Wiley wastewater quality monitoring and treatment_11

Cuốn sách này đã được viết bởi các chuyên gia trong lĩnh vực kiểm soát xử lý nước thải, chính sách và giám sát. Nó cung cấp một cái nhìn tổng quan về kiến ​​thức hiện có trong việc theo dõi xử lý nước thải và xác định nhu cầu đang nổi lên, mà sẽ được quan tâm trực tiếp đến các nhà hoạch định chính sách, nhà khoa học ngành nước, và phòng thí nghiệm kiểm soát phân tích.
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Wiley wastewater quality monitoring and treatment_11JWBK117-3.2 JWBK117-Quevauviller October 10, 2006 20:27 Char Count= 0 Treatability Evaluation 198 Table 3.2.5 N/COD ratios and calculations of the single fractions of TKN Values of N/COD ratios (g N/g COD) Symbol of Calculation N/COD ratio Typical value Range SND = iNSS · SS iNSS 0.02 — XND = iNXS · XS iNXS 0.04 0.02–0.06 SNI = iNSI · SI iNSI 0.01 0.01–0.02 XNI = iNXI · XI iNXI 0.03 0.01–0.06 NBH = iXB · XBH iXB 0.086 — 3.2.5 METALLIC COMPOUNDS The concentration of metals in raw wastewater can differ significantly depending on the domestic, commercial or industrial activities collected by the sewerage. The main interest is in metals characterized by potential toxic impact on health or the environment, such as Cd, Cr , Cu, Hg, Ni, Pb and Zn. The load of these components at the inlet of a WWTP can be several times greater in industrial sites than in residential areas far from industrial activities. Urban run-off during storm events is also a source of metals and other pollutants, and contributes to the total influent load into a WWTP. 3.2.5.1 Treatability of Metallic Compounds Metals in raw wastewater are removed in WWTPs through two different mechanisms: r Primary sedimentation: metals are separated as insoluble precipitates or adsorbed on settled particulate matter and then extracted with primary sludge. In contrast the removal of metals in soluble form is negligible. r Secondary treatment: during the biological process metals are integrated into acti- vated sludge or biofilm (adsorbed on flocs or in extracellular polymers). They are removed at the same efficiency as the sludge solids in the secondary settler and extracted together with the excess sludge. Some values for metal removal in primary and secondary treatments are summa- rized in Table 3.2.6 (European Union, 2001). Similar patterns of removal percentages are observed in primary and secondary treatments. Lower removal is observed in both cases for Ni due to its high solubility that limits the presence of Ni in the particulate matter and sludge. In contrast Pb, oneJWBK117-3.2 JWBK117-Quevauviller October 10, 2006 20:27 Char Count= 0 Metallic Compounds 199 Table 3.2.6 Percentage of metals removed in WWTPs, calculated with respect to the concentration in the influent raw wastewater Removal in primary + Removal in primary Metal treatment (%) secondary treatment (%) Ni 24 40 Cd 40 65–75 Cr 40 75–80 Zn 50 70–80 Cu 50 75–80 Hg 55 70–80 Pb 55 70–80 of the least soluble metals, shows higher removal in both the primary and secondary stages. For the majority of metals a significant percentage of the influent load, up to 70–80 %, is transferred into primary and secondary sludge. As a consequence the concentration of metals in dry sludge (measured as TSS) reaches levels of several thousand mg/kg TSS, about 1000 times higher than the concentration of metals in raw wastewater. In synthesis, the majority of metals entering the WWTPs with the raw waste- water is transferred to the sludge extracted from primary and secondary treatments. Depending on the metal solubility, a smaller amount, ranging from 20 to 40 % (60 % only for Ni), is however discharged in water bodies with the final effluent. With regards to the fate of sludge separa ...