Removal of potentially toxic metal by biochar derived from rendered solid residue with high content of protein and bone tissue.

The purpose of this study was to produce rendering animal carcass residue char (RACR-C) by pyrolyzing the solid residues of low-recyclable rendered pig carcasses and to evaluate their cadmium (Cd) adsorption characteristics and mechanisms. As the pyrolysis temperature increased, the inorganic content of RACR-C increased, while the carbon content decreased. In particular, the surface structure and chemistry of RACR-Cs prepared at different pyrolysis temperatures were well described by SEM-EDS, XRD, XRF, TGA, and FTIR. The Cd adsorption characteristics of RACR-C were in good agreement with the Langmuir isotherm and pseudo-second-order models, and the Cd adsorption capacities of RACR-Cs prepared at various pyrolysis temperatures were in the order of RACR-C500 (73.5 mg/g)> RACR-C600 (53.8 mg/g)> RACR-C400 (41.5 mg/g) " RACR-C250 (15.9 mg/g). The intraparticle diffusion model suggested that the adsorption of Cd by RACR-C is greatly influenced by internal diffusion as well as external boundary. Since the Cd adsorption capacity of RACR-C is greatly influenced by the initial dosage, pH, and co-existing metals, it is necessary to manage these influencing factors when treating wastewater containing heavy metals. Our results suggest that Cd adsorption by RACR-C is a complex adsorption phenomenon by various mechanisms such as adsorption by functional group (CË­C and C-O), precipitation of Cd-P and ion exchange reaction by exchangeable cation occurring rather than by a single specific mechanism.

Exploration of the potential capacity of fly ash and bottom ash derived from wood pellet-based thermal power plant for heavy metal removal.

This study was conducted to explore the potential capacity for the removal of heavy metals from the fly ash (FA) and bottom ash (BA) emitted by wood pellet thermal power plants. Fly ash consists of inorganic compounds such as CaSiO3, P2O5, and K2O, whereas BA shows properties very similar to the biochar derived from organic biomass. The adsorption properties of both FA and BA for Cd were described well by the Langmuir and pseudo-second-order models, and the maximum adsorption capacity of FA for Cd was 4.2 times higher than that of BA. The results indicate that FA can be applied to the treatment of wastewater that contains heavy metals over pH range from 2-6; however, BA is considered to be most effective for application with wastewater that contains heavy metals at a pH of 5-6. Study of the mechanism concluded that the adsorption of Cd by FA is dominated by the formation of Cd2SiO4 complexes by chemical reactions between CaSiO3 and Cd ions as well as via the precipitation of Cd(OH)2 in the neutral and alkaline solutions that is caused by the dissolution of K. It was found that the adsorption of Cd by BA was influenced by the binding of functional groups (CC and COH), coupled CaCO3 dissolution-CdCO3 precipitation reaction and ion exchange between some minerals with Si and Cd ions in weakly acidic conditions. Results indicate that the FA and BA emitted from wood pellet thermal power plants have high potential for heavy metal removal, and their practical use in the purification and restoration of heavy metals could be an effective way to reduce the waste produced by power plants and clean the environment.

Utilization of liquid pig manure for resource cycling agriculture in rice-green manure crop rotation in South Korea.

A 2-year field experiment was carried out on rice (Oryza sativa, Japonica type) cultivation in South Korea. The objective of this study was to investigate the effect of application of liquid pig manure on biomass production and nutrient supply of green barley (Hordeum vulgare L.) and hairy vetch (Vicia villosa Roth) green manure crops and to evaluate the effect of nutrients supplied from these sources on rice yield and soil quality in a rice-green manure crop rotation system. Over the 2-year study period, application of liquid pig manure increased biomass production of green manure crops of barley and hairy vetch by more than 216% and 135%, respectively, compared with without liquid pig manure. Moreover, the results showed that the application of liquid pig manure significantly increased the nutrient supply levels in green barley- and hairy vetch-treated areas. Positive effects related to nutrient supply in green barley and hairy vetch treated with liquid pig manure were observed on rice yield, soil chemical characteristics, and microbial biomass C and N contents. In conclusion, the addition of liquid pig manure systems using green manure crops of green barley and hairy vetch improved rice productivity and soil quality. It is suggested that these combinations can be effective in developing resource cycling agriculture in a rice-green manure crop rotation system as it reduces the need for inorganic fertilizer.

Cadmium adsorption characteristics of biochars derived using various pine tree residues and pyrolysis temperatures.

This study investigated the characteristics of biochars derived using various pine tree residues and pyrolysis temperatures and evaluated their Cd adsorption behaviors. The characteristics of pine tree residue biochars (PRBs) were dominantly affected by the pyrolysis temperature, and the optimum pyrolysis temperature for Cd adsorption was 600 °C. The adsorption of Cd by PRBs was divided into two stages: rapid adsorption on the initial boundary layer and slow adsorption by intraparticle diffusion. The Cd adsorption characteristics of all the PRBs were well described by pseudo-second-order and Langmuir isotherm models, and the maximum adsorption capacity was the highest in pine bark biochar (85.8 mg/g). The amounts of the cations released from the mixed pine tree residue biochars (M-PRBs) during Cd adsorption were increased, while the amount of phosphate released was decreased, indicating that exchangeable cations and phosphate on the biochar affected the Cd adsorption. In particular, the amount of Cd removed by the exchangeable cations corresponds to 23.6% of the total adsorption amount. Spectroscopic analyses using FTIR showed that the Cd adsorption on M-PRB was associated with functional groups such as CC, COH and COOH. Overall, the use of biochars derived from pine tree residue as an adsorbent is considered to be effective for both the treatment of wastewater containing heavy metals and the recycling of forest residues.

Lead sorption characteristics of various chicken bone part-derived chars.

Recycling food waste for beneficial use is becoming increasingly important in resource-limited economy. In this study, waste chicken bones of different parts from restaurant industry were pyrolyzed at 600 °C and evaluated for char physicochemical properties and Pb sorption characteristics. Lead adsorption isotherms by different chicken bone chars were carried out with initial Pb concentration range of 1-1000 mg L-1 at pH 5. The Pb adsorption data were better described by the Langmuir model (R2 = 0.9289-0.9937; ARE = 22.7-29.3%) than the Freundlich model (R2 = 0.8684-0.9544; ARE = 35.4-72.0%). Among the chars derived from different chicken bone parts, the tibia bone char exhibited the highest maximum Pb adsorption capacity of 263 mg g-1 followed by the pelvis (222 mg g-1), ribs (208 mg g-1), clavicle (179 mg g-1), vertebrae (159 mg g-1), and humerus (135 mg g-1). The Pb adsorption capacities were significantly and positively correlated with the surface area, phosphate release amount, and total phosphorus content of chicken bone chars (r ≥ 0.9711). On the other hand, approximately 75-88% of the adsorbed Pb on the chicken bone chars was desorbable with 0.1 M HCl, indicating their recyclability for reuse. Results demonstrated that chicken bone char could be used as an effective adsorbent for Pb removal in wastewater.

Effect of biochar derived from barley straw on soil physicochemical properties, crop growth, and nitrous oxide emission in an upland field in South Korea.

This study was conducted to investigate soil quality, Chinese cabbage growth, and N2O emission after biochar application in an upland field in South Korea. Each of the barley straw biochar (BC, applied at 10 ton ha-1), inorganic fertilizer (IF, applied at N-P-K = 320-78-198 kg ha-1), and BC + IF treatment areas were separated by a control (Cn) treatment area. Soils treated with BC and BC + IF treatments had lower bulk density and higher porosity than those in the Cn treatment areas. Soil chemical properties (pH, TN, Avail. P2O5, and CEC) after biochar addition were improved. In particular, soil pH and CEC related to crop nutrient availability were significantly increased in BC areas compared to those in Cn and IF areas. Fresh weights of Chinese cabbage grown under BC, IF, and BC + IF treatment conditions increased by 64.9, 78.4, and 112.0%, respectively, over that in the Cn treatment area. Total nutrient (TN, TP, and K) uptakes among the treatment areas were, in declining order, BC + IF (14.51 g plant-1) > IF > BC > Cn. More interestingly, the BC application had a positive effect on growth of Chinese cabbage under IF application conditions, and there was a tight relationship between the effect of BC application on Chinese cabbage growth and that of agronomic IF application efficiency. Compared to the IF results, total N2O flux was lower with BC (flux decreased by 60.6%) or BC + IF (flux decreased by 22.3%) treatments. These results indicate that Chinese cabbage yield, when cultivated in soil conditions such as those in an upland field in South Korea, can be increased by application of BC or a combination of BC and IF.

Adsorption of Cd, Cu and Zn from aqueous solutions onto ferronickel slag under different potentially toxic metal combination.

Adsorption characteristics of potentially toxic metals in single- and multi-metal forms onto ferronickel slag were evaluated. Competitive sorption of metals by ferronickel slag has never been reported previously. The maximum adsorption capacities of toxic metals on ferronickel were in the order of Cd (10.2 mg g(-1)) > Cu (8.4 mg g(-1)) > Zn (4.4 mg g(-1)) in the single-metal adsorption isotherm and Cu (6.1 mg g(-1)) >> Cd (2.3 mg g(-1)) > Zn (0.3 mg g(-1)) in the multi-metal adsorption isotherm. In comparison with single-metal adsorption isotherm, the reduction rates of maximum toxic metal adsorption capacity in the multi-metal adsorption isotherm were in the following order of Zn (93%) > Cd (78%) >> Cu (27%). The Freundlich isotherm provides a slightly better fit than the Langmuir isotherm equation using ferronickel slag for potentially toxic metal adsorption. Multi-metal adsorption behaviors differed from single-metal adsorption due to competition, based on data obtained from Freundlich and Langmuir adsorption models and three-dimensional simulation. Especially, Cd and Zn were easily exchanged and substituted by Cu during multi-metal adsorption. Further competitive adsorption studies are necessary in order to accurately estimate adsorption capacity of ferronickel slag for potentially toxic metals in natural environments.

Long-term performance of vertical-flow and horizontal-flow constructed wetlands as affected by season, N load, and operating stage for treating nitrogen from domestic sewage.

To investigate the long-term nitrogen treatment efficiency in vertical-flow (VF)-horizontal-flow (HF) hybrid constructed wetlands (CWs), the nitrogen removal efficiency under different seasons, N loads, and three operating stages (representing age of the wetland) were evaluated over a 12-year period. The average total nitrogen (TN) removal efficiencies in the effluent during the operation period were in the following order: summer (75.2%) > spring (73.4%) ≒ autumn (72.6%) > winter (66.4%). The removal efficiencies of TN in summer, autumn, and spring were generally higher than those in winter. At different stages of operation (years), the average TN removal rates in the effluent were in the following order: middle stage (73.4%; years 2006-2009) > last stage (72.0%; years 2010-2013) > beginning stage (70.1%; years 2002-2005). In VF-HF CWs, the amount of average TN removal (mg N m(-2) day(-1)) over the 12-year period was in the order of summer (5.5) ≒ autumn (5.1) > spring (4.3) ≒ winter (4.2) for the VF bed and in the order of summer (3.5) ≒ spring (3.5) ≒ autumn (3.3) > winter (2.7) for the HF bed, showing that the amount of TN removal per unit area (m(2)) in summer was slightly greater than that in other seasons. The amount of TN removal in the VF bed was slightly greater than that in the HF bed. Using three-dimensional simulation graphs, the maximum TN removal rate was at inflow N loads below 2.7 g m(-2) day(-1) in the summer season, whereas the minimum TN removal rate was at inflow N loads below 1.4 g m(-2) day(-1) in the winter season. Consequently, the TN removal efficiency was very stable over the 12 years of operation in VF-HF hybrid CWs. Results demonstrate that the VF-HF hybrid CWs possess good buffer capacity for treating TN from domestic sewage for extended periods of time.

Competitive adsorption of heavy metals onto sesame straw biochar in aqueous solutions.

Objective of this research was to evaluate adsorption of heavy metals in mono and multimetal forms onto sesame straw biochar (SSB). Competitive sorption of metals by SSB has never been reported previously. The maximum adsorption capacities (mgg(-1)) of metals by SSB were in the order of Pb (102)≫Cd (86)≫Cr (65)>Cu (55)≫Zn (34) in the monometal adsorption isotherm and Pb (88)≫Cu (40)≫Cr (21)>Zn (7)⩾Cd (5) in the multimetal adsorption isotherm. Based on data obtained from the distribution coefficients, Freundlich and Langmuir adsorption models, and three-dimensional simulation, multimetal adsorption behaviors differed from monometal adsorption due to competition. Especially, during multimetal adsorption, Cd was easily exchanged and substituted by other metals. Further competitive adsorption studies are necessary in order to accurately estimate the heavy metal adsorption capacity of biochar in natural environments.

Competitive adsorption and selectivity sequence of heavy metals by chicken bone-derived biochar: Batch and column experiment.

The objective of this research was to evaluate adsorption of heavy metals in single- and ternary-metal forms onto chicken bone biochar (CBB). Competitive sorption of heavy metals by CBB has never been reported previously. The maximum adsorption capacities of metals by CBB were in the order of Cu (130 mg g(-1)) > Cd (109 mg g(-1)) > Zn (93 mg g(-1)) in the single-metal adsorption isotherm and Cu (108 mg g(-1)) >> Cd (54 mg g(-1)) ≥ Zn (44 mg g(-1)) in the ternary-metal adsorption isotherm. Cu was the most retained cation, whereas Zn could be easily exchanged and substituted by Cu. Batch experimental data best fit the Langmuir model rather than the Freundlich isotherms. In the column experiments, the total adsorbed amounts of the metals were in the following order of Cu (210 mg g(-1)) > Cd (192 mg g(-1)) > Zn (178) in single-metal conditions, and Cu (156) > Cd (123) > Zn (92) in ternary-metal conditions. Results from both the batch and column experiments indicate that competitive adsorption among metals increases the mobility of these metals. Especially, Zn in single-metal conditions lost it adsorption capacity most significantly. Based on the 3D simulation graphs of heavy metals, adsorption patterns under single adsorption condition were different than under competitive adsorption condition. Results from both the batch and column experiments show that competitive adsorption among metals increases the mobility of these metals. The maximum metal adsorption capacity of the metals in the column experiments was higher than that in the batch experiment indicating other metal retention mechanisms rather than adsorption may be involved. Therefore, both column and batch experiments are needed for estimating retention capacities and removal efficiencies of metals in CBB.

Enhanced sulfamethazine removal by steam-activated invasive plant-derived biochar.

Recent investigations have shown frequent detection of pharmaceuticals in soils and waters posing potential risks to human and ecological health. Here, we report the enhanced removal of sulfamethazine (SMT) from water by physically activated biochar. Specifically, we investigated the effects of steam-activated biochars synthesized from an invasive plant (Sicyos angulatus L.) on the sorption of SMT in water. The properties and sorption capacities of steam-activated biochars were compared with those of conventional non-activated slow pyrolyzed biochars. Sorption exhibited pronounced pH dependence, which was consistent with SMT speciation and biochar charge properties. A linear relationship was observed between sorption parameters and biochar properties such as molar elemental ratios, surface area, and pore volumes. The isotherms data were well described by the Freundlich and Temkin models suggesting favorable chemisorption processes and electrostatic interactions between SMT and biochar. The steam-activated biochar produced at 700 °C showed the highest sorption capacity (37.7 mg g(-1)) at pH 3, with a 55% increase in sorption capacity compared to that of non-activated biochar produced at the same temperature. Therefore, steam activation could potentially enhance the sorption capacities of biochars compared to conventional pyrolysis.

Development of an online sulfur-oxidizing bacteria biosensor for the monitoring of water toxicity.

A toxicity monitoring system based on the metabolic properties of sulfur-oxidizing bacteria (SOB) in continuous and fed-batch modes has been applied for the detection of nitrite (NO2 (-)-N). In this study, the effects of different concentrations of NO2 (-)-N (0.1 to 5 mg/L) on the SOB bioreactors were tested. We found that 5 mg/L NO2 (-)-N was very toxic to the SOB bioreactors in both continuous (R1) and fed-batch (R2) modes, showing complete inhibition of SOB activity within 2 h of operation. R1 and R2 were operated in different ways; however, the EC inhibition and recovery patterns were very similar. The EC rate increased with an increasing NO2 (-)-N concentration in both continuous and fed-batch modes. The addition of 5 mg/L NO2 (-)-N in continuous mode decreased the average EC rate by 14.38 ± 2.1 µS/cm/min; while in fed-batch mode, the EC rate decreased by 23 µS/cm/min. Although the toxicity monitoring system could detect 0.5-5 mg/L NO2 (-)-N, it could not detect 0.1 mg/L NO2 (-)-N in either continuous or fed-batch operation. Thus, the SOB biosensor method presented is useful to detect toxic agents such as NO2 (-)-N within a few minutes or hours.

Inhibitory effect of veterinary antibiotics on denitrification in groundwater: a microcosm approach.

Veterinary antibiotics in groundwater may affect natural microbial denitrification process. A microcosm study was conducted to evaluate the influence of sulfamethazine and chlortetracycline at different concentrations (0, 0.01, 0.1, and 1.0 mg/L) on nitrate reduction in groundwater under denitrifying condition. Decrease in nitrate removal and nitrite production was observed with the antibiotics. Maximum inhibition of nitrate removal was observed after seven days of incubation with 0.01 mg/L sulfamethazine (17.0%) and 1.0 mg/L chlortetracycline (15.4%). The nitrite production was inhibited with 1.0 mg/L sulfamethazine to 82.0% and chlortetracycline to 31.1%. The initial/final nitrate concentrations indicated that 0.01 mg/L sulfamethazine and 1.0 mg/L chlortetracycline were most effective in inhibiting activity of denitrifying bacteria in groundwater. After 12 days of incubation, the sulfamethazine biodegradation was observed whereas chlortetracycline was persistent. Sulfamethazine and chlortetracycline in groundwater could inhibit the growth and capability of naturally occurring denitrifying bacteria, thereby threatening nitrate pollution in groundwater.

Speciation and phytoavailability of lead and antimony in a small arms range soil amended with mussel shell, cow bone and biochar: EXAFS spectroscopy and chemical extractions.

Mussel shell (MS), cow bone (CB) and biochar (BC) were selected to immobilize metals in an army firing range soil. Amendments were applied at 5% (wt) and their efficacies were determined after 175 d. For metal phytoavailability test, maize (Zea mays L.) plants were cultivated for 3weeks. Results showed that all amendments decreased the exchangeable Pb by up to 99% in planted/unplanted soils. Contrarily, exchangeable Sb were increased in the MS- and CB-amended soils. The rise in soil pH (~1 unit) by the amendments affected Pb and Sb mobility in soils. Bioavailability of Pb to maize was reduced by up to 71% in the amended soils. The Sb uptake to maize was decreased by up to 53.44% in the BC-amended soil. Sequential chemical extractions showed the transformation of easily available Pb to stable residual form with the amendment treatments. Scanning electron microscopic elemental dot mapping revealed the Pb association with Al and Si in the MS-amended soil and that with P in the CB- and BC-amended soils. Additionally, the extended X-ray absorption fine structure spectroscopic analysis indicated the transformation of organic bound Pb in unamended control soil to relatively more stable Pb-hydroxide (Ksp=10(-17.1)), chloropyromorphite (Ksp=10(-84.4)) and Pb-phosphate (Ksp=10(-23.8)) in soils amended with MS, CB and BC, respectively. Application of BC was the best in decreasing the phytoavailability of Pb and Sb in the studied army firing range soil.

Assessment of chromium-contaminated groundwater using a thiosulfate-oxidizing bacteria (TOB) biosensor.

The effect of Cr(6+)-contaminated groundwater was assessed using thiosulfate-oxidizing bacteria (TOB). Electrical conductivity (EC), pH, and sulfate production were determined based on thiosulfate oxidation. Final pH values in the different test treatments of Cr(6+)-contaminated groundwater (50-1000 µg Cr(6+)L(-1)) ranged from 2.02 ± 0.09 to 7.76 ± 0.07 and EC ranged from 5.95 ± 0.03 to 3.63 ± 0.03 mS cm(-1). Inhibition of TOB due to Cr(6+) was between 16.7% and 100%, with higher levels of inhibition occurring at higher Cr(6+) concentrations. The median effective concentration (EC50) was 78.96 µg Cr(6+)L(-1). These data demonstrate that TOB can detect less than 100 µg L(-1) of Cr(6+) in the groundwater and can be used as an effective bioassay for toxicity assessment.

Terriglobus aquaticus sp. nov., isolated from an artificial reservoir.

A pink-pigmented, chemo-organotrophic bacterium, designated strain 03SUJ4(T), was isolated from the freshwater of Juam reservoir, Republic of Korea (35° 03' 43'' N 127° 14' 15'' E). Cells were aerobic, Gram-reaction-negative and non-motile rods. Strain 03SUJ4(T) grew at pH 6-7 (optimum, pH 6) and at 15-30 °C (optimum, 25 °C). Phylogenetic analysis based on 16S rRNA gene sequences indicated that the isolate belonged to the genus Terriglobus, showing sequence similarities of 97.09 % and 96.82 % to Terriglobus roseus DSM 18391(T) and Terriglobus saanensis SP1PR4(T), respectively. Low rpoB gene sequence similarity with members of the genus Terriglobus and different fingerprints with the repetitive primers BOX, ERIC and REP indicated that the isolate represented a novel species of the genus Terriglobus. The major cellular fatty acids were iso-C15 : 0, C16 : 0, C20 : 1ω9c, C14 : 0 and summed feature 3 (C16 : 1ω7c/C16 : 1ω6c). The DNA G+C content of strain 03SUJ4(T) was 63.2±0.1 mol% (mean±sd of three determinations). The predominant menaquinone was MK-8. The major polar lipids were phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylglycerol and two unidentified phospholipids. Several phenotypic characteristics served to differentiate the novel isolate from recognized members of the genus Terriglobus. On the basis of the evidence presented in this study, a novel species, Terriglobus aquaticus sp. nov. is proposed for strain 03SUJ4(T) ( = KCTC 23332(T) = JCM 17517(T)).

Trichloroethylene adsorption by pine needle biochars produced at various pyrolysis temperatures.

In this study, pine needles were converted to biochar (BC) at different pyrolysis temperatures of 300, 500, and 700 °C to sorb trichloroethylene (TCE), and the changes in BC properties with each temperature were evaluated. Pyrolysis temperature showed a pronounced effect on BC properties. Decreases in molar H/C and O/C ratios resulted from removing O- and H-containing functional groups with increasing temperature, and produced high aromaticity and low polarity BCs. BCs produced at higher temperature showed greater TCE removal efficiency from water due to their high surface area, micro-porosity, and carbonized extent. The performance of various BCs for TCE removal was assessed by the Freundlich, Langmuir, Temkin, and Dubinin-Radushkevich adsorption models, among which the Temkin and Dubinin-Radushkevich models best described TCE adsorption onto various BCs, indicating prevailing sorption mechanism as pore-filling.

Constitutive overexpression of the calcium sensor CBL5 confers osmotic or drought stress tolerance in Arabidopsis.

Calcium serves as a critical messenger in many adaptation and developmental processes. Cellular calcium signals are detected and transmitted by sensor molecules such as calcium-binding proteins. In plants, the calcineurin B-like protein (CBL) family represents a unique group of calcium sensors and plays a key role in decoding calcium transients by specifically interacting with and regulating a family of CBL-interacting protein kinases (CIPKs). In this study, we report the role of Arabidopsis CBL5 gene in high salt or drought tolerance. CBL5 gene is expressed significantly in green tissues, but not in roots. CBL5 was not induced by abiotic stress conditions such as high salt, drought or low temperature. To determine whether the CBL5 gene plays a role in stress response pathways, we ectopically expressed the CBL5 protein in transgenic Arabidopsis plants (35S-CBL5) and examined plant responses to abiotic stresses. CBL5-overexpressing plants displayed enhanced tolerance to high salt or drought stress. CBL5 overexpression also rendered plants more resistant to high salt or hyperosmotic stress during early development (i.e., seed germination) but did not alter their response to abiscisic acid (ABA). Furthermore, overexpression of CBL5 alters the gene expression of stress gene markers, such as RD29A, RD29B and Kin1 etc. These results suggest that CBL5 may function as a positive regulator of salt or drought responses in plants.

Evaluation of a hybrid constructed wetland for treating domestic sewage from individual housing units surrounding agricultural villages in South Korea.

The treatment efficiency of 2- and 3-stage constructed wetlands (CWs) was evaluated for treating domestic sewage from houses surrounding agricultural villages. The optimum depth of filter media was 90 cm. The optimum volume ratio of vertical flow (VF) and horizontal flow (HF) beds was 1:2, and the optimum filter medium was broken stone in the VF-HF 2-stage hybrid CWs. Based on the above optimum conditions, removal efficiency of biochemical oxygen demand (BOD), chemical oxygen demand (COD), suspended solids (SS), total nitrogen (T-N), and total phosphorus (T-P) were 99, 98, 99, 68, and 72%, respectively. However to utilize constructed wetlands (CWs) for treating domestic sewage for an individual house, would require downsizing of the 2-stage hybrid CWs. In addition, the low removal efficiency of T-N and T-P in 2-stage hybrid CWs would require improvements necessary to meet acceptable water quality discharge standards. Thus, to reduce the CWs' area and improve the T-N and T-P removal efficiencies, VF-HF 2-stage hybrid CW was modified into VF/HF(I)-HF(II) and VF/HF(I)-HF(III) 3-stage hybrid CW. The optimum reduced size of 3-stage hybrid CW was the VF/HF(I)-HF(II) configuration which also increased T-N removal. Using this system, removal efficiency of BOD, COD, SS, T-N, and T-P were 99, 98, 99, 83, and 75%, respectively. In VF/HF(I)-HF(II) CW, the removal velocity of BOD, COD and SS was rapid on the order of VF (1st stage) >> HF(II) (3rd stage) > or = HF(I) (2nd stage), VF (1st stage) >> HF(II) (3rd stage) > HF(I) (2nd stage) and VF (1st stage) >> HF(I) (2nd stage) > HF(II) (3rd stage), respectively. The removal velocity of T-N and T-P in VF/HF(I)-HF(II) CWs was rapid on the order of HF(I) (2nd stage) > HF(II) (3rd stage) > or = VF (1st stage) and VF (1st stage) > HF(I) (2nd stage) > HF(II) (3rd stage), respectively.

Phosphorous retention capacity of filter media for estimating the longevity of constructed wetland.

The filter medium could be selected and the longevity of the filter medium by the phosphorus saturation could be predicted in the constructed wetland system, accordingly proposing the scheme to remove the phosphorus for a long period. The phosphorus adsorption capacities of various filter media were investigated in relation to the size and types of filter media to screen the optimal condition. The objective of this study was to evaluate the constructed wetland longevity by improving P adsorption capacity. The maximum P adsorption capacities of filter media A (4--10 mm), B (2--4 mm), and C (0.1--2 mm) were 7.7, 11.6, and 22.5 mg/kg, respectively, showing that they increased as the filter media size decreased. Among the experimental media, the optimal filter media size was 0.1--2 mm. When Ca, Mg, Al and Fe were added to the filter medium C, which is the optimal filter medium, the addition of Ca improved mostly the P adsorption capacity. In the alternative proposal to use these facts, the oyster shell was added to the filter medium and the P adsorption capacity was examined: adding 2% oyster shell increased the P adsorption capacity from 23 to 36 mg/kg. In the column where the oyster shell was mixed, when the oyster shell content was 5%, 10%, 20%, 40%, 60%, 80%, and 100% in the filter medium C, the respective saturation times of the P adsorption were about 6, 9, 17, 30, 43, 56, and 70 days. When the oyster shell content was 0%, 5%, 10%, 20%, 40%, 60%, 80%, and 100% after 1 month in the column, the P adsorption amount was about 180, 600, 1560, 4280, 6157, 7089, 7519, and 7925 mg/kg, respectively. The increment of the P adsorption amount was small if the oyster shell content was 60% or more, because the filter medium with more than 60% oyster shell content did not approach the saturation time by the P adsorption yet. The P adsorption amount for 60%, 80%, and 100% could be predicted as about 9702, 12,879, and 16,056 mg/kg, respectively. The largest amount of extracted P in the filter media with oyster shell after 30 days of P solution application was bound to Ca, followed by water soluble-P, Al--P, and Fe--P. Therefore, it was concluded that the adsorption amount of the phosphorus could be increased by adding the oyster shell to the filter medium. Also, it was concluded that adding the oyster shell to the filter medium in the constructed wetland was the scheme to extend the longevity of the constructed wetland by the phosphorus saturation, and using the oyster shell would be useful in aspect of economical efficiency and easiness. Especially, it would be the alternative proposal to reduce the environmental pollution in aspect of recycling wastes.