Abstract—The present study aims to optimize the effectiveness of

slow release biostimulant ball (BSB) on pH and COD reduction in contaminated coastal sediment in Northport, Busan. The slow release BSB containing 1kg of uncontaminated dredged sediment mixed with 0.5M sulfate, 1M nitrate, 0.5M acetate and polysulfone (PS) coated BSB were prepared for this study. The effect variables of different BSB size varied from 1 to 5cm, distances varied from 1 to 10cm and month interval varied from 1 to 4 months were used to estimate the changes of physicochemical parameter of pH and COD reduction were investigated. Variables are determined using Response surface methodology (RSM) in central composite design (CCD). ANOVA result showed that the coefficient determination value (R2) of 0.9252 in pH and COD (R2) value 0.9291. This result concluded that BSB with 3cm size and 5.5 cm distance were promising effort for reduction of COD in coastal sediment.

Keywords—Biostimulant ball, Coastal sediment, COD reduction, Response Surface Methodology.

I. INTRODUCTION N the coastal region nearby urban and suburban region, a wide variety of organic and inorganic pollutants are discharged into water and air from industries, agricultural,

and urban sources [1]. The pollutants are adsorbed onto the fragmented particles and transported into coastal water, and eventually become the contaminated sediments. The contaminated sediments can exert toxic effects on the benthic community that lives in the coastal sediments. Dredging is most common method for elimination of contaminated sediment, and the sediment was stabilized, detoxified by using physico-chemical and biological methods and finally disposed. However, the dredging needs big-budget for moving to land and treatment and further disrupts the ecosystem [2]. Direct use of conventional fertilizers may lead to concentration levels that are too high for effective action. A high concentration may

B.Subha is with the Korea Maritime and Ocean University, Busan, South Korea. She is with the department of Environmental Engineering, Busan. (e-mail: subhabak@gmail.com)

Y.C.Song is with professor in Korea Maritime and Ocean University, Busan, South Korea. He is with the department of Environmental Engineering (corresponding author:+82 010 7151-4417; fax:051-410-4977; (e-mail: soyc@kmou.ac.kr).

J.H.Woo is with the Korea Maritime and Ocean University, Busan, South Korea. She is with the department of Environmental Engineering, Busan. (e-mail: sky-woo@hanmail.net)

produce undesirable side effects that either could lead to damage in the target area or in the surrounding environment.

Slow-release fertilizers may be produced by chemically or physically prepared and they have low solubility and can provide a gradual nutrient supply for a long period of time, which improves the nutrient uptake efficiency and reduce the leaching losses. The initial goal is to determine the applicable method for preparation of biostimulant ball which useful for indigenous microbial communities in in-situ bioremediation process. The aim of the study is an experimental design approach to optimize the effectiveness of biostimulant ball in coastal sediment and study variables are ball size, distance with month effective were chosen for the study.

II. MATERIALS AND METHODS

A. Sediment Sampling And Characterization Sediment samples were collected from Busan Newport and

Busan North Port, South Korea. Sediment samples obtained from sampling site and characterized for physico-chemical properties (TABLE 1). Busan new port sample was used for biostimulant preparation purpose because, permissible amount of heavy metal contamination and low microbial population and north port sample was chosen for contaminated sediment respectively. Chemical oxygen demand (COD) of the sediment was analyzed using potassium permanganate oxidation method. Other parameters analyzed according to standard methods [3].

B. Experimental Design A three-level factorial design was established with the help

of the Design Expert software version 9.0.3 for the statistical design expert of experiments and data analysis. Response Surface Methodology (RSM) is a collection of statistical tools and techniques for exploring an approximate functional relationship between a response variable and a set of design variables [4]. In the present study the selected variables were BSB size (X1), BSB distance (X2) and month (X3) were chosen for analyses of selective responses of pH and COD. The behavior of the system is explained by the following second-degree quadratic polynomial equation

Y=Bo+B1X1+B2X2+B3X3+B11X12+B22X2

2+B33X32+B12X1X2

+B13X1X3+B23X2X3…………………………………….... (1)

An Experimental Design Approach to Optimize the Effectiveness of Biostimulant Ball in Coastal

Sediment B.Subha, Y.C.Song, and J.H.Woo

I

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Where Y was predicted response, X1 X2 and X3 were input variables and the low, middle and high levels of each variable are coded as –1.682, 0, and 1.682 respectively (TABLE 2). Generally the quadratic model is used for predicting the optimal conditions. Analysis of variance (ANOVA) was used for graphical analysis of the data. The quality of the fit polynomial model was expressed as R2 (coefficient of determination) and its statistical significance was checked by F- test [5]. Three dimensional plots with their contours were obtained for COD reduction.

C. Biostimulant Ball Preparation Biostimulating agent solution was prepared based on the

preliminary batch experiments conducted for biostimulation of microorganisms and degradation of organic matter [6]. For preparing biostimulant ball, 1kg of uncontaminated sediment soil was thoroughly mixed with biostimulant solution (0.5M sulfate, 1M nitrate, 0.5M acetate) and then partially air dried for 48h at room temperature. After partial drying, biostimulant ball was made ball shape using approximately 1g of mixed sediment. The diameters of the balls were prepared based on RSM model as in Table 2. After making biostimulant ball, it was dried in an oven at 60°C for 48 h and stored for further experiments.

D. Polymer Coating Biostimulant Ball The dried balls were coated with polymer solution of

polysulfone (10 wt %) polymer solution prepared by mixing of polymer and N,N-dimethylacetamide (90 wt %). The coating was performed by phase inversion technique using water as precipitation bath [7]. Biostimulant balls were gradually added to the polymer solution to cover a thin layer of coating solution. Double coating was achieved by immersion of the single-coated biostimulant ball into adequate polymer solution followed by the precipitation in water and drying.

III. RESULTS AND DISCUSSION

A. Fitting The Second Order Polynomial Equation And Statistical Analysis

Experiments were performed to study the effect of BSB size, BSB distance and month interval on pH and COD were chosen for analysis and its play a vital role in coastal sediment. Table 3 shows the full factorial design of the conducted experiments and the relationship between the actual and predicted values of Y. Any factor or interaction of factors with p< 0.05 is considered to be significant [7]. As per model summary statistics, quadratic model was found to have maximum adjusted and predicted and hence it was chosen for further analysis. The final equations obtained in terms of coded factors for pH and COD were presented in Equation 2 and 3 respectively.

pH (Y1)=9.26-7.27X1-5.84X2+0.12 X3-0.016 X12-0.016

X22-1.504 X3

2+1.210 X1X2 +1.262 X1X3 +1.247 X2X3……(2) COD (Y2)=84.60+1.11X1- 1.59X2+27.27 X3-

3.22X12-3.49X2

2-16.13 X32-2.04X1X2 -2.42 X1X3 -2.73

X2X3.………………………………………………. (3)

ANOVA is fitted for pH and COD reduction and the associated p value is used to estimate whether F is large enough to indicate statistical significance. The model gave coefficient of determination (R2) value of 0.9252 in pH and COD (R2) value of 0.9291. The ANOVA thus proves that the form of the model chosen to explain the relationship between the factors and the response is correct. The pH model F-value of 4.30 implies the model is significant. There is only a 1.62% chance that an F-value this large could occur due to noise. Values of "Prob > F" less than 0.0500 indicate model terms are significant. In this case month is a significant model.

TABLE II PROCESS VARIABLES AND THEIR LEVELS

Variables

Factors Levels X -1 .6

8 2 -1 0 +1 +

1 .6 8 2 Biostimulant ball size

X1 1 1.75 3 4.25 5

Biostimulant ball distance

X2 1 2.8 5.5 8.2 10

Month X3 0 1 2 3 4

TABLE III EXPERIMENTAL DESIGN ALONG WITH THE OBSERVED AND PREDICTED VALUES

BASED ON CCD Run orde

r

X 1

X2

X3

pH COD reduction

Exp value

Pre value

Exp value

(%)

Pre value

(%) 1 3 5.5 3 9.26 9.26 85.87 86.40 2 4.25 2.8 1 9.04 9.11 41.26 46.19

3 1.75 2.8 1 9.04 9.11 24.48 35.05 4 4.25 8.2 3 9.36 9.35 86.08 88.63 5 3 1 2 9.26 9.22 85.03 79.20 6 3 5.5 2 9.26 9.26 85.87 86.40 7 3 10 2 9.26 9.22 86.57 73.85 8 1.75 8.2 1 9.04 9.11 20.98 30.49 9 4.25 8.2 1 9.04 9.11 21.68 33.46 10 3 5.5 2 9.26 9.26 85.87 86.40 11 3 5.5 2 9.26 9.26 85.87 86.40 12 4.25 2.8 3 9.36 9.35 86.82 90.43 13 1 5.5 2 9.26 9.22 86.71 75.43 14 3 5.5 0 9.20 9.06 10.49 5.07 15 3 5.5 4 9.40 9.46 89.65 86.65 16 3 5.5 2 9.26 9.26 85.87 86.40 17 1.75 2.8 3 9.36 9.35 87.62 88.96 18 5 5.5 2 9.26 9.22 86.43 79.16 19 3 5.5 2 9.26 9.26 85.87 86.40 20 1.75 8.2 3 9.36 9.35 87.13 95.32

X1- BSB size, X2- BSB distance, X3- Month

TABLE 1 PHYSICOCHEMICAL PARAMETERS

Parameters Busan northport

Sand (%) 14.3 Silt (%) 18.6

Clay (%) 67.1 CODMn g/kg 28.6

TS (%) 7.2 VS (%) 4.6

Water content (%) 48

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Fig. 1 Three dimensional surface plot of pH: (a) Effect of BSB size

(cm) and distance (cm) (b) Effect of BSB size and Time (month) (c) Effect of BSB size (cm) and Time (month)

(a)

(b)

(c) Fig. 2 Three dimensional surface plot of COD reduction: (a) Effect of BSB size (cm) and distance (cm) (b) Effect of BSB size and Time

(month) (c) Effect of BSB size (cm) and Time (month).

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B. Effect of Variables on pH and COD Reduction Fig.1 and 2 (a) depicts the three dimensional plot and the

effects of BSB size and distance on pH and COD reduction and month is fixed as optimal constant. And Fig 1 and 2 (b) explained the effects of BSB size and month with constant distance of 5.5cm and Fig 1 and 2 (c) for the effect of distance and month with constant ball sixe 3cm. From this figure a, b explained that size has significant interaction with BSB distance as is evident from the elliptical nature of the contour plot. Fig 1 and 2, a, c variables of size and month effect on pH and COD of coastal sediment and the result showed the pH around above 9.04 to 9.5 But 9.46 pH with BSB 3cm size and 5.5cm distance and 4 month is very effective and maximum COD reduction 89.6% was observed at BSB 3cm ball size and 5.5cm distance with 4month time interval. This result concluded that BSB is very effective for coastal sediment. The reduction in COD could be predicted to the indigenous microorganism activity present in the sediment. These pollutants which can be converted into CO2, H2O and other intermediates [9]. The biostimulant could remove COD more than 10% higher than without added biostimulant in agriculture waste sample [10]. Biologically and biochemically mediated processes are the important in the marine ecosystem and also sediment microbes are the driving force behind the processes including the transformation of organic matter [11] and nutrient release [12]. The biostimulant is play an important role for nutrient release and enhance the absorption of microorganism and also enzymatic activity was high in biostimulant containing sample [13] and that biostimulant are slow releaser and have the slowly enhance the microbial activity and organic amendments which can stimulate the activity of microorganisms[14]. This is due to nutrient inputs for microbial development derived from the organic amendments and changes in the microbial community.

IV. CONCLUSION

The succeeding important conclusions were derived from the results obtained in this study. The biostimulant ball is a cost effective, biodegradable and slowly release the nutrient could be applied in-situ to remediate the contaminated sediments. RSM is an experimental design to apply in the study to optimize the effectiveness of BSB size and distance with time interval. The result concluded that BSB 3cm ball size, 5.5cm distance with 4month time interval is effective for treatment coastal contaminated sediment.

ACKNOWLEDGMENT

This research was a part of the project titled “Development of sustainable remediation technologies for marine contaminated sediments” funded by the Ministry of Oceans and Fisheries, Korea.

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