Environmental Investigation And Risk Assessment Of A Retired Chemical Plant And Study On The Degradation Of P-chlorophenol In Groundwater

For a plot of a retired chemical plant,a site environmental survey was conducted according to the national technical guidelines,and a risk assessment was conducted for pollutants exceeding the standard.Further,using p-chlorophenol（p-CP）as the model of chlorinated organic compounds,a dechlorination system of sodium hydroxide（NaOH）and tannic acid（TA）co-activated persulfate（PS）was developed,the reaction conditions were optimized and the degradation mechanism was proposed.The main research contents are as follows:（1）Environmental survey and risk assessment of a retired chemical plantThe retired chemical plant has a land area of approximately 17,536 square meters,and the site is planned for industrial use in the future.According to the professional judgment method,a total of 10 soil sampling points and 4 groundwater monitoring wells were set.37 soil samples（including parallel samples）and 5 groundwater samples（including parallel samples）are colleceted.The survey results showed that none of the pollutants detected in the soil samples exceeded the screening value;the maximum detec Tab.contents of ethylbenzene and 1,2-dichlorobenzene in the groundwater samples were 9.13×10⁴μg/L and 1.69×10⁵μg/L,respectively,exceeding 152 times and84.5 times of the selected screening value.After human health risk assessment,the carcinogenic risk of ethylbenzene in groundwater is 1.35E-05,which exceeds the accep Tab.level.The non-carcinogenic hazard indexes of ethylbenzene and 1,2-dichlorobenzene were 4.76E-02 and 5.89E-02,respectively,which did not exceed 1.The ecological assessment results show that the risk quotient of ethylbenzene in groundwater is RQ=0.50,which is a medium risk;the risk quotient of 1,2-dichlorobenzene in groundwater is RQ=6.52,which is a high risk.It is recommended to perform the remediation on the groundwater in the site.（2）The co-activation of persulfate with sodium hydroxide and tannic acid for the degradation of p-chlorophenolp-Chlorophenol（p-CP）was selected as the model,and a new dechlorination system was developed,that is,sodium hydroxide（NaOH）and tannic acid（TA）were used together to activate persulfate（PS）.The effect of TA,NaOH,PS,temperature,different ions and humic acid on the degradation of chlorophenol was investigated.According to the free radical quenching experiments results,the reaction mechanism was proposed for PS/TA/NaOH system.The results show that when 150 mg/L of TA,0.2 M of NaOH and 100 m M of persulfate were used,the degradation efficiency of p-chlorophenol（50 mg/L）can reach 99.9 wt.%.There is no significant change in degradation efficiency when the reaction temperature is changed from 20 ^oC to 40 ^oC.HA will promote the degradation of p-CP,while the presence of Cl^-and SO₄^2-will inhibit the degradation of p-CP.The hydroxyl radicals and superoxide radicals play an important role in the degradation of p-CP.Further,a remediation plan was proposed for the contaminated groundwater from the retired chemical plants.