[Aspartic Acid Generated in the Process of Chlorination Disinfection By-product Dichloroacetonitrile].

In this study, a method was developed for the determination of dichloroacetonitrile (DCAN) in drinking water by liquid- liquid micro-extraction and gas chromatography/mass spectrometry ( LLE-GC/MS), which used 1,2-dibromopropane as the internal standard and methyl tertiary butyl ether (MTBE) as the extractant for high accuracy. The aspartic acid was used as the precursor of the DCAN formation during chlorination and the influencing factors were evaluated. The formation mechanism of DCAN was also discussed. The results showed that the DCAN amount increased with the increase of pH value under the neutral and acidic conditions, however, the amount of DCAN decreased with the increase of pH value under the alkali condition. And the final amount of DCAN under the alkali condition was much less than that under the neutral and acidic conditions. It was also found that the DCAN amount increased with the increase of chlorine addition, while the temperature in the range of 10-30°C had little influence on the DCAN formation. The formation process of the DCAN from aspartic acid by chlorination included seven steps, such as substitution, decarboxylation, oxidation, etc and ultimately formed DCAN.

[Performance Study of Bromochloracetonitrile Degradation in Drinking Water by Fe/Cu Catalytic Reduction].

The paper used the method of iron copper catalyst reduction to degrade low concentrations of bromochloracetonitrile (BCAN) to lighten the damage to human being, which is a kind of disinfection by-products (DBPs) produced during the chlorination process of drinking water. The removal efficiency of BCAN and its influencing factors were investigated. The mechanism of degradation and kinetics were also explored. The results indicated that iron copper had a greater degradation ability towards BCAN, and the degradation rate of iron copper (mass ratio of 10:1) was 1.5 times that of the zero-valent iron. The removal of BCAN increased obviously with the increase of Fe/Cu dosage. When the initial concentration was set at 20 microg x L(-1), after a reaction time of 150 min, removal of BCAN was improved from 51.1% to 89.5% with the increase of iron copper (mass ratio of 10:1) dosage from 5 g x L(-1) to 10 g x L(-1). The temperature also had great impact on BCAN removal and the removal increased with the increase of temperature. However, BCAN removal did not change a lot with the variation of the initial concentration of BCAN when it was at a low level. The BCAN degradation by iron copper catalytic-reduction followed the first-order kinetics model.

[Formation Mechanism of the Disinfection By-product 1, 1-Dichloroacetone in Drinking Water].

A novel method using methyl tertiary butyl ether (MTBE) as extractant and 1,2-dibromopropane as internal standard for the determination of the disinfection by-producs 1,1-dichloroacetone (DCAce) by gas chromatography mass spectrometry (GC-MS) was described. The formation process of DCAce and its influencing factors were discussed with L-leucine as the precursor during the chloramination process. The results indicated that the DCAce production increased with the increase of chloramine dosage when the chloramine addition was in the range of 5-30 mg · L(-1). The DCAce amount produced under alkaline condition was higher than those produced under the neutral and acidic conditions, and the DCAce amount reduced with the increase of pH value. Temperature was another important factor that affected the DCAce formation from methylamine especially in the range of 15-35°C , and the higher the temperature, the more the DCAce produced. The formation process of DCAce from L-leucine by chloramine consisted of a series of complicated reactions, including substitution, oxidation, bond breaking, amino diazotization, reduction and so on, and eventually DCAce was formed.

[Formation process of nitrogenous disinfection byproduct trichloronitromethane in drinking water and its influencing factors].

A novel method is described in this paper, which uses methyl tertiary butyl ether (MTBE) as extractant and 1,2-dibromopropane as internal standard for the determination of nitrogenous disinfection byproduct trichloronitromethane (TCNM) by gas chromatography mass spectrometry (GC-MS). The formation process of TCNM and its influencing factors were evaluated with methylamine as the precursor during chlorination. The results indicated that the TCNM amount produced under alkaline condition was higher than those produced under the neutral and acidic conditions, and the TCNM amount increased with the increase of pH value. It was found that the TCNM amount increased with the increase of chlorine addition when the chlorine dosage was in the range of 2-8 mmol x L(-1). However, the TCNM amount was reduced when the chlorine dosage was enhanced from 8 mmol x L(-1) to 12 mmol x L(-1), under which conditions the concentration of free chlorine was higher and methylamine was turned into nitriles and aldehydes through other reactions. It was also found that the TCNM amount increased with the increase of methylamine addition when the methylamine dosage was in the range of 0.5-4 mmol x L(-1). Temperature was another important factor that affected the TCNM formation from methylamine especially in the range of 10-30 degrees C and the higher the temperature, the more the TCNM amount produced. The formation process of TCNM from methylamine by chlorination was in accordance with the mechanism of an electrophilic reaction, in which HClO and ClO(-) could be used as the electrophilic reagents to attack methylamine and then to form TCNM.

[Influencing factors on the paranitrobenzoic acid wastewater treatment by chlorine dioxide and activated carbon catalysis-oxidation technology].

The effect of activated carbon dosage, chlorine dioxide dosage, pH value and reaction time on the paranitrobenzoic acid wastewater treatment on chlorine dioxide (ClO2 ) and activated carbon (AC) catalysis-oxidation technology were analyzed, and the efficiencies of the process to remove COD and increase biodegradation capacity (BOD5/COD ratio) were also examined under the optimum conditions as the pretreatment method for paranitrobenzoic acid wastewater with high-concentration. The result showed that the COD removal efficiency of the ClO2/AC catalysis-oxidation system was 10% higher than that of the system with only ClO2 when the COD concentration of paranitrobenzoic acid wastewater was 10 960 mg/L. It was also found that the COD removal was decreased by 35% with the concentration of 7 100 mg/L under the conditions of pH value 4.1, AC dosage 200 g/L, reaction time 30 min and ClO2 dosage 300 mg/L. In addition, the BOD, concentration was increased to 1 810 mg/L and the biodegradability was improved greatly with the BOD5/COD ratio increased from 0.10 to 0.25. In a word, the chlorine dioxide (ClO2) and activated carbon (AC) catalysis-oxidation process is an effective pretreatment method for paranitrobenzoic acid wastewater treatment.

[The affect of the skin stretch on the biomechanical changes of skin].

OBJECTIVE: To investigate the biomechanical changes in skin after employing the skin stretch. METHODS: Skin samples were took from the test group which was stretched for 7 days and control group without stretch respectively in the end of 1, 2, 3, 4, 6, 8 week. The biomechanical index were measured by tensiometer. RESULTS: The mean destroy stress, breaking load, stretch rate of the test group decreased obviously in the first week (the breaking load was increasing at the beginning) and the three index increased subsequently, they reached the climax during the fourth week and turned to normal subsequently to the level of some higher than control group and normal value in the sixth week. The stiffness of the test group reached the climax at the first week and than decreased gradually to the level of some higher than normal value and control group. The biomechanical changes of te control group was not evident by comparing with the test gropu. CONCLUSIONS: Skin stretch may injured the biomechanical property during the early time and turned to normal soon afterwards. The stiffness of the skin was increased and its elasticity was decreased after performing skin stretch.