methodology shows that the claims made regarding the
relative toxicity of ECF and TCF are misleading and incorrect. The data
used to make these claims are insufficient and the comparison methodology
is flawed for the following reasons:
- The observations
were not consistent. Neither primary treated whole mill effluent
produced using an ECF bleaching sequence nor primary
treated whole mill effluent produced using a TCF bleaching
sequence exerted a toxic response for three of the five biological
tests used;
- The comparison
cannot account for confounding factors, such as the contribution
of toxic substances from other sources within the mill, because the
biological tests were performed on whole mill effluent;
- Bleaching
effluents are not compared. Rather whole mill effluents were tested,
therefore biological responses due to changes in bleaching practice
cannot be assessed with certainty;
- Toxicity comparisons
use Toxicity Emission Factor (TEF). This is not a valid
methodology for comparing non-toxic effluents. It was designed
to normalize toxic effluents only, and is meaningless when no toxicity
is observed; and
- Biological tests
of other pulp mill bleaching effluents produced from both ECF
and TCF processes have shown no significant difference in toxicity
in other investigations.
References
- "Response from
Södra Cell". Spring 1994. pp.6-7.
- Lövblad,
R. and Malmström, "Biological Effects of Kraft Pulp Mill Effluents-A
Comparison Between ECF and TCF Pulp Production". Proceeding, 1994
International Non-Chlorine Bleaching Conference. March 1994.
- Flink, J., Grundelius,
R. and Swan, B., "Modern ECF and TCF Bleaching". Proceedings, 1993
Non-Chlorine Bleaching Conference. March 1993.
Acknowledgment
This report was
reviewed by Dr. Keith Solomon, Environmental Toxicologist, Centre for
Toxicology, University of Guelph and Dr. Stella Swanson, Aquatic Biologist,
Golder Associates. Their comments were incorporated into the document.
The Alliance for Environmental Technology (AET) gratefully acknowledges
their contribution.
