In this year, Koreans have a shortage in agricultural and drinking water due to severe algal blooms generated in major lakes. Waste oyster shells were obtained from temporary storage near the workplace at which oysters were separated from their shells. Heating ($1000^{\circ}C$ for 1 h in ...
In this year, Koreans have a shortage in agricultural and drinking water due to severe algal blooms generated in major lakes. Waste oyster shells were obtained from temporary storage near the workplace at which oysters were separated from their shells. Heating ($1000^{\circ}C$ for 1 h in air) was employed to convert raw oyster shell powders into calcium oxide powders that reacted efficiently with phosphorus and nitrogen to remove algal blooms from eutrophicated wastewater. As the dispersed amount of heated oyster shell powders was increased, water clarity and visual light penetration were improved. Coagulation, precipitation and carbonation process of the heated oyster shell powders in a water purifier facilitated removal of eutrophication nutrient such as phosphorus and nitrogen, which is both beneficial and economically viable. $CO_2$ implantation by carbonation treatment not only produced thermodynamically stable CaO in oyster shells to derive precipitated calcium carbonate (PCC) but also accelerated algal removal by activation of coagulation and precipitation process. The use of oyster shell powders led to a mean reduction of 97% in total phosphate (T-P), a mean reduction of 91% in total nitrogen (T-N) and a maximum reduction of 51% in chemical oxygen demand (COD), compared with the total pollutant load of raw algal solution. Remarkable water quality improvement of algal removal by heated oyster shell powders and PCC carbonation treatment will allow utilization as water resources to agricultural or industrial use.
In this year, Koreans have a shortage in agricultural and drinking water due to severe algal blooms generated in major lakes. Waste oyster shells were obtained from temporary storage near the workplace at which oysters were separated from their shells. Heating ($1000^{\circ}C$ for 1 h in air) was employed to convert raw oyster shell powders into calcium oxide powders that reacted efficiently with phosphorus and nitrogen to remove algal blooms from eutrophicated wastewater. As the dispersed amount of heated oyster shell powders was increased, water clarity and visual light penetration were improved. Coagulation, precipitation and carbonation process of the heated oyster shell powders in a water purifier facilitated removal of eutrophication nutrient such as phosphorus and nitrogen, which is both beneficial and economically viable. $CO_2$ implantation by carbonation treatment not only produced thermodynamically stable CaO in oyster shells to derive precipitated calcium carbonate (PCC) but also accelerated algal removal by activation of coagulation and precipitation process. The use of oyster shell powders led to a mean reduction of 97% in total phosphate (T-P), a mean reduction of 91% in total nitrogen (T-N) and a maximum reduction of 51% in chemical oxygen demand (COD), compared with the total pollutant load of raw algal solution. Remarkable water quality improvement of algal removal by heated oyster shell powders and PCC carbonation treatment will allow utilization as water resources to agricultural or industrial use.
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제안 방법
To measure the removal efficiencies of PO43− by calcium, Ca(NO3)2 solution was prepared according to the concentration ratios of Na(PO4)3 at pH 12. All water quality analyses were conducted by well-known conventional methods such as total nitrogen (chromotropic acid method, analyzed wavelength of 410 nm,, analysis limit of 1.0 ~ 50 mg/L), total phosphorous (ascorbic acid method, analyzed wavelength of 880 nm, analysis limit of 0.01 ~ 3 mg/L), and CODMn (reactor digestion method, analyzed wavelength of 540 nm, analysis limit of 0.6 ~ 20 mg/L), measured by purchasing each test kit solutions with an UV-Visible Spectrophotometer (Humas. Co., LTD, HS-3300). In measuring the removal efficiencies for algal bloom, each solution was diluted by 5 times to avoid the effects of absorption wavelengths on green color of the raw algal solution.
Waste oyster shell powder was calcined at ambient air condition inside an electric furnace under constant temperatures of 800℃ and 1000℃ for 1 h after arising as a temperature heating rate of 10℃/min. For surface analyses of waste oyster shell powders and the calcined powders, a scanning electron microscopy equipped with energy dispersive x-ray spectroscopy (SEM-EDS) was employed and 10 nm Au coating was conducted to provide surface conductivity on each powders. Through X-ray diffraction (XRD), crystallinities were measured for the calcined formation, the hydrated formation of calcined powders and the precipitated calcium carbonate formation of waste oyster shell powders, respectively.
3. XRD pattern and TG/DTA analysis of comminuted and calcined oyster shell powders.
성능/효과
(b), T-N removal percentage was increased from 85% (1g→T-N 1.14) to 96% (5g→T-N 0.29) with the mean value of 91% as the dispersed amounts of calcined oyster shell powders were increased when compared with T-N concentrations (0g→T-N 7.38) in the raw algal solution.
Through continuous carbonation reaction treatment, activation of coagulation and precipitation for removing organic algal blooms with organic nutrients were accelerated in the process where the hydrated formation calcined waste oyster shell powders was converted to the precipitated calcium carbonate powders. Finally, for the total pollutant load of raw algal solution, the mean T-P removal percentage was 97%, the mean T-N removal percentage 91%, and the maximum reduction of COD 51%, respectively. Quick and effective technologies for removing severe algal bloom such as our trials are essential to sustainable utilization and development of water resources conforming to the regulations of Ministry of Environment.
For the total phosphorus load of raw algal solution (0 g → T-P 4.25), T-P removal percentage was increased from 95%(1 g → T-P 0.2) to 98%(5 g → T-P 0.1) with the mean value of 97%.
후속연구
For the reactant mass of 5 g, a tendency where the increase of hydrated formation [Ca(OH)2] of calcined waste oyster shell powders may be the reason that the powders are slowly settled down and some dispersed powders are uniformly floated as fine powders. Since the equivalent amounts of CO2 gas are injected, in order to perform accurate quantitative analysis between two powders, additional experiments are required to figure out the detail information for carbonation contents ratios reacted with between CO2 gas and hydrated formation. Continued additional experiments are also including concerning more precise water quality analyses with the solutions before and after conduct carbonation process to the precipitated calcium carbonate powders for the raw algal solution.
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