Significance of pressure and recirculation in sludge thickening by dissolved air flotation

• Published in: WATER QUALITY CONSERVATION IN ASIA Vol. 36; no. 12; pp. 223 - 230
• Main Authors: Chung, Tai Hak, Kim, Doo Yeon
• Format: Journal Article Conference Proceeding
• Language: English
• Published: New York NY Elsevier Ltd 01-01-1997; Oxford Pergamon Press; IWA Publishing
• Subjects: Activated sludge; Aerodynamics; Applied sciences; Batch flotation; bubble size; Concentration gradient; Constants; Diffusers; dissolved air flotation; Efficiency; empirical constants; Empirical equations; Exact sciences and technology; Flotation; Fluid dynamics; High pressure; interface rising; Mathematical models; Other industrial wastes. Sewage sludge; Pollution; Pore size; Porosity; Pressure; recirculation; Separation techniques; Skimming; Sludge; Sludge thickening; Thickening; Turbulence; Wastes; Wastewater treatment; bubble size; dissolved air flotation; empirical constants; concentration gradient; interface rising; pressure; recirculation; Batch flotation; sludge thickening; Flotation; Dissolved gas; Air; Conditioning; Dehydration; Sewage sludge; Thickening
• ISBN: 0080433782; 9780080433783
• ISSN: 0273-1223; 1996-9732
• DOI: 10.1016/S0273-1223(97)00747-6

An experimental study was conducted to identify the effect of each operating variable on the liquid-solids separation efficiency using a bench scale batch flotation system and waste activated sludge. Interpretation of the experimental results was performed by use of the characteristic constants of an empirical equation proposed. Minimum A/S ratio for reliable operation of dissolved air flotation should be greater than 0.009. However, unstable sludge rising took place at the initial clarification stage due to excessive shear and turbulence when the pressure was high in spite of high A/S ratio. The efficiency increased as the A/S ratio increased except a case of high pressure coupled with high A/S ratio. High recirculation flow with a saturator pressure less than 5 atm is recommended for stable and efficient operation. The pore size of a diffuser did not affect the thickening efficiency significantly. Concentration gradient of the float solids became larger as flotation continued. Skimming of a top layer or a long skimming interval is desirable for high thickening efficiency.