Characteristics of sludge from sewage discharge channels of Tianjin, China

In 1998, sludge samples were taken from the sewage discharge channels of Tianjin, China, and concentrations of 50 elements and total organic carbon (TOC) were detected by inductively coupled plasma-atomic emission spectrometry (ICP-AES), inductively coupled plasma-mass spectrometry (ICP-MS), instrumental neutron activation analysis (INAA), and other conventional methods, and the results are reported in this study. The sludge samples contain high concentrations of organic matter, with the median value of TOC 15.5%. Compared with sediments from the intertidal flats of Bohai Bay, high concentrations of Sn, Zn, Cu, Pb, Sb, Bi, Cr, Ni, P and Ba are observed in the sludge. However, rare earth elements, alkali elements, Ti and Al do not show a correlation with pollution. From the urban side to the coastal side, the spatial variation of concentrations of the pollution-related elements is quite irregular, indicating that the channels receive discharges along the course. No significant pollution in sediments at the outlets of the sewage discharge channels was observed, which may be attributed to the dispersion of pollutants and purification of the Bohai Bay. Factor analysis has revealed the two controlling factors of 'pollution' and 'background' on the elemental composition of the sludge.