Development of a Novel Circular Secondary Clarifier for Improving Solids Liquid Separation in Wastewater Treatment

• Published in: Water environment research Vol. 81; no. 2; pp. 140 - 149
• Main Authors: Pophali, G. R., Kaul, S. N., Nandy, T., Devotta, Sukumar
• Format: Journal Article
• Language: English
• Published: Alexandria, VA Water Environment Federation 01.02.2009
• Subjects: Activated sludge; Applied sciences; Biodegradation, Environmental; Bioreactors; Chemical engineering; energy dissipation; Exact sciences and technology; Flocculation; Flow velocity; General purification processes; Humans; Hydraulics; Inlets; Particle Size; plume; Plumes; Pollution; Secondary clarifier; Sewage - chemistry; Sintering, pelletization, granulation; Sludge; Solid-solid systems; Suspended solids; velocity gradient; Waste Disposal, Fluid - methods; Wastewater; Wastewater treatment; Wastewaters; Water Purification - methods; Water treatment and pollution; Design; Solid liquid separation; Particle size; Stability; Clouds; Energy dissipation; Flocculation; Agglomeration; Physicochemical purification; Plume; Waste water purification; Retention time
• ISSN: 1061-4303; 1554-7531
• DOI: 10.2175/106143008X390816

A novel circular secondary clarifier was developed to obviate the shortcomings of conventional clarifiers. The novel clarifier provides natural flocculation, which occurs as a result of hydraulic energy dissipation and the formation of sludge cloud referred to as plume. The efficiency of the clarifier depends on the stability of the plume, which in turn depends on the velocity gradient. For natural flocculation to occur, a velocity gradient of 10 to 15 s⁻¹ was found to be favorable. This velocity also keeps the plume-rise well below the free-surface. The mean particle size of mixed liquor suspended solids increases from 41 to 83 µm in the plume, which indicates agglomeration of particles and confirms that natural flocculation is occurring within the plume. The hydraulic improvement achieved by improving inlet design dissipates hydraulic energy, uniformly distributes flow, minimizes sludge blanket disturbances, and promote flocculation. The improved clarifier operates at 1-h hydraulic retention time.