The effect of liquid waste addition on degradation of paper
products
Vijesh Karatt, Karthik Manchala, and John T. Novak*
Department of Civil and Environmental Engineering
Virginia Polytechnic Institute & State University, Blacksburg, VA 24061
*
phone 540-231-6132, jtnov@vt.edu
KEYWORDS: solid waste, inhibition, bioreactor landfill, cellulose, lignin, volatile solids,
volatile acids
FINAL REPORT
Prepared for the
Environmental Research and Education Foundation
Alexandria, VA
Submittal Date - May, 2009
Executive Summary
INTRODUCTION:
The RD&D rule in the Resource Conservation and Recovery Act (RCRA) allows for
wastes that do not pass the paint filter test to be added to landfills. Outside commercial
liquids and sludges can be added to provide nutrients and needed moisture as necessary in
many bioreactor landfills to insure that the treatment cells achieve optimum moisture in a
timely manner. In order to reach 30% to 45% moisture by weight, sites must add 25 to 70
gallons of water per cubic yard of in-place waste. Leachate volumes at most properties
cannot meet this demand. This need, coupled with opposition to land application of
biosolids and tightening regulations at local wastewater treatment plants for industrial
wastes, makes the disposal of liquids to bioreactor landfills a convenient outlet for these
materials.
Before accepting outside liquids or sludges it must be insured that the liquids will not
have an adverse effect on the microbiological processes within the landfill. Waste
stream(s) should be profiled just like any other special waste and supporting analytical
test data should be kept on file to prove that it is not a hazardous waste. Waste streams
that could have an adverse effect on methane production, odor generation, and air
emissions require a detailed investigation to insure that these liquids do not cause
problems.
The purpose of this study was to determine the effect of three types of liquid wastes on
the anaerobic degradation of paper products that would be typical of landfill materials. A
major constituent of landfilled solid waste is paper products. This material accounts for
most of the cellulose and lignin that enters the waste stream so focusing on paper
products as a first step in assessing the impact of liquid waste on degradation in
bioreactor landfills receiving liquid waste.
The liquids selected were beverage waste, paint waste and surfactants. The beverage
waste and paint waste was provided by Gary Hater from Waste Management, Inc. The
beverage and paint wastes were delivered to the Outer Loop landfill in Louisville, KY.
No surfactant waste was available so synthetic surfactant waste was used.
METHODS AND EXPERIMENTAL DESIGN:
The beverage waste with a COD of 250,000 mg/L was initially added at 15, 22.5 and
30% by weight to a mixture of paper, water and sewage sludge. Sewage sludge was
added to provide anaerobic organisms as a seed at 15% by weight. The mixed paper
sample was 30% by weight and the combined beverage waste and water was 55%. The
55% was needed to provide free water for sampling and analysis. A second phase was
conducted after evaluation of the data using 5 and 10% beverage waste.
Two separate experiments were conducted using paint waste with a COD of 237,500
mg/L. The first set of studies was conducted using 30, 22.5,15 and 7.5%. These samples
2
exhibited inhibition of methane generation so a second set was run using lower
concentrations at 7.5, 5 and 1%.
Surfactants were added at 50, 150, 250 and 500 mg/L. An equal mixture of dodecyl
benzene sulfonate and sodium lauryl sulfate was used as the surfactant waste. The
surfactant waste mixture was added to the liquid fraction on w/v basis. Based on these
results, a second phase was added using 500, 1000 and 2000 mg/L surfactants.
The experimental matrix is shown in Tables 1 and 2 for the two phases of the study.
Table 1 Experimental; Matrix for the First Phase of the Study
Control
Number
of
Reactors
Sample
by weight
Water
content
Waste
added
Anaerobic
seed
Beverage Waste
Surfactant Waste
Paint Waste
3
3
3
3
3
3
3
3
3
3
3
3
30%
30%
30%
30%
30%
30%
30%
30%
30%
30%
30%
30%
55%
25%
32.5%
40%
55%
55%
55%
55%
25%
32.5%
40%
47.5%
0
30%
22.5%
15%
50
mg/L
150
mg/L
250
mg/L
500
mg/L
30%
22.5%
15%
7.5%
15%
15%
15%
15%
15%
15%
15%
15%
15%
15%
15%
15%
X = none added
Table 2 Experimental; Matrix for the Second Phase of the Study
Control
Beverage Waste
Surfactant Waste
Paint Waste
Number of
reactors
Sample by
weight
Water
content
3
3
3
3
3
3
3
3
3
30%
30%
30%
30%
30%
30%
30%
30%
30%
55%
45%
50%
55%
55%
55%
54%
50%
45%
Waste added
0
10%
5%
500 mg/l
1000
mg/l
2000
mg/l
1%
5%
10%
15%
15%
15%
15%
15%
15%
15%
15%
15%
3000 mg/l
3000
mg/l
3000
mg/l
3000
mg/l
3000
mg/l
3000
mg/l
3000
mg/l
3000
mg/l
3000
mg/l
2000 mg/l
2000
mg/l
2000
mg/l
2000
mg/l
2000
mg/l
2000
mg/l
2000
mg/l
2000
mg/l
2000
mg/l
50 mg/l
50 mg/l
50 mg/l
50 mg/l
50 mg/l
50 mg/l
50 mg/l
50 mg/l
50 mg/l
Anaerobic
seed
Sodium
bicarbonate
Ammonium
chloride
Ferrous
sulfate
KEY FINDINGS:
3
Each of the liquids added to reactors containing mixed paper resulted in different
responses.
• Beverage waste, the largest volume of waste that is added at the Outer Loop Landfill
resulted in greatly decreased gas production and decreased volatile solids degradation. As
the quantity of waste increased, the effects on pH and degradation were more severe.
Even the addition of 5% beverage waste by weight resulted in decreased methane
production and slower degradation compared to a control reactor with no additional
liquid waste. It appears that beverage waste, with a COD of 250,000 mg/L is very readily
degradable so volatile fatty acid generation is rapid, resulting in a dramatic drop in pH.
Care should be taken when adding beverage wastes to a bioreactor landfill to reduce the
impact of rapid production of volatile fatty acids on the pH and degradation.
• Paint waste with a COD of 237,500 mg/L was added to reactors containing paper in
two trials. In the first trial, paint waste was added at concentrations of 7.5 to 30% by
weight. The paint waste resulted in inhibition of gas production and degradation. The pH
remained in a satisfactory range (7.0 to 8.0), indicating that the paint waste was toxic to
the microbial culture. In the second phase, buffering and nutrients were added. As a result
of the additives, the paint waste degraded rapidly, with more gas generated as the amount
of paint waste increased from 1% to 10. It is not clear how the additives reduced the
inhibition. However, it is likely that the additives resulted in precipitation of heavy
metals, either as sulfides (ferrous sulfate was added) or as carbonates (sodium
bicarbonate was added) or from a nutrient deficiency.
• Commercial surfactants were used to assess the impact of surfactant waste because
Waste Management, Inc. could not supply the necessary waste. At concentrations up to
2000 mg/L, little effect of surfactants was noted. It appears that surfactants at the
concentrations used in this study had no positive or negative impacts on paper
degradation. However, studies at higher concentrations may be warranted.
CONCLUSIONS:
Based on the data collected in this study, the following conclusions are made:
• Beverage waste is readily degradable. As a consequence, it has the potential to rapidly
produce volatile fatty acids through fermentation of the beverage constituents, primarily
sugars and alcohols, and lower the pH to levels that stop or slow degradation of paper and
methane generation.
• Paint waste appears to be inhibitory. Addition of a combination of sodium bicarbonate,
ferrous sulfate and ammonium chloride eliminated the inhibition, resulting in degradation
of the paint waste constituents. It was thought that the inhibition was not due to toxic
materials, but rather, to a nutrient deficiency. Once the nutrient deficiency was
eliminated, the paint waste degraded readily.
• Surfactants added to the waste paper had no negative or positive benefits. At the levels
tested, surfactants could be safely added to landfills.
4
Potential Applications:
Although waste liquids can add much needed moisture to bioreactor landfills, the
potential for disrupting the degradation by either lowering the pH by generating excessive
amounts of volatile fatty acids or adding inhibitory compounds should be considered.
Therefore, liquid wastes should be added in uniformly and distributed throughout the
waste to avoid high concentration that might interfere with degradation. Monitoring of
gas generation or leachate pH can be used to insure that excessive amounts are not added.
Both beverage waste and paint waste, the two most common wastes added to the Outer
Loop Landfill show the potential to disrupt degradation.
5
Table of Contents
Executive Summary
Introduction
Methods and experimental design
Key findings
Conclusions
Introduction
Potential Methane Disruption
Odor Causing Waste Streams:
Potential Air Emission
2
2
2
3
4
7
7
7
8
Results and Discussion
10
Beverage Waste
Control reactor:
Beverage Waste Reactors:
Surfactants
Paint Waste
10
10
11
17
22
Conclusions
29
Methods and Materials
30
Experimental Setup:
Materials:
Reactors:
Sample
Seed:
Wastes
Sampling
Analytical Methods
pH
Total Solids (TS), Volatile Solids (VS) and Water content:
Gas generation, methane and carbon dioxide:
Lignin, Cellulose and Hemicellulose :
Volatile fatty acids:
30
31
31
32
32
32
32
32
32
33
33
33
33
Acknowledgements
34
References
34
6
Introduction
The RD&D rule in RCRA allows for wastes that do not pass the paint filter test to
be added to landfills (Hater, 2003). Outside commercial liquids and sludges can be added
to provide nutrients and needed moisture is necessary in many bioreactor landfills to
insure that the treatment cells achieve optimum moisture in a timely manner. In order to
reach 35% to 45% moisture by weight, sites must add 25 to 70 gallons of water per cubic
yard of in-place waste. Leachate volumes at most properties cannot meet this demand.
This need, coupled with opposition to land application of biosolids and tightening
regulations at local wastewater treatment plants for industrial wastes, makes the disposal
of liquids to bioreactor landfills a convenient outlet for these materials.
Before accepting outside liquids or sludges it must be insured that the system will
be in compliance with all environmental regulations and that the waste stream will not
have an adverse effect on the microbiological processes within the landfill. Waste
stream(s) should be profiled just like any other special waste and supporting analytical
test data should be kept on file to prove that it is not a hazardous waste. Waste streams
that could have an adverse effect on methane production, odor generation, and air
emissions require a detailed investigation to insure that these liquids do not cause
problems.
Potential Methane Disruption
At least two mechanisms exist that can result in methane production disruption.
These are rapid fermentation resulting in a large drop in pH and the inhibition of the
methane producing organisms by inhibitory wastes. Waste streams that contain high
percentages of sugar by weight or CODs greater than 100,000 mg/l should be added
carefully to avoid dropping the mass of the landfill below a pH of 5.5. If large quantities
of honey, beverages, or corn syrup are added, the pH of the landfill may drop and
interfere with the biological degradation of waste. Also, some canning wastes have large
amounts of natural sugar and organic acids that can result in low pH conditions that will
inhibit bioactivity. Experience suggests that keeping the highly fermentable materials in
the center of the waste mass and away from the slopes on existing cells is mandatory.
Large continuous volumes of surfactants can inhibit methane generation and in
some cases act as a biocide. If surfactants or surfactant wash waters are being added, care
should be taken to dilute the incoming waste stream or avoid these waste streams
altogether. Waste streams from cosmetic manufacturers that contain significant amount
of siloxanes should be avoided, as they will affect the end use of the gas generated. High
levels of siloxanes will precipitate, causing problems with mechanical equipment and
pipes.
Odor Causing Waste Streams:
7
Odorous waste streams should be infiltrated (injected) into the waste mass in
trenches or equivalent and not be spread on the working face. Waste streams containing
any appreciable amount of sulfates should be avoided. Liquid waste streams containing
sulfates should be under 1000 ppm.
Potential Air Emission
Liquid waste streams and sludges from the petroleum industry (UST waters, tank
farms, rain water from tank farms, refineries etc.) should be screened in the profiling
process. Only trace amounts of VOC’s should be accepted and free product should be
avoided.
Below is a graph from a case history to be published by the USEPA in the second
interim report from the USEPA / WM CRADA (Cooperative Research & Development
Agreement) in early 2006. The referenced site in Louisville, Kentucky has 25+ major
liquid waste streams profiled for liquid addition to three bioreactor cells. The minimum
size of each cell is six acres. This system is accepting as much as 200,000 gallons per
week of outside commercial liquids.
Gallons
1000000
beverage waste
dry well water
dye water
oily waste
paint waste
food process water
ink water
septage
leachate
800000
600000
400000
200000
0
J
F M A M J
J
2004
A S O N D J
F M A
2005
Figure 1. Liquid Waste Stream Acceptance in Louisville Kentucky:
The major waste added to the Outer Loop Landfill is beverage waste. This
material contains primarily sugar and alcohols so is readily degradable. The second major
waste is paint waste. These two wastes were provide by Waste Management, Inc. for this
project. In addition, surfactant waste was of interest because of its potential to alter
degradation, either positively or negatively. All three wastes were studied in this project.
8
Specific Objectives were:
To evaluate the impact of beverage waste, paint waste and surfactants on the
anaerobic degradation of mixed paper in a simulated landfill environment. Specific items
to be evaluated were gas generation and content, volatile solids, cellulose, hemicellulose,
lignin, pH and volatile fatty acids.
9
Results and Discussion
Beverage Waste
The initial set up of the experiment consisted of reactors containing mixed paper
samples with dehydrated beverage syrup, primarily soft drink and beer residue, at
250,000 mg/L as COD, in triplicate at 3 different syrup concentrations. This was termed
as phase 1 of the project. A triplicate set of controls were set up with water added in place
of the liquid wastes. Later, an additional 12 reactors were added after the first half of the
research was completed and is termed as phase 2 of the project. The actual moisture
content of bioreactor landfills is expected to be 30 to 40% moisture. For this study, the
moisture content of the reactors was kept at 70%. This included the liquid waste. This
higher moisture content was necessary to provide free liquid in the reactors since the
sample was mainly paper products that absorb a large quantity of moisture.
Since paper and cardboard constitutes major part of the landfill material, the
sample used was a mixture of paper, cardboard and office paper. Further, plastic was
added for about 10% of the dry sample by weight. The combined paper and plastic was
30% by weight of the total reactor contents. As a source of microbes, anaerobically
digested sludge from the Peppers Ferry wastewater treatment plant in Dublin, VA was
added at 15% of the total weight of the reactor. The different concentrations of sugar
waste used in phase 1 were 30, 22.5 and 15% by weight. In phase 2 of the project,
reactors were added with 5% and 7.5% beverage wastes.
Samples were collected and analyzed once in every 15 days for the first 13
samplings and then monthly afterwards. Since the pH dropped in the sugar waste reactors
and remained low, they were brought up to neutral using NaHCO3 on the 150th day of
sampling.
Control reactor:
The gas volume and content generated by the control reactor is shown in Figure 2.
The carbon dioxide and methane generation curves are similar to what one would expect
for an ideal batch reactor, with more CO2 being generated initially and then larger
amounts of methane being produced. The data indicates that the control system is
operating satisfactorily. Additional data for the control reactor is included with the data
for the liquid wastes. All data are an average for three reactors.
10
Gas Composition by Volume (%)
60
50
40
30
20
CO2 PERCENTAGE
METHANE PERCENTAGE
10
`
0
0
50
100
150
200
Period of Decomposition (days)
250
300
Figure 2 Gas Composition for the Control Reactors
Beverage Waste Reactors:
It can be seen in Figure 3 that the pH in the beverage waste reactors decreased
drastically and was below 5.0 for several of the reactors whereas the control pH was
between 7 and 8 for the entire experimental period. The pH decrease in the beverage
waste reactors most likely occurred as a result of volatile fatty acids accumulation. At day
150, the pH was raised to neutral using NaHCO3 to further assess the performance. It can
be seen that the pH in the 30% waste reactors began to decline again, indicating
additional VFA production.
9
8
7
6
pH
5
4
3
control
Beverage waste 30%
2
`
Beverage waste 22.5%
Beverage waste 15%
Beverage waste 10%
Beverage waste 5%
1
0
0
50
100
150
200
250
300
period of decomposition(days)
Figure 3. Variation in pH for Reactors Containing Beverage Waste
11
The gas generated from the sugar waste reactors was much less than that of the
controls (Figure 4), even after the pH was raised. The maximum cumulative gas in the
control reactors was about 1.67 liters whereas the maximum cumulative gas in the
reactors containing beverage waste was 5,700 ml from the reactors containing 22.5%
beverage waste. All other beverage waste reactors had cumulative gas production less
than that of 22.5% with the 30% beverage waste reactors comparable to that of 22.5%.
Carbon dioxide emission also followed the same trend (Figure 5). There was no
appreciable gas production after 75 days (Figures 4 and 5). Similar trends were seen for
gas accumulation in reactors containing 5% and 10% beverage waste that were added in
phase 2. Methane production in the reactors was also consistent with the beverage
concentration in the reactors (Figure 6). The reactors with 5% beverage waste had the
highest methane production, but it was still substantially below the control. The data
show that beverage waste is capable of almost complete inhibition of methane
production, even at modest concentrations. It can also be seen that when the pH was
adjusted to between pH 7 and 8 on day 150, the gas production increased slightly but the
systems did not recover.
18000
16000
control
Beverage waste 30%
Beverage waste 22.5%
Beverage waste 15%
14000
total gas(ml)
12000
10000
Beverage waste 10%
Beverage waste 5%
8000
`
6000
4000
2000
0
0
50
100
150
200
250
300
period of decomposition(days)
Figure 4. Variation in Total Gas Production for Reactors Containing Beverage
Waste
12
control
Beverage waste 22.5%
Beverage waste 10%
8000
7000
Beverage waste 30%
Beverage waste 15%
Beverage waste 5%
cumulative CO2(ml)
6000
5000
4000
3000
2000
1000
0
0
50
100
150
200
250
300
period of decomposition(days)
Figure 5. Variation in CO2 Generation for Reactors Containing Beverage Waste
10000
cumulative methane(ml)
9000
8000
7000
control
6000
Beverage waste 30%
5000
Beverage waste 22.5%
4000
Beverage waste 15%
3000
Beverage waste 10%
2000
Beverage waste 5%
1000
0
0
50
100
150
200
250
300
period of decomposition(days)
Figure 6. Variation in Methane Generation for Reactors Containing Beverage
Waste
The reason for the inhibition in the reactors containing beverage waste was likely
due to rapid volatile fatty acid accumulation, resulting in the inhibition of methanogenic
activity (Veeken et al., 2000). This is supported by data for volatile fatty acid
concentrations in the reactors shown in Figure 7. The maximum total VFA in the
beverage waste reactor was found in the reactors containing 30% and 22.5% sugar
13
content. These VFAs were about 4 to 5 times higher than the maximum VFA content in
the control reactor. The VFA content in the other beverage reactors was less, and
consistent with the order of decreasing waste content. The minimum VFA concentration
in the 5% and 10% beverage waste reactors was almost equal to the maximum
concentration in the controls which occurred at the initial stages of the control operation.
6000
VFA concentration(mg/L)
5000
4000
control
Beverage waste 15%
3000
Beverage waste 30%
2000
Beverage waste 22.5%
Beverage waste10%
1000
Beverage waste 5%
0
0
50
100
150
200
250
300
Period of decomposition(days)
Figure 7. Volatile Fatty Acids in Reactors Containing Beverage Waste
The breakdown of individual VFA was also analyzed. It was seen that out of the
four major volatile fatty acids, acetic, propionic, butyric and valeric acid, the maximum
concentration of acetic acid and propionic acids was found in beverage waste reactors
containing 30% beverage waste, whereas the concentrations of valeric and butyric acids
were maximum in the 22.5% beverage waste reactors. However, there was little
difference in the VFA concentrations in the reactors containing 30%, 22.5% and 15%.
The VFA concentration in 10% and 5% sugar reactors was much less than reactors with
the highest beverage waste, but was more than the control reactors and as can be seen
from Figure 3, was enough to depress the pH to less than 5.
Further analysis of the degradation was carried out using analytical parameters for
landfill stability. An examination of the volatile solids (VS) of the beverage waste
reactors and controls shows that the decrease in VS concentration in the controls was
about 9% higher than any of the beverage waste reactors (Figure 8). There was not much
difference between the degradation trend of the VS among reactors containing 30%,
22.5% and 15% beverage waste. The VS degradation in the beverage waste reactors for
30%, 22.5% and 15% reactors were 6, 5 and 4% respectively whereas that of the control
reactors was about 9%.
14
control
Beverage waste 30%
Beverage waste 22.5%
Beverage waste 10%
Beverage waste 15%
Beverage waste 5%
100
96
VS(%)
92
88
84
80
76
0
50
100
150
200
250
300
Period of decomposition(days)
Figure 8 Volatile Solids in Reactors Containing Beverage Waste
An examination of lignin values revealed that lignin did not undergo appreciable
degradation in either the beverage waste reactors or the controls (Figure 9). The
maximum lignin percentage in the control was found to be about 21%. A decrease of 4%
lignin was observed in control reactors during the experiment while a degradation of
about 2% was observed in reactors containing 30%, 22.5% and 15% beverage content.
Although there was a decrease in the lignin content in reactors with 5 and 10% beverage
content, the trend was not clear due to the lack of sufficient data.
25
20
lignin(%)
15
10
control
Beverage waste 22.5%
Beverage waste 10%
5
Beverage waste 30%
Beverage waste 15%
Beverage waste 5%
0
0
50
100
150
200
Period of decomposition(days)
250
300
Figure 9 Change in Lignin in Reactors Containing Beverage Waste
15
Cellulose degradation was found to be a maximum in the control reactors
compared to the beverage waste reactors (Figure 10). A maximum degradation of 18%
was found in control reactors (from 59% to 41%) while the beverage waste reactors with
30% sugar showed a cellulose loss of about 9%. Both the reactors containing 22.5% and
15% show a maximum cellulose degradation of 12%. The beverage waste reactors
containing 10% and 5% sugar show a cellulose degradation of 9 and 10%, respectively
within the 120 days of the experiment. Over the same time period, the control reactors
showed a cellulose degradation of 13% while the 30% beverage waste reactors had a
cellulose degradation of only 5%.
70
60
Cellulose(%)
50
40
30
20
10
control
Beverage waste 30%
Beverage waste 22.5%
Beverage waste15%
Beverage waste 10%
Beverage waste 5%
0
0
50
100
150
200
Period of decomposition(days)
250
300
Figure 10 Change in Cellulose in Reactors Containing Beverage Waste
The main hemicellulose monomer in all the reactors was xylose. Hemicellulose
accounted for a maximum of about 23% of the total components in the control reactors
prior to degradation (Figure 11). This was degraded to 10% within 240 days while the
reactors containing 30% sugar decreased from 24% to about 13%. Reactors with a sugar
content of 22.5% and 15% decreased to a hemicellulose content of 13 and 15%
respectively. Over 120 days, the hemicellulose in 10% and 5% beverage waste reactors
degraded less than the control at the same time period.
16
Control
Beverage waste 22.5%
Beverage waste 10%
30
hemicellulose(%)
25
Beverage waste 30%
Beverage waste 15%
Beverage waste 5%
20
15
10
5
0
0
50
100
150
200
250
300
Period of decomposition(days)
Figure 11 Change in Hemicellulose in Reactors Containing Beverage Waste
The Cellulose/Lignin ratio (C/L) is a widely used parameter to describe the
landfill stability (Kelly et al., 2006). The cellulose to plastic ratio (C/P) can also serve as
a stability parameter and this was also examined. Plastics were manually removed during
the sampling and were weighed. The C/L value for control at the end of the degradation
period was 2.2 whereas the reactors with 30%, 22.5% and 15% beverage content had
values of 2.6, 2.85 and 2.7, respectively (figure not shown). It had been reported that a
most stable landfill will have a C/L of 0.23 (Kelly et al., 2006) which suggests that
degradation in all reactors was incomplete. The C/P data did not produce any clear trends
and this was thought to be due to incomplete collection of plastics which made the C/P
values highly variable.
In general, the data show that beverage waste has the potential to reduce the pH in
landfills if added at concentrations that overcome the buffering capacity of the waste. In
this study, as little as 5% beverage waste (12,500 mg/L COD), by weight, was sufficient
to drop the pH to less than 5, resulting in very low gas production and poor degradation
of cellulose and hemicellulose. Although the beverage waste is highly degradable, care
must be taken to avoid creating conditions that will decrease the rate of degradation.
When buffer was added at day 150, the reactors did not recover, indicating that the
inhibition was not reversible.
Surfactants
Surfactant waste was unavailable for this study so two surfactants, dodecyl benzene
sulfonate and sodium lauryl sulfate, were mixed 50% to 50% by weight and added to
mixed paper to determine the effect of surfactants on paper degradation. The
concentrations used were 50, 150, 250 and 500 mg/L and in a second phase, an additional
set of three surfactant concentrations of 500, 1000 and 2000 mg/L mg/L were studied.
17
The surfactants had little effect on degradation of paper as evidenced by the
volatile solids destruction shown in figure 12 for the phase 1 study and Figure 13 for the
phase 2 study. The data in Figure 12 suggests that the higher surfactant levels of 250 and
500 mg/L may have slowed degradation but the phase 2 data indicate that there is little
effect on degradation. The difference appears to be in the initial VS content in the various
reactors and that is likely the result of small differences in the amount of paper and
sludge initially added. Overall, the rates of degradation, as evidenced by the slope of the
plot, indicates that the degradation rates were similar for all surfactant additions and they
are similar to the control data.
100
95
90
VS(%)
85
80
75
control
surfactant 150 mg/L
surfactant 500 mg/L
70
surfactant 50 mg/L
surfactant 250 mg/L
65
0
50
100
150
200
250
300
Period of decomposition(days)
Figure 12. Effect of surfactants on volatile solids destruction, Phase 1.
18
surfactant 500mg/l
surfactant 1000mg/l
surfactant 1500mg/L
control
95
94
93
VS(%)
92
91
90
89
88
87
0
50
100
150
200
Period of decomposition(days)
Figure 13. Effect of surfactants on volatile solids destruction, Phase 2.
The effect of surfactants on the solution pH is shown in figure 14. It can be seen
from the data in Figure 14 that the surfactants had little impact on pH. The pH was
initially near 7.5 for the control and the surfactant amended reactors and increased
slightly as degradation proceeded.
9
8
pH
7
6
control
surfactant 150 mg/L
surfactant 500mg/L
5
suractant 50 mg/L
surfactant 250 mg/L
4
0
50
100
150
200
250
300
period of decomposition(days)
Figure 14. Effect of surfactants on pH
The pH data is consistent with the volatile fatty acid (VFA) data shown in Figure
15. In general, the VFAs dropped to 500 mg/L by day 100 and remained low. What is of
interest is the distribution of VFAs. It was expected that much of the VFAs would be
19
acetic acid. However, as shown in figures 15-18, the major VFA was propionic acid.
Propionic acid is a 3 carbon fatty acid. Since paper was the main ingredient in the
reactors, it is highly likely that propionic acid was generated from the anaerobic
degradation of cellulose. Because propionic acid can be inhibitory, its production may be
of importance. For the beverage waste, the major VFA was acetic acid with butyric acid
being the second most abundant. The fatty acids in beverage waste most likely came from
the breakdown of constituents in the beverage waste and not the paper so it would be
expected to differ from surfactant waste where the fatty acids likely originated from
degradation of paper products.
Total VFA
concentration(mg/L)
3000
2500
control
surfactant 50mg/L
surfactant 150mg/L
surfactant 300mg/L
surfactant 500 mg/L
2000
1500
1000
500
0
0
50
100
150
200
250
300
Period of decomposition(days)
acetic acid concentration(mg/L)
Figure 15. Total VFAs in Reactors Receiving Surfactants
350
control
surfactant 50mg/L
300
surfactant 250mg/L
surfactant 500mg/L
surfactant 150mg/L
250
200
150
100
50
0
0
50
100
150
200
250
300
period of decomposition(days)
Figure 16. Acetic Acid in Reactors Receiving Surfactants
20
propionic acid concentration(mg/L)
1600
control
surfactant 50mg/L
surfactant 150mg/L
surfactant 250 mg/L
surfactant 500 mg/L
1400
1200
1000
800
600
400
200
0
0
50
100
150
200
250
300
period of decomposition(days)
butyrci acid
concentration(mg/L)
Figure 17. Propionic Acid in Reactors Receiving Surfactants
800
control
surfactant 50mg/L
700
surfactant 150mg/L
surfactant 250mg/L
600
surfactant 500 mg/L
500
400
300
200
`
100
0
0
50
100
150
200
250
300
period of decomposition(days)
Figure 18. Butyric Acid in Reactors Receiving Surfactants
Finally, there was little difference in cellulose, hemicellulose and lignin
degradation patterns for the surfactant amended reactors. In Figure 19, data for the
cellulose to lignin ration is shown. It can be seen that the effect of surfactants is minimal.
It appears that threw is little impact of surfactant waste on degradation. The only
unusual pattern in degradation was the high initial concentration of propionic acid in the
reactors. However, all VFAs degraded readily and the pH was maintained between 7.5
21
and 8.0. In general, it appears that surfactants have little impact on degradation of paper
in a simulated landfill environment.
5
4
Control
surfactant 50 mg/L
surfactant 150 mg/L
surfactant 250 mg/L
surfactant 500mg/L
C/L
3
2
1
0
0
50
100
150
200
250
300
period of decomposition(days)
Figure 19. Cellulose to Lignin (C/L) Ratio in Reactors Receiving Surfactants
Paint Waste
Paint waste was the second most common liquid waste provided to the Outer Loop
Landfill. Waste Management, Inc. provided a sample of paint waste for use in this study. The
COD of the paint waste was 237,500 mg/L. In the initial phase of the study, phase1, paint
waste was added at 7.5, 15, 22.5 and 30% by weight. Because some of the data indicated
potential inhibition of gas production, a second phase was undertaken using lower
amounts of paint waste and nutrients and buffers. The amount of paint waste in the
second phase was 1, 5 and 10% and the chemicals added were 3000 mg/L sodium
bicarbonate, 2000 mg/L ammonium chloride and 50 mg/L ferrous sulfate. Although the
pH was satisfactory in phase 1, sodium bicarbonate was added so that if the inhibition
were eliminated, the pH would not drop dramatically as was the case for the beverage
waste.
In phase 1, the pH of all the paint waste reactors was between 7.0 and 8.0 (Figure
20). The pH of the buffered paint waste reactors in phase 2 also followed a similar trend
to the control reactors (Figure 21), indicating no inhibition.
22
9
8
PH
7
6
5
control
paint 30%
paint 15%
paint 7.5%
paint 22.5%
4
0
50
100
150
200
250
300
period of decomposition(days)
Figure 20. Variation in pH for Reactors Containing Paint Waste, Phase 1.
9
8
pH
7
6
5
4
control
3
paint 1%
paint 5%
paint 10%
2
0
50
100
150
200
period of decomposition(days)
Figure 21. Variation in pH for Reactors Containing Paint Waste, Phase 2.
The gas emission in phase 1 paint waste reactors suggested that inhibition might
be occurring. This was consistent in the case of total gas (Figure 22) and methane
generation (Figure 23). The total gas generation in all of the phase 1 reactors plateaued at
about 6000 ml. The amount of gas generation was relatively constant when paint waste
was added, irrespective of the concentration of paint waste in the reactors. The maximum
methane generation in the phase 1 paint waste reactors was about 4000 ml.
23
cumulative gas(ml)
20000
control
paint 30%
paint 22.5%
paint 15%
paint 7.5%
16000
12000
8000
4000
0
0
50
100
150
200
250
300
period of decomposition(days)
Figure 22. Variation in Total Gas Generation for Reactors Containing Paint Waste,
Phase 1.
cumulative methane(ml)
10000control
paint30%
paint 22.5%
paint 15%
paint 7.5%
8000
6000
4000
2000
0
0
50
100
150
200
250
300
period of decomposition(days)
Figure 23. Variation in Methane Generation for Reactors Containing Paint Waste,
Phase 1.
The gas generation for the phase 1 reactors was similar for the first 100 days of
incubation and after that, the gas generation stopped for the paint amended systems. It
was thought that this could be due to the absence of nutrients, especially nitrogen because
paint would be expected to be low in nutrients. Since the COD of the paint waste was
substantial, the degradation of paint could have resulted in nutrient utilization and
stopped further degradation. Therefore, in phase 2, nitrogen, iron and bicarbonate were
added.
The cumulative total gas generated from the phase 2 paint waste reactors show a
much higher gas and methane production rate (Figures 24 and 25). Unlike the phase 1
reactors, the total gas emitted from the 10% paint waste reactors was 2.5 times more than
24
that of the control. The gas generation trend in the phase 2 paint waste reactors was
similar to the control which indicates that the addition of paint waste in the buffered
reactors did not result in negative performance of the reactors. The reason for high
amount of gas emission in the paint waste reactors might be the presence of a high COD
in the paint waste. The COD value of paint waste was measured at 237,500 mg/l. It was
observed that the rate of gas generation increased with an increase in the amount of paint
waste added in the phase 2 reactors, indicating that this material was readily
biodegradable.
The volatile solids reduction was consistent with the reduced gas generation as
indicated in Figure 26. The rate of VS destruction was similar for all the reactors up to
100 days and then the degradation rate slowed for the paint amended reactors. The initial
VS for the paint amended systems was higher than the control, reflecting the high organic
content of the paint waste.
control
80
paint 1%
paint 5%
paint 10%
volume in liters
70
60
50
40
30
20
10
0
0
50
100
150
200
period of decomposition(days)
Figure 24. Variation in Total Gas Generation for Reactors Containing Paint Waste,
Phase 2.
control
methane gas volume in liters
30
paint 1%
paint 5%
paint 10%
25
20
15
10
5
0
0
50
100
150
200
period of decomposition (days)
25
Figure 25. Variation in Methane Generation for Reactors Containing Paint Waste,
Phase 2.
control
paint 30%
paint 22.5%
paint 15%
paint 7.5%
96
VS(%)
92
88
84
80
0
50
100
150
200
250
300
Period of decomposition(days)
Figure 26. Volatile Solids Reduction for Reactors Containing Paint Waste, Phase 1.
It was evident from the gas emission curves that degradation in the phase 1 paint
waste reactors was inhibited. It was not be because of acid accumulation since the pH did
not decrease. This was consistent with the volatile fatty acid results as shown in Figure
27. The VFAs increased initially in all the reactors including the control, but decreased to
below 500 mg/L by day 100. It was only after day 100 that the differences between the
paint waste and the controls was evident.
2500 control
paint 30%
paint 22.5%
paint 15%
paint 7.5%
VFA concentration(mg/L)
2000
1500
1000
500
0
0
50
100
150
200
Period of decomposition(days)
250
300
Figure 27. Volatile Fatty Acids in Reactors Containing Paint Waste, Phase 1.
26
The trend in degradation of volatile solids (Figure 28) and in the generation of
volatile fatty acids (Figure 29) for the phase 2 reactors show that the generation and
consumption of volatile fatty acids was consistent with the amount of gas generated and
the extent of degradation observed. The VFAs in the phase 2 reactors were higher than in
the phase 1 systems, yet the degradation was faster and continued through the entire
incubation period of 180 days.
volatile solids in %
94
92
90
88
86
84
control
paint 1%
paint 5%
paint 10%
82
0
50
100
150
200
period of decomposition (days)
Figure 26. Volatile Solids Reduction for Reactors Containing Paint Waste, Phase 2.
vfa concentration in mg/L
6000
control
paint 1%
paint 5%
paint 10%
4000
2000
0
0
50
100
150
200
period of decomposition (days)
Figure 27. Volatile Fatty Acids in Reactors Containing Paint Waste, Phase 2.
It is evident from the Phase 1 reactor data that paint waste showed inhibition of paper
degradation, even at a concentration of 7.5%. To better understand the nature of the
inhibition, the phase 2 experiments with nutrient and buffer additions were added. The
27
inhibition was eliminated in the phase 2 systems. The increased degradation of volatile
solids in the phase 2 reactors was likely due to increased degradation of the paint waste
because as can be seen in Figures 28 and 29, the cellulose and hemicellulose degraded in
a similar manner for the controls and paint amended systems. Because the paint was
thought to contain little nutrients, the addition of iron (which is known to enhance
anaerobic degradation (Park, et al., 2006)) and nitrogen was thought to be critical in
increasing paint waste degradation.
30
%cellulose
25
20
15
10
5
control
paint 1%
paint 5%
paint 10%
0
0
50
100
150
200
period of decomposition (days)
Figure 28. Cellulose in Reactors Containing Paint Waste, Phase 2.
25
% hemicellulose
20
15
10
5
control
paint 1%
paint 5%
paint 10%
0
0
50
100
150
200
period of decomposition (days)
Figure 29. Hemicellulose in Reactors Containing Paint Waste, Phase 2.
28
Conclusions
Based on the data collected in this study, the following conclusions are made:
• Beverage waste is readily degradable. As a consequence, it has the potential to rapidly
produce volatile fatty acids through fermentation of the beverage constituents, primarily
sugars and alcohols. In this study, the volatile fatty acids lowered the pH to levels that
stopped degradation of paper and reduced methane generation. Addition of a buffer to
relieve the inhibition was successful in raising the pH but did not result in recovery of
methane generation. Caution should be used when adding readily degradable organics to
landfills due to the potential to disrupt degradation.
• Paint waste appears to be inhibitory. Addition of a combination of sodium bicarbonate,
ferrous sulfate and ammonium chloride eliminated the inhibition, resulting in degradation
of the paint waste constituents. It was thought that the inhibition was not due to toxic
materials, but rather, to a nutrient deficiency. Once the nutrient deficiency was
eliminated, the paint waste degraded readily.
• Surfactants added to the waste paper had no negative or positive benefits. At the levels
tested, surfactants could be safely added to landfills.
29
Methods and Materials
Experimental Setup:
The study was divided into 2 sections. The first phase (Phase 1) produced the
initial results and the second phase (Phase 2) provided a second round of testing based on
an evaluation of the data from phase 1. Three types of liquid waste were investigated,
beverage waste, paint waste and surfactants. The beverage waste initially consisted of
dehydrated soft drink liquid with a COD of 250,000 mg/L.
The paint waste consisted of residue with a COD of 237,500 mg/L. Residue
analysis indicated this material was low in heavy metals. No surfactant waste was
available during this study so a surfactant mixture was prepared based on the expected
types and concentration of surfactants. Two surfactants, dodecyl benzene sulfonate and
sodium lauryl sulfate, were mixed 50% to 50% by weight and added to the paper in the
bioreactors.
The initial set up of the experiment consisted of reactors containing sample mixed
with either beverage waste, paint waste or surfactants, in triplicate sets at 3 or four
different concentrations. This was termed as phase 1 of the project. A triplicate set of
controls were set up without adding any of the liquid wastes. Later, an additional 12
reactors were added and is termed as phase 2 of the project. The actual moisture content
of Bioreactor landfills are maintained at 30-45%. Instead, the moisture content of the
reactors was kept at 70%. This includes the liquid waste being tested. The higher
moisture content was used to facilitate the availability of some free liquid in the reactors
since the sample was mainly paper and paper products which absorb high amounts of
moisture.
Since paper and cardboard constitute a major part of the landfill material, the
sample used was a mixture of paper, cardboard and office paper. Further, plastic was
added at 10% of the sample by weight. The combined paper and plastic was 30% by
weight of the total reactor contents. As a source of bacteria, anaerobic seed from the
Peppers Ferry wastewater treatment plant at 15% of the total weight of the reactor was
added.
The different concentrations of beverage waste used in phase 1 were 30, 22.5 and
15% by weight, the paint waste was 30, 22.5, 15 and 7.5%, and the surfactant
concentrations used were 50 mg/L, 150 mg/L and 250 mg/L. In phase 2 of the project,
reactors were added with 5% or 10% beverage wastes, 1, 5 and 10% paint waste and 500,
1000 and 2000 mg/L of surfactants.
Tap water was added to increase the total water content (including liquid waste)
to 70% of the total weight. When calculating the mass, anaerobic seed and wastes were
considered as liquid only and no allowance been given to the solids in them. The
experimental matrix for phase 1 is shown in Table 1 and the matrix for phase 2 is shown
in Table 2. All reactor set ups were carried out in a glove box, purging with ultra pure
nitrogen gas in order to assure complete anaerobic condition. Reactors were then closed
air tight to ensure that no air is intruded and then they were connected to a Tedlar bag
through an opening made at the top. All connections were prior checked for leaks and the
reactors were then incubated at 35°C.
30
Table 1 Experimental; Matrix for the First Phase of the Study
Control
Number of
reactors
Sample by
weight
Water
content
Waste
added
Anaerobic
seed
Beverage Waste
Surfactant Waste
Paint Waste
3
3
3
3
3
3
3
3
3
3
3
30%
30%
30%
30%
30%
30%
30%
30%
30%
30%
30%
55%
25%
32.5%
40%
55%
55%
55%
25%
32.5%
40%
47.5%
0
30%
22.5%
15%
50
mg/l
50 mg/l
50 mg/l
30%
22.5%
15%
7.5%
15%
15%
15%
15%
15%
15%
15%
15%
15%
15%
15%
X = none added
Table 2 Experimental; Matrix for the Second Phase of the Study
Control
Beverage Waste
Surfactant Waste
Paint Waste
Number of
reactors
Sample by
weight
Water
content
3
3
3
3
3
3
3
3
3
30%
30%
30%
30%
30%
30%
30%
30%
30%
55%
45%
50%
55%
55%
55%
54%
50%
45%
Waste added
0
10%
5%
500 mg/l
1000
mg/l
2000
mg/l
1%
5%
10%
15%
15%
15%
15%
15%
15%
15%
15%
15%
3000 mg/l
3000
mg/l
3000
mg/l
3000
mg/l
3000
mg/l
3000
mg/l
3000
mg/l
3000
mg/l
3000
mg/l
2000 mg/l
2000
mg/l
2000
mg/l
2000
mg/l
2000
mg/l
2000
mg/l
2000
mg/l
2000
mg/l
2000
mg/l
50 mg/l
50 mg/l
50 mg/l
50 mg/l
50 mg/l
50 mg/l
50 mg/l
50 mg/l
50 mg/l
Anaerobic
seed
Sodium
bicarbonate
Ammonium
chloride
Ferrous
sulfate
Samplings were conducted once in every 15 days for the first 13 samplings and
then monthly afterwards. Since the pH dropped under normal in sugar waste reactors,
they were brought up to neutral using NaHCO3 on the 150th day sampling.
Materials:
Reactors:
Reactors used were 1L PTFE Nalgene bottles from Fischer scientific. These are
attached to a 1 L tedlar bag from Fischer scientific to collect gas emerging from the
reactor.
Sample:
The sample used was 50% newspaper, 25% office paper and 25% cardboard. To
assure consistency, newspaper used was the Collegiate Times, office paper was generated
by Environmental Engineering wing of CEE department of Virginia Tech and cardboard
was packing from Fischer Scientific. These were cut down to approximately one inch
squares. Plastics added were one inch strips of black trash bags and were thoroughly
mixed with the sample and weighed. The total sample in each reactor was about 30% by
weight of the total reactor content.
31
Seed:
Anaerobic seed from Pepper’s Ferry, an anaerobic digester is used as the source
for methanogenic bacteria.
Wastes:
Initially it was not possible to procure sugar waste so it was artificially
synthesized in the laboratory. For this, Pepsi was used. Pepsi was continuously distilled
in the laboratory till it reached a COD of 250,000 mg/L. Chemical oxygen demand
(COD) tests were conducted periodically on the solution and the distillation was
continued until the desired concentration was obtained. The solution was then cooled and
added to the paper mixture.
Surfactant waste was also synthesized by mixing surfactants in the laboratory.
The surfactants chosen for this were sodium salt of dodecyl benzene sulfonate and
sodium lauryl sulfate from Sigma Aldrich Ltd. Both are anionic surfactants and are used
in detergents, textile and metal industries and would best represent surfactant wastes
delivered to some landfills.
Sampling:
Reactors were sampled once in every 15 days till the 13th sampling (195 days) and
once in every month after that until 240 days (15th sampling) in phase 1 reactors. Phase 2
reactors which were started after 9 samplings of phase 1 were sampled once in every 15
days for first 6 samplings and once in every month after that. During samplings, for a
short while, the reactors were taken out into a glove box at room temperature. After
purging with ultrapure nitrogen gas, the reactors were opened and 10-15 mg of the
sample was quickly transferred to a loaf pan. Four to five ml of leachate was collected
from each reactor and was transferred to a 15 ml centrifuge tube and centrifuged to
remove solids. The reactors were then sealed and were transferred back to 35°C
temperature incubation. The leachate was frozen and stored for further analysis.
Plastics were removed manually from the samples and were weighed. Samples
were then dried at 105°C for 24 hours and were milled using a Wiley mill using a mesh
of 10mm size. This ground powder was used for further analysis.
Analytical methods:
pH:
Samples were mixed with 50/50 distilled water and were kept for 5 hours to
equilibrate. pH was then measured using a pH meter.
Total Solids (TS), Volatile Solids (VS) and Water content:
Total Solids were measured using Standard method 2540G (APHA, 1998).
Gas generation, methane and carbon dioxide:
The gas generated from reactors was collected in tedlar bags. These bags were
detached at the time of sampling and were measured using a syringe. Total gas was
32
expressed in milliliters. The carbon dioxide content and methane content in percentage in
the gas were measured using a Shimadzu GC 14A with thermal conductivity detector,
injecting 0.5ml of the gas. Calibration graphs were made out of different concentrations
of 99.9% methane and carbon dioxide for the analysis of gas samples. Multiplying total
gas with the percentage gave the total CO2 and CH4 generation out of the reactors.
Lignin, Cellulose and Hemicellulose :
The lignin, cellulose and hemicellulose were determined as per ASTM E 1758e1
95 .
Volatile fatty acids:
Leachate from the reactors was analyzed for acetic acid, butyric acid, iso butyric
acid, heptanoic acid, hexanoic acid, propionic acid, valeric acid, isovaleric acid and
caprionic acid. Frozen leachates were thawed and filtered using 0.2 m, 0.45 μm filters
after centrifuging for 10 minutes. 0.99 ml of the filtrate is then added to a 2ml vial
containing 0.01ml of 30% phosphoric acid to acidify the solution. These were then
analyzed using a Shimadzu GC 14A with a flame ionization detector. Five standards were
made out of standard volatile fatty acid from Supelco. Standards and blanks made out of
nanopure water were also treated the same way and analyzed. Blank values were
deducted to avoid any seed interference.
33
Acknowledgements
The assistance of Waste Management, Inc for finaicial support and waste manterials is
appreciated. Mr. Gary Hater (WMI) and C. Doug Goldsmith (Alternative Natural
Technologies) provided oversight of the project. Their comments and suggestions are
appreciated.
References
APHA. (1998). Standard Methods for the Examination of Water and Wastewater , 20th
Edition., American public health association, American water works association,
Water environment Federation, Washington DC, Washington DC.
Hater, G. R. (2003) "Outer Loop Bioreactor Project-Data for the US EPA Second Interim
Report."
Kelly, R. J., Shearer, B. D., Kim, J., Goldsmith, C. D., Hater, G. R., and Novak, J. T.
(2006). "Relationships between Analytical Methods Utilized as Tools in the
Evaluation of Landfill Waste Stability." Waste Manag, 26(12), 1349-56.
Park, C, Abu-Orf, M.M., and Novak, J.T. (2006) “Predicting the Digestability of Waste
Activated Sludges” Wat Envr Res, 78, 1, 59-68.
34