Sammenligning af kompressiblet og shear yield stress for kloakslam og uorganiske partikulære suspensioner
Translated title
Comparison of Shear and Compressive Yield Stress Ratio for Sewage Sludge and Inorganic Particulate Suspensions
Author
Kristjansson, Maria
Term
4. term
Education
Publication year
2008
Pages
95
Abstract
This thesis compares the shear and compressive yield stresses of three particulate suspensions—a coagulated alumina, a municipal sewage sludge, and a dual‑polymer flocculated alumina formulated to emulate sludge—to examine how the ratio Py/τy varies with solids volume fraction. Shear yield stress was measured using the vane method (Nguyen and Boger, 1983) with multiple vane sizes, covering 0.9–15,000 Pa. Compressive yield stress was determined via equilibrium pressure filtration, centrifugation, and batch settling, spanning 0.007–300 kPa. All three suspensions yielded more readily in shear than in compression, and Py/τy increased with solids concentration: from 2 to 14 for coagulated alumina (φ = 0.075–0.50 v/v), from 5 to 8 for sewage sludge (φ = 0.035–0.09 v/v), and from 8 to 11 for flocculated alumina (φ = 0.09–0.43 v/v). Filtration of the coagulated alumina was traditional, with an approximately constant solids diffusivity of about 1×10−7 m2/s above the gel point. The flocculated alumina showed non‑traditional filtration at 5–20 kPa and non‑classified behavior at 40–300 kPa; its solids diffusivity ranged from about 1×10−7 to 2×10−6 m2/s, peaking near the gel point, then decreasing and rising again with increasing volume fraction. Sewage sludge exhibited a similar trend at much lower values (approximately 6×10−11–5×10−9 m2/s). Because sewage sludge is difficult to characterize due to slow dewatering, the flocculated alumina was explored as a surrogate; the results provide a consistent basis to compare shear and compressive strength and separation behavior across ideal and sludge‑like suspensions.
Denne afhandling sammenligner shear- og kompressions-yield stress for tre partikulære suspensioner—en koaguleret aluminiumoxidsuspension, et kommunalt kloakslam og en dobbelt-polymer flokkuleret aluminiumoxidsuspension designet til at efterligne slam—for at undersøge, hvordan forholdet Py/τy ændrer sig med tørstofvolumenfraktionen. Shear yield stress blev målt med vanemetoden (Nguyen og Boger, 1983) med flere vane-størrelser og dækkede 0,9–15.000 Pa. Kompressibel yield stress blev bestemt ved ligevægts-trykfiltrering, centrifugering og batch-sedimentering i intervallet 0,007–300 kPa. Alle tre suspensioner gav lettere efter i shear end i kompression, og Py/τy steg med tørstofkoncentrationen: fra 2 til 14 for koaguleret aluminiumoxid (φ = 0,075–0,50 v/v), fra 5 til 8 for kloakslam (φ = 0,035–0,09 v/v) og fra 8 til 11 for den flokkulerede aluminiumoxid (φ = 0,09–0,43 v/v). Filtrering af den koagulerede aluminiumoxidsuspension var traditionel med en omtrent konstant tørstofdiffusivitet på ca. 1×10−7 m2/s over gelpunktet. Den flokkulerede aluminiumoxidsuspension udviste non-traditionel filtrering ved 5–20 kPa og uklassificeret adfærd ved 40–300 kPa; tørstofdiffusiviteten varierede fra ca. 1×10−7 til 2×10−6 m2/s, med maksimum nær gelpunktet, efterfulgt af et fald og senere stigning med voksende volumenfraktion. Kloakslam viste et lignende forløb, men ved langt lavere værdier (ca. 6×10−11–5×10−9 m2/s). Da kloakslam er vanskeligt at karakterisere på grund af langsom afvanding, blev den flokkulerede aluminiumoxidsuspension anvendt som mulig surrogat; resultaterne giver et konsistent grundlag for at sammenligne shear- og kompressionsstyrke og separationsadfærd i både ideelle og slam-lignende suspensioner.
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