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| Publication: |
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Operation of Municipal Wastewater Treatment Plants
Manual of Practice-MOP 11 Sixth Edition
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| Medium: |
| Download Chapter |
| Pages |
| 43 |
| Publisher: |
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Water Environment Federation (WEF) |
| Year: |
| 2005 |
| Order No: |
| MOP1119 |
| DOI: |
| 10.2175/1-57278-232-3-19 |
Table of Contents
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Index
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Cover Art
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Front Matter
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| Order Additional Chapters of MOP 11 |
Order a Hard Copy of MOP 11
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Abstract:
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Primary treatment separates the readily settleable and floatable solids from wastewater by providing a tank where the velocity of the wastewater is reduced to a fraction of a centimeter per second (foot per second). Other benefits of primary settling include equalization of sidestream flows and removal of the biochemical oxygen demand associated with settleable solids.
To improve settling performance, preaeration or chemical addition sometimes precedes the sedimentation basins. Some treatment facilities install chemical-feed equipment strictly for the addition of chemicals to the wastewater influent flow to enhance floc formation to enhance settling. Other treatment plants use chemicals for odor control or phosphorus removal and, in the process, receive the additional benefit of increased settling in the primary sedimentation tanks. However, most primary sedimentation tank facilities do not use any chemicals to enhance settling.
Many treatment plants use primary sedimentation tanks for thickening primary sludge in addition to separating solids from wastewater. In these cases, the primary tanks are sized to accommodate sedimentation and thickening. Some treatment plants use primary sedimentation tanks to cosettle primary sludge and waste activated sludge. In this instance, the primary sedimentation tank is also used as a thickening unit.
In recent years, wastewater specialists have investigated the use of fine screens for primary treatment in place of primary sedimentation tanks. In addition, recent research has also included using primary sedimentation tanks as fermenters to increase the production of volatile fatty acids to enhance and improve biological nutrient removal in the secondary treatment process. This chapter will discuss standard primary treatment systems, dissolved air flotation primaries, combined grit removal/primary treatment systems, primary sludge fermentation, and fine screen treatment systems.
There have been several full-scale and current operational modifications and improvements to the primary treatment process since 1996 that have been included in this latest edition of the chapter. The latest upgraded primary treatment chapter includes new expanded discussions on primary sludge fermentation, enhanced primary treatment, dissolved air flotation primary systems, and combined grit removal/primary treatment processes. This revised chapter also provides a brief description about the ways that computer systems can assist with the operation of the primary treatment process.
The primary treatment process appears to be a simple process to operate compared to other processes within a wastewater treatment plant; however, new advances to the primary treatment process are being made to improve removal efficiencies within the primary tanks and improve process reliability in downstream biological processes.
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©2000 Water Environment Federation