Research Progress of Influencing Factors of Biological Contact
Oxidation Method
Leixiang Wu
*
, Zhuowei Wang, Ronghao Guan and Xingchen Liu
State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and
Hydropower Research, Beijing, 100038, China
Keywords: Surface Water Pollution, Sewage Treatment, Biological Contact Oxidation Method.
Abstract: The biological contact oxidation method has the advantages of low operating cost, stable treatment effect,
and good effluent quality, and is widely used to treat domestic and industrial sewage. Based on a large
amount of literature, this research expounds the origin, development, and decontamination mechanism of
the biological contact oxidation method. The main factors affecting the biological contact oxidation method
and its research progress were systematically analysed to provide a reference basis for the further
development of this technology.
1 INTRODUCTION
In recent years, with the acceleration of
urbanization, the contradiction between the rapid
development of agriculture and water pollution has
intensified, and it is urgent to solve the problem of
rural water pollution (Ma, 2021). Traditional water
treatment technology has not adapted to the current
requirements of rural sewage treatment. As a new
and high-efficiency water treatment process, the
biological contact oxidation method has the
characteristics of activated sludge method and
biofilm method and the advantages of stable
treatment effect, impact load resistance and simple
management (Hu, 2015). Since the late 1970s, the
biological contact oxidation method has been widely
used in China, and many scholars have studied the
biological contact oxidation method and made
certain achievements (Jiang, 2013).
2 THE ORIGIN AND
DEVELOPMENT OF
BIOLOGICAL CONTACT
OXIDATION
Biological contact oxidation method is a kind of
biofilm method, which is developed on the basis of
biological filter. At the end of the 19th century,
Blaring first proposed the concept of biological
contact oxidation, and Closs applied for a related
patent in Germany in 1912. Before the 1950s, due to
the small specific surface area of the filter material,
low filter load, large floor space, high cost of
spraying water, and high energy consumption, the
practical application of this method was limited, and
it was not a mainstream water treatment technology
[4]. By the 1960s, with the development of plastic
technology, the filler of the biofilm method was
made into honeycomb or foam, which has the
advantages of light weight, easy processing and
molding, and large specific surface area. It has been
widely used in the contact oxidation process. In the
1970s, Japanese scholars studied the biological
contact oxidation method in depth, further improved
the contact filler, and promoted the engineering
application of the process. At present, the biological
contact oxidation method is widely used in sewage,
water supply purification treatment and river
ecological restoration (Li, 2008).
3 POLLUTANT REMOVAL
MECHANISM
Biological contact oxidation method is an efficient
biological treatment technology that organically
combines activated sludge method and biological
filter technology. It is composed of tank body, filler,
Wu, L., Wang, Z., Guan, R. and Liu, X.
Research Progress of Influencing Factors of Biological Contact Oxidation Method.
DOI: 10.5220/0011186300003443
In Proceedings of the 4th International Conference on Biomedical Engineering and Bioinformatics (ICBEB 2022), pages 95-99
ISBN: 978-989-758-595-1
Copyright
c
2022 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved
95
water distribution system and aeration system
(Figure 1). Biological contact oxidation method is
also called submerged biological filter, which
evolved from biological filter and contact aeration
oxidation. The biological contact oxidation method
is to fill the pond with a certain density of fillers and
aerate through the air from the bottom of the pond.
The sewage immerses all the fillers and extensively
contacts with the biofilm on the fillers to achieve the
purpose of purifying sewage under the function of
microbial metabolism. Following the law of
microbial growth cycle, the biofilm purification
effect is not good during the decay period. At this
time, under the impact of wastewater and gas, the
biofilm on the filler falls off quickly and is
discharged from the reactor with the water flow. At
the same time, the biofilm is replenished and
updated in time. As a result, the system can stably
and efficiently remove pollutants in the water body
during the entire operation process (Zhang, 2012).
Figure 1: River simulation device based on biological contact oxidation method.
4 FACTORS AFFECTING THE
REMOVAL OF POLLUTANTS
The pollutant removal effect of biological contact
oxidation method depends on the biological quantity
and activity of the biofilm. The factors affecting the
treatment effect of biological contact oxidation
method mainly include water temperature, pH value,
DO, filler properties, gas-water ratio, organic matter
load, and hydraulic load.
4.1 Water Temperature
Water temperature mainly affects biological
reactions in two aspects: on the one hand, it affects
the rate of enzyme-catalysed reactions; on the other
hand, it affects the rate of matrix diffusion into cells.
In the process of nitrification, the suitable growth
temperature of nitrate bacteria is 35~42℃, and that
of nitrite bacteria is 35℃. Temperature affects the
effect and rate of nitrification reaction of nitrifying
bacteria. The suitable temperature range for the
nitrification reaction is 15~35℃. When the
temperature is lower than 10℃, the nitrification will
be significantly inhibited. The influence of
temperature on nitrogen removal is significantly
higher than that on phosphorus removal, but the
decrease of temperature will change the phosphorus
release and absorption rate of phosphorus
accumulating bacteria (Helmer, 1998).
4.2 pH Value
The pH value is of great significance to the growth
of microorganisms. For most bacteria, the optimal
pH range is 4~7. The pH value is too high or too
low, not only restricts the osmotic function of the
microbial cell surface, but also inhibits the
enzymatic reaction inside the cell. Biological contact
oxidation method has good adaptability to pH.
According to the research results of Villaverde S.,
the suitable pH range for the growth of
microorganisms in the biological contact oxidation
method is 5~9. When the pH=8.2, the
microorganisms grow in the best condition, and the
maximum amount of biofilm will be obtained in this
case (Villaverde, 1997). In the actual operation of
ICBEB 2022 - The International Conference on Biomedical Engineering and Bioinformatics
96
sewage treatment, if the pH value is not in the range
of 5~9, the pH should be adjusted first.
4.3 Dissolved Oxygen
The biological contact oxidation method uses an
aeration device to aerate the water body of the
reactor, which has three main functions: 1) Provide
oxygen for the oxidation of microorganisms and
synthesize endogenous respiration; 2) Stirring to
maximize water turbulence and improve the mass
transfer effect between biofilm, pollutants, and
oxygen; 3) Promote the renewal of biofilm, improve
biological activity, prevent filler blockage, and
improve treatment effect. Therefore, to improve the
ability of the biological contact oxidation reactor to
remove pollutants, it is necessary to ensure that the
dissolved oxygen concentration in the system is
maintained above the minimum concentration level
required for bacterial metabolism. With the increase
of dissolved oxygen concentration, the ability of
nitrification reaction to remove NH
3
-N increases
significantly, and tends to a stable level when the
dissolved oxygen concentration is 7 mg/L. When the
dissolved oxygen concentration in the system is
lower than 0.5 mg/L, the nitrification reaction
basically stops.
4.4 Filler Properties
Filler is one of the important design parameters of
the biological contact oxidation method. The
performance, quantity, and layout of the filler not
only directly affect the effect of the contact
oxidation method in treating sewage, but also affect
the economic cost of the project. The filling rate of
the filler is between 30% and 70% of the effective
volume of the filter. Insufficient fillers will affect the
removal of pollutants. Too much filler will not only
increase the construction cost, but also hinder the
oxygen transfer rate. The physical and chemical
characteristics of common biological contact
oxidation fillers are shown in Table 1 (Zhang, 2015).
4.5 Gas-Water Ratio
The gas-water ratio is the key to the design of the
application of biological contact oxidation
technology, and it plays a decisive role in the
treatment effect, the project investment, and the
operating cost. The gas-water ratio must be
maintained in a reasonable range, too high or too
low, it will have an adverse effect on the system.
When the air-to-water ratio exceeds a certain
threshold, long-term high-intensity aeration will
cause turbulence in water flow, produce a large
shear force to act on the biofilm, cause the biofilm to
fall off more seriously, and increase system
operating costs. When the air-to-water ratio is too
low, the DO content and mass transfer power in the
system will be insufficient, which will adversely
affect the metabolic activity of the aerobic
community and cause the system effluent water
quality to not meet the standard. The death of
aerobic microbes and the proliferation of anaerobic
microbes caused by insufficient aeration will
produce metabolic gas (H
2
S, NH
3
, etc.), resulting in
more voids in the biofilm, significantly weakened
biofilm adhesion, and even large areas of biofilm
shedding, which will eventually lead to the quality
of treated water deteriorated. Nitrogen and
phosphorus removal in bioreactors is a continuous
and complex reaction mechanism (Liu, 2003).
Existing research results show that, during the
intermittent aeration operation of the biological
contact oxidation system, the gas-water ratio is
preferably in the range of 5:1 to 10:1.
4.6 Volume Load of Influent Pollutants
The volume load of influent pollutants is one of the
important parameters that affect the design and
operation of the contact oxidation process. In the
biological treatment process, it comprehensively
reflects the concentration of organic matter in the
influent water and the hydraulic retention time.
There will be an optimal balance between influent
load, pollutant treatment effects and economic
benefits. When the volume load increases within a
certain range, the concentration of organic matter in
the sewage is relatively high, and the advantage of
easy cultivating bacteria has a strong metabolic
effect, thereby promoting the biodegradation of
pollutants (Ge, 2015). The small-scale trial study of
Zhang et al. with Xiaosha River sewage as the
treatment object in Shandong Province has similar
results (Zhang, 2012). When the volumetric load of
COD
Cr
increases to a certain range, it may change
the dominant bacteria in the reactor to heterotrophic
bacteria, inhibit the nitrification reaction, and
ultimately affect the removal effect of NH
3
-N (Lin,
2015).
Research Progress of Influencing Factors of Biological Contact Oxidation Method
97
Table 1. Physical and chemical properties of various fillers.
Compare items Honeycomb
packing
Soft filler Semi-soft
material
Combination
packing
Elastic filler Suspended
packing
Factory-supplied
specific surface
area (m
2
/m
3
)
150~200 500~700 150~200 200~300 200~300 150~250
Use specific
surface area
(m
2
/m
3
)
SAB
a
SAC
b
SS
c
SS SL
d
SL
Increase
oxygenation rate
-5% -10% 30%~40% 25%~35% 70%~100% 1%~30%
Water and air
distribution
performance
Poor Poor General Better Good Better
Film performance General Good General General Good General
Drag film
p
erformance
Poor Poor General General Good General
Blockage More serious No No General No No
Clumping and
broken wire
No More serious General No No No
Service life 4~6 years 1~2 years 5~8 years 5~8 years 7~10 years 5~8 years
Replacement of
filling
INC
e
INC INC INC INC CON
f
Support CON CON CON CON CON INC
Transport INC CON CON CON CON INC
Price (Yuan/m
3
) 700 100 220 200 250 1000
a
SAB: Small after blockage
b
SAC: Small after clumping
c
SS: Slightly smaller
d
SL: Slightly larger
e
INC: Inconvenient
f
CON: Convenience
4.7 Hydraulic Load
Hydraulic load is the amount of wastewater treated
per unit volume of filter media per day and is an
important parameter for the design and operation of
sedimentation tanks and biological filters. Studies
have shown that for treatment systems of different
sizes, when the hydraulic load increases within a
certain range, it has little effect on the performance
of the biological contact oxidation system COD
Cr
and NH
3
-N. As the hydraulic load further increased,
the removal rate of COD
Cr
and NH
3
-N decreased
significantly. This also shows that the biological
contact oxidation method has better resistance to
hydraulic load impact.
5 CONCLUSION
At present, surface water sources are generally
polluted, which has become a major factor
threatening the quality of water supply. The
improvement of the traditional treatment process and
the introduction of biological contact oxidation
treatment technology into the water treatment
process has gradually become an effective means to
treat micro-polluted source water and improve the
quality of drinking water. This research expounds
the origin, development, and decontamination
mechanism of biological contact oxidation method
by consulting many literature, and systematically
analyses the main factors affecting biological
contact oxidation method, including water
temperature, pH value, DO, filler properties, gas-
water ratio, organic matter load, and hydraulic load.
Biological contact oxidation method has become one
of the main technologies for wastewater treatment in
China. This study provides a reference for the
further development of this technology.
ICBEB 2022 - The International Conference on Biomedical Engineering and Bioinformatics
98
ACKNOWLEDGEMENTS
This work was supported by the National key
research and development plan special (No.
2018YFC0407702), the National Natural Science
Foundation of China (No. 51879279, 51879278) and
the Ministry of Water Resources Department Project
(No. 12630100100020J002).
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