Pre-evacuated Exetainers are commonly used as measurement vials for the determination of methane (CH 4 ) and nitrous oxide (N 2 O) concentrations in liquid and gaseous samples from aquatic environments. The impact of residual air in these Exetainers on measurement accuracy is assessed. Residual air pressure in commercially available, pre-evacuated Exetainers varied between 0.071 6 0.008 atm and 0.180 6 0.031 atm in examined batches. This background contamination can lead to large errors when determining dissolved and gaseous CH 4 and N 2 O concentrations particularly at low concentrations. A method for Exetainer pretreatment is suggested and verified, to reduce the residual CH 4 and N 2 O. Vials are flushed (needle 30 G 3 0.5 00 , 0.3 mm) with nitrogen gas (N 2 ) for 5 min, which reduces the background CH 4 and N 2 O concentrations to 0.092 6 0.008 ppm and 0.016 6 0.001 ppm, respectively, approximately 3-4% of their respective concentrations in air. To avoid an alteration of sample concentration by variable residual gas levels left during a preevacuation step, liquid and gaseous samples are injected into the N 2 filled Exetainers. For gaseous samples where large volumes of gas are available, Exetainers can alternatively be flushed with 100 mL of sampling gas. For gaseous samples, measured CH 4 and N 2 O concentrations of standard gases were statistically identical to their known concentrations. For liquid samples, measured CH 4 and N 2 O concentrations of liquid standard dilution series showed strong linear correlations with theoretically calculated concentrations (slope CH 4 : 1.04, slope N 2 O: 1.12). Sample concentrations remained constant over a minimum storage period of 6 weeks.
Volatile organic sulfur compounds (VOSCs) are important sources of unpleasant odor in wastewater systems. However, the study of VOSCs is usually hindered by their complicated measurement method and highly reactive nature. In this work, a static headspace method utilising gas chromatography (GC) with a sulfur chemiluminescence detector (SCD) was developed to quantitatively analyze VOSCs in wastewater matrices. The method has low detection limits and requires no pre-concentration treatment. Three typical VOSCs, namely methanethiol (MT), dimethyl sulfide (DMS) and dimethyl disulfide (DMDS), were chosen as examples for this study. The calibration curves of all three compounds covering a wide range from 0.5 ppb to 500 ppb showed good linearity (R(2) > 0.999). The method detection limits (MDL) were 0.08, 0.12 and 0.21 ppb for MT, DMS and DMDS, respectively. The reproducibility (relative standard deviation) was approximately 2%. The recovery ratio of MT, DMS and DMDS in spiked wastewater samples were 83 ± 4%, 103 ± 4% and 102 ± 3%, respectively. Sample preservation tests showed that VOSCs in wastewater samples could be preserved in vials without headspace under acidified conditions (pH ∼1.1) for at least 24 h without significant changes (<1.8 ppb). The analysis of real wastewater samples from both a laboratory-scale sewer system and a full-scale sewer pipe demonstrated the suitability of this method for routine wastewater VOSC measurement.
The homogeneous advanced oxidation process of UV/H 2 O 2 was utilized to decolourize CI Reactive Red 195A (RR195A) as one of the most used dyes in the textile industry in Queensland. The UV radiation source was a lowpressure mercury arc lamp (60W emitting at 253.7nm). In this study, the effects of initial hydrogen peroxide (H 2 O 2 ) dosage, dye concentration, pH and temperature were examined to find out the optimum operating conditions of the treatment process. Complete decolourization was achieved in the relatively short time of 20-30 minutes irradiation. Faster decolourization was achieved at low pH and high temperature. The removal rate increased with increasing initial concentration of H 2 O 2 up to an optimum value. The decolourization reaction was found to follow at least initially first order kinetics with respect to the dye concentration. However, even after near complete removal of the active dye from the solution, approximately 60% of the COD was still remaining, indicating only partial breakdown of the dye molecule. In general, the result indicates that the UV/H 2 O 2 technology proved to have good potential for removing dyestuff from wastewater but further treatment might be necessary to achieve complete mineralization of the organic intermediates.
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