Highly sensitive determination method for total carbonate in water samples by flow injection analysis coupled with gas-diffusion separation

Blackening and odorization of urban rivers: a bio-geochemical process

Urban rivers constitute a major part of urban drainage systems, and play critical roles in connecting other surface waters in urban areas. Black-odorous urban rivers are widely found in developing countries experiencing rapid urbanization, and the mismatch between urbanization and sewage treatment is thought to be the reason. The phenomena of blackening and odorization are likely complex bio-geochemical processes of which the microbial interactions with the environment are not fully understood. Here, we provide an overview of the major chemical compounds, such as iron and sulfur, and their bio-geochemical conversions during blackening and odorization of urban rivers. Scenarios explaining the formation of black-odorous urban rivers are proposed. Finally, we point out knowledge gaps in mechanisms and microbial ecology that need to be addressed to better understand the development of black-odorous urban rivers.

An exploiting of cost-effective direct current conductivity detector in gas diffusion flow injection system

In this work, a homemade direct current (DC) conductivity detector as an alternative cost-effective detection device has been fabricated and investigated to use in flow analysis system. Under the selected appropriate conditions of flow system, the electrolysis of a carrier stream at the conductivity detector was negligible and provides well-defined signal. The cost-effective DC conductivity detector was demonstrated to couple with gas diffusion flow injection system for determination of dissolved inorganic carbon (DIC) in water. The method is based on the conversion of DIC (dissolved CO₂, HCO₃^- and CO₃^2-) presented in the injected sample to carbon dioxide in an acidic donor stream and then CO₂ gas diffuses through a hydrophobic porous membrane to an acceptor stream. As a result, the change of conductivity signal was observed corresponding to DIC concentration. A linear calibration range of DIC in 1.0-10mmolL^-1, with limit of detection of 70µmolL^-1, repeatability of <3% RSD and 15 injections h^-1 sample throughput can be obtained. This method was applied for DIC determination in natural water.

Metabolism in anoxic permeable sediments is dominated by eukaryotic dark fermentation

Permeable sediments are common across continental shelves and are critical contributors to marine biogeochemical cycling. Organic matter in permeable sediments is dominated by microalgae, which as eukaryotes have different anaerobic metabolic pathways to prokaryotes such as bacteria and archaea. Here we present analyses of flow-through reactor experiments showing that dissolved inorganic carbon is produced predominantly as a result of anaerobic eukaryotic metabolic activity. In our experiments, anaerobic production of dissolved inorganic carbon was consistently accompanied by large dissolved H2 production rates, suggesting the presence of fermentation. The production of both dissolved inorganic carbon and H2 persisted following administration of broad spectrum bactericidal antibiotics, but ceased following treatment with metronidazole. Metronidazole inhibits the ferredoxin/hydrogenase pathway of fermentative eukaryotic H2 production, suggesting that pathway as the source of H2 and dissolved inorganic carbon production. Metabolomic analysis showed large increases in lipid production at the onset of anoxia, consistent with documented pathways of anoxic dark fermentation in microalgae. Cell counts revealed a predominance of microalgae in the sediments. H2 production was observed in dark anoxic cultures of diatoms (Fragilariopsis sp.) and a chlorophyte (Pyramimonas) isolated from the study site, substantiating the hypothesis that microalgae undertake fermentation. We conclude that microalgal dark fermentation could be an important energy-conserving pathway in permeable sediments.

Novel structurally tuned DAMN receptor for “in situ” diagnosis of bicarbonate in environmental waters

A novel receptor for specific and prompt bicarbonate anion (HCO₃⁻) recognition is presented. HCO₃⁻ triggers facile ICT, which provides “in situ” recognition of water soluble carbonates. For the first time, “on-site” estimation of HCO₃⁻ in environmental waters is demonstrated.

Membraneless vaporization unit for direct analysis of solid sample

A new apparatus, called 'membraneless vaporization' (MBL-VP) unit was designed and developed for direct analysis of solid samples. Solid analyte was converted into a gaseous form which then reacts with an indicator reagent. Change in absorbance was used to quantitate the analyte. Stirring with a magnetic bar was employed to facilitate the evaporation of the gas. Unlike the pervaporation technique, hydrophobic membrane was not required for this MBL-VP technique. Application of the membraneless technique for direct determination of calcium carbonate in calcium supplements, has shown to be very precise (R.S.D.=2.5% for 0.16 mmol CO3(2-)), with detection limit of 0.5 mg CaCO3. Results by this method agreed well with flame atomic absorption spectrometric method. Sample throughput was 20 samples h(-1).