Distribution of Total Organic Carbon in Wastewater Discharged from Daya Bay Petrochemical Industrial Zone to the South China Sea

Total organic carbon is a comprehensive index of the degree of organic pollution in a water body and can be used to evaluate organic pollution in the sea. Huizhou Daya Bay petrochemical industrial area is world-class and the wastewater from this industrial area is discharged,after standard treatment,into the northeast sea area of Sangzhou Island and the northwest sea area of Bijia Port. The primary contaminant is petroleum wastes,causing a high chemical oxygen demand( COD),and this has become the most critical concern of all the interested parties since the industrial area was put into production. In this study,we investigated the spatial distribution and temporal changes in four water quality parameters in Daya Bay near the petrochemical wastewater outlet: total organic carbon( TOC),permanganate chemical oxygen demand( CODMn),oil and chlorophyll-a( Chl-a). TOC was determined on a Liqui TOC analyzer,CODMnand petroleum content were determined according to the national marine measurement standard( GB17378. 4-2007),and Chl-a concentration was detected by the fluorescence method. The correlation between TOC and the other three parameters was analyzed using SPSS software to help understand the organic pollution level and provide scientific data to better protect the environment and conserve the ecology of Daya Bay.Twelve monitoring stations( No. 1- No. 12) were selected in the study area and samples were collected at 0. 5m below the surface on July 22,2013. Hourly sampling of 12 consecutive hours for the same parameters at station No.1 was conducted on July 23( 08 ∶ 00- 19 ∶ 00). TOC concentration in the study area ranged from 1. 23 to 1. 49 mg·L- 1,with no significant differences among the twelve monitoring stations. The hourly samples collected at station No. 1 ranged from 1. 30 to 1. 57 mg·L- 1,indicating little temporal variation in TOC concentration. No elevated levels of TOC,CODMnor oil pollution were detected in the waters around the Daya Bay petrochemical wastewater outlet,indicating that petrochemical wastewater discharges do not cause obvious organic pollution. Correlation analysis reveals a significant positive correlation between TOC concentration and oil pollution,and positive correlation was also observed between TOC and CODMn,but was not statistically significant. It is well known that TOC is associated with many environmental variables including monsoon rains and seasonal runoff,hydrodynamic factors,biogeochemistry and biology. This study is a preliminary exploration of the feasibility of TOC as organic pollutant indicator for the waters around Daya Bay petrochemical wastewater outlet because of insufficient monitoring frequency and samples. Further study must be carried out in terms of the feasibility of TOC as organic pollution indicator and the accuracy of TOC for organic pollution assessment in Daya Bay.