Environmental Considerations of Engineering Design

Bo HuJohn Nieber

Importance

• Since late 1970, many developing countries including US have moved the environmental protection from a secondary to a primary issue for the manufacturing and transportation sectors!

• More and more developing countries are having same regulations now!

Wastes and Pollution

• Air pollution• Wastewater• Solid waste• Others

– sound, radiation, odor, etc

Environmental Issues• Burning of fossil fuels for power generation and

transportation• Handling of toxic wastes• Bioaccumulated chemicals

– For examples: DDT, insect and pest control, banned by EPA in 1972

• Toxic metals and minerals– Lead, banned in the paint in 1978, banned in the gasoline

and replaced by MTBE– Mercury– Cadmium– Asbestos, ceiling materials

Environmental Factors in Design

• Handling of toxic wastes – 97% of hazardous waste generated by the chemicals and nuclear

industry is wastewater (1988 data).– In process design, it is essential that facilities be included to remove

pollutants from waste-water streams.• Reaction pathways to reduce by-product toxicity

– As the reaction operations are determined, the toxicity of all of the chemicals, especially those recovered as byproducts, needs to be evaluated.

– Pathways involving large quantities of toxic chemicals should be replaced by alternatives, except under unusual circumstances.

• Reducing and reusing wastes– Environmental concerns place even greater emphasis on recycling, not

only for un-reacted chemicals, but for product and by-product chemicals, as well. (i.e., production of segregated wastes - e.g., production of composite materials and polymers).

Environmental Factors in Design (Cont’d)

• Avoiding non-routine events– Reduce the likelihood of accidents and spills through the reduction of

transient phenomena, relying on operation at the nominal steady-state, with reliable controllers and fault-detection systems.

• Material characterization– To maintain low concentrations of such chemicals below the limits of

environmental regulations, it is important to use effective and rapid methods for measuring or deducing their concentrations from other measurements.

• Design objectives, constraints and optimization– Environmental goals often not well defined because economic objective

functions involve profitability measures, whereas the value of reduced pollution is often not easily quantified economically.

– Solutions: mixed objective function (“price of reduced pollution”), or express environmental goal as “soft” or “hard” constraints.

– Environmental regulations = constraints

Environmental Factors in Design (Cont’d)

• Regulations– Some environmental regulations can be treated as constraints to be

satisfied. The design team needs to check that these constraints are satisfied after the mathematical model is set up

– Other regulations, however, are more difficult to quantify. These involves expectations of the public and the possible backlash should the plant be perceived as a source of pollution. Plant location is restricted.

• Intangible costs– Cost of liability when a plant is found to be delinquent in satisfying

regulations, including legal fees, public relations losses, delays incurred when environmental groups stage protests.

• Properties of dilute streams• Properties of electrolytes

– Ionic species such as acids, bases, and salts– Strong electrolytes dissociate into ionic species whose interactions with

water and organic molecular are crucial to understanding the state of a mixture

Cost!

Environmental ProtectionU.S. Environmental Protection Agency (US EPA www.epa.gov)

Air, Water, LandAir – Clean Air Act (1990 revision of 1970’s Act)

NAAQS – National Ambient Air Quality StandardCriteria air pollutants are : Ozone, CO, Pb, NO2, SO2, Particulates (PM-10, PM-2.5)…

Air Toxics (PCB’s, PAH’s,…)Toxic Release Inventory (TRI)

Water – Clean Water Act (1977 amendment to previous pollution Act)Chemicals : Mercury, Urea, Phosphorus, Arsenic…

Land – Landfills, garbage dumps, radioactive waste, electronic products,Mining (open cast, underground), urban expansion.

Overview of the Clean Air Act (CAA)

• The CWA and its amendments have been this country’s fundamental legislation controlling water pollution since 1972. Most of the CWA allegations against ranges involve the National Pollutant Discharge Elimination System (NPDES) program.

• Under this program of the CWA it is illegal to “discharge” any “pollutant” from a “point source” into “waters of the United States” without a permit to do so. Under the CWA, waters of the United States encompass essentially all rivers, streams, lakes, ponds, drainage-ways, wetlands and similar features in the United States, including those entirely on private property.

• It is important to note that the CWA does not prohibit the discharge of pollutants into waters of the U.S; it merely requires a permit to do so.

Overview of the Clean Water Act (CWA)

• The CWA and its amendments have been this country’s fundamental legislation controlling water pollution since 1972. Most of the CWA allegations against ranges involve the National Pollutant Discharge Elimination System (NPDES) program.

• Under this program of the CWA it is illegal to “discharge” any “pollutant” from a “point source” into “waters of the United States” without a permit to do so. It is important to note that the CWA does not prohibit the discharge of pollutants into waters of the U.S; it merely requires a permit to do so.

• Under the CWA, waters of the United States encompass essentially all rivers, streams, lakes, ponds, drainage-ways, wetlands and similar features in the United States, including those entirely on private property.

Solid waste disposal regulations

• Solid Waste Disposal Act (1965)– To promote better management of solid wastes– To support resource recovery and disposal

• U.S. Public Health Service– To promulgate and enforce regulations for solid

waste collection, transportation, recycling, and disposal

• Resource Recovery Act (1970)– Emphasis from solid waste disposal to recycling

and energy recovery

Solid waste disposal regulations

• Resource Conservation and Recovery Act (1976)– Significant requirements for the control of

hazardous waste storage, treatment and disposal

• Hazardous and Solid Waste Amendments (1984)– Revise of criteria for landfills

State and Local Laws and Regulations

• federal environmental laws always permit the states to adopt standards more stringent than the federal standards.

Typical Treatments Methods

• Municipal Wastewater Systems • Solid waste

Physical Characteristics of Domestic Wastewater

•Color: gray (fresh), black (septic)•Odor: offensive •Temp: 10-20oC•Density: 1000 kg/m3 (almost same as that of water)•Solids: half of the weight is solids - 50% soluble, 50% insoluble (1/2 settled, and 1/2suspended)

Chemical Characteristics of Domestic Wastewater

a measurement of total organic and inorganic N in wastewater

Characteristics of Industrial Wastewater

•Vary greatly from one industry to another•EPA grouped 3 categories:

1 2

Characteristics of Industrial Wastewater

3 Priority Pollutants (table 1-6)

Wastewater Treatment Standards

The Congress requires municipalities and industries to provide secondary treatment before discharging water into natural water bodies.

Secondary treatment is based on three characteristics:•BOD5

•SS•pH

Second Treatment Standards

NPDES

National Pollutant Discharge Elimination System (NPDES):

•Under NPDES program, any facility that discharge wastewater is required to obtain a NPDES permit•Before the permit is granted, administering agency will model the potential pollution (recall what you have learnt in “water quality management”)•The permit requires secondary treatment standards, or stricter.

Wastewater Treatment Plant (WWTP)

A birdview of a WWTP

Objectives of Wastewater Treatment

• Transform dissolved and particulate BOD into acceptable end products (i.e. CO2, H2O, stable products, and biomass)

• Incorporate nonsettlable colloidal material into biological floc

• Remove nutrients (N,P)• Remove trace organic constituents

Land treatment

Protect subsequent equipments in WWTP

Remove pollutants that settle or float60% of SS removal; 35% of BOD5 removalNo removal of soluble BOD5

Remove soluble BOD5;85% of SS and BOD5 removal

Remove soluble BOD5;99% removal of SS, BOD5 , P, and bacteria95% removal of N

Land treatment

Sludge (solid):Need to be handled and disposed of

Solid Wastes• Non-liquid, non-soluble materials ranging from municipal

garbage to industrial wastes that contain complex and sometimes hazardous substances. Solid wastes also include sewage sludge, agricultural refuse, demolition wastes, and mining residues.

Solid waste sources

• Four categories– Municipal, industrial, mineral extraction,

and agricultural• Municipal waste sources

– The materials discarded from residences, business and commercial waste

– More recycling and energy recovery in the future will decrease the total amount of material that must be landfilled.

Distribution of materials in MSW (mass) (US, 2003)

60% from residential

Ratio of MSW

40% from commercial

Typical composition of residential MSW (by weight) (excluding recycled materials, 1990)

Organic Food wastes 9%Paper 34%Cardboard 6%Plastics 7%Textiles 2%Rubber 0.5%Leather 0.5%Yard wastes 18.5%Wood 2%Mis. Organics -

Inorganic Glass 8%Tin cans 6%Aluminum 0.5%Other metals 3%Dirt, ash, etc. 3%

Total 100%

Solid waste management

Generation

Collection

Transport

Landfill

Recycled

/Recovery

/Reuse

Energy Recovery /Thermal Reduction

Rear-loading refuse collection vehicle for backyard pickup

Landfill• Defined as a land disposal site employing an engineered

method of disposing of solid wastes on land in a manner that minimizes environmental hazards by spreading the solid wastes on the smallest practical volume, and applying and compacting cover materials at the end of each day.

Homework IV• Think about possible pollutants from your process• Check with the local government and agencies about the

requirements of the emission levels from your projected process• Find strategies to treat the wastes and decrease the emission level• Topic Discussion: There is a great push from our whole society to

make regulations, restrictions and safety procedures in order to make our living environment cleaner and our working environment safer. However, many industries, especially heavy polluting industries, have been moved to places where there are less requirements to cut the cost. If you are the project manager, what is your choice between environment protection and profit? What can we do, in your opinion, to solve this problem?