eCommons

 

Uncovering the mysteries of the floc blanket: an exploration with inlet jets, flocculators, and polyaluminum chloride precipitates

Other Titles

Abstract

Floc blankets are used in water treatment plants to improve plant performance and aid in sludge removal and consolidation. Maintaining a fully functioning floc blanket in sedimentation tanks requires that the floc blanket remain fluidized and sludge prevented from building up on the bottom of the tank. A laboratory water treatment system was used to evaluate the range of energy dissipation rates (EDR) of the inlet to the sedimentation tank to determine when the settled effluent turbidity of the system would exceed drinking water quality standards.. Increasing the inlet jet EDR up to approximately 300 mW/kg did not increase effluent turbidity of the system. Small inlet jets with high EDR can be used to ensure resuspension of the floc density current without adversely affecting water treatment plant performance. The design of flocculators is based on mean shear (G) and hydraulic residence time (θ) and the product (Gθ). Guidelines for these values are conservative and designs outside the suggested range could lower plant capital costs. The following flocculator parameters were evaluated: 1) increasing G (range of 74-251 s-1) while decreasing θ from 269 to 80 s (maintaining a constant Gθ) and 2) maintaining a constant G (72 s-1) and varying θ (24 to 1425 s). Flocculator θ below recommended design guidelines performed well indicating that shorter flocculators could be used in the presence of floc blankets. Three potential hypotheses by which residual particles aggregate with other flocs in the floc blanket were considered: residual particles aggregate with 1) other residual particles, 2) small flocs (transitional), or 3) large flocs (hindered). Three coagulant doses (0.625, 1.25, and 2.5 mg/L) were tested with four hydraulic flocculators with constant Gθ but varying G (72, 126, 251, and 340 s-1) and θ (269, 159, 102, and 59 s) on the combined system. A classification system of flocs in the floc blanket was defined based on floc size and time-scale. Results strongly suggest that hypothesis 2 is valid, however, research is needed on floc sizes at specific locations within the system.

Journal / Series

Volume & Issue

Description

Sponsorship

Date Issued

2017-08-30

Publisher

Keywords

floc blanket; flocculation; sedimentation; water treatment; Environmental engineering

Location

Effective Date

Expiration Date

Sector

Employer

Union

Union Local

NAICS

Number of Workers

Committee Chair

Lion, Leonard William

Committee Co-Chair

Committee Member

Desjardins, Olivier
Cowen, Edwin Alfred, III
Weber-Shirk, Monroe

Degree Discipline

Civil and Environmental Engineering

Degree Name

Ph. D., Civil and Environmental Engineering

Degree Level

Doctor of Philosophy

Related Version

Related DOI

Related To

Related Part

Based on Related Item

Has Other Format(s)

Part of Related Item

Related To

Related Publication(s)

Link(s) to Related Publication(s)

References

Link(s) to Reference(s)

Previously Published As

Government Document

ISBN

ISMN

ISSN

Other Identifiers

Rights

Rights URI

Types

dissertation or thesis

Accessibility Feature

Accessibility Hazard

Accessibility Summary

Link(s) to Catalog Record