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Description: Liquid Stream Fundamentals: Sedimentation
Liquid Stream Fundamentals: Sedimentation
Sedimentation is one of the processes most commonly used in wastewater treatment and in many cases the last barrier before the effluent leaves the water resource recovery facility (WRRF). Despite being vital components of the WRRF, sedimentation processes are sometimes overlooked. This fact sheet discusses the key design and operational considerations for the sedimentation processes and their role in achieving optimal plant performance. This fact sheet is part of a series on liquid stream fundamentals.
Author(s)
Water Environment Federation
Contributing authorsNandita Ahuja
SourceFact Sheet of the Water Science and Engineering Center
Project IDWSEC-2017-FS-022
CommitteeMRRDC
Sub CommitteeWEFTEC Session 306
Document typeFact Sheet
PublisherWater Environment Federation
Print publication date Oct 2017
Volume / Issue
Content sourceWater Science and Engineering Center
First / last page(s)1 - 10
Copyright2017
Word count5,293
Subject keywordsWastewater Treatment
Associated keywords:Design
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Description: Liquid Stream Fundamentals: Sedimentation
Introduction
Liquid Stream Fundamentals: Sedimentation
Sedimentation refers to the physical process where gravity forces account for the separation of solid particles that are heavier than water (specific gravity > 1.0). The common sedimentation unit processes in a wastewater liquid treatment train include grit removal, primary sedimentation, secondary sedimentation and tertiary sedimentation. This fact sheet primarily focusses on the primary and...
PublisherWater Environment Federation
Copyright2017
Word count365
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Description: Liquid Stream Fundamentals: Sedimentation
Clarifier Functions
Liquid Stream Fundamentals: Sedimentation
Generally, clarifiers in a wastewater treatment plant are designed to serve four main functions discussed below.
PublisherWater Environment Federation
Copyright2017
Word count111
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Description: Liquid Stream Fundamentals: Sedimentation
Primary Sedimentation
Liquid Stream Fundamentals: Sedimentation
Primary sedimentation is one of the key processes for TSS and BOD removal in the liquid treatment train and for reducing the load to the downstream biological process(es). Primary sedimentation is principally governed by discrete settling (Type I) along with minimal flocculation/flocculent (Type II) settling (Griborio et. al, 2014). Compression settling (Type IV) occurs in the sludge blanket...
PublisherWater Environment Federation
Copyright2017
Word count711
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Description: Liquid Stream Fundamentals: Sedimentation
Secondary Sedimentation
Liquid Stream Fundamentals: Sedimentation
The purpose of secondary clarifiers is to separate the incoming biomass from the biological reactors into clarified effluent and thickened sludge. For processes such as trickling filters and rotating biological contactors, the solids are typically settled and wasted, similar to primary sedimentation. For activated sludge, it is necessary to recycle most of the settled solids and return settled...
PublisherWater Environment Federation
Copyright2017
Word count1,071
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Description: Liquid Stream Fundamentals: Sedimentation
Geometry Features
Liquid Stream Fundamentals: Sedimentation
Geometry features of clarifiers can have a significant impact on clarifier performance and capacity and should therefore be carefully selected. This section discusses some of the main geometry features pertinent to both primary and secondary clarifiers.
PublisherWater Environment Federation
Copyright2017
Word count2,272
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Description: Liquid Stream Fundamentals: Sedimentation
Instrumentation
Liquid Stream Fundamentals: Sedimentation
While clarifiers are not instrumentation-intensive unit processes, some instrumentation-based controls can be useful for regulating and monitoring clarifier performance. One of the most commonly used instrumentation devices are sludge blanket readers/trackers (e.g. light emitting analyzers, ultrasonic analyzers, optical sensors). Sludge blanket measurement devices are mostly used in secondary...
PublisherWater Environment Federation
Copyright2017
Word count112
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Description: Liquid Stream Fundamentals: Sedimentation
Operation and Maintenance
Liquid Stream Fundamentals: Sedimentation
Operation and control of clarifiers can range from completely manual to completely automated. In either scenario, the key operator responsibilities for clarifier operation are controlling RAS/primary sludge flow rates to maintain clarifier blankets and prevent solids carryover in the effluent, especially during high flows. Additionally, attention should be paid to monitoring flows, influent TSS,...
PublisherWater Environment Federation
Copyright2017
Word count66
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Description: Liquid Stream Fundamentals: Sedimentation
Design Tools
Liquid Stream Fundamentals: Sedimentation
Clarifier design is complex and the resources for design and evaluation range from design standards (such as the Ten State Standards, local, state and federal standards) and literature guidelines (WEF MOP 8, Metcalf and Eddy, etc.) to limiting solids flux theory and sophisticated mathematical models (computational fluid dynamics, CFD). Since design standards and some literature-based resources do...
PublisherWater Environment Federation
Copyright2017
Word count290
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Description: Liquid Stream Fundamentals: Sedimentation
References
Liquid Stream Fundamentals: Sedimentation
WEF Municipal Resource Recovery Design Committee
PublisherWater Environment Federation
Copyright2017
Word count228
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Liquid Stream Fundamentals: Sedimentation
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