The Counts and Environmental Risks of Pathogens in Sewage Sludge from Yangtze River Delta

In order to understand land application of sewage sludge, the characterization of fecal coliform, salmonella and helminth in sewage sludge was invested from 45 different wastewater treatment plant in Yangtze River Delta, and Fecal coliform and water content were detected at 7th, 14th, 21st and 28th air-drying days to know the relationship between the counts of fecal coliform and water contents of sludges. The results showed that fecal coliform were found in 89.6% of the sludge samples, the counts of fecal coliform ranged from 0 to 3.4times10⁶ MPN g^-1, average 3.8times10⁵ MPN g^-1. The counts had very high ranges among the tested samples, for the river water sludge and sludge products, fecal coliform counts were much lower than that of domestic and domestic-industrial mixed flow sludge. The detection rate of ascarid ova, entamoeba histolytica and giardia lamblia cysts were 24.4%, 22.0% and 7.3%, respectively. Salmonella was also found in some sludge samples. Counts of Fecal coliform decreased during early drying days, re-growth phenomenon was seen in about 3-4 weeks. Fecal coliform counts fell down along with the decrease of water content. In conclusion, the pathogens counts were greatly different in all kinds of sludge, they exceeded the guidance level in some sludge samples, and fecal coliform is an important factor to restrict sludge land use in Yangtze River Delta.