Key Caboratory of Chinese Ministry of Education of northwest Water Resource and Environmental ecolog School of environmental and Municipal Engineering 声建墨群骨 xi'an University of Architecture and Technology Settleability evaluation Methods Plain settling of raw sewage for 2 hours Analysis of the raw sewage and the supernatant Parameters for the evaluation Suspended solids, COD, BOD5, total nitrogen(TN and total phosphorous (TP)Key Laboratory of Chinese Ministry of Education of Northwest Water Resource and Environmental Ecology School of Environmental and Municipal Engineering Xi’an University of Architecture and Technology