Improved wastewater ultraviolet disinfection by ultrasonic
pre-treatment 
Jin Xin
University of Science and Technology Beijing
School of Civil and Environmental Engineering
Centre for Sustainable Environmental Sanitation
Xueyuan Road 30 / Haidian District
Tu Mu Huan Jing Lou - Office 1214 - Beijing, 100083 - P.R. China
Phone / Fax +86 10 6233 4378 website: www.susanchina.cn
• Background
• Introduction
• Materials and Methods
• Results and Discussion
• Conclusions
1. Background
Infectious diseases
• Highly pathogenic avian influenza
• Epidemic situation of “SARS”
• Epidemic situation of H1N1
Cause problems • Ecological safety
• Environmental sanitation
• Other aspects.
The environmental safety of WWTPs tail water plays an important
role in the whole ecological environment protection, thus tail water’s
disinfection became a significant defense line in both protecting the
receiving water’s ecological safety and preventing the epidemic
situation from being spread out.
People have been pay more attention on the disinfection
of wastewater treatment plants effulents. Traditional
disinfectants have many disadvantages, finding new
safety and efficiency disinfection technologies became
more and more important.
The work was carried out based on project of “Research
on Mechanism of Ultrasonic Synergy Disinfection”-----
which supported by NATURAL SCIENCE FOUNDATION of
CHINA (NSFC).
2. Introduction
The project “Research on Mechanism of Ultrasonic
Synergy Disinfection”-- (NSFC) focus on studying
the synergy disinfection effect. The main work :
• Find out the mechanism of ultrasonic disinfection
as a pre-treatment method;
• How it works with other disinfectants;
• The key influence factors in ultrasonic disinfection.
The objective of this work is
• To evaluate the newly proposed method of applying a
ULTRASONIC (US) as a pretreatment step in combination
with ultraviolet irradiation to improve the disinfection
efficiency of wastewater by breaking up the large particles;
• To explore the fundamental characteristics of how
particles and bacterias in wastewater respond to
ultrasonic (US);
• To find the mechanism of synergistic disinfection.
3. Materials and Methods
Ultrasonic generator and
transducer are made according to
our specially need. Ultrasound
frequencies are 21.51kHz (horn)
and 83.03kHz (column);
UV light: SJD-I desktop UV
germicidal lamp, AC220V-50HZ,
quartz tube lamp’s power is 15W.
Lab scale experiment equipment
3. Materials and Methods
Main Elements:
• CODcr (potassium dichromate method)
• SS
• E.Coli (multiple-tube fermentation technique)
• Energy Consumption
4. Results and Discussion
a.CODcr
Ultrasonic has gteat effect on CODcr
during the first 50 seconds, The value of
CODcr increasing rapidly with time
increase.
b. SS
The experimental results
show that, SS
concentration decreaseing
with the increase of US
acting time. The size of big
particle became smaller,
samples became turbid.
c. E.coli
The number of E.coli
increased with disinfection
time in the initial stage of
the experiment, and then
decreased rapidly, it will
below the initial value after
20 minutes.
d. E.coli
The number of E.coliform decreased
with time increasing of ultraviolet
irridiation.
The total coliform number reduced by
2.8 log units when UV light disinfect
for 30S, the total coliform number
reduced by 3.4 log units when UV light
disinfect for 40S, sterilization rate
reach to 99.9%. However, the number
of coliform became more and more
during the following two days. Some
bacterias which seem be killed
reappeared.
d. Synergy effect
In the synergy disinfection
experiment, US can improve the
UV disinfection effect noticeably.
With US pretreatment it only takes
about one-third of the ultraviolet
light exposure time to achieve the
same disinfection results as
ultraviolet treatment.
The results of Orthogonal test:
e. Energy consumption
The energy consumption is large when
only using ultrasonic for disinfection.
Very short time of US pretreatment, It
can not only improve the disinfecton
effect of ultraviolet radiation, but also
achieve the same premising effects
take shorter UV radiation time. At the
same time, the energy consumption is
smaller than UV alone.
4. Conclusions
• Ultrasonic working as a pre-treatment method and followed by UV
radiation for disinfection is a much better way in practice;
• The experiment results revealed that the particle size distribution
(PSD) in the test samples were apparently shifted toward the small size
range;
• The synergy effects can raise the disinfect efficiency compare with
single UV. It can reduce radiation time in reaching the same disinfect
efficiency;
• The application of a US step might also be beneficial in terms of costeffectiveness.
• During the follow-up monitor, the phenomenon of photoreactivation
was under control.
The experimental results in this study showed some
degree of variation for similar experiments. This is not
unusual for this kind of study, due to many uncontrolled
factors,such as:
Characteristics of tested samples,
Random error in the microbiology tests.
However, these experiments clearly showed that the
proposal of using the US to pre-treat wastewater could be
a very attractive alternative to enhance ultraviolet
disinfect efficiency.
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