Assessment of metal contamination in water and sediments from major rivers in South Korea from 2008 to 2015.

This study is the first report to evaluate (8 years data) the contamination degree and distribution characteristics of metals in the surface water and sediments of four Korean rivers (Nakdong, Yeongsan, Geum, and Han). Eight years of data were evaluated, and metal concentrations in the river water were found to be below permissible limits but high enough to cause detrimental effects (under chronic exposure) to aquatic organisms. The analysis of metals in the river sediments showed the following trend: Zn > Cu > Cd > Pb > Ni > As > Cr > Hg. The concentrations of metals in sediments (especially in the Geum and Han rivers) were above the permissible limits reported by international agencies. Concentrations of Cu, Ni, and Zn were high enough to pose risks to aquatic communities. In sediments, metals pollution was also evaluated using different indices, such as enrichment factor (EF), geoaccumulation index (Igeo), contamination factor (CF), degree of contamination (Cd), modified degree of contamination (mCd), and pollution load index (PLI). The CF, EF, and Igeo indices demonstrated that most of the river sediment samples were moderately to heavily contaminated by Cd, Cu, Pb, and Zn. The PLI values were above one in the Geum and Han river sediments, which indicated polluted conditions. Similarly, Cd indicated a considerable to very high degree of contamination, while mCd indicated a low to moderate degree of contamination in all four river sediments. Finally, it was found that the extent of metals pollution in the Korean rivers reached a critical condition, which could be detrimental to the biota of the rivers, as well as to humans in the long term.

Sludge Reduction by H2O2 Oxidation with Fe/MgO Catalyst.

This study aimed to determine whether catalytic pretreatment can be used as a method to reduce the amount of wastewater sludge. In this study, H2O2 oxidation in the presence of a heterogeneous Fe/MgO catalyst was added to the pretreatment step. Initially a laboratory-scale test showed a TCOD (total chemical oxygen demand) was reduced 27.4% during catalytic oxidation compared to 2.1% in a catalyst-free option. Catalytic pretreatment was then evaluated in a bench-scale flow-loop test. Two bench systems were composed of identical serial processes that included anaerobic digestion, aerobic digestion, and coagulating sedimentation. The only difference between the two processes was whether catalytic pretreatment of sediment sludge was used or not. Results showed that catalyst-free oxidation TCOD gradually increased from 4200 to 7800 mg/L while catalytic oxidation maintained TCOD values at 4200 ± 200 mg/L. In addition, catalytic pretreatment reduced total nitrogen from 46.9 to 41.0 mg/L and phosphate from 3.1 to 2.3 mg/L.

Enhanced ammonia nitrogen removal using consistent biological regeneration and ammonium exchange of zeolite in modified SBR process.

The modified zeo-SBR is recommended for a new nitrogen removal process that has a special function of consistent ammonium exchange and bioregeneration of zeolite-floc. Three sets of sequencing batch reactors, control, zeo-SBR, and modified zeo-SBR were tested to assess nitrogen removal efficiency. The control reactor consisted of anoxic-fill, aeration-mixing, settling, and decanting/idle phases, meaning that nitrogen removal efficiency was dependent on the decanting volume in a cycle. The zeo-SBR reactor was operated in the same way as the control reactor, except for daily addition of powdered zeolite in the SBR reactor. The operating order sequences in the zeo-SBR were changed in the modified zeo-SBR. Anoxic-fill phase was followed by aeration-mixing phase in the zeo-SBR, while aeration-mixing phase was followed by anoxic-fill phase in the modified zeo-SBR to carry NH4(+)-N over to the next operational cycle and to reduce total nitrogen concentration in the effluent. In the modified zeo-SBR, nitrification and biological regeneration occurred during the initial aeration-mixing phase, while denitrification and ammonium adsorption occurred in the following anoxic-fill phase. The changed operational sequence in the modified zeo-SBR to adapt the ammonium adsorption and biological regeneration of the zeolite-floc could enhance nitrogen removal efficiency. As a result of the continuous operation, the nitrogen removal efficiencies of the control and zeo-SBR were in 68.5-70.9%, based on the 33% of decanting volume for a cycle. The zeo-SBR showed a consistent ammonium exchange and bio-regeneration in the anoxic-fill and aeration-mixing phases, respectively. Meanwhile, the effluent total nitrogen of the modified zeo-SBR showed 50-60 mg N/L through ammonium adsorption of the zeolite-floc when the influent ammonium concentration was 315 mg N/L, indicating the T-N removal efficiency was enhanced over 10% in the same HRT and SRT conditions as those of control and zeo-SBR reactors. The ammonium adsorption capacity was found to be 6-7 mg NH4(+)-N/g FSS that is equivalent to 40 mg NH4(+)-N/L of ammonium nitrogen removal.