Effect of Dehydration Process Conditions on Oily Sludge in a Fenton
Advanced Oxidation System
Hongpan Liu
1,2,3
, Yongting Chen
1
, Yulin Zheng
1
, Zhongqing Yang
2,*
, Jiangtao Yu
3,*
and Heshan Yang
1
1
Chongqing Key Laboratory of Environmental Materials & Remediation Technologies, College of Chemistry and
Environmental Engineering, Chongqing University of Arts and Sciences, Chongqing, 402160, China
2
School of Energy and Power Engineering, Chongqing University, Chongqing, 400044, China
3
China Power Investment of Yuanda Environmental Protection Engineering Co. Ltd, Chongqing, 401122, China
Keywords: Oily Sludge, Fenton, Dehydration, Orthogonal Experiment.
Abstract: Oily sludge is the main solid waste produced by the petrochemical industry and has attracted increasing
attention due to its complex composition, containing a large number of heavy metals and organic toxic
substances. Advanced oxidation technology has attracted much attention as an oily sludge treatment method
as it can be used to reduce the harmful organic matter content and improve the dewatering performance of
oily sludge. Taking oily sludge as the research object, this study adopted an orthogonal experimental design
to investigate the water content and specific resistance of oily sludge by controlling the pH, reaction time
and the mass ratio of hydrogen peroxide to ferrous sulfate (m
H2O2
/m
FeSO4
) of the reaction system. Results
showed that the water content of oily sludge treated using the Fenton reagent was optimal under reaction
conditions of pH 3, with a reaction time of 40 min and m
H2O2
/m
FeSO4
of 10/1. In contrast, the specific
resistance of oily sludge treated using the Fenton reagent was optimal under the conditions of pH 3, with a
reaction time of 50 min and m
H2O2
/m
FeSO4
of 14/1. Among the three factors assessed, the m
H2O2
/m
FeSO4
mass
ratio had the greatest influence on both the water content and specific resistance of oily sludge.
1 INTRODUCTION
Oily sludge is an oily solid waste produced during
the process of oil exploitation, transportation,
refining and oil field oily wastewater treatment in
the petrochemical industry. It generally consists of a
stable suspension emulsion of oil in water (O/W),
water in oil (W/O) and suspended solids. The
composition of oily sludge is highly complex,
containing a large amount of water and numerous
refractory organic substances, heavy metals and
other toxic substances, causing it to be classified as
hazardous waste (Hu 2013). The high moisture
content results in oily sludge having a large volume,
while the untreated heavy metal residues can
accumulate to dangerous concentrations which
endanger human health. Extracellular polymeric
substances (EPS) and metal ions are important
components of oily sludge (Liu 2016). EPS accounts
for about 80% of the sludge content, contributing to
the formation of highly hydrated biofilms
comprising various microorganisms, which adsorbs
a large amount of water and constitutes the sludge
floc skeleton. The EPS content has been reported to
be the most important factor affecting sludge
dewatering (Xiao 2017).
Previous studies have investigated the
mechanism of sludge conditioning using the Fenton
reaction. Hydroxyl radicals (·OH) are produced by a
chain reaction in Fenton systems and have a very
high redox potential (up to 2.8V), which can quickly
oxidize EPS, changing the sludge structure and
achieving sludge conditioning. Zhang et al. studied
the changes in EPS and sludge morphology during
the process of Fenton sludge conditioning via three-
dimensional fluorescence electron microscopy,
finding that oxidation is more important than
flocculation in the process of Fenton sludge
conditioning. After the oxidation of ·OH, the EPS
composition and the morphology of sludge changed,
resulting in a change of floc structure and particle
size (Zhang 2015, Yang 2017). Xu et al. showed that
Liu, H., Chen, Y., Zheng, Y., Yang, Z., Yu, J. and Yang, H.
Effect of Dehydration Process Conditions on Oily Sludge in a Fenton Advanced Oxidation System.
DOI: 10.5220/0011182700003443
In Proceedings of the 4th International Conference on Biomedical Engineering and Bioinformatics (ICBEB 2022), pages 79-83
ISBN: 978-989-758-595-1
Copyright
c
 2022 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved
79

fulvic acids disappear and that EPS was destroyed
after sludge was treated using a Fenton-like system,
while SEM exhibited that stable sludge flocs were
destroyed using a Fenton-like system and
acidification, with the water in flocs more easily
released and therefore, the sludge dewatering
performance improved. The floc structure of sludge
changes, allowing the bound water to be released
and the polymer to become smaller after EPS
oxidation and degradation (Xu 2016).
Previous reports on sludge dewatering using
Fenton advanced oxidation systems, have mainly
focused on urban sludge, while few reports have
investigated oily sludge from specific industries and
there is no general consensus on the optimal Fenton
reagent dosage, or conditions for the dehydration
and reduction of oily sludge. This paper
comprehensively analyzes the dehydration
performance of oily sludge after conditioning using
a Fenton advanced oxidation system. The
influencing factors and optimal conditions for
Fenton reaction conditioning of oily sludge were
determined by investigating the changes in moisture
content and specific resistance of sludge after
conditioning. These findings lay a foundation for the
practical application of Fenton advanced oxidation
technology in the oil sludge industry.
2 MATERIALS AND METHODS
2.1 Materials
The oily sludge used in this experiment originated
from Sichuan province and was produced during
shale gas exploitation. The sludge was gray black
with a moisture content of 30-85%, as shown in Fig.
1 and Fig. 2. According to the results of XRF
analysis, the main components of the oily sludge
were found to be inorganic minerals such as BaSO
4
,
CaO and Al
2
O
3
, as shown in Table 1. FeSO
4
, H
2
O
2
and HCl were all of analytical purity.
Figure 1: Sample of oily sludge
Figure 2: SEM of oily sludge.
Table 1: Composition analysis of XRF oily sludge containing oily sludge.
Components SiO
2
CaO Al
2
O
3
BaO SO
3
Fe
2
O
3
Others
Wt (%) 39.26 15.32 11.45 10.69 8.26 5.65 9.37
2.2 Methods
Oily sludge was poured into a beaker and combined
with the Fenton reagent, with continual agitation
using a magnetic stirrer and the reaction maintained
under different temperatures and different durations.
The conditioned oily sludge was then poured into a
Brinell funnel equipped with quantitative filter paper
for vacuum suction filtration and dehydration. The
amount of filtrate in the measuring cylinder was
recorded at specific times, allowing the sludge
specific resistance (SRF) to be calculated. The
moisture content of sludge was determined using the
gravimetric method.
3 RESULTS AND ANALYSIS
In order to establish the effect of varying pH,
reaction time and m
H2O2
/m
FeSO4
, each factor was
compared at three levels, using the L
9
(3
4
) orthogonal
table, in which A indicates pH (A
1
(pH=2), A
2
(pH=3) and A
3
(pH=4)); B indicates reaction time
(B
1
(30 min), B
2
(40 min) and B
3
(50 min); C
indicates the mass ratio of hydrogen peroxide to
ferrous sulfate (m
H2O2
/m
FeSO4
) (C
1
(m
H2O2
/m
FeSO4
=10/1), C
2
(m
H2O2
/m
FeSO4
=12/1) and C
3
(m
H2O2
/m
FeSO4
=14/1)). Factors A, B and C are listed
in columns 1, 2 and 3 of L
9
(3
4
), respectively.
ICBEB 2022 - The International Conference on Biomedical Engineering and Bioinformatics
80

Table 2: Orthogonal experimental design.
Level
Factors
pH（A）
Reaction time
（B）
Mass ratio（C）
1
2（A
1
） 30（B
1
） 10/1（C
1
）
2
2（A
1
） 40（B
2
） 14/1（C
3
）
3
2（A
1
） 50（B
3
） 12/1（C
2
）
4
3（A
2
） 30（B
1
） 12/1（C
2
）
5
3（A
2
） 40（B
2
） 10/1（C
1
）
6
3（A
2
） 50（B
3
） 14/1（C
3
）
7
4（A
3
） 30（B
1
） 14/1（C
3
）
8
4（A
3
） 40（B
2
） 12/1（C
2
）
9
4（A
3
） 50（B
3
） 10/1（C
1
）
3.1 Apparent Analysis of Orthogonal
Experimental Results
Results show that the appearance of oily sludge was
a black solid block prior to treatment, changing to a
dissolved state after pH adjustment treatment. The
oily sludge expanded during treatment, with gas
escaping during the reaction process. Under different
reaction conditions the intensity of oily sludge
expansion varied, with the resulting dried oily
sludge being a black gray loose block. As shown in
Fig. 2, the oily sludge is in a mass shape with an
uneven surface, containing a high mass of
extracellular polymer micelles which contain a large
amount of bound water, which is not conducive to
the dehydration of oily sludge. As shown in Fig. 4,
the extracellular polymer structure was destroyed by
the Fenton reaction, improving the dewatering
performance of oily sludge.
Table 3 Orthogonal experimental results of oily sludge dewatering under Fenton advanced oxidation system
NO. m
1
(g) m
2
(g) m
3
(g) w
j
(%) c
j
(%) SRF (s
2
/g)
1 28.8968 48.9740 46.2095 13.77 86.23 7.53×10
14
2 28.9030 49.0111 46.3609 13.18 86.82 1.18×10
14
3 28.8980 49.3161 46.6438 13.09 86.91 5.12×10
14
4 28.8556 49.0637 46.1923 14.21 85.79 6.87×1014
5 28.6968 48.7183 46.1493 12.83 87.17 7.13×10
14
6 28.8584 48.8695 45.9478 14.60 85.40 1.01×10
14
7 28.8651 48.9668 46.2897 13.32 86.68 3.28×10
14
8 31.6662 51.7520 49.0044 13.68 86.32 4.60×10
14
9 28.8564 48.9887 46.1100 14.30 85.70 4.04×10
14
Effect of Dehydration Process Conditions on Oily Sludge in a Fenton Advanced Oxidation System
81

Figure 3: Oily sludge after treatment.
Figure 4: SEM of oily sludge after treatment.
3.2 Analysis of Water Content of Oily
Sludge under Fenton Advanced
Oxidation System
Analysis of orthogonal experimental results showed
that the water content of treated oily sludge varied
between 12-15% depending on the level of different
experimental factors. The lowest treated sludge
specific resistance had the highest water content of
14.60%, which was achieved under reaction
conditions of pH 3, with a 50 min reaction time and
m
H2O2
/m
FeSO4
ratio of 14/1. The lowest moisture
content of 12.83% was achieved under reaction
conditions of pH 3, with a reaction time of 40 min
and m
H2O2
/m
FeSO4
of 10/1, which were the optimal
experimental conditions in terms of moisture content
according to the orthogonal experimental results.
Table 4 Variance analysis of moisture content.
Source Class III sum
of squares
Freedom Mean square F Significance
Modified model 1.409
a
6 0.235 0.301 0.893
Interce
p
t 1680.453 1 1680.453 2156.240 0.000
pH
(
A
)
0.474 2 0.237 0.304 0.767
Reaction time
(
B
)
0.929 2 0.464 0.596 0.627
Mass ratio
(
C
)
0.007 2 0.003 0.004 0.996
Erro
r
1.559 2 0.779
Total 1683.421 9
Analysis of variance showed that among the
influencing factors, pH, reaction time and
m
H2O2
/m
FeSO4
ratio had a significant impact on the
water content of oily sludge. The primary and
secondary relationships among the three factors was
ranked in the order of m
H2O2
/m
FeSO4
(C) > pH(A) >
reaction time(B). The optimum level of each factor
was: pH 3, reaction time of 40 min and m
H2O2
/m
FeSO4
of 10/1.
3.3 Analysis of Sludge Specific
Resistance of Oily Sludge under
Fenton Advanced Oxidation
System
It was found that the specific resistance of oily
sludge after treatment varied from 1.00×10
14
-
8.00×10
14
s
2
/g, with the analysis of orthogonal
experimental results showing that the specific
resistance of oily sludge under different factor
conditions varied according to both the factor and
the factor level. The highest specific resistance of
oily sludge (difficult to filter sludge) was
7.53×10
14
s
2
/g under reaction conditions of pH 2,
with a reaction time of 30 min and a m
H2O2
/m
FeSO4
of
ICBEB 2022 - The International Conference on Biomedical Engineering and Bioinformatics
82

10/1. In contrast, the lowest sludge specific
resistance was 1.01×10
14
s
2
/g under the reaction
conditions of pH 3, with a reaction time of 50 min
and a m
H2O2
/m
FeSO4
of 14/1, which were the optimal
experimental conditions for specific resistance
according to the orthogonal experimental results.
Table 5 Variance analysis of sludge specific resistance.
Source Class III sum of
s
q
uares
Freedom Mean square F Significance
Modified
model
4.50×10
29a
6 7.505×10
28
7.235 0.126
Interce
p
t 1.85×10
30
1 1.846×10
30
177.998 0.006
pH
(
A
)
1.62×10
28
2 8.106×10
27
0.781 0.561
Reaction time
(B)
9.64×10
28
2 4.822×10
28
4.648 0.177
Mass ratio
(C)
3.38×10
29
2 1.688×10
29
16.276 0.058
Erro
r
2.07×10
28
2 1.037×10
28
Total 2.32×10
30
9
Analysis of variance showed that among the
influencing factors, pH, reaction time and
m
H2O2
/m
FeSO4
ratio had a significant impact on the
specific resistance of oily sludge. The primary and
secondary relationships among the three factors
were ranked in the order pH(A) > reaction time(B) >
m
H2O2
/m
FeSO4
(C). The optimum level of each factor
was: pH 3, with a 50 min reaction time and
m
H2O2
/m
FeSO4
(C) of 14/1.
4 CONCLUSION
Orthogonal experimental results for oily sludge
treatment using the Fenton advanced oxidation
system show that the optimal moisture content of
12.83% was achieved under the experimental
conditions of pH 3, with a reaction time of 40 min
and m
H2O2
/m
FeSO4
of 10/1. The optimal specific
resistance of 1.01×10
14
s
2
/g was achieved under
experimental conditions of pH 3, with a reaction
time of 50 min and a m
H2O2
/m
FeSO4
of 14/1. These
results confirm that the Fenton advanced oxidation
system can effectively destroy the extracellular
polymer structure of oily sludge, releasing some of
the bound water and converting it into free water,
improving the dewatering performance of sludge.
ACKNOWLEDGEMENTS
This work was financially supported by National
Natural Science Foundation of Yongchuan
(Ycstc,2019nb0803), Science and Technology
Research Program of Chongqing Municipal
Education Commission (Grant No.
KJQN201901310) and Natural Science Foundation
of Chongqing (cstc2020jcyj-msxmX0833).
REFERENCES
Hu G J, Li J B, Zeng G M. (2013). Recent development in
the treatment of oily sludge from petroleum industry:
A review. J. Hazard. Mater. 261(13):470-490.
Liu J B, Wei Y S, Li K, et al. (2016). Microwave-acid
pretreatment: A potential process for enhancing sludge
dewaterability. Water Res. 90:225-234.
Xiao K, Chen Y, Jiang X, et al. (2017). Microwave-acid
pretreatment: A potential process for enhancing sludge
dewaterability. Water Res. 90:225-234.
Xu H, Shen K, Ding T, et al. (2016). Dewatering of
drinking water treatment sludge using the Fenton-like
process induced by electro-osmosis. Chem. Eng. J.
293: 207-215.
Yang Q, Sun J, Wang D B, et al. (2017). Effect of nickel
on the flocculability, settleability, and dewaterability
of activated sludge. Bioresource Technol. 224: 188-
196.
Zhang W, Yang P, Yang X, et al. (2015). Insights into the
respective role of acidification and oxidation for
enhancing anaerobic digested sludge dewatering
performance with Fenton process. Bioresource
Technol. 181:247-253.
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