Euiso Choi

Sediment characteristics, phosphorus types and phosphorus release rates between river and lake sediments

The Han river is 469.7 km long with 26219-km2 area watershed, and is the primary drinking water source for the 20 million people that live in Seoul, Kangwon-Do and Kyunggi-Do, Korea. Phosphorus release from sediments impacts water quality, and is endangering the beneficial use of the river. This research measures phosphorus release and predicts future releases from bottom sediments of two tributary areas (Chungpyung Lake (CPL) and Jamsil submerged dam (JSD) area in the Han river). Sediment samples were taken over a 4-year period from four points in the Jamsil dam area and from 92 points in CPL. The sediments were analyzed for total phosphorus, the form of the phosphorus and release rates under different conditions to the water column. Sediment phosphorus distribution from CPL was 3-5% adsorbed-P (Ads-P), 15-20% non-apatite-P (NAI-P), 25-30% apatite-P (A-P) and 45-57% residual-P (R-P). In the JSD area, the phosphorus distribution ranges were 1-3% Ads-P, 22-39% NAI-P, 26-40% A-P and 30-39% R-P. Laboratory experiments showed that phosphorus release rates from 60 to 80 mg/m2 week in JSD area and ranged from 25 to 40 mg/m2 week in CPL sediments.

Removal of Reactive Dye Using UV/TiO2 in Circular Type Reactor

Abstract Photocatalytic degradation of reactive dye, Red 120, was carried out on TiO2 particles as photocatalyst under UV irradiation. In this experiment, comparison on the removal of reactive dye by photolysis using UV light alone, photocatalyst adsorption using TiO2 alone and photocatalysis using UV light with photocatalysts as well as the effect of experimental parameters such as the number of column employed, intensity of the light, pH and TiO2 dosage affecting the reaction efficiency of photocatalytic degradation of reactive dye in circular type reactor was examined. The results of this indicate that with both UV light illumination and TiO2 present, reactive dye was more effectively eliminated than with either UV or TiO2 alone. Photocatalytic degradation of reactive dye increased linearly with increasing UV light intensity. However, over 18 mW cm−2 of UV light intensity, the efficiency reached a plateau. The photocatalytic degradation rate was greater in acid media than in alkaline media. Photocatalytic removal efficiency of reactive dye increased with increasing TiO2 dosage. However, over 1.5 g L−1 of TiO2 dosage, the efficiency reached a plateau.

Appropriate Design of Activated Sludge Systems for Nitrogen Removal from High Strength Wastewaters

Abstract The study is focused on defining a conceptual approach for the design of activated sludge systems treating strong wastewater for nitrogen removal. The effect of major factors such as COD/N ratio, denitrification potential, available nitrate, anoxic volume fraction, and recycle ratio is evaluated in terms of basic stoichiometry. An algorithm for appropriate design is developed for a continuous flow activated sludge and sequencing batch reactor, both operated in a pre-denitrification mode. The design approach is tested for two types of strong industrial wastewaters with different N contents and COD/N ratios and a typical domestic sewage for comparative evaluation.

Modelling of inhibition of nitrite oxidation in biological nitritation processes by free ammonia

To understand nitrite build-up in the nitritation process, the inhibition kinetics of free ammonia (FA) on nitrite oxidation were investigated. FA inhibition on nitrite oxidation was the key factor of nitrite build-up and its type was mixed inhibition. Therefore, the mixed inhibition model should be adapted to a Michaelis–Menten equation to set up a process rate equation for nitrite oxidation in the nitritation process.

Effect of biologically mediated pH change on phosphorus removal in BNR system for piggery waste treatment

Since applicable amount of animal waste to farm land has been greatly reduced because of the nutrient overload, nitrogen and phosphorus removal from animal waste has received a great attention. This study was conducted to evaluate how phosphorus was removed during biological nutrient removal (BNR) from piggery waste using laboratory and full scale units operated at 25 to 40°C. The phosphorus removal was performed by chemical precipitation with struvite and hydroxyapatite (HAP), cellular formation, it is basically related with pH and organic and nitrogen loads resulting in influent COD/N ratios. The removal efficiencies increased from 50 to 90% as COD/N ratios increased to 6 to 7, but carbon was not limited beyond this ratio for denitrification resulting in a stable pH. Overall, about 70% of the phosphorus removal was due to the precipitates of struvite and/or HAP, and the remaining removal was due to the cellular P formation. Any significant temperature effect on phosphorus removal was not observed within the operating temperature. In order to maximize phosphorus removal in BNR system, additional anoxic stage must be furnished prior to discharge its final effluent after oxic stage.

Practical Aspects of Nitrogen and Phosphorous Removal with Floating Media SBBR

Abstract Practical aspect on the application of floating media for the sequencing batch biofilm reactor (SBBR) has not been studied in detail, especially focused on settling step, nutrient removal and temperature effects. Two types of floating media (sponge and plastic) had been examined for SBBR operation with sewage. Based on the observations with various experimental variables including temperature, media volume, operating methods, both SBBR units with sponge and plastic media generally produced a stable nitrified effluent, but depicted unstable phosphorus removal. The sponge media showed better nitrogen removal, while plastic media showed better phosphorus removal. Overall nutrient removal capability for SBBR was better than a typical SBR without media. In addition, SBBR with sponge media was capable to absorb shock loads, but could not effectively nitrify at a lower temperature even with an increased media volume. In order to produce lower SS effluent as well as minimize P release during the settling step, the floating media SBBR systems would require a dual settling stage.