Scholarly article on topic 'Study on Mechanism of Simultaneous Nitrification and Denitrification with Four Kinds of Fillers in Simulated Situ Bioremediation for Taihu Lake'

Study on Mechanism of Simultaneous Nitrification and Denitrification with Four Kinds of Fillers in Simulated Situ Bioremediation for Taihu Lake Academic research paper on "Materials engineering"

CC BY-NC-ND
0
0
Share paper
Academic journal
Procedia Environmental Sciences
OECD Field of science
Keywords
{Biofilm / "In Situ bioremediation" / "Simultaneous nitrification and denitrification" / "Nitrogen removal"}

Abstract of research paper on Materials engineering, author of scientific article — Xu Yan, Liu Jing-ming, Wang Ai-hui, Yu Sheng

Abstract Four kinds of different fillers are selected to investigate effects of simultaneous nitrification and denitrification by biofilm process in simulated situ bioremediation in laboratory scale for Taihu Lake. Water temperature and filling rate are both investigated to optimize nitrogen removal effects at the water temperature of 30°C, 20°C, 10°C and the filling rate of 30%, 50%, 70%, respectively. Under the conditions of 30°C water temperature and 70% filling rate, nitrogen removal effects of filler 1# is best, nitrogen removal efficiency of simultaneous nitrification and denitrification (SND) is 95.44%, nitrogen removal effects of filler 3# is worst, its SND removal efficiency is 79.30%. Moreover, the surface of filler 1# and filler 2# is rough enough to have a hydrophilia for the growth of microorganisms, compare with filler 3# and filler 4#. Thus, the filler 1# and filler 2# could remove more TN and protect polluted surface water, water quality is promoted from class V to class III.

Academic research paper on topic "Study on Mechanism of Simultaneous Nitrification and Denitrification with Four Kinds of Fillers in Simulated Situ Bioremediation for Taihu Lake"

Available online at www.sciencedirect.com

SciVerse ScienceDirect PfOCSd ¡0

Environmental Sciences

Procedia Environmental Sciences 10 (2011) 715 - 720

2011 3rd International Conference on Environmental Science and Information Application Technology (ESIAT 2011)

Phytoremediation of Copper-contaminated Soil by Chlorophytum Comosum

Nannan Wanga, Youbao Wanga*, Jie Daia and Jiemin Taoa

aCollege of Life Sciences, Anhui Normal University, Wuhu, Anhui, 241000, China

Abstract

In this research, we wanted to investigate the potential of Chlorophytum comosum in restoring copper-contaminated soil. C. comosum were planted in soil with CuSO4 solution at different contaminations. According to experiments and data analysis, the results showed that the tolerance index (TI) of C. comosum was 102.89% at 50mg-kg-1. Malondialdehyde (MDA) content and electrical conductivity (EC) both reached their lowest values at 50mg-kg-1 before rising. The value of Chla/b had no significant difference in all treatments. Catalase (CAT) and peroxidase (POD) showed a slightly climbing trend with increasing copper(Cu), whereas superoxide dismutase (SOD) was the most sensitive enzyme which dropped by an average of 30.798 % than the control. From these analysis above, we found that low concentration of Cu would improve the growth of C. comosum, while high levels would inhibite. At the same time, the bioaccumulation coefficient (BC) of C. comosum were all above 0.5 except CK, which suggested strong enrichment ability. Consequently, it is possible to apply C. comosum in phytoremediation of Cu-contaminated soil.

© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Conference ESIAT2011Organization Committee.

Keywords: Phytoremediation; Copper-contaminated; Chlorophytum comosum; Bioaccumulation.

1. Introduction

Metal pollution has become one of the most serious environmental problems today. Due to their immutable nature, metals are a group of pollutants of much concern [1]. Copper (Cu) is a structural and catalytic cofactor of enzymes and is necessary for normal growth and development of plants [2]. When absorbed in excess, Cu can be considered as a toxic element [3].

The idea of using rare plants which hyperaccumulate metals to selectively remove and recycle

* Corresponding author. E-mail address: wybpmm@126.com

1878-0296 © 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Conference ESIAT2011 Organization Committee. doi:10.1016/j.proenv.2011.09.115

excessive soil metals was introduced by Chaney [4]. Phytoremediation has been reported to be an effective, non-intrusive, inexpensive, aesthetically pleasing, socially accepted technology to remediate polluted soils [5], and it is widely viewed as the ecologically responsible alternative to the environmentally destructive physical remediation methods currently practiced [6].

Many scholars in various countries have made considerable researches on searching plants of high biomass and super-accumulation of heavy metals, nowadays ornamental plant have become a new source of phytoremediation species for they not only be used for landscaping but also have practical applications in the pollution monitoring and control [7, 8].

The aim of this investigation was to research the Cu resistance and accumulation of one popular ornamental plant Chlorophytum comosum. So as to prove the possibility of applying C. comosum in phytoremediation and provide the scientific basis of it.

2. Materials and methods

2.1. Cultivation

The C. comosum seedlings with prop-aerial root were gathered from the same matrix plant and seedlings in similar growth stage were taken for experiments after 2 weeks.

The soil for test is yellow brown soil collected from the back mountain in Anhui Normal University. The soil was homogenized, put through a 3mm sieve and air dried. In this experiment we chose plastic pots whose diameter were 12.5cm and put 250g soil in each pot.

The CuSO4 solution was added in order to obtain 7 levels of Cu ion contamination: CK (a soil sample with no additional Cu), 50, 100, 200, 400, 500 and 800 mg-kg-1 of dried soil.

After these soils in pot equilibrated for 2 weeks at room temperature, two seedlings were planted in each pot and the soil was maintained wet. Each treatment had three replicate.

2.2. Experiment

After 40 days cultivation, we uprooted C. comosum carefully and removed soil around the roots, then removed the surface water on them with filter paper after watering them with demonized water. Departed roots and the aboveground parts by forfex. Measured the length and the fresh weight (FW) of them.

When we determinated the physiological indicators of fresh leaves, the contents of photosynthetic pigments were determined by spectrophotometry, the electrical conductivity (EC) was determined by conductivity meter of DDS-11A type, and the Malondialdehyde (MDA) content was measured by thio-barbital method of Lin et al. (1988).

The activities of protective enzymes were all calculated on the base of FW. Catalase (CAT) were measured by KMnO4-titration, peroxidase (POD) were determined by guaiacol colorimetric method and superoxide dismutase (SOD) were measured by the inhibition of nitroblue tetrazolium (NBT) reduction.

Baked the aboveground parts and the roots for half an hour at 105 °C, over night at 75 °C, then weighed their dry matters (DW). Grinded them to pass through the sieve, then digested the aboveground parts and the roots of C. comosum with mixed-acid over night (HNO3:HClO4:H2SO4=8:1:1). The concentrations of Cu were analyzed by atomic absorption spectrphotometry of Japan Shimazu AA6800 type.

2.3. Analysis

In this paper, we used Microsoft Excel and SPSS 17.0 to deal with these data and do statistical analysis of them. All measurements were replicated three times. Average values and standard deviations (S.D.)

were calculated by the Microsoft Office Excel 2003 for all the data. In SPSS, Paired-Samples T Test was employed to compare the changes between different treatments, and Bivariate Correlations was used to compare the correlations between different treatments.

Tolerance index (TI) and bioaccumulation coefficient (BC) were calculated by the formulas as follow:

TI (%) = the average length of roots in experimentalgroup*100/the average length of roots in control group [9]. (1)

BC= the heavy metal concentration in the plant / the heavy metal concentration in the soil [10]. (2) 3. Results and discussion

3.1. Growth indicators of C. comosum

Under Cu stress above 500 mg-kg-1, C. comosum died. It said that 400mg-kg-1 of Cu might be the threshold that C. comosum could tolerate. Therefore, in this paper we would just discuss the experiments at 0, 50, 100, 200, 400 mg-kg-1.

Root systems are especially susceptible to metal stress, so that the root length of a plant can be used as an important tolerance index [11]. As shown in Fig. 1, low concentration of Cu in soil could stimulate the TI of C. comosum to rise, and TI reached its peak value which was 102.89% at 50mg-kg-1. That means 50mg-kg-1 of Cu could improve C. comosum to grow. Although TI dropped obviously in the range from 50 - 400 mg-kg-1, it still reached 57.71% at least.

110.00 100.00 90.00

Q 80.00 ©x

^ 70.00 H 60.00 50.00 40.00

CK 50 100 200 400 Cu stress (mg-kg"1) Fig. 1 Effect of Cu on Tolerance index

Meanwhile, some growth indicators, such as length of aboveground parts, FW and DW, were inhibited with the increase of Cu stress, but no statistical difference with the control was observed in them until 100mg-kg-1. Based on these growth traits, it seemed that C. comosum could maintain normal growth under low stress of Cu and have a certain endurance to Cu pollution.

3.2. Physiological indicators of C. comosum

Damage on membrane was an important reflection of heavy metal stress. MDA, a decomposition product of polyunsaturated fatty acids hydroperoxides, results in oxidative damage and has been frequently used as a biomarker for lipid peroxidation [12]. In Table 1, MDA content was raised with the increasing Cu after showing a downward trend till 50mg-kg-1, but there was no statistical difference with the control observed until 400mg-kg-1. Similarly, as the most widely accepted indicator of cell membrane selectivity, EC reached its lowest value at 50mg-kg-1 of Cu before rising. These might suggest that

J_i_i_i_i

membrane of C. comosum was insensitive to the Cu stress at low levels which could even increase the selectivity of cell membrane.

Several studies have shown that photosynthetic efficiency of many plants is affected by heavy metals. The excess of Cu, Cd, or Pb would inhibit directly the photosynthetic electron transport [13], as well as alter the photosynthetic activity indirectly, decreasing the content of photosynthetic pigments or damaging the photosynthetic apparatus on every level of its organisation, structure of chloroplasts [14]. From Table 1, we could find that with the rise of Cu stress, the photosynthetic pigments in leaves decreased, but the trend was not evident. And the value of Chla/b, which could be used as the indicator of leaf damage under Cu stress, showed no significant difference in all treatments in this study. It seemed that Cu stress had no markedly harmful effect on the contents of chlorophyll (Chl).

Table 1. Effect of Cu on physiological indicators of C. comosum

Cu stress (mg-kg"1) MDA (umol-L"1) EC (^s-cm"1) Chla (mg-L"1) Chlb (mg-L"1) Chla/b a

CK 0.849±0.029a b 66.90±0.99ab 4.765±0.696ab 1.776±0.302ab 2.688±0.065a

50 0.802±0.096ab 65.55±5.02a 4.286±0.417abc 1.601±0.188a 2.680±0.053a

100 0.815±0.117ab 74.65±4.03b 3.616±0.023ad 1.245±0.100ab 2.912±0.216a

200 1.009±0.003ab 73.05±4.60b 3.029±0.051bc 1.318±0.229a 2.329±0.366a

400 1.035±0.037b 73.25±6.29ab 3.028±0.715cd 1.067±0.218b 2.828±0.093a

a Chla/b = the content of Chla to the content of Chlb.

b Values followed by different letters for a given treatment are significantly different at p<0.05.

3.3. Protective enzyme system

Reactive oxygen species (ROS) such as O2^-and H2O2 are continuously generated in plant tissues as by-products of several metabolic processes. To cope with ROS plant cells possess an antioxidative system consisting of both enzymatic and non-enzymatic antioxidants. SOD catalyzes disproportionation of O2^- to H2O2 and O2. Influencing the concentrations of these two Haber-Weiss reaction substrates, SOD is considered to be the first line of defense against ROS. CAT is responsible for converting H2O2 to H2O andO2. POD catalyzes oxidation of many phenolic compounds at the expense of H2O2 and is considered to be a key enzyme in biosynthesis of lignin [15].

In Table 2, the activity of SOD had no statistical differences with the control until 400 mg-kg-1 of Cu, while the ones of CAT and POD had no significant difference in all treatments. That means the antioxidative system in C. comosum was slightly affected by copper, and the protective enzymes could basically keep their functions.

In spite of no significant difference, CAT and POD showed a slightly climbing trend with increasing Cu, whose maximum values were at 400 mg-kg-1 and 100 mg-kg-1 respectively. In contrast, SOD was most sensitive to Cu stress, which dropped by an average of 30.798 % than the control. The changes suggested that lower concentrations of Cu could stimulate the protective enzyme system to protect plants from oxidative damage, but higher levels of Cu concentration in leaves could induce large amounts of oxygen free radicals which would bring oxidative damage and affect the structure and synthesis of enzyme, so that enzymatic activity would be inhibited.

XU Yan et al. / Procedia Environmental Sciences 10 (2011) 715 -Table 2. Effect of Cu on activities of protective enzymes

Cu stress (mg • kg"1) CAT (0.1NKMnÖ4, ml • g"1) POD (u / min • FWg) SOD (u • g"1)

CK 10.45 +0.07a a 108.333 + 5.657a 73.739±2.738a

50 10.50 + 0.14a 109.667 + 24.984a 61.799 +54.766ab

100 10.68 + 0.04a 142.500 +19.092a 66.478+ 23.047ab

200 10.65 + 0.07a 123.833 + 3.536a 48.084+37.195ab

400 10.80 + 0.00a 119.500 + 1.179a 27.753 +0.228b

a Values followed by different letters for a given treatment are significantly different at p<0.05.

3.4. Phytoremediation by C. comosum

The last question we need to answer was how about the bioaccumulation of C. comosum. According to experiments and data analysis, we found that the Cu concentrations in roots, aboveground parts, and whole plant were all raised obviously along with increasing Cu stress. The correlation coefficients between the three above and soil were 0.939**, 0.907** and 0.936 ** respectively. (* means significant correlation, P<0.05. ** means very significant correlation, P<0.01.)

The BC of good species for repairing heavy metals-contaminated soils should be above 0.5. From Fig.2 , the BC of C. comosum were above 0.5 in all treatments except CK. These indicated that C. comosum had strong enrichment ability. So it is possible to apply C. comosum in phytoremediation of Cu-contaminated soil.

1.200 r 1:I52 1.000 -0.800 -^ 0.600 -0.400 -0.200 -0.000

CK 50 100 200 400 Cu stress (mg-kg-1) Fig. 2. Effect of Cu on Bioaccumulation coefficient

4. Conclusions

From this paper, we had found that the growth of roots and the selectivity of cell membrane in C. comosum were not inhibited evidently by Cu stress at low levels which could even be of benefit to the plants. Likely, Cu of low concentration had no markedly harmful effect on the contents of chlorophyll and protective enzyme either. Of course, higher level of Cu stress could induce large amounts of oxygen free radicals, which would bring oxidative damage and affect the structures of membranes and enzymes, to influence the physiological activity of C. comosum. On bioaccumulation, we could say that C. comosum had strong enrichment ability due to the high BC. In addition, C. comosum possesses the advantages of widely geographic distribution, easy cultivation, low risk at secondary pollution and high

ornamental value, which are the lacks of most found hyperaccumulators.

Based on the points above, we can get a conclusion that as a popular ornamental plant, C. comosum has dual merits of beautification and remediation. Therefore, C. comosum is a good resource for repairing Cu-contaminated soil, and will have a tremendous prospect of application in phytoremediation.

Acknowledgements

The author acknowledges the financial support from the National Natural Science Foundation of China (No. 31070401), the Key Foundation of Education Department of Anhui Province (No. KJ 2009 A 104, KJ 2010 A 152), the Foundation of the Provincial Key Laboratory of the Conservation and Exploitation of Biological Resources in Anhui and the Key Laboratory of Biotic Environment and Ecological Safety in Anhui Province.

References

[1] Alkorta I, Herna'ndez-Allica J, Becerril JM, Amezaga I, Albizu I and Garbisu C. Recent findings on the phytoremediation of soils contaminated with environmentally toxic heavy metals and metalloids such as zinc, cadmium, lead, and arsenic. Reviews in Environmental Science and Bio/Technology 2004;3:71-90.

[2] Clijsters H and Van Assche F. Van Assche. Inhibition of photosynthesis by heavy metals. Photosynth. Res. 1985;7:31-40.

[3] Verkieij JAC and Schat H. Mechanisms of metal tolerance in higher plants. Heavy metal tolerance in plants: evolutionary aspects 1990:179-193.

[4] Chaney RL. Plant uptake of inorganic waste constituents. Land Treatment of Hazardous Wastes 1983:50-76.

[5] Alkorta I and Garbisu C. Phytoremediation of organic contaminants. Bioresource Technol. 2001;79:273-276.

[6] Meagher RB. Phytoremediation of toxic elemental and organic pollutants. Curr. Opin. Plant Biol. 2000;3:153-162.

[7] Nouri J, Khorasani N, Lorestani B, Karami M, Hassani AH and Yousefi N. Accumulation of heavy metals in soil and uptake by plant species with phytoremediation potential. Environmental Earth Sciences 2009;59(2):315-323.

[8] Hemndez-Apaolaza L, Gasco AM, Gasco JM and Guerrero F. Reuse of waste materials as growing media for ornamental plants. Bioresource Technology 2005;96:125-131.

[9] Rout GR, Samantaray S and Das P. Differential cadmium tolerance of mung bean and rice Genotypes in hydroponic culture. Acta Agriculturae Scandinavica, Section B - Soil & Plant Science 1999;49:234-241.

[10] Tanhan MKP, Kruatrachue M, Pokethitiyook P and Chaiyarat R. Uptake and accumulation of cadmium lead and zinc by Siam weed [Chromolaena odorata(L.)King&Robinson]. Chemosphere 2007;68:323-329.

[11] Meerts P and Isacker NV. Heavy metal tolerance and accumulation in metallicolous and non-metallicolous populations of Thlaspi caerulescens from continental Europe. Plant Ecol 1997;133:221-231.

[12] Bailly C, Benamar A, Corbineau F and Dome D. Changes in malondialdehyde content and in superoxide dismutase, catalase and glutathione reductase activities in sunflower seed as related to deterioration during accelerated aging. Physiol Plant 1996;97:104-110.

[13] Krupa Z and Baszynski T. Some aspects of heavy metals toxicity towards photosynthetic apparatus - direct and indirect effects on light and dark reactions. Acta Physiol. Plant 1995;17:177-190.

[14] Molas J. Changes of chloroplast ultrastructure and total chlorophyll concentration in cabbage leaves caused by excess of organic Ni(II) complex. Environ. exp. Bot. 2002;47:115-126.

[15] Gaspar T, Penel C, Hagege D and Greppin H. Peroxidases in plant growth, diDerentiation, and development processes. Biochemical, molecular and physiological aspects ofplant peroxidases. 1991:249-280.