Calibrationless determination of creatinine and ammonia by coulometric flow titration

A precise and sensitive working microflow titration procedure was developed to determine creatinine and ammonia in urine samples. This procedure is based on enzymatic conversion of creatinine, gas diffusional membrane separation of the released ammonia into an acid acceptor stream, and coulometric titration of ammonia with hypobromite. The hypobromite is formed after the electrogeneration of bromine in an electrolyte containing 1.0 M NaBr and 0.1 M sodium borate adjusted to pH 8.5. The electrolysis current follows a triangle-programmed current-time course. An amperometric flow detector records the resulting mirror symmetrical titration curves, which show two equivalence points. The analyte concentration is calculated from the time difference between the equivalence points. For quantitative conversion of creatinine and quantitative separation of present and released ammonia no calibration is necessary to get accurate results. Both ammonia/ammonium and creatinine were determined in the range between 2 microM and 2 mM with relative standard deviations between 3.0 and 1.0% (n = 5). High recoveries were obtained for the analysis of diluted urine samples for both creatinine and ammonia.     

Photoelectrochemical treatment of landfill leachate in a continuous flow reactor

Leachate from a municipal landfill site, which has been treated by biological process, was treated by photoelectrochemical oxidation in a pilot scale flow reactor, using DSA anode and UV light irradiation. At a current density of 67.1 mA/cm² and 2.5 h reaction time, the removal rates achieved were for 74.1% COD, 41.6% for TOC, and 94.5% for ammonium in the electrolysis process with UV light irradiation. In comparison, the removal rates of COD, TOC, and ammonium were decreased in the individual electrolysis process, respectively. The increase induced by the UV light irradiation was analyzed. The removal rates increased with the increase of current densities in the photoelectrochemical process. Combined with UV–vis spectra and gas chromatography–mass spectroscopy analysis, it is believed that the organic contaminants were efficiently mineralized into small molecular acids. At the meantime, the concentrations of metal ions in the landfill leachate were largely reduced.     

Determination of dissolved carbon dioxide by coulometric titration in modified atmosphere systems

The solubility of carbon dioxide (CO₂) in microbiological media at different pH values, water activities ( a_w ), temperatures, buffering capacities and ratios of headspace to media volumes was determined by using a coulometer. Buffering capacity and ratio of headspace to media volume were shown to be the major factors influencing the solubility of CO₂ in modified atmosphere model systems. The growth inhibitory effects of different dissolved CO₂ concentrations (0–50 μmol ml^-1) were determined for Pseudomonas fragi at 8°C and 22 C. Pseudomonas fragi was shown to be strongly affected by the CO₂ concentration in the media. A carbon dioxide concentration of 40 μmol ml^-1 was needed to inhibit Ps. fragi at 8°C. The importance of measuring dissolved CO₂ concentrations in modified atmosphere packaging applications was shown and the coulometer proved to be an excellent tool for this purpose.     

容量滴定法和库伦滴定法测定冻干疫苗水分含量的比较

目的在适宜的温度和湿度条件下,评价容量滴定法和库伦滴定法测定冻干疫苗水分是否具有差异性。方法确定冻干疫苗水分测定的适宜温度和湿度条件,在此条件下,分别从水分含量区间、冻干疫苗类型和进样量三个主要影响方面,对容量滴定法(volumetric titration)和库伦滴定法(coulometric titration)进行比较。结果冻干疫苗水分测定的适宜条件为:温度25℃、湿度45%。冻干疫苗水分的质量分数为1.0%～2.0%时,容量滴定法和库伦滴定法的检测结果差异有统计学意义(P0.05);水分的质量分数在2.0%～3.0%时,两种滴定法的检测结果差异无统计学意义(P0.05)。对于不同类型冻干疫苗和不同进样量的冻干疫苗,两种滴定法检测结果差异均无统计学意义(P均0.05)。结论在适宜的温度和湿度条件下,库伦滴定法更适用于低水分含量冻干疫苗的水分测定;其他情况下两种滴定法无明显差异。     

Kinetics of nitrogen removal from sanitary landfill leachate

Leachates from municipal landfill ‘Lublinek‘ in Lodz city (Poland) were treated in two-sludge sequence batch reactor systems (type ND). The external carbon source—sodium acetate was used in denitrification. Two versions were tested—with and without supernatant recirculation from D-SBR to N-SBR. The 99% removal of inorganic nitrogen compounds was achieved in both versions. Due to recirculation, the buffering (by means of sodium bicarbonate) was not necessary. Kinetic models for nitrification and denitrification processes were proposed. Kinetic parameters of the models were estimated by the optimization method. The experimental results of both nitrification steps (oxidation of ammonia to nitrites and nitrites to nitrates) were best fitted with the interactive limitation model of nitrogen compounds and oxygen. The denitrification process was limited only by the concentration of nitrogen compounds.     

Fermentative hydrogen production from fresh leachate in batch and continuous bioreactors

This research for the first time investigated hydrogen production from the fresh leachate originated from municipal solid wastes. We found that fermentation of the leachate generated H₂ and was very much enhanced in the presence of extra phosphate in the batch reactor. The continuous expanded granular sludge bed (EGSB) reactor started to generate H₂ at day 20 and continued to 176 days with 120 mg/l of extra phosphate present. The highest chemical oxygen demand (COD) removal efficiency (66.9%) was achieved at liquid up-flow velocity of 3.7 m/h and hydraulic retention time of 12 h. Under proposed optimal operation conditions, the mean H₂ production rate reached up to 2155 ml/(l day). We also found that over 80% liquid metabolites were acetic acid and ethanol, suggesting the ethanol-type fermentation was dominant in the bioreactor. These findings indicate that the fresh leachate can be used as the source for continuous hydrogen production.     

Hydrogen sulphide production by Zymomonas and its elimination in a mutant strain

Strains of Zymomonas mobilis grown in media containing either glucose or sucrose were assessed for the production of hydrogen sulphide (H₂S). In a liquid medium with low glucose concentration (20 g l^?1) only a proportion of the strains tested formed H₂S, but in medium containing a higher glucose concentration (100 g l^?1) all the strains tested produced H₂S. Four Z. mobilis strains were assayed quantitatively for H₂S production and strain ZM4 was found to produce the most H₂S in glucose medium. The amount of yeast extract and glucose, and the type of sugar used in the medium affected the amount of H₂S formed by strain ZM4. A mutant, designated ZM4701, of strain ZM4 was isolated which did not produce any detectable H₂S in liquid medium containing yeast extract plus either glucose or sucrose. The nutritional requirements of ZM4701 were investigated.     

Ratio of biological and chemical oxidation during the aerobic elimination of sulphide by colourless sulphur bacteria

Summary Culture conditions were evaluated for their relevance to chemical and biological oxidation of sulphide in aqueous solution. With a mixed culture of colourless sulphur bacteria sulphide oxidation was investigated over a concentration range of 0.005 to 3.5 mm S^2–, a pH range from 1.0 to 9.0 and temperatures from 10 to 40° C. Biological sulphide oxidation quickly decreased when fermentation conditions were suboptimal and the proportion of chemical oxidation increased with high pH values and sulphide concentration and increasing temperature. The optimal conditions for biological activity were found to be 3 mm S^2–, pH 7.0, and a mesophilic temperature (40° C).Offprint requests to: C. Plas     

In situ simultaneous organics and nitrogen removal from recycled landfill leachate using an anaerobic-aerobic process

An anaerobic-aerobic process including a fresh refuse landfill reactor as denitrifying reactor, a well-decomposed refuse reactor as methanogenesis reactor and an aerobic activated sludge reactor as nitrifying reactor was operated by leachate recirculation to remove organic and nitrogen simultaneously. The results indicated that denitrification and methanogenesis were carried out successfully in the fresh refuse and well-decomposed landfill reactors, respectively, while the nitrification of NH(4)(+)-N was performed in the aerobic reactor. The maximum organic removal rate was 1.78 kg COD/m(3)d in the well-decomposed refuse landfill reactor while the NH(4)(+)-N removal rate was 0.18 kg NH(4)(+)-N/m(3)d in the aerobic reactor. The biogas from fresh refuse reactors and well-decomposed refuse landfill reactors were consisted of mainly carbon dioxide and methane, respectively. The volume fraction of N(2) increased with the increase of NO(3)(-)-N concentration and decreased with the drop of NO(3)(-)-N concentration. The denitrifying bacteria mustered mainly in middle layer and the denitrifying bacteria population had a good correlation with NO(3)(-)-N concentration.     

Influence of recirculation over COD and N-NH4 removals from landfill leachate by horizontal flow constructed treatment wetland

Abstract

Treatment of landfill leachate is a challenge due to its complex chemical composition and high recalcitrance and because of high costs for conventional wastewater treatment. In our study, leachate from the Quitaúna Landfill, Sao Paulo Metropolitan Region, Brazil, was treated at a laboratory scale with a horizontal subsurface flow constructed treatment wetland (HF-CTW) operating under a recirculation regime. Two units planted with Heliconia psittacorum (HP) and Cyperus papyrus (CP), and one unplanted control unit were assessed. With a recirculation regime over 21?days, the planted units removed 40% of chemical oxygen demand (COD) while the control unit removed only 29%. True color removal efficiencies were 2, 22, and 23% for the control, HP, and CP HF-CTWs, respectively. The ammonium nitrogen removal efficiencies for a 21-day hydraulic retention time (HRT) were 63–81% for planted units and 72% for the control. The increase of the HRT from 7 to 21?days led to the enhancement of ammonium nitrogen removal but did not affect the COD and total nitrogen removals. This phenomenon is a consequence of leachate’s low biodegradability. The present study shows the importance of the HRT and plant presence for landfill leachate treatment using HF-CTWs.     

Modeling continuous cultures of microalgae colimited by nitrogen and phosphorus

It is well documented that the combination of low nitrogen and phosphorus resources can lead to situations where colimitation of phytoplankton growth arises, yet the underlying mechanisms are not fully understood. Here, we propose a Droop-based model built on the idea that colimitation by nitrogen and phosphorus arises from the uptake of nitrogen. Indeed, since N-porters are active systems, they require energy that could be related to the phosphorus status of the cell. Therefore, we assumed that N uptake is enhanced by the P quota. Our model also accounts for the biological observations that uptake of a nutrient can be down-regulated by its own internal quota, and succeeds in describing the strong contrast for the non-limiting quotas under N-limited and P-limited conditions that was observed on continuous cultures with Selenastrum minutum and with Isochrysis affinis galbana. Our analysis suggests that, regarding the colimitation concept, N and P would be better considered as biochemically dependent rather than biochemically independent nutrients.     

Colour removal from landfill leachate by coagulation and flocculation processes

A study was conducted to investigate the efficiency of coagulation and flocculation processes for removing colour from a semi-aerobic landfill leachate from one of the landfill sites in Malaysia. Four types of coagulant namely aluminium (III) sulphate (alum), ferric (III) chloride, ferrous (II) sulphate and ferric (III) sulphate were studied using standard jar test apparatus. Results indicated that ferric chloride was superior to the other coagulants and removed 94% of colour at an optimum dose of 800 mg/l at pH 4. The effect of coagulant dosages on colour removal showed similar trend as for COD, turbidity and suspended solids. This suggested that colour in landfill leachate was mainly contributed by organic matters with some insoluble forms that exhibited turbidity and suspended solids readings. The results from this study suggested that ferric chloride could be a viable coagulant in managing colour problems associated with landfill leachate.     

Nucleic acid quantitation by continuous flow fluorometry

A system for rapid and sensitive fluorometric measurement of nucleic acids is described. Samples can be analyzed virtually as fast as they can be injected into the analyzer (three to five per minute). 5-microliter samples ranging in concentration from 0.05 to 40 micrograms/ml can be measured accurately. The sample can easily be recovered.     

Chronic catchment nitrogen enrichment and stoichiometric constraints on the bioavailability of dissolved organic matter from leaf leachate

1. Chronic nitrogen (N) deposition may alter the bioavailability of dissolved organic matter (DOM) in streams by multiple pathways. Elevated N deposition may alter the nutrient stoichiometry of DOM as well as nutrient availability in stream water. 2. We evaluated the influence of a decadal‐scale experimental N enrichment on the relative importance of DOM nutrient content and inorganic nutrient availability on the bioavailability of DOM. We measured the consumption of dissolved organic carbon (DOC) and changes in nutrient concentration, DOM components and enzyme activity in a bottle incubation assay with different DOM and nutrient treatments. To evaluate the effect of DOM stoichiometry, we used leaf leachates of different carbon/N/phosphorus (C : N :P) ratio, made from leaf litter sourced in the reference and N‐enriched catchments at the Bear Brook Watershed in Maine (BBWM). We also manipulated the concentration of inorganic N and P to compare the effect of nutrient enrichment with DOM stoichiometry. 3. DOC from the N‐enriched catchment was consumed 14% faster than that from the reference catchment. However, mean DOC consumption for both leachates was more than doubled by the simultaneous addition of N and P, compared to controls, while the addition of N or P alone increased consumption by 42 and 23%, respectively. The effect of N and/or P enrichment consistently had a greater effect than DOM source for all response variables considered. 4. We subsequently conducted DOC uptake measurements using leaf leachate addition under ambient and elevated N and P in the streams draining the reference and N‐enriched catchments at BBWM. In both streams, DOC uptake lengths were shorter when N and P were elevated. 5. Although both DOM stoichiometry and inorganic nutrient availability affect DOM bioavailability, N and P co‐limitation appears to be the dominant driver of reach‐scale processing of DOM.     

Analyzing cell fate control by cytokines through continuous single cell biochemistry

Cytokines are important regulators of cell fates with high clinical and commercial relevance. However, despite decades of intense academic and industrial research, it proved surprisingly difficult to describe the biological functions of cytokines in a precise and comprehensive manner. The exact analysis of cytokine biology is complicated by the fact that individual cytokines control many different cell fates and activate a multitude of intracellular signaling pathways. Moreover, although activating different molecular programs, different cytokines can be redundant in their biological effects. In addition, cytokines with different biological effects can activate overlapping signaling pathways. This prospect article will outline the necessity of continuous single cell biochemistry to unravel the biological functions of molecular cytokine signaling. It focuses on potentials and limitations of recent technical developments in fluorescent time‐lapse imaging and single cell tracking allowing constant long‐term observation of molecules and behavior of single cells. J. Cell. Biochem. 108: 343–352, 2009. © 2009 Wiley‐Liss, Inc.     

Rapid titration of retroviral vectors encoding intracellular antigens by flow cytometry.

Flow cytometry was used to detect cells infected with retroviral vectors encoding both simian virus 40 large T antigen and G418 resistance after indirect immunofluorescence staining using a T-antigen-specific monoclonal antibody and a fluorescein-conjugated secondary antibody. Titers of viral stocks determined by flow cytometry were equivalent to those determined by quantitation of G418-resistant colonies.