The Background Investigation Of Perchlorate In Harbin Groundwater And Investigation On Photocatalytic Reduction Process

As a new type of persistent pollutant, perchlorate is easy to transfer, hard to be degraded and has very high stability. Nowadays, research on perchlorate both at home and abroad focuses on the origin, status of pollution investigation, improvement of detection methods and physiological toxicity of perchlorate, as well as rehabilitation technology of the polluted water.In this study, solid-phase extraction pre-treatment (SPE) and ion chromatography (IC) are used to concentrate micro-trace samples and establish detection method respectively. Representative sampling points are selected to analyze perchlorate in Harbin groundwater and the concentration and distribution of perchlorate in Harbin groundwater are achieved. Meanwhile, the groundwater quality in Harbin can be simply evaluated by the content of ammonium, fluoride and TOC.Through single-factor test, the best ion chromatographic conditions are investigated: eluent concentration 45mmol/L, eluent flow rate 1.0mL/min, inhibitory current 110mA and column temperature 30℃. Under this condition, the concentration range from 100ug/L to 1500μg/L and peak area give a good linear relationship with correlation coefficient 0.999 and detection limit 20μg/L when injection volume is 50μL.AgelaPWAX is selected as solid phase extraction column and orthogonal test is used to optimize the solid-phase extraction conditions and to obtain the optimal conditions: sample flow rate 4mL/min, eluent pH=13, eluent flow rate 5mL/min and column temperature 30℃. Under the optimal conditions, when 1L water sample is tested, it can be concentrated 167 times. The SPE-IC detection method of perchlorate is set up with the method detection limit (LOD) 120ng/L and limit of quantity (LQD) 600ng/L, the method recommended by EPA is used as quality control.The detection results of the groundwater sampling points show that the concentration of perchlorate in Harbin is relatively low ranging from 0.1μg/L to 1.7μg/L, and in Jinjia village, Xiangyang town, Xiangfang, perchlorate cannot be detected and the biggest concentration 1.7μg/L is detected in Lvgangtun Songbei district, the average concentration of perchlorate being 0.541μg/L. There is relatively higher perchlorate concentration in Ashi River floodplain. The average concentration of the seven samples collected along the Ashi River is 0.8857μg/L, which is 1.64 times of the whole average concentration as a result of the region's hydrological and geological conditions. The groundwater quality is appraised by the content of ammonium, fluoride and TOC. Test results show that the concentration of ammonium ranges from 0.30mg/L to 3.88mg/L, among which ammonium concentration is 0.5mg/L greater than the standard threshold in 93.10% of the sampling points; fluoride concentration between 0.006mg/L and 0.837mg/L that is below the lower limit of healthy drinking levels 0.5mg/L. TOC concentration ranges from 2.10mg/L to 11.45mg/L, higher than 4mg/L accounts for more than 89.66%, indicating that groundwater suffered serious organic pollution.Furthermore, primary research is done for the photo-catalytic reduction of perchlorate, with different catalyst types, preparation methods. Three kinds of hole scavenger: formic acid, methanol, formaldehyde are examined, with the increase of initial perchlorate concentration, formic acid is verified to have better effect, besides when the molar ratio of formic acid and ClO4- being 150:1, the best catalytic effect being obtained. Research on titanium dioxide photo-catalytic reduction of perchlorate testifies that catalytic effect of catalyst doping metal ions such as Fe³⁺and Pt⁴⁺is better than TiO₂ only, and the results gets better with the increase of doping amount; 1% doping ratio of the Fe³⁺/TiO₂ with 8h reaction time with 10.28% perchlorate removal and 0.5% and 0.1% doping ratio cause removal rate of 9.61% and 7.81% respectively. Catalytic effect can be greatly influenced by calcination temperature, four different calcination temperatures 400℃, 500℃, 600℃, 700℃are compared, and the result show that catalyst displays the best catalytic effect at 500℃.