Section Ten Water Treatment

distribution network must maintain a minimum pressure of ___psi

20 (to avoid cavatation)

normal working pressure in the distribution system should be approx ___ psi to ___ psi and shall not be less than ___ psi

60 to 80 and 35

purpose of water distribution system

1.) supply systems users with water demand

2.) supply user with adequate pressure

used to increase energy to the water and represented by a distinct jump in the HGL in the direction of flow

pumping station

needed to equalize pump discharge near an efficient operation point in spite of varying demands, to provide supply during outage of individual components, to provide water for fire fighting, and to dampen out hydralic transient

distribution storage

closed conduit under pressure, valve regulate flow or pressure in distribution system.

distribution piping

four parts of determination of water demand

1.) design period selection

2.) estimation of population

3.) estimation of the unit water use

4.) estimation of the variability of the demand

max daily water demand is usually ___% of average daily water demand

180

max hourly water demand takes into account the daily cycle of water. _____% of max daily water demand

150

population growth is growing at constant increments per year, decade , or other unit of time. Growth is a straight line , slow growth

arithmetic growth method

rate of increase is proportional to population, project areas experiencing fast growth

geometric growth method

rate of growth is function of its population deficit compared to saturated population and growth reaches to sat limit, previously experienced high growth rates and are currently experiencing growth at a slower pace due to resources and space limitations

declining growth method

the increase is compounding at specific interval, during a period when the population growth rate remains constant

constant percentage growth rate

project exists for larger population (state, country), use this method for projecting the total population size for a small region

ratio and correlation growth

fire hydrants useage

1.) fire suppression

2.) flushing water mains

3.) utilities

4.) testing

5.) construction

device which the flow of fluid may be started stopped or regulated by a movable part that opens or obstructs passage

distribution system valves

isolation valves are placed into the system to isolate a portion of the system for repair, inspection, or maintenance. Isolation valves are normally installed at junction.

shutoff valve/ isolation valve

used to modulate flow or pressure by operating in a partly open position , creating head loss or pressure diff between US and DS locations

control valves

single direction valve that allows flow in one direction and stops reverse flow. cause significant pressure loss and a recommended for use only where reverse flow operation would be catastrophic

check valves

dead end in water distribution where water can become stagnant (culdesacs) opened to allow stagnant water to be removed from the system

blow offs

installed with pipelines to admit or vent air, at highest point in water mains, where air can accumulate provisions shall be made to remove the air

air release/ vacuum relief valves

size the tank, considered elevated or ground level storage tank to maintain pressure

design of storage tanks

functional design of water tank involves summing up the storage required for each purpose

equalization, fire protection, and emergencies other than fires

used to enable the source and pumping facilities to operate at a predetermined rate, depending on the preference of a particular utility

equalization storage

how do you calculate equilizatoin storage from a graph

shaded area under the curve above 100 % of average demand (or used mass diagram / rippl diagram)

if capacity of the water suppply is such that it can provide fire flow while still meeting max daily demand ___ (yes/no) fire storage is needed (large cities)

no

no formula exist for determining the amount of emergency storage . decision made on a judgement about prerceived vulnerability of the water supply

emergency storage

storrage voume = ___ + ___ +____

equilization + fire + emergency

pressure = ___x ___

gamma x height (rememebr to calcualte pressure in feet is psi x 2.31 feet )

equilization basin __ fluctuations in water flow and pollutant concentration (increase, eliminiates, minimize, delays)

eliminates, and minimizes

to design a water distribution system which should be used to calc design flow (max daily demand + fire demand, max hourly demand, average daily demand)

max daily demand + fire demand, max hourly demand

Water storage facilities for water distribution systems are req primarily for (provide fluctating demands of water ususage , increase operating convenience, provide large quantities of water to meet fire demands)

provide fluctating demands of water ususage , increase operating convenience, provide large quantities of water to meet fire demands

which type of valve should be used for filling an elevate tank if full system pressure would overflow the tank (pressure relief valve, altitude valve, air release valve, globe)

altitude valve

conditoins the water for removal of algae and other aquatic nuisances

chemical pretreatment

removes gravel, sand , silt and other gritty materials

presedimentation

removes algae, aquatic plants, small debris

microstraining

adds chemicals (coagulants, ph , adjusters ) to water

chemical feed and rapid mix

converts nonsettleable to settable particles

coagulation and flocculation

removes settable particles

sedimentation

removes particles of solid matter which can include bilogical contamination and turbidity

filtration

kills disease causing organisms

disinfection

removes radon and many organic chemicals such as pesticieds, solvents, and trihalomethanes

adsorption (gac)

removes volatile organic chemcials, radon, H2S, other dissolved gases, oxidezes iron and manganese

aeration/ air stripping

removes nearly all inorganic contaminants (except water)

reverse osmosis

removes some inorganic contaminants including hardness

ion exchange

removes some inorganic contamination

activated aluminar

removes some inorganic contaminants (iron, manganese, radium)

oxidation filtration

total hardness expressed in two ways

1.) (calcium, magnesium - sometimes iron) in mg/L caco3

2.) carbonate hardness + noncarbonated hardness

hardness that is hard is ___ to < 150 mg/L caco3

100

used to remove carbonate hardness (CH)

lime- used to increase pH

quick lime cemcial make up, also why is it used mostly

CaO, cheap

slack lime / hydrated lime checmical make up

Ca(OH)2

used to remove noncarbonate hardness (NCH)

soda ash -used to increase pH

soda ash chemical make up

Na2CO3

what else can be used instead of lime and soda ash, cost is higher but there is less sludge

caustic soda (sodium hydroxide, NaOH)

true or false step one in softening reactions is carbon dioxide removal which can increase the pH

true

softening consist of only what two elements

Calcuim and magnesium

order of difficulties to remove hardness (cch, cnh, mch, mnh)

CCH, MCH, CNH, MNH

to convert the mg/L of CaCO3 into its own mg/L instead of CaCO3

divide CaCO3 mg/L by / [(EW CaCO3 - 50)/ (EW of compound)]

for selective calcium removal, can be used on waters with Mg concentration less than 40 mg/L as CaCO3

single stage softening

for practicle solubility limit, excess lime added with a flash mixer to raise pH to 11 or higher to precipitate magnesium

two stage softening

portion of raw water is bypassed around the softening reaction tank and settling tank

split treatment softening

chemicals quickly and uniformily dispersed in wawtaer, essential for coagulation and softening, rxn form precipiates, precipiates my be brought into contact to create flocs

mixing/ rapid mixing

precipitaties from coagulation (2)

Al(OH)3 and Fe (OH2)

precipitaties from coagulation (2)

CaCO3 and Mg(OH)2 - in handbook for chemical softening

rapid mixing is the ________ as flocculation

opposite

rapid mixing needs _______

rapid, turbulent mixing

flocculation mixing needs _______

slow and gentile mixing

important design parameter for rapid mixers is the ___ needed to drive it

power

most important physical factor affecting coagulant efficiency (rapid mix or flocculation)

rapid mix

most important physical factor affecting particle removal efficiency (rapid mix or flocculation)

flocculation

if the velocity gradient is too low then colloisions are ___ and ____ floc formation

low and low

if the velocity gradient is too high then colloisions are ___ and ____ floc formation

rapid , low

sedimentation is characterized by particles that settle discretely at a constant settling velocity . They settle as individual particles and do not flocculate during settling

discrete settling - type one

typically occurs in conventional sedimentation basins following coagulation

flocculate settling - type 2

process by which suspended solid particle are separated from a liquid by passing the liquid through a porous medium (sand bed) capable of entrapping the suspended particles

filtration

filtration is very effective for removing flocs of ____, ______, other _______, and _______ (____,_____)

bacteria , algae, other microorganisms, and protoza (giardia and cryptrosportidium)

what is the driving force for filtration ? _____ generated across the filter bed

pressure gradient

what process _______ composes of filtration usually follows coagulation , flocculatoin, and sedimentation (covnetional or direct)

conventional

treatment scheme that omits flocculation and sedimentation steps prior to filtration (covnetional or direct)

direct

particles in water are trapped in the bed , but also upper layer becomes colonized by bacteria (need to clean often)

slow sand filter

developed to increase water flow through (increases pressure drop across them) by cleaning frequently via fluidization. not enough time between cleaning (backwashing) operations to upper layer . filtering action occurs throughout the entire filter bed. PRODUCES A BETTER UTILIZATION OF THE ENTIRE FILTER

rapid sand filter

out of rapid or slow sand filter what has better REMOVAL EFFICIENCY

slow sand

out of rapid or slow sand filter what has better UTILIZATION

rapid sand

most common parameter to characterize filter medium

uniformity coeff D60/D10 - in media filtration section handbook

when to use backwash for a filter (3)

1.) after 24-96 hr

2.) head loss is 8-10 feet

3.) turbidity reaches .20 NTU

four types of pressure driven membranes increasing in pressure

micro, ultra, nano, reverse

membrane that removes particles, sediment, algae, protozoa, bacteria

microfiltration (.1 micromm pores)

membrane that removes small colloids , viruses

ultrafiltration (.01 micromm pores)

membrane that removes dissolved organic matter, and hardness

nanofiltration (.001 micromm pores)

membrane that removes monovalent species na and cl

reverse osmosis (non porous)

rough estimation of the potential for colloidal fouling in nanofiltration

silt density index

the most suitable method for forecasting population of a rapidly growing city is the (arithmetical method, geometrical method, contstant % growth method, graphic method)

geometrical

the type of valve which is provided to control the flow of water in distribution system at street corners and where pipe lines intersect

control valve

what type of valve allows water to flow in one direction but prevents it in the reverse

check valve

a very high G value in flocculation basin will

may destroy flocs

in general which causes an increase in taste and odors issue when natural waters lack dissolved oxygen

anaerobic decomposition (no oxygen)

major disadvantage to lime soda process of water softening

huge amount of precipitate is formed which creates a disposal problem

permanent hardness of water is caused by (bicarbonates of calcium and magnesium, or chlorides and sulfates of calcium and magnesium)

chlorides and sulfates of calcium and magnesium

the reaction to form slacked lime (hydrated lime) is (endothermic, exothermic, a and b , none)

exothermic, produces heat