Remediation of Coastal Marine Sediment using Iron

Ahmad Seiar Y.

1,*

, Y. Nakamura

, T. Miyatuji

, Y. Hagino

, T. Kobayashi

Y. Shigeoka

and T. Inoue

Institute of Urban Innovation, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama, Japan

Tokyo Kyuei Co. Ltd. 3-1-15 Nihonbashi, Chuoh-ku, Tokyo, Japan

Environment Information Research Group, Port and Airport Research Institute, 3-1-1 Nagase, Yokosuka, Japan

Keywords: Sedimentary Sulfide-release, Iron, Iron Hydroxide, Anoxia, Laboratory Experiment.

Abstract: Laboratory experiments were conducted to evaluate the effectiveness of iron application to surface sediment

on the suppression of hydrogen sulfide release from sediments. By using sediments cores collected from

Mikawa Bay, Japan at every month from June to September 2017, incubation experiments were made for

three weeks under anoxic conditions with or without application of the iron containing compounds; the iron

oxide or iron hydroxide. The results revealed that both uses of the iron oxide and iron hydroxide significantly

reduced sulfide release flux from the sediment into the overlying water. Iron hydroxide was more effective

than iron oxide in the suppression of sulfide release, as concluded from 21

day of incubation. While, no

significant difference was observed among the control group after 21day incubation. Therefore, it can be

conclude that the application of iron to the sediment is a promising method to remediate contaminated

sediments in eutrophic water body.

1 INTRODUCTION

Sediment is the important habitat for organisms living

in the surface and into the bottom ground. It acts as

the storehouse of nutrients in aquatic ecosystems.

Eutrophication because of excess amount of nutrients

supply to a water body causes high productivity that

results in large amount of organic matters settle to the

sediments. As the excess organic material is left to be

decomposed, and if the amount of oxygen is

insufficient, decomposition processes continue due to

bacterial activities employing electron acceptors

other than oxygen, this results in the reduction of

sulfate, (Wang and Chapman, 1999; Levin et al.,

2009; 2002; Yakushev et al., 2007; Ueda, 2013), as

per equation,

+ Organic Matter (OM

)



.

→

S + CO

In the absence of dissolved oxygen (DO) and in the

presence of soluble Biological Oxygen Demand

(BOD), Desulfovibrio desulfuricans (SRB) and other

sulfate-reducing bacteria (SRB’s) convert the sulfate

ion to sulfide, which is highly toxic and fatal to

benthic organisms. However, the irons have capacity

to regulate the formation of sulfide by poisoning the

http://www.cvg.ynu.ac.jp/G2/member_e.html

redox sequence and to form insoluble iron sulfide and

pyrite compounds. The chemical equation showing

this process is

keeping these points in view, for marine

environmental remediation, we aim to propose a

method for improving the sediment environment and

conduct an elution experiment using an undisturbed

sediment core added with various iron materials in

laboratory experiments to precipitate hydrogen

sulfide over a long period of time.

2 MATERIALS AND METHODS

Figure 1: A schematic view of the experimental apparatus.

Y., A., Nakamura, Y., Miyatuji, T., Hagino, Y., Kobayashi, T., Shigeoka, Y. and Inoue, T.

Remediation of Coastal Marine Sediment using Iron.

DOI: 10.5220/0007756303350339

In Proceedings of the 5th International Conference on Geographical Information Systems Theory, Applications and Management (GISTAM 2019), pages 335-339

ISBN: 978-989-758-371-1

335

2.1 Sampling Locations

Intact sediment cores were taken from a fix point in

the innermost part of Mikawa Bay, Japan, in order to

evaluate the suppression effects of iron application to

surface sediment on sulfide release rates. Mikawa

Bay is a eutrophic coastal embayment’s in which

seasonal density stratification and associated hypoxic

condition in the bottom water develop, in general,

from June to September. In this study, sediment core

samples were collected with acrylic pipe whose inner

diameter of 10 cm and length of 50 cm, every month

from June to September 2017. Temperature, salinity,

DO, and turbidity were measured at every sampling

occasions. All sampled sediment cores were

immediately transferred to a laboratory to conduct

sulfide release experiments with or without iron

application to the surface sediment.

2.2 Laboratory Experiments

Total 6 (for experiments in June, July and August) or

9 (September) core samples were selected for

incubation experiment. In the laboratory, the

overlying water of each core was replaced with

deoxygenated filtered seawater. For iron application

cores, predetermined amount of iron compounds were

applied to the surface of the sediment. Cores were

then sealed by a top cap to keep anoxic condition

during the course of the incubation period. DO meter

to check anoxic condition and a stirrer to circulate the

overlying water were also installed to a lid of pipe for

each core. Cores were then incubated into a container

keeping the same temperature of each the in-situ

conditions. Bottom water temperature for June, July,

August, and September experiments were 20.3, 21.7,

25.7 and 24.0 degree in Celsius, respectively.

The experiment was conducted with total four

kind of treatments (Reference core A, core B with

iron oxide applied to the surface, Unused core C, and

core D added with iron hydroxide, which was

performed only in September). In addition, each

experimental treatment was performed in triplicate

except the treatment B in June. Table 1 shows the

amount of iron compounds applied for each

experiment. Note that 5 g of iron oxide and 5.6 g of

iron hydroxide are equivalent to the same Fe amount

of 3.5 g.

The incubation experiments continued for three

weeks. Water samples were collected to measure the

dissolved sulfide and dissolved iron concentrations in

the overlying water at appropriate time intervals

during the incubation.

Table 1: List of treatments of the release experiment.

Treatments

Iron

compounds

Amount of iron compounds

applied [g]

June July Aug. Sept.

A: Control

Reference-1 0 0 0 0

Reference-2 0 0 0 0

Reference-3 0 0 0 0

B: Iron

oxide

addition

-1 0.41 5 5 5

-2 0.85 5 5 5

-3 1.61 5 5 5

Experiment

unused

Only use in chemical analysis and preparative

D: Iron

hydroxide

addition

Fe (OH)

-1 - - - 5.6

Fe (OH)

-2 - - - 5.6

Fe (OH)

-3 - - - 5.6

2.3 Chemical Analysis

Dissolved sulfide was analysed by the methylene blue

method. In this method, a sulfide colouring reagent

comprising iron chloride III (FeCl

.6H

O) and N, N-

dimethyl-p-phenylenediamine sulphate dissolved in 6

M HCl solution were added into the sample for

analysis. The absorbance of the solution was

measured with a spectrophotometer at a wavelength

of 667 nm. Dissolved divalent iron concentration was

also analysed by the phenanthroline method.

Sediment quality was analysed after completion

of the experiment. Sediments were sliced to 1.5 cm

intervals, and water content, loss in ignition, TOC,

COD, sulfide, TN, TP, T-Fe, and T-Mn were analysed

for each sediment samples. Sediment pore water was

obtained by squeezing over a 0.45 µm filter, then

dissolved-sulfide concentrations were measured in

pore waters. A part of the collected sediment samples

was also used to analyze the hydrogen ion

concentration index (pH), oxidation-reduction

potential.

The data were analyzed using one-way analysis of

variance (ANOVA) at 0.05% level of significance

with the SPSS package (version 23 IBM).

3 RESULTS AND DISCUSSIONS

3.1 Dissolved Sulfide Concentration in

the Overlying Water

Temporal changes of dissolved sulfide concentrations

in the overlying water in each treatment are shown in

Figure. 2 (a), (b), (c), and (d) for the experiments

ONM-CozD 2019 - Special Session on Observations and Numerical Modeling of the Coastal Ocean Zone Dynamics

336

conducted in June, July, August and September,

respectively. For every cases, the concentration of

dissolved sulfide in the overlying water

monotonically increased related to sediment

remediation in all the cores.

Result for the experiments in June shows

relatively lower release of the dissolved sulfide into

the overlying water even in the control cases (A1, A2,

and A3). Order of the final concentration of dissolved

sulfide for B-1, B-2, and B-3 did not follow the

application amount of iron. Additionally, the final

concentration for cases of the application of iron

(Group B) showed no statistically significant

difference from the control case (Group A).

Therefore, for later experiments we used larger

amount of iron compounds for triplicate sediment

cores.

Table 2: Analysis of variance for reading comprehension of

the studied variables in the sediment.

Parameter Periods F Value P Value Result

Dissolved

sulfide

concentrations

in the overlying

water

June 3.845

.568

The result is not

significant at p < .05.

July and

August

6.643 0.011

The result is significant

at p < .05.

September 8.924 0 .000

The result is significant

at p < .01.

Dissolved

sulfide increase

rate

(mg/m

/day)

June 0.064 0.804

The result is not

significant at p < .05

July 0.891 0.367

The result is not

significant at p < .05

August 5.515 0.407

The result is significant

at p < .05.

September 9.401 0.002

The result is significant

at p < .01.

(a)

(b)

(c)

(d)

Figure 2: Temporal changes in dissolved sulfide

concentration in the overlying water for (a) June, (b) July,

Remediation of Coastal Marine Sediment using Iron

337

Results obtained from cores for July, August and

September show a significant difference (p<0.05)

between the two treatment groups. Based on data

obtained in July, for example, the final concentration

of dissolved sulfide in the control cores (A-2, A-3, A-

1) were 44.4, 40.6, and 31.9 mg/L, respectively.

Whereas the final concentrations in the iron

treatments core (B-2, B-3, B-1) indicated 9.4, 12.5,

and 14.6 mg/L, respectively. These results showed

remarkably lower values compared to the control

cases as shown Figure 2 (b). The same tendency was

observed for the third August experiments.

In the last experiment in September, iron

hydroxide was also added to treatment groups. The

final concentration of dissolved sulfide in the

overlying water for iron hydroxide core (D-2, D-1, D-

3) indicates 0.4, 3.8, and 10.7 mg/L, respectively, as

shown in Figure 2 (d). These values were much

smaller than iron oxide application core (B-3, B-1, B-

2), in which those values were 23.2, 25.2, and 29.5

mg/L. The dissolved sulfide concentrations were

quite high in the control core (A-3, A-1, A-2) with

values of 73.6, 49.6, and 43.4 mg/L, respectively.

Although the averaged final concentration was

highest in the control case (A) in September, it was

lowest in the iron hydroxide application (D) This

suggests the relatively higher effectiveness of the iron

hydroxide for the suppression of sulfide release. The

lag time to appear significant increase in 5 mm

dissolved sulfide concentration was longest in June.

More than five days were necessary even in the

control case. The lag time became gradually shorter

in the later experiments. Especially in September, no

apparent lab time was observed.

3.2 Dissolved Sulfide Release Rate

One of the practically inmportant parameters is the

release rate of dissolved sulfide from the sediment

under anoxic conditions. Averaged release rates

calculated for each time interval of the experimtns are

shown in Figure 3(a), (b), and (c), for July, August,

and September experiments.

In July and August experiments, the release rate

of dissolved sulfide in the control cores (A-1, A-2, A-

3) in turn ranged from 2 to 556 mg/m

/day and 8 to

637 “mg m

-1

”. However, in the experiment with

iron material added, it ranged from 1 to 521

mg/m

/day and 8 to 422 mg/m

/day.

Results of September experiment demonstrated

that the release rate as well as dussolved sulfide

concentrations in the overlying water were

significantly low with iron hydroxide core (D-2, D-1,

D-3) ranging from 1 to 269 mg/m

/day. As shown in

Figure 3(c), the second lowest value of the release

rate of dissolved sulfide were obtained from core (B-

3, B-1, B-2) were 116 to 845 mg/m

/day,

respectively. The release rate were quite high in the

control core (A-3, A-1, A-2) with values ranged from

409 to 1,014 mg/m

/day.

(a)

(b)

(c)

Figure 3: Release rate of dissolved sulfide for (a) July, (b)

August, and (c) September experiments.

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338

3.3 Sulfide Release Rate and Iron

Concentration

Figure 4 shows comparison between sulfide erlease

rates and divalent iron concentrations for July,

August and September experiments. The divalent

iron can react with dissolved sulfide to form

particulate iron sulfide, which will precipite to the

sediment. Such reaction may under-estimate the

release rates of dissolved sulfide. However, the

concentration range of divalent iron is relatively low

in these experiments.

(a)

(b)

(c)

Figure 4: Comparison of sulfide release rates and divalent

iron concentrations for (a) July, (b) August, and (c)

September experiments.

Further quantitative analysis on this point would

be necessary for further arguments.

4 CONCLUSIONS

The results revealed that both uses of the iron and

iron-hydroxide significantly reduced sulfide release

flux from the sediment into the overlying water. After

the 21 days incubation, the average dissolved sulfides

concentration in the overlying water of treatment

group was significantly decrease (p = .0001). No

significant difference was observed between the

control group after 21 day incubation. Therefore, the

application of iron to the sediment is a promising

method to remediate contaminated sediments in

eutrophic water body.

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Ueda, K., 2013. Modeling of dissolved oxygen

concentration recovery in water bodies and application

to hypoxic water bodies. World Envi., vol. 3, no. 2, pp.

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Levin, L. A., Ekau, W., Gooday, A. J., Jorissen, F.,

Middelburg, J. J., Naqvi, W., Neira, C., Rabalais, N. N.,

and Zhang, J., 2009. Effects of natural and human-

induced hypoxia on coastal benthos. Biogeosciences

Discuss., vol. 6, pp. 3563–3654.

Yakushev, E. V., Pollehne, F., Jost, G., Kuznetsov, I.,

Schneider, B., and Umlauf, L., 2007. Analysis of the

water column oxic/anoxic interface in the Black and

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vol. 107, pp. 388–410.

Wang, F. and Chapman, P. M., 1999. Biological

Implications of Sulfide in Sediment – A Review

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