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Module 6:
EFFLUENT TREATMENT AND RESIDUALS
MANAGEMENT
Program for North American Mobility
in Higher Education
Structure of this module
This module is divided into 3 “tiers”, each with a specific
goal:
Tier 1.- Basic introduction
Tier 2.- Case study of the pulp & paper sector
Tier 3.- Open-ended problem
Tier 1. Contents:
1.
Introduction
2.
Industrial pollution problems.
The petroleum industry.
The pulp and paper industry.
3.
Programs for reducing pollution.
4.
Treatment processes.
5.
Process selection.
6.
Volume and disposal reduction.
Effluent Treatment and Residuals
Management
Tier I:
Introductory concepts
Tier 1
G o a l s:

To provide information about the significance of treating effluents
from industry and others facilities (or sources)

To extreme the necessity of minimize pollutant concentration in
the effluents and reduce the wastes production, and,

To suggest strategies to reduce pollutant wastes production and
their emission to the environment
Tier 1
What is pollution?
Pollution means:
…changes in the physical, chemical and biological characteristics
of air, land and water
…harms for the human and other living species, and,
…degradation of the ecosystems
...the undesirable state of the natural environment being
contaminated with harmful substances as a consequence of
human activities
For example, Water Pollution refers to contaminants in aquatic
ecosystems (streams, lakes, etc) which render them unfit for a
particular use.
Tier 1
Pollutants can reach:
1.
Air
2.
Water
3.
Solid waste
This module focuses on water pollution from industrial sources
Tier 1
Water standards:
Drinkable
Recreation: swimming, fishing.
Irrigation
Water impurities may or may not be harmful; it depends on:
• The amounts and nature of these impurities,
• The next use to which the water will be put, and
• The tolerance of these impurities for the next use.
Tier 1
Types and characteristics of wastewaters:
Contaminants
Reason for importance
Physical suspended solids
They can lead to the development of sludge
deposits.
Chemical biodegradable
organics
When discharged untreated to the
environment, they lead to the depletion of
natural oxygen resources.
Nutrients
If discharged, they can lead to water
pollution.
Hazardous
Because of their characteristics
(e.g.,toxicity, flammability) are dangerous
for human health and the environment.
Heavy metals
They can negatively impact upon biological
waste treatment processes.
Dissolved inorganic solids
They are result of water use, and may have
to be removed if the wastewater is to be
reused.
Biological pathogens
Communicable diseases can be transmitted
by the pathogenic organism in wastewater.
Tier 1
Water standards
Industrial effluent standards
Parameter
Total suspended
solids, (mg/l)
BOD5, (mg/l)
pH
Mexico a
USA b
Canada c
150
27
15
20
56
15
5-10
6-9
6-10.5
Tier 1
Tier 1
What is BOD?
By definition, BOD is the quantity of oxygen required for the
stabilization of the oxidizable organic matter present over 5 days
of incubation at 20 oC; that can be explained as a measure of the
oxygen required by microbes to degrade a sample of effluent.
The organic content of the water can be estimated by the BOD.
Tier 1
Why should we minimize the use of
water?
Water is such an important part of many manufacturing processes
that we must consider Effluent Treatment as a part of the main
process because of the great amount always involved.
Water is abstracted from aquifers and rivers, treated and supply to
industries and homes for different uses; used water is supposed
to be treated and discharged again into the rivers. Most of the
times, this water returns to its natural environment but
unfortunately, with a greater heat content or with some
substances added.
Tier 1
Why should we minimize the use of
water?
It is also important to minimize use of water because of several
reasons:
 Fresh water is often scarce. High costs involved operating
effluent treatment plants.
 Difficult to separate all the elements that pollute water.
Tier 1
Industrial pollution problems
Tier 1
Industrial pollution problems:
The main pollution problems are related to :
 Increasing use of water for agriculture.
 The increase of aqueous effluent to receiving water.
 Population growth.
 Industrial products and services.
 The mental, technical, financial, regulatory and institutional
barriers to implement preventive modern technologies.
RESULTS:
Ecosystems decline.
Industrialization social costs.
The increase of human diseases.
Tier 1
The petroleum industry
Tier 1
The Petroleum Industry:
Crude oil refining operations involve extracting useful petroleum
products from crude oil. Crude oil contains fractions of napthas,
gasoline, gas oils, diesel fuel, asphalt, jet fuel and lubrication
fuels.
Large quantities of production wastes are produced during
exploration and production:
 Wastewater
 Solid waste
 Toxic pollutants
Tier 1
The Petroleum Industry:
Production wastes in the petroleum industry can be grouped broadly
into 2 classes:
• Wastes related to drilling including chemical additives: treatment
and disposal of oil drilling wastes takes place either on or off the
drilling site.
• Wastes related to oil production, primarily produced water:
The volume of produced water exceeds the volume of drilled
wastes.
If environmental quality standards are not exceeded the remainder
may be discharged to surface waters. The majority of produced
water is disposed of underground through injection wells and it is
permitted under U.S. EPA control programs.
Tier 1
What is refinery effluent?
Petroleum refineries use large volumes of water in their processes.
The wastewater contains hazardous chemicals:
Tier 1
Refinery wastes:
Emissions from refineries include:
 Sulfur oxides
 Nitrogen oxides
 Benzene, toluene and xylene
 VOC
 Wastewater containing BOD levels
 Heavy metals
Tier 1
Wastes generated:
Pollution
Cooling systems
Polluted wastewater
Solid waste and sludge
VOC emissions
Others emissions
Approximate Quantities
3.5-5 m3 of wastewater generated per ton of crude.
BOD 150-250 mg/l
COD 300-600 mg/l
phenol 20-200 mg/l
oil 100-300 mg/l (desalted water)
oil 5000 mg/l in tank bottom
benzene 1-100 mg/l
heavy metals 0.1-100 mg/l
3 to 5 kg per ton of crude (80 % should be considered as hazardous
waste because of the heavy metals and toxic organic presence).
0.5 to 6 kg/ton of crude.
BTX (Benzene, Toluene and Xylene) 0.75 to 6 g/ton of crude
Sulfur oxides 0.2-0.6 kg/ton of crude
Nitrogen oxides 0.006-0.5 kg/ton of crude
(Pollution Prevention and Abatement Handbook World Bank Group)
Tier 1
The pulp and paper industry
Tier 1
How paper is made:
Most of the raw material needed for paper manufacture is supplied
by trees.
The main steps in the pulp and paper manufacture are raw material
preparation, such as wood debarking, and chip making; pulp
manufacturing; pulp bleaching; paper manufacturing and fiber
recycling. Pulp mills and paper mills may exist separately or as
integrated operations.
The characteristics of the paper (smoothness, glazed finish) are
given by a process called calendering.
The paper undergo coating, whereby a thin layer of coating pigment
or filler is spread onto the paper surface.
Tier 1
Pulp and paper industry:
The pulp and paper industry has made significant steps toward
conserving water and energy.
Significant water reductions are achieved through better reuse
methods and by separating cooling water from process water.
The waste streams generated in this industry are best classified by
their origins as show in the next slide.
Tier 1
Types of waste products in the pulp and
paper industry:
 Material originated in raw materials (dirt and bark with wood).
 Nonfiber components in wood.
 Contaminants in waste paper and make-up chemicals.
 Reaction products (dissolved wood substance from mechanical or
chemical action).
 Fiber fragments.
 By-products of chemical recovery and combustion.
 Fiber and nonfiber process looses and discharges of water, air
and heat.
Tier 1
The pulp and paper industry
Water use and effluent discharges:
Liquids discharges from the process contain solids, mainly fiber,
fillers, and colloidal and dissolved material. The fiber and fillers
are minimized and reused. Colloidal and dissolved materials are
by-products of the refining of the fibers or carried over from the
pulp mill.
Discharges of dissolved material are minimized by washing the
stock and displaced carryover from pulp mills and by practicing
good water reuse strategies that reduce the volume and
concentrations of waste in wastewater.
Tier 1
Programs for reducing pollution
Tier 1
Government programs for reducing
pollution:
For sustainable development, governmental pollution prevention
programs can best counteract the pressure to invest in “end of
pipe” pollution solutions by demonstrating the economic and
environmental benefits of a source reduction approach, making
technical information available and providing technical
assistance.
EPA has been working with industry and government representing
environmental, community and work force issues to prevent
pollution at the source prior to “end of pipe” treatment.
Tier 1
Government programs for reducing
pollution:
Laws such as NEPA, TCSA, CAAA and PPA remain outside the scope
of most pollution control work. The following options were
suggested for USEPA for moving forward interaction in the US:
1.
Add multi-media provisions to the existing regulations.
2.
Correct laws in other policy sectors with environmental
measures.
3.
Make NEPA a stronger statute.
4.
Make TSCA a law which can use EPA programs to control and
reduce toxic substances.
5.
Establish pollution prevention approaches.
Tier 1
Programs for reducing pollution:
Manufacturers could implement a variety of
improved management procedures
that would aid pollution reduction:

Environmental audits. Identify (inventory) and correct problems
(strategies to achieve reductions) that generate wastes.

Regular preventive maintenance. Inspection, maintenance and
replacement of equipment.

Material handling and storage. Emissions of hazardous material must be
avoided. There should be labels of all containers and first aid
recommendations.

Employee training. Well informed employees are better able to make
valuable waste reduction suggestion.

Operating manual and record keeping. Good facility documentation:
process procedures, control parameters, hazards and operator
responsibilities.
Tier 1
Environmental programs:
Some industries may see no difference between end of pipe pollution control and
a front end pollution prevention control.
The importance is that those industries may not go beyond the first stage of
waste reduction.
As the environmental concern deepens, industries have to move further up the
production chain:

End of pipe solution to wastes and pollutants; and later

Internal process modifications to reduce emissions and wastes, and
eventually

Redesign products to achieve a maximum level of recycling of raw
materials and minimization of wastes after the products are used.
Tier 1
Some measurements to save water:
 Keep water effluent streams separated.
 Reuse water as close to source as possible.
 Recycling whenever it is possible.
 Better control of usage with automated systems.
 Checking and control of leaks.
 When buying new equipment, evaluate water-efficiency
models including accessories.
 Reducing the quantities of chemicals so that the amount
of dilution water will be reduced.
Tier 1
Reusing water:
It is not only possible but necessary to reuse wastewater of a
process stream before it leaves the plant accomplished by piping,
diluting or treating some of the effluents before using them
again.
Some plants are now using closed systems, so that there are no
water discharges.
Zero discharges has been practiced in locations where water is
scarce, and may involve technologies for removing suspended
and dissolved solids.
Complete demineralization is relatively expensive, however, in some
cases wastewater discharges can be reduced significantly with
other less expensive technologies.
Tier 1
Treatment processes
Tier 1
Expectations of a water treatment program:
The expectations from a water treatment program should be
integrated to include all aspects of the program, from the
proposal through to the implementation stages.
Tier 1
Treatment Program
As we will see in the next diagram, the expectations that a
good treatment program should give us are listed below:






Overview of a new or existent problem.
Lab study of all system and water composition.
Submit a proposal.
Program implementation.
Monitoring to optimize.
Use of modern treatment techniques.
Program under control
Tier 1
Treatment Program
New or
Problem
System
Plant
Study
Proposal
Lab
Study
Implement
Program
System
under
control
Follow-up
New Product
Technology
Tier 1
Wastewater treatment processes:
Wastes are generated by every industrial enterprise, and this
wastes can either be liquids or solids.
Wastewater treatment can be divided into three stages:
1.
Primary treatment that uses physical operations to remove
free oil and/or suspended solids.
2.
Secondary treatment to remove dissolved contaminants
through chemical or biological action, and
3.
Tertiary treatment for the removal of residual contaminants.
Tier 1
Separation order
This list shows how separation is carried out:
 Primary treatment
• Sedimentation
• Aeration
 Secondary treatment
 Tertiary treatment
Tier 1
Treatments…
Primary treatment prepares the wastewater for biological
treatment. Large solids are removed by screening, and grit.
Equalization in a mixing basin, levels out the flows variation and
concentrations. Neutralization, where required, follows
equalization. Oils, greases and suspended solids are removed by
flotation, sedimentation of filtration.
Secondary treatment is a biological degradation of soluble organic
compounds from input levels of 50- 1000 mg/l BOD or greater to
effluent levels under 15 mg/l. Aerobic treatment in an open
vessel is done. After biotreatment, the microorganisms and solids
suspended are allowed to settle.
Tier 1
Treatments…
The tertiary treatment remove specific residuals. By filtration,
suspended colloidal solids can be removed; adsorption removes
organics by granular activated carbon (GAC); and chemical
oxidation also removes organic compounds.
Tertiary systems have to treat great amounts of wastewater, so
they are expensive.
When streams rich in heavy metals, pesticides or other substances
that may pass through primary treatment and inhibit biological
treatment are present, in-plant treatments are necessary.
Precipitation, activated carbon adsorption, chemical oxidation, air or
steam stripping, wet air oxidation, ion exchange, reverse osmosis
are some of the methods useful when in-plant treatments are to
be used.
Tier 1
The tertiary treatment…
Tertiary treatment is a polishing step. Its importance is that rather
than have to find solutions at the end of pipe, where primary and
secondary treatments are used to, it is possible to minimize
some toxics or hazardous components in the process before they
are combined with other less “hazardous”.
Biological treatment usually produces a ’30/20’ effluent with no
more than 30 mg/l suspended solids and 20 mg/l BOD.
Tier 1
Tertiary treatment
However, river flows have decreased owing to drought conditions. In
these circumstances, new limits are imposed on the quality of
the final effluent. The treatment processes beyond the secondary
treatment to achieve the required limits in the process are well
known as tertiary treatments.
Tier 1
In plant treatment
Before end of pipe wastewater treatment, a program of waste
minimization should be initiated.
1.
Recirculation. In the paper board industry, white water from a
paper machine can be put through a save all to remove the
pulp and fiber and recycled to various points in the process.
2.
Segregation. Clean streams are separated for direct discharge.
3.
Disposal. In many cases, the total discharge BOD and
suspended solids can be reduced by removal of residue in
semidry state for disposal.
4.
Reduction. The use of automatic cutoffs can reduce the
wastewater volume.
5.
Substitution. The substitution of chemical additives of a lower
pollutional effect in processing operations.
Tier 1
Wastewater treatment processes:
Process selection
.
Tier 1
Figure 1. Conceptual treatment program for
organic and toxic industrial wastewater
For wastewaters containing nontoxic organics, process design criteria can be obtained from lab
studies.
To define the wastewater treatment problems, a preliminary analysis should be carried out:
Organic
streams
Biodegradable
volatile
Streams containing
heavy metals
Mineral
streams
Toxic and/or
nonbiodegradable
Source control
Figure 3.
Equalization
Neutralization
Oil/grease removal
Suspended solids
Biological treatment
Final disposal
(Eckenfelder, 2000)
Tier 1
Source treatment:
 Source reduction is any activity that reduces or eliminates the
generation of hazardous wastes at the source
 The fundamental goal is to enact changes in consumption, use
and waste generation patterns associated with products
Tier 1
Source treatment:
Source treatments involves different definitions of source reduction,
but the general consensus appears to be that include any inplant actions to reduce the quantity or the toxicity of the waste
at the source.
Examples include equipment modification, design and operations
changes of the process and products and substitution of raw
materials.
Tier 1
Figure 2. Laboratory studies for heavy
metals/volatile organics
start
Equalized
sample
Priority
pollutants
scan and
bioassay
Fed
batch
reactor
VOC/NH3
Air or steam
stripping
Heavy metals
Chemical
oxidation
reduction
Precipitation
When toxic and nontoxic organics and
Nondegradable/ toxic
Source
treatment
Degradable
inorganics are present, it is necessary
to evaluate the existence of heavy
metals or volatile organics.
Long-term
biodegradation
Granular
activated
carbon
Priority
pollutants
scan and Priority pollutants/toxic
bioassay
Powder
activated
carbon
Reverse
osmosis
Ion
exchange
TDS/inorganics
(Eckenfelder, 2000)
Tier 1
Figure 3. Treatment of toxic wastewater:
In-plant treatment
To discharge
recycle or
treatment
Reverse
osmosis
If the wastewater is
nonbiodegradable or
toxic, it should be
Ion
exchange
Polymeric
resins
Filtration
Granular
carbon
adsorption
Precipitation
Anaerobic
treatment
Oxidation
reduction
Wet air
oxidation
considered source
treatment or in-plant
modification.
Process
wastewater
(Eckenfelder, 2000)
Heavy
metals
Organic
chemicals
Chemical
oxidation
Air or steam
stripping
Volatile
organics
ammonia
Tier 1
Methods for suspended solids removal

Sedimentation is the more common technique in wastewater
treatment because it involves little mechanical equipment and it
is very stable to operate. However, there are some situations
where flotation is a better choice.

Flotation is a good technique for solids removal when the
density difference between water and the solids is marginal, or
the solids have a high fat or oil content.
Tier 1
Methods for suspended solids removal

Coagulation is employed for removal of waste materials in
suspended or colloidal form. Colloids are particles within the size
range of 1 nm to 0.1 nm, do not settle out on standing and can
not be removed by conventional physical treatment processes.

Precipitation. In the water treatment, the precipitation
process is used for softening (removal of the hardness caused by
calcium and magnesium) and removal of iron and manganese.
Tier 1
Sedimentation:
 Reduce solids by at least 50%, with proportional reduce of BOD.
 Addition of chemicals to assist settlement by coagulating particles
or chemical precipitation can be essential.
 Can have acceptable discharge standards with regular desludging
without a secondary treatment.
 Primary tanks are desludged at intervals of between 8 and 24
hours.
 Secondary settlement follows any form of biological aeration or
filtration to produce an effluent low in solids.
 Particularly demanding discharge consents may dictate a tertiary
treatment to remove solids and BOD by a further 50%.
Tier 1
Flotation:
Dissolved air flotation, which is a common technique. This technique
basically consists on injecting an aqueous stream containing
dissolved air into the wastewater . The dissolved air forms
bubbles when it comes out of solution and carries suspended
particles, which tend to concentrate at the bubble wastewater
interface, to the surface, where they form an emulsion.
Tier 1
Flotation:
General diagram for flotation methods:
Tier 1
Coagulation:
Paperboards wastes can be effectively coagulated with low dosages
of alum. Silica or polyelectrolyte will aid in the formation of a
rapid settling floc.
Wastes that contain emulsified oil can also be clarified by
coagulation.
For effective coagulation, alkalinity should first be added, . After
addition of alkali and coagulant, a rapid mixing is recommended.
Tier 1
Precipitation:
Chemical precipitation in wastewater treatment involves the
addition of chemicals to alter the physical and chemical state of
dissolved and suspended material and to facilitate their removal.
It is usually combined with coagulation, flocculation, separation.
Principle: Dissolved compounds, for instance heavy metal ions, are
brought into their insoluble hydroxides by pH increase through
dosing of lime or NaOH. Using coagulation, flocculation
techniques these small hydroxide nuclei become larger flocs for
separation. With proper precipitants these flocs also serve as
entrapment for other dissolved (organic) compounds; a form of
co-precipitation.
Tier 1
Heavy Metals Removal:
HEAVY METALS REMOVAL TECHNOLOGIES
Conventional precipitation
Hydroxide
Sulfide
carbonate
coprecipitation
Enhanced precipitation
Dimethyl thio carbamate
Diethyl thio carbamate
Trimercapto-s-triazine, trisodium salt
Other methods
Ion exchange
Adsorption
Recovery opportunities
Ion exchange
Membranes
Electrolytic techniques
Tier 1
The Biological Treatment
Influent
wastewater
When biological
treatment is
needed, there
are several
Physical and
chemical treatment
No
Biodegradable
Yes
High
High
strength
strength
Yes
Anaerobic
treatment
options:
Yes
Discharge
Yes
PACT
Inhibitory
No
Nondegradable
fraction
Polished
effluent
No
Discharge
Complete mix
system
No
Readily
degradable
Yes
Plug
flow system
Selector
system
No
Nitrogen
removal
required
No
Dispersed
growth system
Fixed
Growth system
Yes
Intermittent
process
Nitrification/
Denitrification
system
Yes
Polished
effluent
No
Discharge
(Eckenfelder, 2000)
Discharge
Tier 1
The biological treatment: typical operating
parameters and dimensions
Treatment
method
Mode of operation
Degree of
treatment
Land requirements
Lagoon
Intermittent or continuous
discharge; facultative or
anaerobic
Intermediate
Earth dug; 10-60 days’
retention
Activated
Completely mixed or facultative
lagoons
continuous basins
deep, 8-16
acres/(million gal/d)
floating surface
aerators or
subsurface diffusers
Solids separation in
lagoon; periodic
dewatering and sludge
removal
Excess sludge
dewatered and
disposed of
employ effluent recycle
Intermediate or
high, depending on
loading
225-1400 ft /(million
gal/d)
Plastic packing 2040 ft deep
Pretreatment before
POTW or activated
sludge plant
Multistage continuous
Intermediate or high
Plastic disks
Solids separation
required
Intermediate
Gas collection
required;
pretreatment before
POTW or activated
sludge plant
Complete; water
percolation into
groundwater and
runoff to stream
Aluminum irrigation
pipe and spray
nozzles; movable for
relocation
sludge recycle
Continuous application; may
Complete mix with recycle;
upflow or downflow filter,
fluidized bed; upflow sludge
blanket
Spray
Intermittent application of
irrigation
waste
(Eckenfelder, 2000)
Pier-mounted or
> 90% removal of
organics
sludge
Anaerobic
Odor control
frequently required
Diffused or
mechanical aerators;
clarifier for sludge
separation and
recycle
Completely mixed or plug flow;
RBC
Earth basin, 8-16 ft
Remarks
Earth or concrete
basin; 12p20 ft deep;
75000350000ft3/(million
gal/d)
Activated
Trickling filter
High in summer;
less in winter
Equipment
40-300 gal/(min.acre)
Solids separation
required; salt content
in waste limited
Tier 1
Advanced wastewater treatments
Advanced wastewater treatment is defined as the processes that remove
more pollutants from wastewater than the conventional treatments. This
term may be applied usually as tertiary treatment, but most of their
goals are to remove nitrogen, phosphorus, and suspended solids.
Advanced treatments include:

Chemical coagulation of wastewater

Granular media filters

Ultrafiltration

Nanofiltration

Wedge-wire screens

Microscreening

Diatomaceous earth filters
Tier 1
Volume and disposal reduction
Tier 1
Volume reduction
Volume reduction can be used to reduce treatment cost and to
reduce handling and disposal costs for residues remaining after
treatment. Volume reduction can be accomplished by using a
variety of methods:
 Reuse of treated wastewater and wastes
 Treatment modifications to reduce solid residues
 Segregated treatments to reduce hazardous waste mixtures
 Incineration to reduce waste volume and to render a hazardous
waste nonhazardous.
Tier 1
Reduction of waste production and disposal
volumes
 Simple dewatering: the sludge is discharged into a series of
tanks and allowed to settle. Top water can then be decanted.
This method reduce the volume of sludge for disposal.
 Composting: the material is mechanically turned at intervals,
force aerated and often contained in a building where heat
losses, odor and water content can be controlled.
Tier 1
Reduction of waste production and disposal
volumes
 Digestion: is the slow degeneration of the organic content of
sludge by obligate anaerobic bacteria to simpler compoundscarbon dioxide, water and anions (nitrate, sulphate, phosphate).
Digestion is one of the few sludge treatment processes in which a
significant reduction of pathogens is possible.
The digestor gas produced is 65-70% methane, 30-34% carbon
dioxide, and traces of sulphur compounds. The collected gas is
burnt in a boiler to keep the digestor warm and the excess put to
further heating or power generation purposes.
Tier 1
Reduction of waste production and disposal
volumes
 Incineration: its main advantages lie in the complete destruction
of organic compounds, the ash being inert and usually less than
25% of the original sludge volume.
Most incinerators are of the fluidized bed variety.
Tier 1
A waste management diagram…
Upgrade
operation
Waste
recycle
Redesign
process
Waste
treatment
Increasing Effectiveness
of waste management
Substitute
raw material
Waste
disposal
Tier 1
Multiple choice questions
Tier 1
Tier 1: Quiz
1. What is pollution?
a)
Pollution refers to harmful environmental contaminants and to the act
or process of polluting the environment.
b)
Any undesirable change in the characteristics of the air, water, soil or
food that can affect the health called pollution.
c)
Unwanted chemicals or other materials found in the environment.
Pollutants can harm human health, the environment, and property.
d)
All of the above.
Tier 1
Tier 1: Quiz
2. What is BOD?
a)
The quantity of oxygen required for the stabilization of the oxidizable
organic matter present over 7 days of incubation at 20 oF.
b)
An empirical test used for measuring waste, evaluating the
measure of the oxygen required by microbes to degrade a
sample of effluent.
c)
A test used to evaluate the quantity of oxygen present in the stream.
d)
The quantity of oxygen required to develop a biochemical test.
Tier 1
Tier 1: Quiz
3. Why is it important to reduce hazardous contaminants?
a)
Because if discharged, they can lead to water pollution.
b)
Because of its radioactive characteristics, its effects on human health
and development of cancer.
c)
Communicable diseases can be transmitted when in contact to them.
d)
Because of their dangerous characteristics for human health
and the environment.
Tier 1
Tier 1: Quiz
Tier 1