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CE 548

Wastewater Engineering: An Overview

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OverviewOverviewDefinition: Wastewater may be defined as a combination of

the liquid- or water-carried wastes removed from residents, institutions, and commercial and industrial establishments, together with such groundwater, surface water, and stormwater as may be present.

Problems with wastewater. The organic material in untreated wastewater will decompose and consume the available oxygen causing the water to go septic having undesirable effects such as odors. In addition, nutrients may stimulate unwanted algal blooms and toxic materials present in the ww may be carcinogenic.

Wastewater engineering is concerned with the treatment and reuse of wastewater.

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Wastewater management infrastructureWastewater management infrastructure

Oxygen SagOxygen Sag

Source: Cunningham, William P., Mary Ann Cunningham, Barbara W. Saigo, Environmental Science: A Global Concern. (2003) New York. McGraw-Hill Higher Education.

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TerminologyTerminologyTable 1-1 gives Terminology commonly used in the field of

wastewater engineering

 Contaminants, impurities, and pollutants --- replaced by

constituents

Sludge, biosolids, and solids

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Regulations Regulations Treatment Focus

• From 1900-1970, objectives were: removal of solids, treatment of biodegradables, elimination of pathogens.

• 1970-1980s, objectives included the above plus removal of nutrients, nitrogen and phosphorus.

• Since 1980, all of the above but the emphasis have shifted to the definition and removal of constituents that may cause long-term health effects and environmental impacts.

Regulations (T1-2, p.5)• Established the permitting system. A treatment works cannot

discharge effluent into a public waterway (lake, stream, ocean) unless it has a permit.

• In the US minimal national standards for secondary treatment. T1-3, p.6. BOD5 and TSS of 30 day average not to exceed 30mg/l.

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Health and Environmental ConcernsHealth and Environmental ConcernsThe technical ability to detect constituents has far outstripped

the treatment technology required to remediate the problem. Examples of previously undetected chemicals include: n-nitrosodimethylamine (NDMA) from rocket fuel and methyl tertiary butyl ether (MTBE) a gasoline additive.

Water quality issues arise when treated wastewater are discharged to water bodies that are eventually used as water supplies.

Other issues relate to VOCs, Volatile Organic Compounds; TACs, Toxic Air Contaminants; chorine disinfections and disinfection byproducts, DPBs.

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Wastewater TreatmentWastewater TreatmentMain Goal Protect public health and the Environment

 Main challenge facing engineers and public health officials is

What levels of treatment must be achieved in a given application – beyond those prescribed by discharge permits – to ensure protection of public health and the environment? The answer requires:

• Details analysis of local conditions and needs

• Application of scientific knowledge and engineering judgment based on past experience

• Considerations of lows and regulations

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Wastewater TreatmentWastewater Treatment Treatment methods: 

• Unit Operation: Method of treatment in which the application of physical forces predominates. 

• Unit Process: Method of treatment in which removal of constituents is brought about by chemical or biological reactions.

At the present time, wastewater treatment, employs unit operations and processes:

• Preliminary: Physical operation removal of the gross solids

• Primary: Physical operation removal of the floating and settleable materials

• Secondary: biological and chemical process (removal of organic)

• Advanced or Tertiary: Unit operations and processes for removal of other constituents (N, P).

• The emphasis in the future will be on upgrading wastewater treatment plants to provide secondary and advanced wastewater treatment facilities

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Wastewater TreatmentWastewater TreatmentNew Directions & Concerns:

Changing wastewater characteristics

• More than half a million organic compounds have been synthesized since the turn of the century.

• Some 10,000 new compounds are added each year.

• VOC and VTOC are of great concern due to emission of these compounds. In California an estimated 800 tons/yr of VTOC are released to the atmosphere.

• Increase in hydrogen sulfide (H2S) in the collection systems due to decrease of metals in wastewater.  

Sulfide produced reacts with metals to produce metallic sulfides. 

Problems of H2S: Accelerated corrosion of concrete sewers and headwork structures. Release of odors.

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Wastewater TreatmentWastewater TreatmentNew Directions & Concerns:

The problem of industrial wastes

• The number of industries discharging wastes to municipal sewers has increased significantly.

• The new direction is to provide higher degree of treatment at the point of origin.

Combined sewer overflows:

• Carry both municipal and storm flows

• Overflow is bypassed to receiving systems

• Control is very costly

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Wastewater TreatmentWastewater TreatmentNew Directions & Concerns:

Treatment Operations, Processes & Concepts

• Most of the unit operations and processes are undergoing investigations.

• More modifications are needed stringent requirements. (VOC)

• Alternative treatment systems and technologies under development (aquatic plants).

Health & Environmental Concerns:

• Release of VOCs and VTOCs is of concern.

• Odors serious concern to public special efforts are being made to minimize odors and provide proper treatment.

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Wastewater TreatmentWastewater TreatmentNew Directions & Concerns:

Treatment Process Effectiveness:

• Many wastewater treatment plants did not meet performance standards. 

• Improved designs that are easier to operate and maintain are required. 

• Conservation of energy is a new direction in design. 

Retrofitting and upgrading treatment plants:

• Old aging plants that have served their useful time need to be replaced. However, replacement is very costly

• Emphasis on retrofitting and upgrading

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Wastewater Reclamation and ReuseWastewater Reclamation and ReuseCurrent Status:

• Wastewater is considered as a potential water source

• Wastewater reuse is currently practiced in most countries for non-potable uses such as landscaping and agricultural irrigation.

• Plans are proceeding slowly for groundwater recharge and industrial uses.

New Directions and Concerns• Expand wastewater reuse beyond conventional uses

• However, the potential impact of emerging new trace contaminants raises concerns.

• Therefore, new technologies that offer significantly improved level of treatment need to be tested and evaluated.

• Processes might include: membranes and carbon adsorption.

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Biosolids Disposal and ReuseBiosolids Disposal and ReuseOverview

One of the most difficult and expensive problems, due to:

• legislation to ban certain methods of disposal (ocean disposal).

• concern over air and groundwater pollution.

• number and capacity of landfills have been reduced.

Current Status:Methods Used:

• Land application and landfilling are widely used

• Strict regulation and limited land Composting is becoming popular

• Incineration used by large municipalities

• Emission Control is required

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Biosolids Disposal and ReuseBiosolids Disposal and ReuseNew Directions and Concerns

• In general as the level of treatment increases, the sludge production increases.

• Direction is to search for better methods for processing, disposal and reuse.