Introduction
Zidovudine wastewater was disposed from the producing of Zidovudine, one of medicine to cure aids.
Zidovudine wastewater is difficult to treat due to complex components, big toxicity, and high
concentration [1]. Usually, Zidovudine wastewater is mixed with others to treat, which the
degradation is poor and the cost is high. Recently, some researchers have been concerned with
Micro-electrolysis technology to treat pesticides, dying wastewater, phenol, natural organism, fatty
acid and other wastewater [2-7]. However, the degradation capability of micro-electrolysis is limited
and the reaction tank is easily jammed [8]. Ultrasonic assisting other technologies to degrade complex
organism is a new kind of method [9-12]. Ultrasonic synergying iron-carbon micro-electrolysis can
raise the degradation rate of phenol and pulp wasterwater [13, 14]. Thus, study on synergetic
degradation of Zidovudine wastewater by ultrasonic and micro-electrolysis is useful.

Materials and methods
NaOH, H2SO4, K2Cr2O7 and other reagents were of analytically pure, commercially available and used
without further purification.
Zidovudine wastewater in the experiment derived from Northeast General Pharmaceutical Factory
and the analyses results of the wastewater were pH 2.3-2.5, COD about 120000 mg/L，BOD5/COD
was about 0.15. initial wastewater dilute 10 times in the experiments.
The scrap iron, derived from Northeastern University Machinery Plant, was selected by passing
through 40 mesh screen in order to get tenuous iron scurf without impurities. Then the scrap iron was
immersed in 10% NaOH solution for 10 minutes to exclude oil, and washed by pure water, followed
by being immersed in 3% H2SO4 solution for 1 min to activate it. Meanwhile, in order to exclude the
absorption ability, the activated carbon is immersed in the wastewater for 24 hours.
A cone-shaped bottle was laid in the ultrasonic cleaner (KQ-V100VDB), and some Azade
wastewater was injected into the cone-shaped bottle where the scrap iron and activated carbon had
been mixed beforehand. A series of parameters including initial pH value, iron-to-carbon ratio,
iron-to-water ratio, reaction time, and ultrasonic frequency were studied to get the optimal reaction
conditions. The pH value is measured by pHS-2C pH-meter, COD by potassium dichromate method
and BOD5 by MODELⅡ BOD analyzer.

Results and Discussions
Orthogonal test of iron-carbon micro-electrolysis
The result of iron-carbon micro-electrolysis orthogonal test shows as Table 1.
As Table 1 shown, according to the taxis of the R and COD removal rate, the importance of the
reaction parameters is reaction time and initial pH. And the highest COD removal rate can reach
51.4% when the reaction conditions such as reaction time 90min, mass ratio of iron and wastewater
3/4, mass ratio of iron and carbon 1/2, initial pH 4 are arranged.
Effect of ultrasonic frequency on COD removal
The effect of ultrasonic frequency on COD removal rate shows as Fig.1. The results show that with
the increasing of ultrasonic frequency, the COD removal rate also rise. It is because that ultrasonic can
decompose water to hydrogen radical and hydroxyl radical, which can degrade some pollutants. When
the frequency is low, the air bubble, produced by ultrasonic, can exist for a long time. Therefore the
hydrogen radical and hydroxyl radical increase contacting possibility and deactivate in the air bubble,
resulting in the degradation rate of pollutants decreasing.
Effect of initial pH on COD removal rate
The effect of intial pH on COD removal rate shows as Fig.2. As Fig.2 shown, without the synergy
of ultrasonic, the COD removal rate is higher in the acidic condition, and the highest COD removal
rate is up to 54.3% when the pH is 4. The reason of poor micro-electrolysis efficiency is that the
concentration of hydrogen ion is low, and the surface of scrap iron easily forms passivation layer,
which inhibiting the electron to transfer between iron and organism, leading the efficiency of
micro-electrolysis poor when the pH is too high. However, when the pH is too low, iron reacts with
acid to produce hydrogen, which inhibiting the contact of iron and carbon. The synergy of ultrasonic
and micro-electrolysis can improve the COD removal rate remarkably because the cavitation of
ultrasonic can form local high temperature and pressure, which benefits the mass transfer effect of
iron surface. Moreover, the COD removal rate is steady about 80% at pH from 4 to 9. the oxygen can
react with hydrogen ion to produce much hydroxyl radical under the excitation of ultrasonic.
Effect of reaction time on COD removal rate
The effect result of reaction time on COD removal rate shows as Fig.3. The result shows the
synergy of ultrasonic and micro-electrolysis can improve the COD removal rate and speed. Without
ultrasonic synergy, the COD removal rate increases a little, when the reaction time is beyond 90 min.
With ultrasonic synergy, the COD removal rate is very high when the reaction time is 30 min. The
reason is that ultrasonic can produce cavitation to raise the mass transfer speed, benefit washing the
surface of iron and carbon, and ensure enough supply of election acceptor. And the same time,
ultrasonic can decompose macromolecular organic compounds to small organic molecules, which is
useful to raise micro-electrolysis degradation COD.
Effect of reaction temperature on COD removal rate
The effect result of reaction temperatue on COD removal rate shows as Fig.4. The result shows the
synergy of ultrasonic and micro-electrolysis can improve the COD removal rate and speed at any
temperature. Without ultrasonic synergy, the COD removal rate decreases, when the reaction
temperature is beyond 40 ℃. It is due to the high temperature making the reaction speed of iron and
oxygen increase and iron become Fe3+. However, With ultrasonic synergy, the COD removal rate still
stable when the temperature is beyond 40 ℃. The reason is that ultrasonic can enhance cavitation
effect and radical forming speed with the rise of temperatue.

Result of synergetic degradation by ultrasonic and iron-carbon micro-electrolysis.
Result of synergetic degradation of Zidovudine wastewater by iron-carbon micro-electrolysis show
in Table 2 at the optimum conditions including reaction time 30 min, pH 5, mass ratio iron to
wastewater 1/1, mass ratio iron to carbon 1/2, reaction temperature 30 ℃ and ultrasonic frequency
100 KHz.
Conclusions
Iron-carbon micro-electrolysis method can degrade Zidovudine wastewater effectively in narrow pH
range form 3-5. However, when ultrasonic and micro-electrolysis treat Zidovudine wastewater
together, the COD removal rates rise from 54.3 % to 85.2 % in wide pH range from 4 to 9. Moreover,
ultrasonic can accelerate micro-electrolysis decomposing Zidovudine wastewater. And the reaction
time reduces from 90 min to 30 min when the high COD removal rate achieve. Synergetic degradation
of Zidovudine wastewater by ultrasonic and micro-electrolysis method can also improve BOD5/ COD
from 0.15 to 0.35, making the wastewater easily biodegradable.