Performance of an electrochemical COD (chemical oxygen demand) sensor with an electrode-surface grinding unit

An electrochemical COD (chemical oxygen demand) sensor using an electrode-surface grinding unit was investigated. The electrolyzing (oxidizing) action of copper on an organic species was used as the basis of the COD measuring sensor. Using a simple three-electrode cell and a surface grinding unit, the organic species is activated by the catalytic action of copper and oxidized at a working electrode, poised at a positive potential. When synthetic wastewater was fed into the system, the measured Coulombic yields were found to be dependent on the COD of the synthetic wastewater. A linear correlation between the Coulombic yields and the COD of the synthetic wastewater was established (10-1000 mg L(-1)) when the electrode-surface grinding procedure was activated briefly at 8 h intervals. When various kinds of wastewater samples obtained from various sewage treatment plants were measured, linear correlations (r(2)> or = 0.92) between the measured EOD (electrochemical oxygen demand) value and COD of the samples were observed. At a practical wastewater treatment plant, the measurement system was successfully operated with high accuracy and good stability over 3 months. These experimental results show that the application of the measurement system would be a rapid and practical method for the determination of COD in water industries.     

Wastewater treatment plants (WWTPs) as a source of sediment contamination by toxic organic pollutants and fecal sterols in a semi-enclosed bay in Korea

Toxic organic contaminants and a macrobenthic community were assayed in sediments collected near a wastewater treatment plant (WWTP) outfall to assess the impact of WWTP discharges on an aquatic environment. Average concentrations of toxic organic contaminants in sediments from 20 locations were 96.7ng TEQ/kg dry matter for PCDD/Fs, 1.84ng TEQ/kg dry matter for dioxin-like PCBs, 29.1microg/kg dry matter for PBDEs, 411microg/kg dry matter for nonylphenols, 1021microg/kg dry matter for fecal sterols, and 928microg/kg dry matter for PAHs. Concentrations of all the organic contaminants and fecal sterols varied widely and there was a clear decrease in concentration gradients with increasing distances from the WWTP outfall. This result suggests that WWTP activities contribute to contamination by organic chemicals. A survey of benthic organisms showed the dominance of a few polychaete species, indicating a deterioration of the macrobenthic community by the WWTP discharge. Non-parametric multidimensional scaling (MDS) ordination and Spearman correlation analyses showed that organic contamination is associated with the benthic community structure. For polychaete species, the sensitive species for organic contaminants was Paraprionospio pinnata, while contaminant-tolerant species were Spiochaetopterus koreana and Capitella capitata. BIOENV analyses of all locations suggested PCDDs and PCDFs as the major contaminants influencing the structure of the macrobenthic community. The present study highlights that continuous WWTP discharges contribute to severe organic contamination and risks for the benthic community in an aquatic ecosystem.     

Bio-reduction of arsenate using a hydrogen-based membrane biofilm reactor

Arsenate (As(V)) is a carcinogen and a significant problem in groundwater in many parts of the world. Since As(III) is generally more mobile and more toxic than As(V), the reduction of As(V) to As(III) is not a conventional treatment goal. However, reducing As(V) to As(III) may still be a means for decontamination, because As(III) can be removed from solution by precipitation or complexation with sulfide or by adsorption to Fe(II)-based solids. A promising approach for reducing oxidized contaminants is the H2-based membrane biofilm reactor (MBfR). In the case of arsenate, the MBfR allows bio-reduction of As(V) to As(III) and sulfate to sulfide, thereby giving the potential for As removal, such as by precipitation of As2S3(s) or formation of Fe(II)-based solids. When As(V) was added to a denitrifying MBfR, As(V) was reduced immediately to As(III). Decreasing the influent sulfate loading increased As(V) reduction for a fixed H2 pressure. A series of short-term experiments elaborated on how As(V) loading, nitrate and sulfate loadings, and H2 pressure controlled As(V) reduction. Lower nitrate loading and increased As(V) loading increased the extent of As(V) reduction, but increased H2 pressure did not increase As(V) reduction. As(V) reduction was sensitive to sulfate loading, with a maximum As(V)-removal percentage and flux with no addition of sulfate. As(III) could be precipitated with sulfide or adsorbed to Fe(II) solids, which was verified by scanning electron microscopy and energy dispersive X-ray analysis.     

Relationships between the abnormalities of the male reproductive organs and the accumulation of phenol compounds in the striped field mouse, Apodemus agrarius, inhabiting Korea

The relationships between the abnormalities of the male reproductive organs in striped field mice and the accumulation of endocrine-disrupting chemicals were assessed. Most mice collected at three areas were contaminated with phenol or organotin compounds. Fourteen to 42% of the mice at each area had abnormally shrunken reproductive organs, and some of them were contaminated with high levels of phenol compounds. Moreover, all the shrunken reproductive organs were damaged in the histological structure. The damage was observed also from several mice accumulating a high level of phenol compounds even though they had normally developed reproductive organs, although no damage was found in the mice accumulating a high level of organotin compounds. Collectively, the abnormalities of the reproductive organs in the mice seemed to be related to the accumulation of phenol compounds rather than of organotin compounds.     

Colloid mobilization and heavy metal transport in the sampling of soil solution from Duckum soil in South Korea

Environmental Geochemistry and Health - Colloid mobilization is a significant process governing colloid-associated transport of heavy metals in subsurface environments. It has been studied for the...     

Analysis of recycling structures for e-waste in Vietnam

E-waste management in Vietnam poses real challenges such as the lack of specific e-waste legislation, the strong involvement of “craft villages” and the missing of monitoring data. Many issues (e.g., pollution level, generated waste, health of workers and resident living at recycling sites) lead to the limited access to these craft villages. Thus, there is no comprehensive picture on e-waste management in Vietnam available today. This research focuses on the current situation of e-waste management. Sources of e-waste, collection and treatment in Vietnam are investigated by utilizing most available sources of information (published journals, unpublished works from projects and reports from institutes, ministry) together with the interviewed data from experts, collectors, workers and especially, biggest traders in the field. Based on this information, the processes applied in Vietnam, both in the formal and informal sector, have been analyzed systematically in terms of inputs, outputs, potential emissions and related risks for workers. From these aspects, a comparison in terms of legal frameworks, collection and treatment at both formal and informal sector between Vietnam and other countries in Asian region was undertaken. Thus, major challenges of e-waste management and relatively comprehensive image of e-waste management and treatment in Vietnam have been identified.     

Relation of RNA/DNA ratios to growth for the scallop Euvola (Pecten) ziczac in suspended culture

We examined the relation of RNA/DNA ratios to growth for three size groups of the tropical scallop Euvola ziczac maintained in suspended culture at 8, 21 and 34 m in depth in the Golfo de Cariaco, Venezuel. Various growth parameters indicated that production decreased with depth. This was more likely due to a decrease in seston quality with depth than to temperatures or seston abundance (which were similar at the various depths studied). The RNA/DNA ratio was correlated with the G-index of muscle growth for juveniles (r ²=0.55). A much weaker correlation was observed for the maturing scallops (r ²=0.18), probably because of the interaction between reproductive and somatic growth. In fully mature scallops, somatic growth was negligible and the RNA/DNA ratios appeared to be inversely related to the level of physiological stress of the scallops. Whereas RNA/DNA ratios are difficult to interpret for maturing E. ziczac, because an increased ratio can be due to either increased gonadal or somatic growth, they are useful in predicting growth in juveniles and physiological stress in fully mature scallops.