Study On The Recognition Of The Taste And Odor In Jiaxing Area And The Control Of Heptanal

Recently, based on the pollution to water resources and the quality requirements about drinking water, Taste and Odor problems in drinking water resources andpotable water, which is one of water quality judgment standards, become a matter of urgent concern. The taste and odors in drinking water and resources include musty, earthy, putrid, fishy and so on. Taste and odor compounds cause taste and odor problems. For example,2-methylisoborneol and geosmin can cause musty and earthy odor, while dimethyl trisulfide may cause putrid odor. Moreover, heptanal and2,4-heptadienal are fishy concounds. The characteristics of taste and odor compounds are low threshold odor concentration with ng/L level. The water environment in Jiaxing area is heavily polluted, and the concentrations of NH3-N and organics are out limited. These characteristics cause the drinking water unsteady in water quality, poor tasty and unpleasant smell. In this study, the main kinds of taste and odors in water in Jiaxing area, the kinds of taste and odor compounds and their concentrations in the water, the possible causes of taste and odor phenomena, and the removal rate of taste and odor compounds that the water treatment process in Guanjinggang Plant made are conducted. Though the research is based on the water area of Jiaxing, the methods and results can be the example of other drinking water resources. As few papers reported the researches on fishy odor and fishy compounds, and the fishy comcounds are detected in the water in Jiaxing area, the removal of heptanal by powdered activated carbon (PAC) is conducted to complement the blank of research on fishy odor in taste and odor research field, and provide several information about control of fishy compounds.In the process of detecting of water samples in Jiaxing, the results indicated that: the main odor of the water in Jiaxing is musty and earthy, and the odor compounds are2-methylisoborneol, geosmin, dimethyl trisulfide, and β-cuclociral. The concentration of taste and odor compounds varied over seasons, and reaches the highest in summer. The concentration of2-methylisoborneol in Zhuqiaogang River can be over250ng/L, which is25times of its threshold odor concentration of lOng/L, while the concentration of dimethyl trisulfide is about80ng/L in Zhuqiaogang River, which is10times more than its threshold odor concentrationof7.5ng/L. The concentration of odor compounds in Zhuqiaogang River is higher than Guanjinggang Wetland. Human activities may the most possible reason that made this difference since Zhuqiaogang River flows through the downtown of Jiaxing while Guanjinggang Wetland faraway. The odor in distribution system is described as the smell of chlorine, and the main odor compound is dichloramine. the number of the samples that concentration of dichloramine over its threshold odor number (0.15mg/L) is more than50%of the samples that detected. The water treatment of Guanjinggang Plant could remove the odor compounds well, and it can control the concentration of odor compounds under a low level, less than their threshold odor concentration. The biofilter treatment can remove67%of2-methylisoborneol in the water. The ozone oxidation process in the plant can produce more heptanal compound in the water. Fortunately, activated carbon technology can reduce the concentration of heptanal with the removal rate about95%. The transform of NH3-N and orginics in the water, the upper waters that taking high concentration of odor compounds, and human’s activities may be the possible causes about the odor problems in Jiaxing.In the process of removal of heptanal by PAC, the results indicated that:about50%heptanal was removed within1h, and the adsorption process of heptanal fits well both with the pseudo-first-order reaction kinetics and the pseudo-second-order reaction kinetics in the range of experimental concentration, and the adsorption isotherm fits the Langmiur equation better. These results showed that physical adsorption and chemical adsorption control the adsorption of heptanal together. Strong acidic condition has positive effect on adsorption, but the effect decreases when the dosage of PAC increases. While the dosage of PAC is10mg/L, the best pH condition is near neutral, so the pH of heptanal solution has no need to be treated. Increasing the temperature appropriately can make positive effect on adsorption, but the effect is not so obvious while the temperature is over25℃, so the best temperature for adsorption is25℃. The natural organic matters in Guanjinggang Wetland mostly have low molecular weight, so they can compete with heptanal on adsorpted by PAC, which decreasing the removal rate of heptanal by10%. In contrast, because of its higher molecular weight, humic acid not only do no competition on heptanal, but also absorb heptanal. The removal rate of heptanal can increase10%while absorbed by PAC with humic acid.