Tham khảo tài liệu 'wiley wastewater quality monitoring and treatment_2', ngoại ngữ, anh văn giao tiếp phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 24 Sampling Assistance on-line devices is increasing the great majority of wastewater quality measurements is carried out in the laboratory after sampling. Thus before considering analytical methods for wastewater quality monitoring based on either standard or alternative procedures the sampling step must be considered because of its importance as a source of potential errors. With the aim of getting a representative volume of effluent sampling has to face a lot of specific constraints related to wastewater characteristics. Thus wastewater sampling is difficult considering the heterogeneity and variability of effluents and moreover the evolution of samples during transportation from sampling site to laboratory related to sample aging. Heterogeneity As for water there are several types of wastewater. All types are characterized by their composition heterogeneity. A wastewater is composed of water carrying a lot of suspended solids and dissolved substances which were not present originally the pollutants . Wastewater types depend on the nature and concentration of solids and pollutants. The most frequent type is urban wastewater mixing municipal wastewater and industrial ones. The composition of municipal wastewater is rather well known and does not vary a lot from one human being to another or one town to another. Typical compositions of urban wastewater have been published Muttamara 1996 Metcalf and Eddy 2003 Degremont 2005 . The concentration of total suspended solids TSS varies from 200 to 600 mg l the volatile suspended solids from 200 to 600 mg l the biological oxygen demand BOD from 100 to 500 mg l the chemical oxygen demand COD from 200 to 1200 mg l the total organic carbon TOC from 50 to 300 mg l the total nitrogen from 50 to 100 mg l and the total phosphorous from 10 to 20 mg l. These values can be decreased in the case of combined sewer effect of dilution of rainfall or increased depending on the proportion and nature of industrial wastewater .
