CHEM. RES. CHINESE UNIVERSITIES 2011, 27(3), 407
—
412
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*Corresponding author. E-mail: liuna@jlu.edu.cn
Received August 26, 2010; accepted December 29, 2010.
Supported by the National Natural Science Foundation of China(Nos.40702039, 20090879029).
Preparation of Bio-beads and Their Atrazine
Degradation Characteristics
BI Hai-tao, ZHANG Lan-ying, LIU Na
*
and ZHU Bo-lin
College of Environment and Resources, Jilin Universit y, Changchun 1300 26, P. R. China
Abstract Screened atrazine-mi nera lizing bacterium
―
Pseudomonas W4 was embedded inside an improved PVA-
H
3
BO
3
embedment matrix to make bio-beads to degrade atrazine. The atrazine degradation characteristics were
studied. The preparatio n procedure of bio-beads was as follows: (1) preparing a mix ture of 100, 12.5, 10, 1.5 and 1
g/L PVA, bentonite(Ca), activated carbon powder, sodium alginate and centrifuged Pseudomonas W4 bacterium,
respectively ; (2) the mixture was dropp ed into a gently stirred cross linker solution (pH=6.7) and cured at 10 °C for 24
h. The opti mal atrazine degradati on conditions by bio-beads were as follows: pH=7, the auxiliary carbon source was
glucose, and the concentratio n of glucose was greater than 325 mg/L. The bio-bead s demonstrated stron ger tolerance
ability than the free microorganism to the increase of PCBs, hydrogen ion and hydroxide ion. SEM images show the
uniform distribution of the microorganism inside bio-be ad s and the porous cross-linked structure of bio-beads which
provides excellent mass transfer capacity.
Keywords Atrazine; Polyvinyl alcohol(PVA); Embedment; Bio-bead
Article ID 1005-9040( 2011)-03-407-0 6
1 Introduction
Atrazine[6-chloro-N-ethyl-N-(1-methylethyl)-1,3,5-triazi-
ne-2,4-diamine], one of the most commonly used herbicides for
corn and sorghum to control broadleaf weeds and grasses
[1]
,has
been used in corn production for more than 30 years, and an
estimated 36.3 million kilogram of atrazine was applied
annually to more than 69% of all USA corn acreage
[2]
. Atrazine
has been detected in surface water and groundwater
[3―7]
.And
atrazine has been classified as a Restricted Use Pesticide(RUP)
due to its potential for groundwater contamination
[8]
.
There are many methods for the removal of atrazine, like
chemical oxidation, adsorption, hydraulic destruction,
volatilization, phytoremediation, incineration and
biodegradation. And biodegradation is the only method by
which atrazine can be mineralized. Researchers have isolated a
variety of fungi
[9,10]
and bacteria
[1 1―14]
which dealkylate and
dechlorinate atrazine, and a variety of atrazine-mineralizing
bacteria, including members of the genera Pseudomonas,
Rhizobium, Acinetobacter,andAgrobacterium, have been
isolated from soils contaminated by atrazine
[15―20]
.
The use of embedded microorganisms i n polymeric
matrixes rather than free cells in biotransformation of t oxic
compounds is advantageous to enhance the stability of the
biocatalyst and to facilitate its recovery and reuse. These
advantages have encouraged researchers to investigate the
application of immobilized cells in the biodegradation of toxic
compounds, such as phenol
[21]
, pyridine
[22]
,
dibenzothiophene
[23]
, and quinoline
[24,25]
.
Polyvinyl alcohol(PVA) is a synthetically nontoxic, high-
strength polymer that has been used extensively as matrix for
the enzymes and cells immobilization due to their property of
stabilization and preservation of the biological activity
[26―30]
.
PVA and sodium alginate hydrogels have been widely used as
carrier materials to immobilize enzymes and cells but their
properties, such as mechanical strength and swelling behavior,
need to be further improved for application
[31―33]
.
The purposes of this work were as follows: (1) the
PVA-H
3
BO
3
embedment method was improved via sodium
alginate and inorganic materials, which were activated carbon
powder and bentonite(Ca) to prepare bio-beads with high
mechanical strength and good swelling behavior; (2) atrazine-
mineralizing bacterium
―
PseudomonasW4
[34]
was embeded
to make bio-beads and degrade atrazine; (3) the degradation
characteristics of atrazine by bio-beads and shock loading
effect on bio-beads were i nvestigated. Scanning electron
microscope(SEM) images were also taken to examine the
internal structure of bio-beads and the microorganism
entrapped in bio-beads.
2 Materials and Methods
2.1 Chemicals
Analytical standard of atrazine with a purity of 98% was
purchased from ChemService. PVA(1750±50) was purchased
from Sinopharm Chemical Reagent Co., Ltd.(China). Technical
grade atrazine with a purity of 92% was purchased from Jilin
Insecticide Factory(China). All the other reagents were
purchased commercially and used without further purification.