Wastewater Characteristics Physical Chemical

8/13/2019 Wastewater Characteristics Physical Chemical

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Lecture 2:

Wastewater CharacteristicsPhysical and Chemical


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Lecture 2 Outcomes

The students should be able to:

Recognize the various important Wastewater characteristics

Importance of each parameters

Impacts of each Wastewater parameters to Environment


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Whats in Wastewater? Contaminants

Definition of Contaminant:

constituents of air, water, or soil which render them

unsuitable for their intended use.

chemical or biological in nature

from natural forces, life processes of other species, our

own activities


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Principal contaminants of concern

Contaminants Impact

Suspended solids Materials that resis settling may remain suspended in wastewater.Suspended solids in wastewater

must be treated, or they will clog soil absorption systems or reduce the

effective-ness of disinfection systems.

Biodegradable organics If discharged to the environment, their biological stabilisation can

lead to the depletion of natural oxygen resources and development

of septic conditions.

Pathogens Communicable diseases can be transmitted.

Nutrients Discharged in large amount can lead the growth of undesirable

aquatic life and pollution of groundwater.

Priority pollutants Organic & inorganic compounds selected on the basis of their

known or suspected carcinogenicity, mutagenicity, teratogenicity or

high acute toxicity.

Refractory organics Organics that resist conventional methods of wastewater

treatment. E.g. surfactants, phenols & agriculture pesticides

Heavy metals Toxic to human organs, some can cause cancer, metabolism

failure, neurological problems.

Dissolved inorganics

Calcium, sodium & sulfate must be removed if the water is to bereused.


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Wastewater

Physical Characteristics


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Solids

Solids is one of the most common assessments of water quality.

Solids 3 categories

Dissolved

Truly in solution and pass through a filter.

Homogenous and of a single phase

Colloidal

Uniformly dispersed in solution

But form a solid phase that is distinct from the water phase.

Suspended Separate from the solution.

Some are settleable.

Method of analysis is given in APHA Method 2540.


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Solids

Three types of solids measured:

Suspended solids

Dissolved solids

Volatiles suspended solids

Filtration is used to separate suspended

and dissolved solids.

Commonly used filter paper is

Whatman glass fiber filter (1.58 m,

47 mm).


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Solids

Volatile solid

(VS) isassumed to be

organic.

Fixed solid (FS)

is assumed to

be inorganic.

Ratio of VS toFS gives an

approximate

amount of

organic matter

present in

wastewater.


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Chemical Constituents

OrganicInorganic

Oxygen demand

parameter

Oil and grease

Single organic

constituent

Total organic carbon

(TOC)

Aggregate organic

constituents

Nitrogen

Phosphorus

Gases

Trace metals

Alkalinity

Hardness


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Temperature

oxygen is less soluble at hightemperature

increase in biochemical reactions rate

at high temperature

DO (mg/L)

Temperature (C)

KT/K20

Temperature (C)

Temperature

Oxygen

demand

Oxygen

replenishment

Dissolved

oxygen


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Temperature

Other effects

change in fish species

mortality of fishes (thermal shock)

increase growth of water plants and wastewater fungus.

The best temperatures for wastewater treatment probably rangefrom 77 to 95 degrees Fahrenheit. In general, biologicaltreatment activity accelerates in warm temperatures and slows

in cool tempera-tures, but extreme hot or cold can stoptreatment processes altogether.

Therefore, some systems are less effective during cold weatherand some may not be appropriate for very cold climates.

Wastewater temperature also affects receiving waters. Hotwater, for example, which is a byproduct of many manufactur-

ing processes, can be a pollutant.

When discharged in large quantities, it can raise thetemperature of receiving streams locally and disrupt the naturalbalance of aquatic life.


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Taste & Odour

Caused by the presence of decomposed organic material and

volatile chemicals.

Drinking water should be practically free from colour,

tastes,and odour.


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pH

Intensity of acid or alkaline condition of a water

pH = - log [H+] = log 1/[H+]

The acidic or alkaline of wastewater affects both treatment andthe environ-ment.

Low pH indicates increasing acidic while a high pH indicatesincreasing alka-line nature (a pH of 7 is neutral). The pH ofwastewater needs to remain between 6 and 9 to protectorganisms.

Acids and other substances that alter pH can inactivatetreatment processes when they enter waste-water from

industrial or commercial sources.

-14 = log H+

H+= 1 x 10 -14


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pH

Toxicity of many compounds is affected by pH.

H2S ~ toxicity to fish increases as pH is lowered.

Solubility of heavy metals

Lower pH increases solubility of metals

Metals leaches from soil and sediment into surface water

Accumulate to fish gills or cause deformity ~ death


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Hardness

characteristic of water that causes it to require considerable

amounts of soap to produce a lather and that also producesscale in hot-water pipes, heaters, & boilers;

it is caused by divalent metallic cations such as calcium &magnesium.

Hardness is expressed in mg/l of equivalent calcium carbonate.

eg Ca = 200 mg/L ;

mol wt of CaCO3= 100 mg/L; mol wt of Ca = 40equiv. Wt of Ca = 40/2 = 20

equiv. Wt of CaCO3= 100/2 = 50

Ca = 200/20 *50 = 500 mg/L as CaCO3


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Alkalinity

Measure of the capacity of a water to neutralize acids or

capacity to accept protons;

In natural waters, the alkalinity is related to the bicarbonate,carbonate, and hydroxide concentration.

It is primarily caused by HCO3-, CO3

2-, and OH-alkalinity.

Total alkalinityis usually expressed in terms of equivalentcalcium carbonate in mg/l or meq/l.

Carbonate hardness is that part of the total hardness that ischemically equivalent to the bicarbonate and carbonatealkalinities.

Noncarbonate hardness (NCH) is equal to the total hardness

(TH) minus the carbonate hardness (CH).


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Conductivity

Determined by measuring its electrical resistance between two

electrodes and comparing this resistance with the resistanceof a standard solution of potassium chloride at 25C.Most waters, TDS (mg/l) = 0.55~0.7 x conductivity ( s/cm at25C)


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Iron and Manganese

Iron and manganese either dissolved or suspended in any

oxidation state.


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Sulfates

a major anion in natural waters, it can cause cathartic effect

upon humans and can form hard scales in boilers when it ispresent in excessive amounts.


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Fluorides

can cause dental cavities if too high; if too low, may be added

to water for prevention of cavities


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Nitrogen

essential to growth of prostita and plants; too little N will inhibit

biological treatment, too much can cause O2demand andexcessive algae growth in receiving stream

Total Kjeldahl Nitrogen = Organic N + Ammonia N

Ammonia N : toxic to fish

O2demandEutrophication

Nitrite N

Nitrate N : stimulates algal & aquatic growth

Blue babies syndrome (methemoglobenemia)

Phosphorusessential to growth of microorganisms; necessarynutrient for biological treatment; too much can cause

eutrophication


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Nitrogen and Phosphorus

From fertilizer, laundry detergent etc.

Excess nitrate in drinking water cancause BLUE BABY SYNDROME.

Excess nitrogen and phosphorus can

cause EUTROPHICATION or ALGAE

BLOOM.

Eutrophication is

apparent as

increased turbidity

in the northern partof the Caspian Sea,

imaged from orbit.
http://en.wikipedia.org/wiki/Image:Caspian_Sea_from_orbit.jpg


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Eutrophication

Source : www.bbc.co.uk

Note the bright green colour caused

by algae stimulated by the

experimental addition of nutrient for

the 26th consecutive year. The lake

in the background is unfertilized.


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Trace metals

Affect flora and fauna through bioaccumulation

Affect human organs

Arsenic mutagen and carcinogen

Cadmium carcinogen, accumulates in liver and kidney

Chromium carcinogen, corrosive and skin sensitizer

Lead brain and kidney damage

Mercury highly toxic, damage to nervous system

Selenium weakness, depression and red staining

Silver grey colouration of skin

But minute amount of heavy metal is essential for human health


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Single OrganicsPriority Pollutants

www.epa.gov/NE/npdes/permits/generic/prioritypollutants.pdf


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Single Organics

Priority pollutants - based on their known or suspected

carcinogenicity, mutagenicity, tetratogenicity or high acute toxicity.

Volatile organic carbons (VOC) - some are listed as priority

pollutants. In total they cause a great concern because:

in vapour state, they are much more mobile and more likely to bereleased to the environment

the presence of some VOC may pose significant public health

risk

they contribute to a general increase in reactive hydrocarbons in

the atmosphere, which lead to the formation of photochemicaloxidants.


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Single Organics

Disinfection byproducts- some are known or suspected potential

human carcinogens such as trihalomethanes (THMs), haloacticacids (HAAs), trichlorophenol and aldehydes.

Pesticides and Agricultural Chemicals- most are toxic to many

organisms.

Emerging Organic Compounds- veterinary and human antibiotics,

industrial and household wastewater products, human prescriptionand non-prescription drugs and sex and steroidal hormones.


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Typical Pollutants by Industry Sector

Reforming

Derivatives

Hydrocarbons Other pollutants

Methanol, Ammonia, Urea Methanol, heavy alcohols Ammonia, Urea

Hydrocarbons Other pollutants

MTBE Methanol, isobutene

Ethylene OxideEthylene Glycol, CO2, acetaldehyde,

hydrocarbons

Acetic Acid Formic acid, acetates, acetone

Acidic water, iodides,

rhodium

Vinyl Chloride Dichloroethane, hydrocarbons HCl, NaCl

Polyethylene Oil, TSS, catalysts

PVC Methanol, acetates Acidic water, TSS

Source: Degremont Water Treatment Handbook

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Wastewater Characteristics Physical Chemical