Field experiments on chemical and biological changes of thin-layer oyster shells capping sediments in dense aquaculture area.

Thin-layer oyster shell capping has been proposed as a method for improving contaminated coastal environments. Field experiments were conducted to investigate the effects of oyster shell capping on nutrient concentrations, microorganisms, and macrobenthic communities. The concentration of PO4-Pin the experimental area decreased by approximately 38% more than in the control, due to phosphorus fixation of oyster shells and the presence of Proteobacteria. Ammonia-oxidizing bacteria such as the order Pirellulales (phylum Planctomycetes) were related to the low ratio of NH3-N found in dissolved inorganic nitrogen in the experimental area, indicating nitrification promotion. The reduction in annular benthic organisms observed in the experimental area indicates a decline in sediment organic matter, which could potentially mitigate eutrophication. Oyster shell capping was confirmed to be an effective material for restoring coastal sediments by improving their chemical and biological properties.

Evaluation of compressive strength and phosphate fixation characteristics of wastewater filter media using coal bottom ash and oyster shells.

The excessive concentration of phosphate in coastal areas results in environmental problems such as red tide and eutrophication. Filter media (FM) is used in wastewater treatment facilities to decrease phosphate concentration. This study aims to investigate the optimal mixing ratio for high compressive strength and phosphate fixation ability using coal bottom ash (CBA) and oyster shells (OS) -derived FM. Compressive strength experiments were conducted using mixed CBA and OS with different mixing ratios, 1:3 (GBO13), 1:1 (GBO11), and 3:1 (GBO31). The highest compressive strength of 0.93 MPa was observed in GBO11. GBO11 had similar elemental proportions with Portland cement, promoting a pozzolanic reaction and forming calcium-silicate-hydrate. The phosphate fixation capability of GBO11 was evaluated through an up-flow column filtration experiment. GBO11 fixed phosphate through precipitation and adsorption, and the maximum amount of phosphate fixation was estimated to be 1.403 mg-P/g. This study demonstrates that the combination of CBA and OS can be promising FM with high compressive strength and phosphate fixation properties.

Natural Variations in the Benthic Environment and Bacterial Communities of Coastal Sediments around Aquaculture Farms in South Korea.

The aim of this study was to examine the possible seasonal variations in the nutrients (dissolved inorganic nitrogen-DIN and phosphorus) and benthic bacterial communities in marine aquaculture surrounding sediments. The study areas were Geoje, Tongyeong, and Changwon bays in Korea, which are famous for oysters (Magallana gigas), Halocynthia roretzi, and warty sea squirt (Styela clava) farming, respectively. The study sites included semi-enclosed coastal areas with a low seawater exchange rate. Subtidal sediment samples were collected seasonally from the area surrounding the aquacultures between April and December 2020. Seasonal variations in nutrients were observed, with the highest concentration of DIN in August. For phosphorus, site-specific variations were also observed. To investigate the variations in benthic bacterial communities, the advanced technique of 16S rRNA gene amplicon sequencing was applied, and the results indicated a seasonal variation pattern and predominance of Proteobacteria (59.39-69.73%), followed by Bacteroidetes (6.55-12.85%) and Chloroflexi (2.04-4.50%). This study provides a reference for future studies on natural variations in the benthic environment and bacterial communities in the areas surrounding aquacultures. Supplementary Information: The online version contains supplementary material available at 10.1007/s12088-023-01067-8.

Utilization of Spent Coffee Grounds for Bioelectricity Generation in Sediment Microbial Fuel Cells.

This study examined the utilization of spent coffee grounds with different aqueous extraction methods for the bioelectricity generation from coastal benthic sediment through a sediment microbial fuel cell (SMFC) system. Different methods for the aqueous extraction of SCGs were evaluated, including rinsing and drying of the SCG (SMFC-CRD), immersion, rinsing and drying (SMFC-CRID), drying alone (SMFC-CD), and untreated SCG (SMFC-C). The caffeine concentration in the SCG was significantly reduced using pretreatments, with SMFC-CRID achieving the lowest concentration of 0.021 ± 0.001 mg/g. SMFC-CRD contributed to the generation of the highest current density of 213.7 mA/m2 during closed-circuit operation and exhibited the highest power density of 96.9 mW/m2 in the polarization test, due to the suitable caffeine content of 0.275 ± 0.001 mg/g in the SCG. This study could provide a cost-effective method for reusing SCGs (i.e., 128 g) while generating bioelectricity as an alternative energy source. These results suggest that pretreatment with SCGs is essential for achieving optimal power density and reducing the caffeine concentration in the SMFC system.

Utilizing a granulated coal bottom ash and oyster shells for nutrient removal in eutrophic sediments.

Various in-situ capping materials have been studied to remediate contaminated sediments for sustaining a healthy ecosystem in a coastal area. We developed Granulated coal bottom ash and oyster shells (GBO) with different mixing ratios of OS. Pyrolyzed and grounded coal bottom ash and oyster shells were used to produce GBO, which the main chemical elements were analogous to cement. The nutrient-removal abilities of GBO were evaluated through long-term mesocosm experiments. It was found that GBO was an effective in-situ capping material for remediation of eutrophic coastal sediments, decreasing PO4-P and SiO2-Si concentrations in pore water by 88.4% and 56.5%, respectively. The most efficient mixing ratio of coal bottom ash and oyster shells was at a weight ratio of 1:1 for PO4-P and SiO2-Si removal.

Effect of sediment deposition on phosphate and hydrogen sulfide removal by granulated coal ash in coastal sediments.

Granulated coal ash (GCA) is a strong in-situ capping material for removing PO4-P and H2S-S in contaminated coastal sediments. Although GCA performance is weakened by sediment deposition, related research is rare. To evaluate sediment deposition effects on PO4-P and H2S-S removal by GCA, GCA was placed on the top of sediment (C-GCA), was partially mixed with sediment (M-GCA), and was fully covered by sediment (N-GCA). Effective PO4-P and H2S-S removal from sediments occurred in the order of C-GCA > M-GCA > N-GCA. C-GCA and M-GCA significantly decreased PO4-P and H2S-S concentrations by 84- 90% and 100%, respectively, through calcium phosphate and iron sulfide precipitation. N-GCA was less effective in PO4-P and H2S-S removal than the control after 2.5 months, as fine sediment particles blocked the GCA pores, decreasing calcium and iron elution. The results provide a better understanding of how sediment deposition negatively impacted GCA performance.

Physicochemical effects of calcium on suppression of coastal sediment resuspension.

The coastal in-situ capping method can sequester contaminated sediment and suppress sediment resuspension. Few studies have investigated the suppression of sediment resuspension induced by calcium eluted from in-situ capping materials. We investigated the physicochemical suppression of calcium on sediment resuspension. A resuspension experiment was conducted in an annular flume using coastal sediment mixed with 0 g (CSM0), 1 g (CSM1), 5 g (CSM5), and 10 g (CSM10) of Ca(OH)2 under a stepwise increase in bottom shear stress. Calcium enhanced sediment erosion resistance, decreasing suspended sediment concentrations. Exponentially increased SSC in CSM0 and CSM1 was three times higher than that in linearly increased CSM10. Viscosity in CSM10 was approximately three times higher than that in CSM0 and CSM1. Calcium-induced cation exchange increased sediment viscosity via sediment structural rearrangement, calcium-silicate-hydrate production, and the development of larger aggregates. Consequently, calcium suppressed sediment resuspension by physiochemically changing the sediment properties.

Effect of Bacillus subtilis Zeolite Used for Sediment Remediation on Sulfide, Phosphate, and Nitrogen Control in a Microcosm.

Eutrophication is an emerging worldwide issue concerning the excessive accumulation of various pollutants in sediments, owing to the release of industrial or household wastewaters to coastal areas. The coastal sediment of Goseong Bay in the Republic of Korea is organically enriched with pollutants, including heavy metals, sulfide, phosphate, and ammonia. Microbial remediation and capping techniques have been suggested as effective routes for sediment remediation. In this study, Bacillus subtilis zeolite (BZ) was used as a sediment capping material, and effective remediation of coastal sediment was observed in a 40-day laboratory microcosm experiment. A significant decrease in the sediment water content and reduced concentration of acid volatile sulfide were observed in the BZ-capped sediment. In the overlying water and pore water, significant decreases in phosphate and dissolved inorganic nitrogen (DIN; NO2-N + NO3-N and NH4-N) concentrations were observed in the BZ-treated experiment. Based on our findings, we conclude that BZ could be an effective capping material for coastal sediment remediation.

Distribution of Microbial Community Structure in Sediment from the Suyeong River and Bay of Busan, Republic of Korea, Determined by 16S rRNA Gene Amplicon Sequencing.

Here, we report a 16S rRNA gene amplicon sequence analysis presenting the microbial community in sediments from the Suyeong River and Suyeong Bay, Republic of Korea. The dominant phyla in all sediment samples were Proteobacteria (39.69 to 53.62%) and Bacteroidetes (29.78 to 33.89%).

Analysis of the Microbial Community Structure in Coastal Sediment of an Ascidian Farm in South Korea through 16S rRNA Gene Amplicon Sequencing.

Aquaculture places contamination pressure on the coastal environment. We investigated the microbial community structure changes in sediment in an ascidian Styela clava farm. Data profiling of the 16S rRNA gene amplicon sequence shows that the microbial diversity of sediment in the Styela clava farm is dominated by Proteobacteria (relative abundance, 95.34 to 97.85%).

Microbial Diversity Analysis of Sediment from Yeosu New Harbor of South Korea Using 16S rRNA Gene Amplicon Sequencing.

The Yeosu New Harbor in the South Korean benthic environment shows a mesotrophic environment affected by the Tsushima Current and the Seomjin River. Here, we report microbial diversity in sediments of Yeosu New Harbor based on 16S rRNA gene amplicon sequencing. The dominant bacterial phylum was Proteobacteria (relative abundance, 72.5 to 78.1%).