WASTEWATER TREATMENT - Hacettepe

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KMU 347 WASTEWATER TREATMENT

Wastewater Engineering: An Overview

Wastewater ManagementA UN-Water Analytical Brief

Analytical Brief

Wastewater is defined as a combination of one or more of: • domestic effluent consisting of blackwater (excreta, urine and faecal sludge) and greywater (kitchen and bathing wastewater);

• water from commercial establishments and institutions, including hospitals;

• industrial effluent, stormwater and other urban run-off;

• agricultural, horticultural and aquaculture effluent, either dissolved or as suspended matter.

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Sources of wastewater

Wastewater engineering is that branch of environmental engineering in which the basic principles of science and engineering are applied to solving the issues associated with the treatment and reuse of wastewater.

2 Chapter 1 Wastewater Engineering: An Overview

Industrial wastes

DWF treatment

facility

Interceptorfor DWF

Subcatchment

Rainfall

Surface

storage

Infiltration

Domesticwastewater

Dry weather flow(DWF)

Combined sewerpipe flow

Regulatorstructure

Inlet (catch basin)

Combined sewer

overflow

SubsurfacePipe flow

Infiltratio

n

Treatedeffluent

discharge

Flow

Overland flow

CSOtreatment

facility

Figure 1–1

Schematic diagram of awastewater managementinfrastructure.

pathogenic microorganisms that dwell in the human intestinal tract. Wastewater alsocontains nutrients, which can stimulate the growth of aquatic plants, and may containtoxic compounds or compounds that potentially may be mutagenic or carcinogenic. Forthese reasons, the immediate and nuisance-free removal of wastewater from its sourcesof generation, followed by treatment, reuse, or dispersal into the environment is neces-sary to protect public health and the environment.

Wastewater engineering is that branch of environmental engineering in which thebasic principles of science and engineering are applied to solving the issues associatedwith the treatment and reuse of wastewater. The ultimate goal of wastewater engineeringis the protection of public health in a manner commensurate with environmental, eco-nomic, social, and political concerns. To protect public health and the environment, it isnecessary to have knowledge of (1) constituents of concern in wastewater, (2) impacts ofthese constituents when wastewater is dispersed into the environment, (3) the transfor-mation and long-term fate of these constituents in treatment processes, (4) treatment

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To protect public health and the environment, it is necessary to have knowledge of: (1) constituents of concern in wastewater, (2) impacts of these constituents when wastewater is dispersed into the environment, (3) the transformation and long-term fate of these constituents in treatment processes,

(4) treatment methods that can be used to remove or modify the constituents found in wastewater, and (5) methods for beneficial use or disposal of solids generated by the treatment systems.


Table 1–1Terminology commonly used in the field of wastewater engineeringa

Term Definition

Biosolids Primarily an organic, semisolid wastewater product that remains after solids are stabilizedbiologically or chemically and are suitable for beneficial use

Class A biosolidsb Biosolids in which the pathogens (including enteric viruses, pathogenic bacteria, and viablehelminth ova) are reduced below current detectable levels

Class B biosolidsb Biosolids in which the pathogens are reduced to levels that are unlikely to pose a threat topublic health and the environment under specific use conditions. Class B biosolids cannot besold or given away in bags or other containers or applied on lawns or home gardens

Characteristics General classes of wastewater constituents such as physical, chemical, biological,(wastewater) and biochemicalComposition The makeup of wastewater, including the physical, chemical, and biological constituentsConstituentsc Individual components, elements, or biological entities such as suspended solids or ammonia

nitrogenContaminants Constituents added to the water supply through useDisinfection Destruction of disease-causing microorganisms by physical or chemical meansEffluent The liquid discharged from a processing stepImpurities Constituents added to the water supply through useNonpoint sources Sources of pollution that originate from multiple sources over a relatively large areaNutrient An element that is essential for the growth of plants and animals. Nutrients in wastewater,

usually nitrogen and phosphorus, may cause unwanted algal and plant growths in lakes andstreams

Parameter A measurable factor such as temperaturePoint sources Pollutional loads discharged at a specific location from pipes, outfalls, and conveyance methods

from either municipal wastewater treatment plants or industrial waste treatment facilitiesPollutants Constituents added to the water supply through useReclamation Treatment of wastewater for subsequent reuse application or the act of reusing treated

wastewaterRecycling The reuse of treated wastewater and biosolids for beneficial purposesRepurification Treatment of wastewater to a level suitable for a variety of applications including indirect or

direct potable reuseReuse Beneficial use of reclaimed or repurified wastewater or stabilized biosolidsSludge Solids removed from wastewater during treatment. Solids that are treated further are termed

biosolidsSolids Material removed from wastewater by gravity separation (by clarifiers, thickeners, and

lagoons) and is the solid residue from dewatering operations

aAdapted, in part, from Crites and Tchobanoglous (1998).bU.S. EPA (1999).c To avoid confusion, the term “constituents” is used in this text in place of contaminants, impurities, and pollutants.

TERMINOLOGY

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Table 1–1Terminology commonly used in the field of wastewater engineeringa

Term Definition

Biosolids Primarily an organic, semisolid wastewater product that remains after solids are stabilizedbiologically or chemically and are suitable for beneficial use

Class A biosolidsb Biosolids in which the pathogens (including enteric viruses, pathogenic bacteria, and viablehelminth ova) are reduced below current detectable levels

Class B biosolidsb Biosolids in which the pathogens are reduced to levels that are unlikely to pose a threat topublic health and the environment under specific use conditions. Class B biosolids cannot besold or given away in bags or other containers or applied on lawns or home gardens

Characteristics General classes of wastewater constituents such as physical, chemical, biological,(wastewater) and biochemicalComposition The makeup of wastewater, including the physical, chemical, and biological constituentsConstituentsc Individual components, elements, or biological entities such as suspended solids or ammonia

nitrogenContaminants Constituents added to the water supply through useDisinfection Destruction of disease-causing microorganisms by physical or chemical meansEffluent The liquid discharged from a processing stepImpurities Constituents added to the water supply through useNonpoint sources Sources of pollution that originate from multiple sources over a relatively large areaNutrient An element that is essential for the growth of plants and animals. Nutrients in wastewater,

usually nitrogen and phosphorus, may cause unwanted algal and plant growths in lakes andstreams

Parameter A measurable factor such as temperaturePoint sources Pollutional loads discharged at a specific location from pipes, outfalls, and conveyance methods

from either municipal wastewater treatment plants or industrial waste treatment facilitiesPollutants Constituents added to the water supply through useReclamation Treatment of wastewater for subsequent reuse application or the act of reusing treated

wastewaterRecycling The reuse of treated wastewater and biosolids for beneficial purposesRepurification Treatment of wastewater to a level suitable for a variety of applications including indirect or

direct potable reuseReuse Beneficial use of reclaimed or repurified wastewater or stabilized biosolidsSludge Solids removed from wastewater during treatment. Solids that are treated further are termed

biosolidsSolids Material removed from wastewater by gravity separation (by clarifiers, thickeners, and

lagoons) and is the solid residue from dewatering operations

aAdapted, in part, from Crites and Tchobanoglous (1998).bU.S. EPA (1999).c To avoid confusion, the term “constituents” is used in this text in place of contaminants, impurities, and pollutants.

TERMINOLOGY

From about 1900 to the early 1970s, treatment objectives were concerned primarily with (1)  the removal of colloidal, suspended, and floatable material, (2)  the treatment of biodegradable organics, and (3)  the elimination of pathogenic organisms. Clean Water Act (CWA), stimulated substantial changes in wastewater treatment to achieve the objectives of “fishable and swimmable” waters.

IMPACT OF REGULATIONS ON WASTEWATER ENGINEERING

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Summary of significant U.S. federal regulations that affect wastewater management

Table 1–3Minimum national standards for secondary treatment a, b

Unit of Average 30-day Average 7-dayCharacteristic of discharge measurement concentrationc concentrationc

BOD5 mg/L 30d 45Total suspended solids mg/L 30d 45Hydrogen-ion concentration pH units Within the range of 6.0 to 9.0 at all timese

CBOD5f mg/L 25 40

aFederal Register (1988, 1989).bPresent standards allow stabilization ponds and trickling filters to have higher 30-day average concentrations (45 mg/L) and 7-day average concentrations (65 mg/L) of BOD/suspended solids performance levels as long as the water quality of thereceiving water is not adversely affected. Exceptions are also permitted for combined sewers, certain industrial categories, andless concentrated wastewater from separate sewers. For precise requirements of exceptions, Federal Register (1988) should beconsulted.cNot to be exceeded.dAverage removal shall not be less than 85 percent.eOnly enforced if caused by industrial wastewater or by in-plant inorganic chemical addition.fMay be substituted for BOD5 at the option of the permitting authority.


Pursuant to Section 304(d) of Public Law 92-500 (see Table 1–2), the U.S. Envi-ronmental Protection Agency (U.S. EPA) published its definition of minimum standardsfor secondary treatment. This definition, originally issued in 1973, was amended in1985 to allow additional flexibility in applying the percent removal requirements of pol-lutants to treatment facilities serving separate sewer systems. The definition of second-ary treatment is reported in Table 1–3 and includes three major effluent parameters: 5-day BOD, TSS, and pH. The substitution of 5-day carbonaceous BOD (CBOD5) forBOD5 may be made at the option of the permitting authority. These standards providedthe basis for the design and operation of most treatment plants. Special interpretationsof the definition of secondary treatment are permitted for publicly owned treatmentworks (1) served by combined sewer systems, (2) using waste stabilization ponds andtrickling filters, (3) receiving industrial flows, or (4) receiving less concentrated influ-ent wastewater from separate sewers. The secondary treatment regulations wereamended further in 1989 to clarify the percent removal requirements during dry periodsfor treatment facilities served by combined sewers.

In 1987, Congress enacted the Water Quality Act of 1987 (WQA), the first majorrevision of the Clean Water Act. Important provisions of the WQA were: (1) strength-ening federal water quality regulations by providing changes in permitting and addingsubstantial penalties for permit violations, (2) significantly amending the CWA’s formalsludge control program by emphasizing the identification and regulation of toxic pol-lutants in sludge, (3) providing funding for state and U.S. EPA studies for defining non-point and toxic sources of pollution, (4) establishing new deadlines for complianceincluding priorities and permit requirements for stormwater, and (5) a phase-out of theconstruction grants program as a method of financing publicly owned treatment works(POTW).

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HEALTH AND ENVIRONMENTAL CONCERNS IN WASTEWATER MANAGEMENT

•  The constituents that were undetected previously are now of concern: •  n-nitrosodimethylamine (NDMA), a principal ingredient in rocket fuel •  methyl tertiary butyl ether (MTBE), a highly soluble gasoline additive

•  The release of volatile organic compounds (VOCs) and toxic air contaminants (TACs) from collection and treatment facilities

•  Chlorine disinfection •  Disinfection by-products (DBPs)

The research into the characteristics of wastewater has become more extensive

The techniques for analyzing specific constituents and their potential health and environmental effects have become more comprehensive.

•  However, the advancement in treatment technology effectiveness has not kept pace with the enhanced constituent detection capability.

WASTEWATER CHARACTERISTICS

•  Prior to about 1940, most municipal wastewater was generated from domestic sources.

•  After 1940, as industrial development in the United States grew significantly, increasing amounts of industrial wastewater have been and continue to be discharged to municipal collection systems.

•  The amounts of heavy metals and synthesized organic compounds generated by industrial activities have increased, and some 10,000 new organic compounds are added each year.

•  An effective industrial pretreatment becomes an essential part of an overall water quality management program.

•  If a compound cannot be treated effectively with existing technology, it should not be used.

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WASTEWATER TREATMENT

Wastewater collected from municipalities and communities must ultimately be returned to receiving waters or to the land or reused. The complex question facing the design engineer and public health officials is: What levels of treatment must be achieved in a given application to ensure protection of public health and the environment?

•  A detailed analyses of local conditions and needs,

•  The application of scientific knowledge and engineering judgment based on past experience and

•  The consideration of federal, state, and local regulations. •  Methods of treatment in which the application of physical forces predominate

are known as unit operations. •  Methods of treatment in which the removal of contaminants is brought about by

chemical or biological reactions are known as unit processes.

1–5 Wastewater Treatment 11

ses of local conditions and needs, application of scientific knowledge and engineeringjudgment based on past experience, and consideration of federal, state, and local regula-tions. In some cases, a detailed risk assessment may be required. An overview of waste-water treatment is provided in this section. The reuse and disposal of biosolids, vexingproblems for some communities, are discussed in the following section.

Treatment MethodsMethods of treatment in which the application of physical forces predominate are knownas unit operations. Methods of treatment in which the removal of contaminants is broughtabout by chemical or biological reactions are known as unit processes. At the presenttime, unit operations and processes are grouped together to provide various levels oftreatment known as preliminary, primary, advanced primary, secondary (without or withnutrient removal), and advanced (or tertiary) treatment (see Table 1–4). In preliminarytreatment, gross solids such as large objects, rags, and grit are removed that may dam-age equipment. In primary treatment, a physical operation, usually sedimentation, isused to remove the floating and settleable materials found in wastewater (see Fig. 1–4).For advanced primary treatment, chemicals are added to enhance the removal of sus-pended solids and, to a lesser extent, dissolved solids. In secondary treatment, biologi-cal and chemical processes are used to remove most of the organic matter. In advancedtreatment, additional combinations of unit operations and processes are used to removeresidual suspended solids and other constituents that are not reduced significantly byconventional secondary treatment. A listing of unit operations and processes used for

Treatment level Description

Preliminary Removal of wastewater constituents such as rags, sticks, floatables,grit, and grease that may cause maintenance or operational problemswith the treatment operations, processes, and ancillary systems

Primary Removal of a portion of the suspended solids and organic matter fromthe wastewater

Advanced primary Enhanced removal of suspended solids and organic matter from thewastewater. Typically accomplished by chemical addition or filtration

Secondary Removal of biodegradable organic matter (in solution or suspension)and suspended solids. Disinfection is also typically included in thedefinition of conventional secondary treatment

Secondary with Removal of biodegradable organics, suspended solids, andnutrient removal nutrients (nitrogen, phosphorus, or both nitrogen and phosphorus)Tertiary Removal of residual suspended solids (after secondary treatment),

usually by granular medium filtration or microscreens. Disinfection isalso typically a part of tertiary treatment. Nutrient removal is oftenincluded in this definition

Advanced Removal of dissolved and suspended materials remaining after normalbiological treatment when required for various water reuseapplications

aAdapted, in part, from Crites and Tchobanoglous (1998).

Table 1–4Levels of wastewatertreatment a

Levels of wastewater treatment

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Pollutants in domestic wastewater High strength Medium strength Low strength

TSS, Total suspended solids (mg/L) 120 210 400

BOD, 5-day biochemical oxygen demand (mg/L) 110 190 350

Ammonia nitrogen (mg/L as N) 12 25 45

Organic nitrogen (mg/L as N) 8 15 25

Total phosphorus (mg/L) 4 7 12

Oil and grease (mg/L) 50 90 100

Total coliform bacteria (number/100 ml) 106 – 108 107 – 109 107 - 1010

Fecal coliform bacteria (number/100 ml) 103 – 105 104 – 106 105 - 108

Cryptosporidium oocysts (number/100 ml) 0.1 - 1 0.1 - 10 0.1 – 100

Giardia lamblia cysts (number/100 ml) 0.1 – 10 0.1 - 100 0.1 - 1000

0 2 4 6 8 0 0

/m 3

/h

3 /s

10 14 16 18 20 22 24

50

100

150

200

250

300

0.05

0.1

0.2

0.15

Midnight Midnight

Noon

BO

D c

once

ntra

tion,

g

& B

OD

mas

s loa

ding

, kg

Flow

rate

, m

Flowrate

BOD Concentration

BOD Mass Loading

Time of Day Typical hourly variations in flow & strength of domestic wastewater.

Figure by MIT OCW.

Adapted from: G. Tchobanoglous, F. L. Burton, and H. D. Stensel. Wastewater Engineering: Treatment and Reuse. 4th ed. Metcalf & Eddy Inc., New York, NY: McGraw-Hill, 2003.

Sludge thickening

Sludge digestion

Bar Screen

Grit Chamber

Primary settling

Activated sludge biological treatment

Final settling

Contact basin

Chlorination

Activated sludge recycle

Bar Screen

Grit Chamber

Primary settling

Activated sludge biological treatment

Final settling

Contact basin

Chlorination

Activated sludge recycle

Typical wastewater treatment plant Typical wastewater treatment plant

Preliminary treatment

Primary treatment

Secondary treatment

Disinfection

Can also have tertiary treatment to remove nutrients and other pollutants

Table 1–5Unit operations and processes used to remove constituents found in wastewater

Constituent Unit operation or process See Chap.

Suspended solids Screening 5Grit removal 5Sedimentation 5High-rate clarification 5Flotation 5Chemical precipitation 6Depth filtration 11Surface filtration 11

Biodegradable organics Aerobic suspended growth variations 8, 14Aerobic attached growth variations 9Anaerobic suspended growth variations 10, 14Anaerobic attached growth variations 10Lagoon variations 8Physical-chemical systems 6, 11Chemical oxidation 6Advanced oxidation 11Membrane filtration 8, 11

NutrientsNitrogen Chemical oxidation (breakpoint chlorination) 6

Suspended-growth nitrification and denitrification variations 8Fixed-film nitrification and denitrification variations 9Air stripping 11Ion exchange 11

Phosphorus Chemical treatment 6Biological phosphorus removal 8, 9

Nitrogen and phosphorus Biological nutrient removal variations 8, 9Pathogens Chlorine compounds 12

Chlorine dioxide 12Ozone 12Ultraviolet (UV) radiation 12

Colloidal and dissolved solids Membranes 11Chemical treatment 11Carbon adsorption 11Ion exchange 11

Volatile organic compounds Air stripping 5, 11Carbon adsorption 11Advanced oxidation 11

Odors Chemical scrubbers 15Carbon adsorption 11, 15Biofilters 15Compost filters 15


Unit operations and processes used to remove constituents found in wastewater

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Table 1–5Unit operations and processes used to remove constituents found in wastewater

Constituent Unit operation or process See Chap.

Suspended solids Screening 5Grit removal 5Sedimentation 5High-rate clarification 5Flotation 5Chemical precipitation 6Depth filtration 11Surface filtration 11

Biodegradable organics Aerobic suspended growth variations 8, 14Aerobic attached growth variations 9Anaerobic suspended growth variations 10, 14Anaerobic attached growth variations 10Lagoon variations 8Physical-chemical systems 6, 11Chemical oxidation 6Advanced oxidation 11Membrane filtration 8, 11

NutrientsNitrogen Chemical oxidation (breakpoint chlorination) 6

Suspended-growth nitrification and denitrification variations 8Fixed-film nitrification and denitrification variations 9Air stripping 11Ion exchange 11

Phosphorus Chemical treatment 6Biological phosphorus removal 8, 9

Nitrogen and phosphorus Biological nutrient removal variations 8, 9Pathogens Chlorine compounds 12

Chlorine dioxide 12Ozone 12Ultraviolet (UV) radiation 12

Colloidal and dissolved solids Membranes 11Chemical treatment 11Carbon adsorption 11Ion exchange 11

Volatile organic compounds Air stripping 5, 11Carbon adsorption 11Advanced oxidation 11

Odors Chemical scrubbers 15Carbon adsorption 11, 15Biofilters 15Compost filters 15


Unit operations and processes used to remove constituents found in wastewater

New Directions and Concerns

•  Changing nature of the wastewater to be treated •  Emerging health and environmental concerns •  The problem of industrial wastes •  İmpact of new regulations Further, other important concerns include: (1) aging infrastructure (2) new methods of process analysis and control, (3) treatment plant performance and reliability, (4) wastewater disinfection, (5) impacts of stormwater and sanitary overflows and nonpoint sources of pollution, (6) odor control and the control of VOC emissions,

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