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Study on the Biodegradability of Hyperbranched Surfactant
Xuechuan Wang1, a, Yuqiao Fu1, b, Longfang Ren1, c and Taotao Qiang1, d
1Key Laboratory of Chemistry and Technology for Light Chemical Industry, Ministry of Education,
Shaanxi University of Science and Technology, Xi’an 710021, CHINA
a e-mail: wangxc@sust.edu.cn, b e-mail: fyuqiao@126.com,
c e-mail: renlf1010@163.com, d e-mail: qiangtaotao@sust.edu.cn
Key words: hyperbranched surfactant; biodegradability; COD30; respiratory curve.
Abstract. The methods of COD30 and respiratory curve were adopted to evaluate the
biodegradability of hyperbranched surfactant which was used as the substrate of microorganism.
The main results obtained by the method of respiratory curves were as follows. When the
concentration of substrate was 0~250mg/L, the respiratory curves of the substrate were above the
curve of endogenous, which showed that the substrate was easy to utilize by microorganism. The
main results obtained by the method of COD30 were as follows: when sludge concentration was
1000mg/L and pH was 7, the biodegradation rate of 200mg/L hyperbranched surfactant was 97.8%.
The main results obtained by the method of respiratory curves were as follows: When the
concentration of substrate was 200 mg/L, the utilization of the substrate by microorganism was the
most, respectively. Moreover, the effect of pH, inoculation amount and salinity on the
biodegradability of the substrate was obvious. Through experiments, the optimum conditions for the
substrate to be degraded could be listed as follows: pH was 8.5, salinity was 0.3% and the range of
inoculation amount was 3000mg/L.
Introduction
The use of green chemicals has been an important part of clean production in modern industry, as an
important parameter for evaluating the environmental friendliness of organic chemicals;
biodegradable property parameter has been widely acknowledged. A lot of people have studied the
biodegradability of surfactant. [1-4] Wang, et al. have emphasized the importance of surfactant
biodegradability study. [5] However, the study on the biodegradability of hyperbranched surfactant
was limited.
Hyperbranched polymers, a class of polymers characterized by a highly branched
macromolecular architecture and a large number of end groups, have attracted much attention in
recent years because of the expectation that their unique molecular shapes, branching patterns, and
surface functionalities may impart new, unusual properties.[6] First, As shown in Scheme 1 (a, b), a
series of hyperbranched poly (amine-ester) polyols (HPAEPS) were synthesized by the
polycondensation of N,N-diethylol-3-amine-methylpropionate [prepared by the Michael addition
reation of methyl acrylate (MA) with diethanolamine (DEA)] as an AB2-type monomer with
trimethylol propane (TMP) as the core moiety, proceeding in one-step procedure in the melt with
p-toluenesulfonic acid (p-TSA) as catalyst. [7] Then, as shown in Scheme 1 (c), HPAE was
modified by oleic acid to obtain a hyperbranched surfactant. (HPAE and oleic acid in the molar
ratio of 1:1) The biodegradability of the hyperbranched surfactant has been studied.
Advanced Materials Research Vols. 356-360 (2012) pp 223-227Online available since 2011/Oct/07 at www.scientific.net© (2012) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMR.356-360.223
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,www.ttp.net. (ID: 128.118.88.48, Pennsylvania State University, University Park, United States of America-04/06/14,18:13:06)
(a)
(b) (c)
Scheme 1. The steps involved in the synthesis of hyperbranched surfactant. (a) synthesis of AB2 type monomer; (b) synthesis of HPAE (AB2 monomer and TMP in the molar ratio of 3:1) (c) synthesis of hyperbranched surfactant (HPAE and oleic acid in the molar ratio of 1:1)
Experimental
Chemicals. C12H22O11 (purity 99%), (NH4)2FeSO4 (purity 99.5%) and K2Cr2O7 (purity 98.5%) were
purchased from Tianjin Chemical Reagent Co., Ltd, China. A mineral salt medium (MSM) used for
the growth of microorganisms contained (mg/L) NH4Cl, K2HPO4 FeSO4·7H2O 45, CaCl2 45,
MgSO4 30, ZnCl2 30 at pH 7.0. This MSM didn’t contain source of carbon and energy. All the
chemicals were of analytical grades and were purchased from Tianjin Chemical Reagent Co., Ltd,
China. The activated sludge sample was collected from the sludge compression workshop of the 3rd
Sewage Treatment Plant in Xi’an, China.
Microorganism Cultivation. Appropriate amount of collected activated sludge was transferred to a
culture flask filled with 2000mL of sterile MSM containing C12H22O11 as the sole source of carbon
and energy. The microorganism was incubated day by day until the microorganism characteristics
were detected as follows. The collected activated sludge became yellow flocculent sludge, the SV30
was about 30%, and the MLSS was about 3000mg/L, which indicated that the activity of
microorganism was good enough for the followed experiment of organic biodegradability
determination.
Evaluation of the Biodegradability of Hyperbranched Surfactant
The Biodegradability of Hyperbranched Surfactant. As presented by Kong et al. [8] and
Zhang, et al. [9], the methods of organic chemical biodegradability evaluation include Respiratory
curves, COD30, et al.
Respiratory Curves. Respiratory curve was mainly used to evaluate the initial adaptability of the
microorganism to the substrate.
COD30. COD30 was mainly used to evaluate the ultimate biodegradability of the substrate, which
reflected the maximal degree of substrate utilization by the microorganism.
224 Progress in Environmental Science and Engineering
Factors Affecting the Biodegradability of Hyperbranched Surfactant. The method of
respiratory curve was adopted to evaluate the affection of sludge concentration, pH and salinity on
the substrate biodegradation.
Results and discussion
The Biodegradability of Hyperbranched Surfactant
Fig. 1 The relationship Fig. 2 The relationship
between the substrate concentration between the substrate concentration
and biodegradability and biodegradability
Respiratory Curves. BOD of the different concentration substrates (50mg/L, 100mg/L,
150mg/L, 200mg/L and 250mg/L) was measured using BOD analyzer with other measurement
conditions as follows. pH at 7.0, 20˚C, prepared mineral salt medium (MSM), 1000mg/L fully
aerated fresh activated sludge. Moreover, The BOD of blank sample, whose substrate concentration
was 0 mg/L, was measured by BOD analyzer with the same other measurement conditions. During
each sample BOD measurement, the every day BOD value was recorded, and the respiratory curves
was obtained as Fig. 1.
Fig. 1 showed the substrate concentration had great influences on the substrate biodegradability.
Under the experimental conditions, the substrate respiratory curves were all above the endogenous
respiration curve which indicating that the tested different concentration of substrate has effect on
microorganism and could be largely degraded by the microorganism. When the concentration of the
substrate was 200mg/L, the influence of the substrate by microorganism was the most. The next are
250mg/L.
COD30. 250ml different concentration of the substrate (50mg/L, 100mg/L, 150mg/L, 200mg/L
and 250mg/L) were transferred to five conical flasks. Other test conditions were controlled as
follows. pH at 7.0, mineral salt medium (MSM) through adding appropriate content mineral salts in
the conical flasks, 1000mg/L fully aerated fresh activated sludge. The five conical flasks were then
putted in constant temperature shock incubator with the temperature 20˚C constantly. The test was
lasted 30 days. The COD of each sample was determined and recorded every 5 days. The COD30
curves were obtained as Fig. 2.
As shown in Fig. 2, in the condition of pH at 7.0, 20˚C, when the substrate concentration was in
the range of 50~250mg/L, the ultimate biodegradation rates were all above 90%. The
biodegradability of the substrate with the concentration of 200mg/L was the best and the ultimate
biodegradation rate was 97.8%.
Advanced Materials Research Vols. 356-360 225
Factors Affecting the Biodegradability of Hyperbranched Surfactant. Firstly, the substrate
biodegradability was determined at sludge concentration 500mg/L, 1000mg/L, 1500mg/L,
2000mg/L, 3000mg/L with other determination conditions as follows. 200mg/L substrate,
mentioned salt medium conditions, pH 7.0, and salinity 0%; Secondly, the substrate
biodegradability was determined at pH 6, 6.5, 7, 7.5, 8, 8.5with 200mg/L substrate, 3000mg/L
sludge concentration, 0% salinity and the same other determination conditions as before; Thirdly,
the substrate biodegradability was measured at salinity 0%, 0.1%, 0.3%, 0.5%, 0.7%, 0.9% with
200mg/L substrate, 3000mg/L sludge concentration and at pH 8.5, the same other determination
conditions as before.
Fig. 3 The relationship Fig. 4 The relationship
between sludge concentrations between pH and the substrate
and the substrate biodegradability biodegradability
Fig. 5 The relationship between salinity and the substrate biodegradability
Effect of Sludge concentration. As shown in Fig. 3. With the increase of inoculation amount,
the substrate biodegradability became better as the sludge concentration was among 500~
3000mg/L. The more the inoculation amount, the more the substrate degraded by microorganism.
When the inoculation concentration increased to 3000mg/L, the substrate biodegradation rate
increased.
Effect of pH. Fig. 4 showed that the hydrogen ion concentration of the culture medium greatly
influenced the substrate biodegradability. The reason was pH limited the activity of the
microorganism. Under the test conditions, the optimum pH for the substrate biodegraded was 8.5,
which indicated that strong alkaline medium had good influence on the biodegradability of the
substrate.
226 Progress in Environmental Science and Engineering
Effect of Salinity. Fig. 5 showed the salinity of the culture medium had great influences on the
substrate biodegradability. During the process of microorganism using the substrate as the sole
source of carbon, appropriate mineral salts should be provided for the normal activity of the
microorganism. Under too high or too low salinity, the microorganism cells would dehydrate or
hydrate and the microorganism activity would be inhibited as a result of the inapplicable osmotic
pressure environment. Under the test conditions, when the additional NaCl was in the range of
0%~0.3%, the substrate biodegradability became better with the increase of salinity. However, when
the additional NaCl was above 0.3%, the substrate biodegradability became worse with the increase
of salinity. The optimum salinity for the substrate biodegraded by the microorganism was 0.3%
additional NaCl.
Conclusions
(1) Hyperbranched surfactant was used as the substrate of microorganism, when sludge
concentration was 200mg/L, pH was 7 and with no additional NaCl, the biodegradation rate of
200mg/L hyperbranched surfactant was 97.8%.
(2) The methods of respiratory curve showed that the substrate has inhabiting effect on
microorganism, and could easily biodegradation by microorganism. The result of the method of
Respiratory Curve was consistent with that of COD30.
(3) Moreover, as indicated in the respiratory curves, the effect of sludge concentration, pH, salinity
and co-metabolism on the biodegradability of the substrate was obvious.
(4) Under the experimental conditions, when the concentration of the substrate was 200mg/L, the
sludge concentration was 3000mg/L, pH was 8.5 and salinity was 0.3%, the biodegradability of
the substrate was the best.
Acknowledgements
This research was supported by National Natural Science Foundation of China (20876090);
Scientific research team Shaanxi University of Science & Technology (TD09-04) and the Graduate
Innovation Fund of Shaanxi University of Science and Technology.
References
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Advanced Materials Research Vols. 356-360 227
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