Sewage Treatment and Wastewater Engineering Essay

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Definition of wastewater

WASTEWATER ENGINEERING:
AN OVERVIEW

• Wastewater is defined as a combination of the liquid or water-carried wastes removed from residences, institutions, and commercial and industrial establishments, together with groundwater, surface water, and stormwater that may be present.

Goal of wastewater engineering

It is necessary to have knowledge of

• The ultimate goal of wastewater engineering is the protection of public health in a manner commensurate with environmental, economic, social, and political concerns.

1. Constituents of concern in wastewater
2. Impacts of the constituents
3. Transformation and long-term fate of the constituents 4. Treatment methods that can be used to remove or modify the constituents
5. Methods for beneficial use and disposal of solids Treatment concept

Wastewater treatment systems

• Wastewater treatment facilities are designed to speed up the natural purification process that occurs in natural waters and to remove contaminants in wastewater that might otherwise interfere with the natural process in the receiving waters

• Wastewater contains varying quantities of suspended and floating solids, organic matter, and fragments of debris
• Conventional wastewater treatment systems are combinations of physical, biological and sometimes chemical processes to remove these impurities

1

Treatment types
•
•
•
•

Preliminary treatment
Primary treatment (physical process)
Secondary treatment (biological process)
Tertiary or advanced treatment
(combination of physical, chemical and biological process)

Wastewater Treatment Plant Design, 1993, Ed. Vesilind

Preliminary treatment goal

Preliminary treatment systems

• Preliminary systems are designed to remove or cut up the larger suspended and floating materials, and to remove the heavy inorganic solids and excessive amounts of oil and grease
• The purpose is to protect pumping equipment and the subsequent treatment units • Flow measurement devices and regulators
• Racks and screens
• Comminuting devices (grinders, cutters, and shredders) • Flow equalization
• Grit chambers
• Pre-aeration tanks

2

Primary treatment systems
• The object of primary treatment is to reduce the flow velocity of the wastewater sufficiently to permit suspended solids to settle • Floating materials are also removed by skimming Primary clarification
• Primary clarification is achieved in large sedimentation basins
• The settled solids are collected by mechanical scrapers into a hopper and pumped to a sludge treatment unit
• Fats, oils, greases and other floating matter are skimmed off from the basin surface www.epa.gov 3

Settling tanks

Sedimentation removal efficiency

•
•
•
•

•
•
•
•

Plain sedimentation
Two story tanks
Upflow clarifiers
Septic tanks

50-70 percent of TSS
25-35 percent of BOD5
80-90 percent TSS with coagulants
10 percent of phosphorus

Secondary treatment systems
• After primary treatment, the wastewater still contains organic matter in suspended, colloidal and dissolved states
• Secondary treatment removes the soluble and colloidal organic matter using mainly biological processes

www.epa.gov

Biological treatment

Secondary treatment processes

• Biological treatment consists of application of a controlled natural process in which a very large number of microorganisms consume soluble and organic matter over a reasonable time

• Attached growth (trickling filters, rotating biological contactors, intermittent sand filters) • Suspended growth (activated sludge, contact stabilization tanks, sequencing batch reactors, aerobic and anaerobic digesters, anaerobic filters, stabilization ponds and aerated lagoons)

4

Removal efficiency

Advanced treatment

• Secondary treatment processes may remove more than 85 percent of BOD5 and TSS
• However, they are not effective for the removal of nutrients (N and P), heavy metals, nonbiodegradable organic matter, bacteria, viruses, and other microorganisms

• Advanced water treatment is
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