Water/Wastewater Exam 1

Molarity formula

weight concentration/molecular weight

Normality formula

weight concentration/equivalent weight

Equivalent weight

molar weight/ equivalents

what counts as an equivalent

1. # change on the species

2. # H+ or OH- released in acid-base rxn

3. # electrons gained for lost in oxidation-reduction rxn

How to find the concentration of something “as CaCO3”

Normality of species * equivalent weight of CaCO3 (50 mg/meq)

Principle of Electroneutrality 

all waters are electrically neutral, sum of equivalents cations = sum equivalents anions 

What does a bar chart analysis do?

Uses electroneutrality to determine if the chemical analysis of water is correct (cations and anions not equal = something wrong)

How to do bar chart analysis

calculate the normality (meq/L) of all cations, calculate the normality (meq/L) of all anions, check for if the answers need to be in terms of CaCO3, if so divide the given concentration/50 mg/meq CaCO3

add up all of the cations, add up all of the anions, check % error

pH and pOH formula

pH= -log [H], pOH=-log[OH]

equilibrium constant formula

K = [product]/[reactants]

T/F: for solubility constant (Ksp) all solids are equal to 1

T (solids =1)

What is a practical treatment technology based on solubility constant?

Water softening to remove calcium ions, precipitating heavy metals from water

How does a reaction move when either products or reactants are increased?

Products increased, reaction moves back towards making reactants

Reactants increased, reaction moves back towards making products 

T/F: All surface water is in equilibrium with pressure, CO2 and O2 in the atmosphere

T (water in equilibrium)

Organic vs Inorganic compounds

Organic has greater or equal to 1 carbon-hydrogen bond

Physical characteristics of water quality

Color, taste and odor, temperature, turbidity 

Chemical Characteristics of water quality

Chloride, fluoride, iron, lead (corrosive), manganese, sodium, sulfate, zinc, toxic inorganic substances

Water age

How long it takes water to go from WTP to distribution 

What is considered an “indicator” test of pathogens in water

Total Coliform Test

T/F: test for water quality have to go all the way through the pipe network into consumer’s houses

T, pipes in house need to not be corrosive

Take aways from Safe Water Drinking Act

Focus on human health concerns, DON’T conduct human studies, water must be safe to most susceptible populations 

Surface water vs ground water abundance vs usages

Much more surface water available, but most water used is groundwater

How does DPH and EPA determine contaminates

Contaminate Canidate List (CLL),

Risk assessment: hazard identification, animal studies, exposure assessment

Risk Characterization: goal for concentrations

Risk Management: determine existing background levels, regulatory options, byproduct risks, cost, and best available technology

T/F Maximum contaminant level goal is legally enforceable 

F (contaminant level is)

T/F maximum contaminant level is legally enforceable?

T (yes)

Which contaminants are measured at consumer premise

Copper and Lead

T/F secondary maximum contaminant levels are legally enforceable

F (aesthetics)

what are DBPs

Disinfection Byproducts

DPBs examples

chlorite from chlorine dioxide, bromate and bromide from ozone

Who has to meet all of the Maximum contaminant level regulations (MCL)

60,000 community water systems, non-community non-transient systems (factories, schools)

Who has to meet acute regulations of the Maximum contaminant level (MCL)

non-community, transient systems (parks, restaurants, campgrounds)

Issue of Primacy

States can take over their own regulatory control, but their regulations have to be at or above the regulations set by the EPA (CA, NY)

What uses the majority of water in the US

Cooling power plants, irrigation for agricultural use

T/F water is treated to drinking level standards when a very small % is actually used for drinking 

T (other uses: flushing, showers, washing machines, lawns)

T/F: water usage is increasing in the US

F (going down)

Why do water rates decrease for very large usage

to promote industry and economic development

Types of mixing for water treatment

rapid mixing tanks, inline blender for chemical mixing, mechanical flocculators (slow mixing )(horizontal and vertical), baddled flocculation chamber

Types of sedimentation basins

Gravity sedimentation basin, gravity sedimentation with solids removal, dissolved air flotation 

Who would use a package water treatment plant

very small systems

Other treatment options

solids contactor unit for chemical softening, membrane filtration racks, ozone generator

How is water stored after treatment

Clearwell storage bins, or regular containers

Why are cysts hard to remove from water 

Cysts are an “active” cell until a threat (treatment), go inactive during the threat and reactivate when threat is over 

what removal technology removes the smallest particles 

reverse osmosis 

Typical steps for water treatment plant

Coagulation with rapid mix, flocculation, settling basin, filter, disinfection

What is direct filtration

treatment skips flocculation and settling basin, goes from rapid mix directly to filter

Zeta potential

measure of charge on a particle

Physics of coagulation

compression of diffuse layer, charge neutralization, interparticle bridging, enmeshment of precipitate (sweep floc)

Most used coagulant

aluminum sulfate

Alkalinity equation

Alkalinity = [HCO3-] + 2[CO3 -2]

*if pH is greater than 9.5 ignore the CO3 -2

how is alkalinity expressed

in terms of CaCO3

Steps to find alkalinity

Convert CO3, HCO, H, and OH to mg/L as CaCO3

use pH to find [H] and Kw to find [OH]

multiply given concentration by (CaCO3 ew)/ (species ew)

add all species together 

How to find alkalinity with the addition of alum 

Calculate moles of alum

Calculate moles of HCO3 consumed from chemical reaction equation based on the stoichiometric coefficent in front of HCO3 * (alum moles)

convert to mg/L

Rule to estimate the amount of alkalinity consumed by alum

1 mg/L alum destroys 0.5 mg/L of alkalinity as CaCO3

multiply alum dose by 0.5 mg/L  as CaCO3/ mg/L alum 

subtract that number from the natural alkalinity 

Jar test procedure 

One variable is held constant ( alum dose, pH) and the turbidity is measures for varying the other variable

What is commonly used the adjust the pH into an acceptable range when alkalinity is not sufficennt 

quick lime/ calcium oxide

soda ash/ sodium carbonate 

What is G in the flocculation process

velocity gradient, higher value is more violent mixing, dependent on temperature

Detention time

T = V/Q

hydraulic residence time/residence time

What kind of mix basin is best for charge neutralization

inline blender mixer (high G values, very short dentention time)

What kind of coagulation does not require as intense mixing

sweep floc (lower G values, longer detention time)

What values are important in Table 6-4 for in line blender data

C = diameter 

D = length 

What are the regulations for G and T for in line blender

G = 3000 - 5000 s-1

t = 0.5 s

what assumption is always made about water power

80% efficient (multiply calculated power by 0.8)

For mechanical mixing which impeller style has more efficient mixing

radial-flow turbine impeller

G and t values for flocculation

G = 10-100 s-1

t= 30-50 minutes 

Flocculation basin design

usually 3 compartments in series

G values decrease from one basin to the next 

each section has a shaft with typically 3 blades attached that rotate at three different diameters 

T/F: power for flocculation is a function of drag force

T (force acting on particle as it moves through water)

Sedimentation type I

“ideal” settling, discrete particle settling, particles do not flocculate and settle alone, not used in typical process, uses Stokes law, reynolds number, and drag coefficient

What is the required reynolds number for terminal settling velocity

<2

On a graph of settling velocity where is the stokes law reigon

the linear section

what kind of basins are used with ideal settling

horizontal flow clarifying, circular upflow clarifier

How to determine the particle removal for upflow clarifier

if settling velocity (vs) > overflow rate (vo) 100% removal

if settling velocity (vs) < overflow rate (vo) 0% removal

settling velocity relationship with detention time

vs = h/to
settling velocity must be equal to the depth of the tank/ time to reach the bottom (detention time)

How to determine the particle removal for horizontal flow settling tank

P=(vs/vo) x 100%

Overflow rate

the rate water overflows the top of the tank into the weirs (the rate in which particles do not get settled)

Type II sedimentation

particles that flocculate during sedimentation

no adequate mathematical relationship to describe type II, stokes cannot be used bc flocculation particles constantly changing shape and size

Trends for tall and skinny vs wide and flat settling basins

same removal settling velocity? no

larger overflow rate? tall and skinny 

optimal design? wide and flat

Plate and tube settlers purpose

shortens the distance particles need to settle with a ramped design

relationship between density and time to settle

higher density requires less time