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Application of solidified sea bottom sediments into environmental bioremediation materials
⁎Corresponding authors. Address: Department of Chemistry for Materials, Graduate School of Engineering, Mie University, Tsu, Mie 514-8507, Japan. Tel.: +81 59 231 9427 (S. Kaneco). ahmedmie2000@gmail.com (Ahmed H.A. Dabwan), kaneco@chem.mie-u.ac.jp (Satoshi Kaneco)
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Received: ,
Accepted: ,
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Peer review under responsibility of King Saud University.
Abstract
Since dredged sea bottom sediments normally give off a horrible smell, the limitation of disposal places has become a serious problem in Japan. Hence, development of an alternative system to readily treat dredged sea bottom sediments is therefore needed. The development of “value-added” reused products from these sediments offers particular benefits both in terms of resource recovery and protection of the environment. We developed an in situ solidification system for the treatment of sea bottom sediments, the “Hi-Biah-System (HBS)”. Firstly, this review deals with solidified sea bottom sediments for the construction of an artificial tidal flat in Ago Bay, Japan. The environmental conditions (pH, oxidation–reduction potential (ORP), acid volatile sulphide (AVS), loss on ignition (LOI), water content (WC), chemical oxygen demand (COD), total organic carbon (TOC), total nitrogen (T-N), chlorophyll a and particle size) were then monitored in the constructed tidal flat. The number of benthos individuals and growth of short-necked clams (Ruditapes philippinarum) in the artificial tidal flat were also evaluated. The environmental conditions, number of benthos individuals and growth of short-necked clams in the artificial tidal flat were shown to be similar to those observed in a natural tidal flat. Next, the potential use of solidified sea bottom sediments as soil parent material in the germination/growth of seagrass is presented. The soil parent material consisting of solidified sediments obtained using HBS plus soil conditioner and hardener seems to be effective for the germination of Zostera marina. The best growth after six months was observed in plants grown in soil parent material consisting of a mixture of solidified sediments and the sand by weight ration 70:30. The present study may suggest the possible application of solidified sea bottom sediments into growth of other plants.
Keywords
Muddy dredged sediments
Constructed tidal flat
Soil parent material
Disposal of sediments
Ago Bay
1 Introduction
It is well known than tidal flats are normally located in intertidal zones. They are important areas that perform many environmental functions such as serving as a habitat for benthic organisms and areas for recreational activities as well as playing a role in water purification and biological productivity (Ali and Gupta, 2006; Gupta et al., 2009). However, in recent years, many tidal flats have been lost as a result of industrial and urban development of coastal areas. According to the Ministry of the Environment, Japan, the total area of natural tidal flats was about 826 km2 in the 1940s; however, by the 1980s, approximately 40% of these natural flats had been lost (Kimura, 1994). Currently, a number of projects are underway to protect and maintain natural tidal flats and wetland ecosystems. Furthermore, efforts are being made to restore damaged tidal flats and create artificial tidal flats to mitigate those that have been lost (Miyoshi et al., 1990; Cofer and Niering, 1992; Ogura and Imamura, 1995; Lee et al., 1998). Mie prefecture, Japan, is involved in one such project as part of the Collaboration of Regional Entities for the Advancement of Technological Excellence (CREATE), organized by the Japan Science and Technology (JST) Agency, under a proposal entitled, “Environmental Restoration Project on the Enclosed Coastal Seas, Ago Bay”. Ago Bay in Mie prefecture (Fig. 1) is one the world’s most famous original areas of pearl and oyster culture.
To date, about 70% of the natural tidal flats in Ago Bay have been lost and destroyed compared with the 1940s (Kokubu et al., 2004). Moreover, the sea conditions in Ago Bay have recently worsened due to the culturing of pearls and oysters, resulting in accumulation of organically-enriched sediments on the sea bottom. Dredging has therefore been performed since 2000 to prevent further worsening of the sea quality in this area. However, since dredged sea bottom sediments tend to give off a horrible smell, the limitation of disposal places has become a serious problem. Moreover, the large water content of sediments makes their transport and disposal extremely difficult. Hence, the development of an alternative system to treat dredged sea bottom sediments is therefore needed.
In the present project, an in situ solidification system for the treatment of sea bottom sediments, the “Hi-Biah-System (HBS)”, was developed. We review the application of the solidified sediments into the construction of an artificial tidal flat in Ago Bay (Imai et al., 2008a,b). Since its construction, the ecosystem and environmental conditions in the constructed tidal flat have been continuously monitored. Furthermore, we present the potential use of the solidified sediments as soil parent material for the germination/growth of seagrass (Dabwan et al., 2008, 2013).
2 Experimental parts
2.1 Solidification method “Hi-Biah-System” for disposal of sediments
The in situ solidification system, “Hi-Biah-System (HBS)”, was constructed as illustrated in Fig. 2. The HBS consisted of a main stock tank of sediments, a coagulant chamber, reactors 1 and 2 and a dewatering section. The treatment capacity was approximately 1–2 m3/h. The water content of the dredged sediments was 90% by weight. After treatment with HBS, the content was lowered to 60 wt%.
2.2 Application into artificial tidal flat materials
The artificial tidal flat was constructed from February to March 2005 in Ago Bay as shown in Fig. 1. It was then divided into 5 sections (E1–E5), each with an area of 10 m length × 2 m width × 0.5 m depth. In the E1 section, 1.5 wt% of soil conditioner made of paper sludge ash was used as the coagulant in the HBS. The chemical components of the soil conditioner were determined by X-ray fluorescence spectrometer with fundamental parameter (FP) calculations, and the values were 44.2% CaO, 26.9% SiO2, 12.7% Al2O3 and 12.2% SO3 and so on. After the water content of the sediments was reduced to 60 wt%, they were mixed with sand obtained from Ago Bay at a ratio of 3:7, and then an area of artificial tidal flat was constructed from these materials.
In the E2 section, solidified materials with 60 wt% water content were produced in a similar way as in the E1 section. After adding 20 wt% of the same soil conditioner, a pellet was formed with a pelletizer as illustrated in Fig. 3. The shape of the pellet was a column with a diameter of 8 mm and length of 20 mm. The E2 section of artificial tidal flat was then produced from the pellets mixed with sand (weight ratio 3:7).
In the E3 section, the flat was constructed from sand obtained in Ago Bay. In the E4 section, 5 wt% of coagulant consisting of gypsum was used in the HBS solidification treatment. After dewatering, the sediment water content was reduced to 60 wt%, and then the solidified materials were mixed with sand (weight ratio 3:7) and an area of tidal flat constructed.
In the E5 section, approximately 2 wt% of poly aluminium chloride (PAC) was added as the inorganic polymer coagulant. After dewatering, the water content of the solidified materials was reduced to 40 wt% then the solidified sediments were mixed with solidification agents consisting of waste steel slag (20% by weight) and then with sand (weight ratio 3:7). The resulting materials were used for the construction of the E5 area of artificial tidal flat.
Monitoring of the environmental conditions of the artificial tidal flat was conducted every four months. For comparison, the environmental conditions of a nearby natural tidal flat were evaluated. The environmental parameters examined were as follows: pH, oxidation–reduction potential (ORP), acid volatile sulphide AVS (Gas detector tube, GASTEC), loss on ignition LOI (JIS, 2000a), water content WC (JIS, 1999), chemical oxygen demand COD (JIS, 1998), total organic carbon TOC (Vario MAX CHS, Elementar Analysensysteme GmbH), total nitrogen T-N (JIS, 2010), chlorophyll a (N,N-dimethylformamide extraction method) and particle size (JIS, 2000b). These chemical parameters were evaluated using soil materials core-sampled from the surface to 12 cm depth. The amount of chlorophyll a was measured in soil materials from the surface to a depth of 1 cm. For evaluation of benthos individuals, the sediments were sieved with a mesh size of 1 mm then added to 10 vol% formalin. Measurement of the benthos material was then conducted according to general methods. Organisms then were sorted, identified, counted, and weighted (Lee et al., 1998).
Plastic baskets containing 100 short-necked clams (Ruditapes philippinarum) were placed in all sections of the artificial tidal flat. Growth of the short-necked clams (mortality, size and weight) was then checked every four months. The chemical composition of the clam tissues was measured as follows. First, the clam tissues were dried, powdered and accurately weighted then treated with 4 ml of nitric acid (14 M) and 1 ml of perchloric acid (9 M). After decomposition, the solution was evaporated and the remaining residue was dissolved in 1 M nitric acid. Finally, the solution was diluted in a 50 ml volumetric flask. The concentration of heavy metals in the aqueous solution was measured by inductively coupled plasma optical emission spectrometry (ICP-OES, VARIAN, multi-type Vista-PRO) and the amounts of carbon and nitrogen were measured using a CHN-corder (Vario MAX CHS, Elementar Analysensysteme GmbH).
2.3 Application into soil parent materials
The solidified sediments were then mixed with hardener or sand. Two kinds of hardener were used (H1: polyvinyl alcohol (PVA), H2: hardener made of gypsum). The materials were then transferred to small plastic containers (14 × 14 × 7.5 cm). Zostera marina was collected in Ago Bay in the summer of 2004. Seeds were then obtained, cleaned and wet-stored in a refrigerator at 6 °C.
The soil parent material was transferred to a concrete tank (350 × 150 × 50 cm) into which 25 seeds were planted using stainless tweezers in November 2004. The concrete tank was then partially filled with seawater, and after germination, this seawater was continuously overflowed to ensure aerobic conditions. The seawater conditions were as follows: pH 8.2, temperature 12–17 °C, salinity 32 practical salinity units (PSU), dissolved oxygen 11 mg l−1 and turbidity 88 nephelometric turbidity units (NTU). The leaf area was measured by general image analysis using a computer.
3 Results and discussion
3.1 Construction of artificial tidal flat (Imai et al., 2008a,b)
The water content of the sea bottom sediments was reduced to 60 wt% for making full use of the HBS solidification method. The artificial tidal flat was then constructed using the obtained solidified sediments as illustrated in Fig. 4. Seasonal variations in each of the examined parameters are summarized in Table 1. The statistical significance between the artificial tidal flats (E1–E5) could be observed on the base of the evaluation of the statistical tests.
| Section | Time passeda (months) | pH | ORP (mV) | AVS (mg/g) | LOI (%) | WC (wt%) | COD (mg/g) | TOC (mg/g) | T-N (mg/kg) | Chlorophyll a (mg/kg) |
|---|---|---|---|---|---|---|---|---|---|---|
| E1 | 1 | 8.0 | −265 | 0.059 | 5.4 | 33 | 8.9 | 6.8 | 720 | 0.75 |
| 3 | 7.6 | −94 | 0.085 | 5.7 | 32 | 9.8 | 6.8 | 700 | 0.76 | |
| 6 | 7.8 | −243 | 0.085 | 5.4 | 29 | 10 | 8.1 | 800 | 0.69 | |
| 9 | 8.0 | −357 | 0.097 | 4.5 | 31 | 10 | 8.6 | 1400 | 3.50 | |
| E2 | 1 | 8.1 | −55 | 0.026 | 5.0 | 34 | 5.9 | 5.9 | 650 | 0.63 |
| 3 | 7.4 | −55 | 0.004 | 5.2 | 29 | 5.9 | 7.7 | 600 | 0.57 | |
| 6 | 7.9 | −157 | 0.007 | 4.7 | 30 | 6.2 | 6.1 | 600 | 1.10 | |
| 9 | 8.4 | −176 | 0.032 | 4.8 | 32 | 6.4 | 5.1 | 500 | 1.70 | |
| E3 | 1 | 7.3 | −89 | 0.001 | 3.7 | 22 | 2.4 | 2.4 | 440 | 0.25 |
| 3 | 7.5 | 36 | 0.032 | 4.0 | 17 | 1.7 | 1.9 | 300 | 0.18 | |
| 6 | 7.2 | −154 | 0.016 | 3.1 | 19 | 2.1 | 2.1 | 300 | 0.34 | |
| 9 | 7.4 | −4 | 0.010 | 3.5 | 23 | 2.5 | 2.5 | 400 | 4.60 | |
| E4 | 1 | 7.2 | −208 | 0.016 | 4.8 | 29 | 4.9 | 5.4 | 680 | 0.51 |
| 3 | 6.8 | −140 | 0.030 | 5.4 | 27 | 5.3 | 6.6 | 700 | 0.35 | |
| 6 | 7.2 | −196 | 0.037 | 4.9 | 27 | 5.5 | 6.8 | 600 | 1.40 | |
| 9 | 7.4 | −221 | 0.105 | 4.9 | 28 | 6.6 | 4.5 | 600 | 2.90 | |
| E5 | 1 | 9.6 | −405 | 0.051 | 5.5 | 28 | 4.5 | 8.6 | 770 | 0.46 |
| 3 | 8.4 | −322 | 0.079 | 6.3 | 25 | 4.1 | 7.2 | 700 | 0.24 | |
| 6 | 8.1 | −247 | 0.206 | 6.1 | 29 | 5.8 | 8.9 | 900 | 0.74 | |
| 9 | 9.5 | −314 | 0.177 | 5.6 | 27 | 6.5 | 8.6 | 700 | 1.90 | |
| B-3 | April | 7.3 | −124 | 0.016 | 5.5 | 27 | 6.2 | 6.5 | 750 | 0.48 |
| July | 7.5 | −210 | 0.111 | 5.4 | 24 | 6.5 | 6.6 | 1000 | 0.58 | |
| October | 7.3 | −179 | 0.126 | 4.9 | 23 | 5.7 | 7.5 | 700 | 0.50 | |
| January | 7.6 | −151 | 0.114 | 4.9 | 25 | 5.6 | 7.6 | 700 | 2.60 | |
| C-3 | April | 7.4 | −299 | 0.532 | 7.0 | 43 | 12 | 12 | 1200 | 0.60 |
| July | 7.3 | −239 | 0.575 | 8.0 | 47 | 18 | 16 | 1700 | 0.25 | |
| October | 7.4 | −282 | 0.211 | 4.5 | 32 | 6.7 | 7.4 | 600 | 0.40 | |
| January | 7.4 | −240 | 0.026 | 4.8 | 33 | 8.0 | 9.8 | 700 | 1.10 |
In the natural tidal flat (C-3) in April and July, 2005, acid volatile sulphide, chemical oxygen demand, total organic carbon and total nitrogen were larger relative to those obtained in each section of the artificial tidal flat. However, after six months, the values of all chemical parameters were similar between the natural and artificial flats. Table 2 shows the results of the particle size analysis of the artificial tidal flat. In all sections, no coagulation of sand was observed. These results suggested that the artificial tidal flat created using the solidified materials could provide almost the similar ground conditions and chemical organic parameters as the natural tidal flat since the main components of artificial one consisted of the sea bottom sediments.
| Time passeda (months) | E1 | E2 | E3 | E4 | E5 | |
|---|---|---|---|---|---|---|
| 1 | <75 μmb | 35.6% | 28.0% | 16.9% | 36.1% | 25.7% |
| Medianc | 271 μm | 292 μm | 861 μm | 245 μm | 636 μm | |
| 3 | <75 μm | 45.1% | 22.6% | 28.8% | 26.3% | 19.3% |
| Median | 111 μm | 986 μm | 286 μm | 529 μm | 1963 μm | |
| 6 | <75 μm (%) | 33.3% | 20.0% | 15.2% | 23.4% | 20.3% |
| Median | 210 μm | 1504 μm | 666 μm | 480 μm | 631 μm | |
| 9 | <75 μm (%) | 43.6% | 43.3% | 29.1% | 45.8% | 26.0% |
| Median | 107 μm | 115 μm | 207 μm | 109 μm | 346 μm |
Fig. 5 depicts the time course variations of the number of benthos individuals in the artificial tidal flat. The number of individuals was close to zero after one month, however, after three months, this number increased relative to that observed in the natural tidal flat. This observation may be considered to be attributed to the minerals supplied from the solidified sea bottom sediments. These solidified materials would give good ecological conditions for benthic animals. However, no exact conclusion can be drawn on this increase before monitoring further ecological conditions.
Table 3 shows the growth of short-necked clams in the artificial tidal flat. After nine months, in all sections of the flat, the clams grew by approximately two-fold by weight. The concentration of various metals (aluminium, arsenic, barium, cadmium, calcium, chromium, cobalt, copper, iron, manganese, magnesium, molybdenum, nickel, lead, potassium, selenium and sodium) was also evaluated in the clam tissues, revealing less than 1 μg/g-dry weight of aluminium, arsenic, barium, cadmium, chromium, cobalt, copper, iron, manganese, molybdenum, nickel, lead and selenium. Normally, calcium, iron, magnesium, potassium and sodium concentrations are larger than 1 μg/g-dry weight, suggesting that the chemical components of the examined clam tissues were close to the norm. The total organic carbon concentration of the clam tissues was in the range of 31–39%, and the total nitrogen concentration was in the region of 7.6–9.0%. These concentrations can be judged as normal (Katsuyuki, 1995). Consequently, the ecosystem of the artificial tidal flat created with solidified sea bottom sediments can be considered similar to that of natural tidal flats.
| Section | Time passeda (months) | Mortality (%) | Weight (g) | Length (mm) | Height (mm) |
|---|---|---|---|---|---|
| E1 | 0 | 0 | 3.8 | 24.7 | 18.4 |
| 3 | 16 | 8.1 ± 1.3 | 33.2 ± 2.4 | 22.9 ± 1.3 | |
| 6 | 52 | 8.7 ± 1.8 | 34.2 ± 2.1 | 23.8 ± 1.5 | |
| 9 | 72 | 9.9 ± 1.5 | 35.2 ± 2.1 | 25.7 ± 3.2 | |
| E2 | 0 | 0 | 3.8 | 24.6 | 18.5 |
| 3 | 8 | 6.7 ± 1.2 | 31.5 ± 2.1 | 21.9 ± 1.6 | |
| 6 | 40 | 8.2 ± 1.7 | 33.7 ± 2.7 | 23.1 ± 1.8 | |
| 9 | 40 | 8.2 ± 1.7 | 33.7 ± 2.7 | 23.1 ± 1.8 | |
| E3 | 0 | 0 | 3.8 | 24.6 | 18.3 |
| 3 | 24 | 7.3 ± 1.5 | 32.4 ± 2.6 | 22.3 ± 1.7 | |
| 6 | 44 | 7.8 ± 1.5 | 32.6 ± 2.8 | 22.9 ± 1.6 | |
| 9 | 44 | 8.6 ± 1.3 | 34.2 ± 1.8 | 23.8 ± 1.2 | |
| E4 | 0 | 0 | 3.8 | 24.8 | 18.3 |
| 3 | 4 | 7.2 ± 1.2 | 31.7 ± 3.0 | 22.4 ± 1.2 | |
| 6 | 24 | 8.4 ± 1.2 | 33.7 ± 2.0 | 23.4 ± 1.4 | |
| 9 | 32 | 8.9 ± 1.2 | 34.2 ± 1.8 | 23.8 ± 1.1 | |
| E5 | 0 | 0 | 3.2 | 24.5 | 18.3 |
| 3 | 16 | 7.0 ± 1.1 | 30.9 ± 3.0 | 22.3 ± 2.7 | |
| 6 | 24 | 7.6 ± 1.6 | 32.0 ± 2.3 | 22.5 ± 1.9 | |
| 9 | 24 | 8.5 ± 1.5 | 33.3 ± 2.7 | 23.3 ± 1.6 |
3.2 Germination/growth of Z. marina (Dabwan et al., 2008, 2013)
The effect of each hardener in the soil parent material on the germination rate of Z. marina was investigated; the results are shown in Fig. 6. The germination rate is defined as the ratio of Z. marina in which leaf growth was observed to the number of seeds planted. The germination rate of plants grown in the soil parent material consisting of only the sea bottom sediments was worse than that of those grown with a hardener. These findings suggest that soil parent material consisting of solidified sediments obtained using HBS plus soil conditioner and hardener seems to be more effective for the germination of Z. marina.
Next, the effect of the amount of sand in the soil parent material on the germination rate of Z. marina was studied; the results are illustrated in Fig. 7. Soil parent material consisting of a mixture of solidified sediments and sand was more efficient than that consisting of sand only. The reason is not clarified. Probably, it may be attributed to the reducing environment of the sediments. Further, it was observed that the solid strength of the soil parent material could be improved by the addition of sand compared with material consisting of only the sediments. Barko and Smart (1986) have presented the sediment-related mechanisms of growth limitation in submersed macrophytes. In this work, nutrient uptake on low-density organic sediments was apparently limited by long diffusion distances, and limited rates of nutrient diffusion and exchange in coarse-textured sediments, in addition to low nutrient status, may have contributed to their poor ability to support macrophyte growth. They have speculated that mechanisms of growth limitation on both sands and organic sediments appear to involve nutrition. Consequently, the addition of moderate amount of sand (for instance 10–30 wt%) from the viewpoint of solid strength seems to be effective as soil parent material for the germination/growth of seagrass.
After six months, the leaf area of Z. marina was evaluated in order to evaluate its growth; the results are summarized in Table 4. The best growth was observed in plants grown in soil parent material consisting of a mixture of solidified sediments and the sand (weight ratio: 70:30).
| Soil parent material | Germination rate (%) | Leaf area (cm2) |
|---|---|---|
| Sediment (100%) | 80a | 161 |
| Sand (100%) | 52 | 7 |
| Sediment treated with HBSa | 92 | 206 |
| Sediment treated with HBS plus 1 wt% H1b,c | 96h | 167 |
| Sediment treated with HBS plus 3 wt% H2b,c | 80 | 159 |
| Sediment treated with HBS plus 10 wt% sandd,e,f,g | 76 | 225 |
| Sediment treated with HBS plus 30 wt% sandd,e,f,g | 100 | 242 |
| Sediment treated with HBS plus 50 wt% sandd,e,f,g | 92 | 199 |
| Sediment treated with HBS plus 70 wt% sandd,e,f,g | 92 | 99 |
4 Conclusions
We developed an in situ solidification system for the treatment of sea bottom sediments, the “Hi-Biah-System (HBS)”. These solidified sea bottom sediments were then applied to the construction of an artificial tidal flat in the Ago Bay. The ecosystem and environmental conditions of the constructed tidal flat were found to be very similar to those of a nearby natural tidal flat. Moreover, we showed the potential use of solidified sea bottom sediments as soil parent material in the germination/growth of seagrass, suggesting its possible application in the growth of other plants.
Acknowledgements
The main work for the present Review was performed as part of a joint collaboration research project entitled, “Environmental Restoration Project on the Enclosed Coastal Seas, Ago Bay”, supported by CREATE (Collaboration of Regional Entities for the Advancement of Technological Excellence) organized by the Japan Science and Technology (JST) Agency. The Table 4main research was partly supported by the Ministry of Education, Culture, Sports, Science, and Technology of Japan. All experiments were conducted at Mie University, Japan and Tati University College, Malaysia. Any opinions, findings, conclusions, or recommendations expressed in this paper are those of the authors and do not necessarily reflect the view of the supporting organizations.
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