Factors dominating stratification cycle and seasonal water quality variation in a Korean estuarine reservoir

A comprehensive monitoring program was conducted during 2005-2007 to investigate seasonal variations of hydrologic stability and water quality in the Yeongsan Reservoir (YSR), located at the downstream end of the Yeongsan River, Korea. A principal component analysis (PCA) was performed to identify factors dominating the seasonal water quality variation from a large suite of measured data--11 physico-chemical parameters from 48 sampling sites. The results showed that three principal components explained approximately 62% of spatio-seasonal water quality variation, which are related to stratifications, pollutant loadings and resultant eutrophication, and the advective mixing process during the episodic rainfall-runoff events. A comparison was then made between YSR and an upstream freshwater reservoir (Damyang Reservoir, DYR) in the same river basin during an autumn season. It was found that the saline stratification and pollutant input from the upstream contributed to greater concentrations of nutrients and organic matter in YSR compared to DYR. In YSR, saline stratification in combination with thermal stratification was a dominant cause of the longer period (for two consecutive seasons) of hypoxic conditions at the reservoir bottom. The results presented here will help better understand the season- and geography-dependent characteristics of reservoir water quality in Asian Monsoon climate regions such as Korea.     

Effect of Solids Concentration on Bacterial Leaching of Heavy Metals from Sewage Sludge

Abstract

Microbial metal leaching from sewage sludge (2-9% w/v) was carried out with the iron-oxidizing bacterium Thiobacillus ferrooxidans. Measurements of pH, oxidation-reduction potential, and concentration of Fe²⁺ indicated that T. ferrooxidans was effective in removing metals from an incubation bath containing less than 5% sludge solids concentration. Specifically, Cu leaching was completely suppressed at a high solids concentration of 9% (w/v). Results indicated that the deactivation of T. ferrooxidans at a high sludge content was mainly due to the presence of inhibiting materials such as organic matter. A mixed culture of sulfur-oxidizing bacteria was obtained by enrichment from anaerobically digested sewage sludge to enhance the efficiency of the microbial leaching process. These bacteria were much more effective in metal leaching than was iron-oxidizing T. ferrooxidans. At 9% (w/v) solids concentration, the leaching efficiencies of Zn and Cu were 78% (2.66 g/kg dry sludge) and 59% (1.36 g/kg dry sludge), respectively. Therefore, when removing heavy metals from the anaerobically digested sewage sludge, the indigenous sulfur-oxidizing bacteria isolated in the current study were more efficient than T. ferrooxidans, especially at high sludge solids concentrations.     

Influence of pleat geometry on filter cleaning in PTFE/glass composite filter

A pleated filter bag is often used to treat exhaust gas in many industrial applications, due to its fairly high dust collection efficiency and relatively low pressure drop. This work deals with the optimum pleating geometries of a pleated filter made with a newly developed PTFE/glass composite filter. It was found that pleating geometries, including pleat height and pleat pitch, directly affect the cleaning efficiency. The design index, α, which stands for the ratio of pleat height to pleat pitch, is 1.48 for optimum operation. When the α value was higher than 1.48, the pressure drop across the pleated filter medium increased, resulting in a decreased cleaning interval due to the difficulty of filter cleaning. Therefore, it is necessary that the optimum pleating geometry should be determined by employing the dimensionless parameter, α, in the design of cartridge filters.

Implications: A pleated filter bag is often used to treat exhaust gas in many industrial applications due to its fairly high dust collection efficiency and relatively low pressure drop. The present paper introduces an optimum design configuration to make a pleated filter with newly developed PTFE/glass composite filter media. A dimensionless parameter that is the ratio of pleat height to pleat pitch should be considered to make the best quality pleated filter.     

Significance of autochthonous Bacillus sp. KK1 on biomineralization of lead in mine tailings

The aim of the study was to isolate and characterize potential autochthonous bacteria for biomineralization of Pb in mine tailings. A total of four bacteria were isolated from the soil samples and assayed for tolerance to Pb and other heavy metals. Isolate KK1 exhibited maximum Pb resistance and was subsequently identified as Bacillus sp. based on the partial 16S rRNA gene sequences. The isolate KK1 reduced the Pb ions and did not harbor pbrT gene. Selective sequential extraction of bioaugmented soil revealed that the isolate significantly reduced (26%) the exchangeable fraction and increased (38%) the carbonate fraction of Pb. X-ray diffraction studies confirmed the role of bacterially induced calcite precipitation in the bioremediation of mine tailings. A significant increase in the urease (334%), DHO (dehydrogenase) (14%), and phosphatase (37%) activity was observed in the bioaugmented mine soil.     

Identification of the sources of PM10 in a subway tunnel using positive matrix factorization

The level of particulate matter of less than 10 μm diameter (PM₁₀) at subway platforms can be significantly reduced by installing a platform screen-door system. However, both workers and passengers might be exposed to higher PM₁₀ levels while the cars are within the tunnel because it is a more confined environment. This study determined the PM₁₀ levels in a subway tunnel, and identified the sources of PM₁₀ using elemental analysis and receptor modeling. Forty-four PM₁₀ samples were collected in the tunnel between the Gireum and Mia stations on Line 4 in metropolitan Seoul and analyzed using inductively coupled plasma–atomic emission spectrometry and ion chromatography. The major PM₁₀ sources were identified using positive matrix factorization (PMF). The average PM₁₀ concentration in the tunnels was 200.8 ± 22.0 μg/m³. Elemental analysis indicated that the PM₁₀ consisted of 40.4% inorganic species, 9.1% anions, 4.9% cations, and 45.6% other materials. Iron was the most abundant element, with an average concentration of 72.5 ± 10.4 μg/m³. The PM₁₀ sources characterized by PMF included rail, wheel, and brake wear (59.6%), soil combustion (17.0%), secondary aerosols (10.0%), electric cable wear (8.1%), and soil and road dust (5.4%). Internal sources comprising rail, wheel, brake, and electric cable wear made the greatest contribution to the PM₁₀ (67.7%) in tunnel air.

ImplicationsWith installation of a platform screen door, PM₁₀ levels in subway tunnels were higher than those on platforms. Tunnel PM₁₀ levels exceeded 150 μg/m³ of the Korean standard for subway platform. Elemental analysis of PM₁₀ in a tunnel showed that Fe was the most abundant element. Five PM₁₀ sources in tunnel were identified by positive matrix factorization. Railroad-related sources contributed 68% of PM₁₀ in the subway tunnel.     

Effect of sulfate reduction activity on biological treatment of hexavalent chromium [Cr(VI)] contaminated electroplating wastewater under sulfate-rich condition

Electroplating wastewater (EW) containing heavy metals was treated by a two-stage packed-bed reactor system. The EW was highly contaminated with hexavalent chromium and other heavy metals as well as sulfate because sulfuric acid had been mainly used to polish the surface of metals to be electroplated. This acidic EW was effectively neutralized in an alkaline reactor where limestone had been packed. The neutralized wastewater together with organic wastewater from a starch-processing factory (SPW) was fed to a bioreactor packed with waste biomass. The SPW was used to supplement the electron donor in the sulfidogenic bioreactor. During the whole operation, we investigated the stoichiometry of electron to see what could be a major factor to remove Cr in the wastewater. The removal rates of sulfate and Cr(VI) were dependent on the consumption rate of organic materials in the wastewater. The stoichiometric studies also showed that about 63% of electrons from oxidation of organic materials were used to reduce sulfate. When the electrons of sulfide oxidation to elemental sulfur was at least 1.3 times higher than that of Cr(VI) reduction to Cr(III), Cr(VI) was completely removed. This result suggests that Cr(VI) reduction can be expected to take place under sulfate-rich anaerobic conditions, and sulfide produced by sulfate reducing bacteria could be used to immobilize soluble chromium through Cr(VI) reduction.     

Inactivation of Bacillus subtilis spores during ozonation in water treatment plant: influence of pre-treatment and consequences for positioning of the ozonation step

This study reports on quantitative methodology for rational selection of the ozone injection point within unit processes of conventional drinking water treatment plants to improve disinfection efficiencies. The method is based on the fact that a specific inactivation level of microorganisms is achieved at a unique value of ozone exposures, independent of ozone dose and type of water, and quantitatively described by a Delayed Chick-Watson model (C T(lag): 1.03mgl(-1), k: 1.44mg(-1)lmin(-1)). This study demonstrated this phenomenon by performing the inactivation of Bacillus subtilis (B. subtilis) spores with ozone in various types of water collected from a series of unit processes in a water treatment plant. Simple measurements of the ozone decomposition behavior in waters from each unit process of a water treatment plant can allow the quantitative evaluation of the ozone needed to achieve a required level of inactivation. This methodology will be useful for drinking water treatment plants which intend to improve the disinfection efficiencies of their ozonation process.     

Effects of biochar addition on the anaerobic digestion of carbohydrate-rich,protein-rich,and lipid-rich substrates

ABSTRACT

Although biochar addition into the anaerobic digestion of food waste (FW) is an efficient means to enhance methane production, the effects of biochar on various FW components remain unclear. Laboratory batch experiments were conducted to investigate the impact of sewage sludge-derived biochar (SSB) supplementation on the anaerobic digestion (AD) of major FW components, including carbohydrate-rich, protein-rich, and lipid-rich substrates. The lag phase of AD with the carbohydrate-rich substrate was 48.6% shorter when SSB was added, and the cumulative methane yield was 4.74 times higher compared to AD without biochar. SSB supplementation also increased the rate of methane production from the lipid-rich substrate. However, the effect of SSB addition on AD of the protein-rich substrate was minor. Analysis of the microbial communities revealed that methanogen growth was enhanced during AD of the carbohydrate-rich and lipid-rich substrates, but not the protein-rich substrate, following SSB supplementation. Also, the most dominant methanogenic genus varied with the substrates. SSB addition promoted the growth of hydrolytic and fermentative bacteria, particularly phylum Bacteroidetes.

Implications: Biochar supplementation has been studied to overcome the shortcomings of anaerobic digestion (AD). However, the effects of biochar on different substrates remain unclear. This study compared carbohydrate-rich, protein-rich, and lipid-rich substrates in anaerobic digestion with sewage sludge-derived biochar (SSB). SSB supplementation improved methane generation from all but the protein-rich substrate. The study results imply that the effect of SSB addition on AD varied with the substrate due to the substrates underwent different degradation processes with different microbial communities.     

Comparisons of particulate-bound mercury (PBM) compositions in soil and vegetation at a traffic site

This investigation analyzes the particulate-bound mercury (PBM) compositions in soil and vegetation at a traffic sampling site in Taichung, Taiwan, during a sampling period from October to December, 2015. A direct mercury analyzer (DMA-80) was used to measure the particulate-bound mercury (PBM). A T-test was conducted to determine the mean differences between the PBM composition in soil and that in vegetation at the site. The results indicate that 1) the mean particulate-bound mercury compositions in soil and vegetation were the lowest in November, when the (mean OR average) wind speed was the highest (4.1 m/s); 2) Particulate-bound mercury compositions (PBM) in both soil and vegetation correlated weakly with temperature, humidity and wind speed; 3) T-test statistical results denoted that the PBM compositions did not significantly differ between soil and vegetation in the three-month sampling period.