Conventional System

8/11/2019 Conventional System

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Conventional System

Conventional treatment consists of the following unit processes: coagulation, flocculation,

clarification, and filtration, and is typically followed by disinfection at full-scale. Figure 1

describes conventional treatment. Conventional treatment is often preceded by pre-

sedimentation, may be accompanied by powdered activated carbon (PAC) addition, utilize

granular activated carbon (GAC) as a filter media, and in some cases be followed by GAC

adsorption. Conventional treatment is often preceded by pre-oxidation, or oxidation takes

place concurrently. Oxidants common to conventional treatment are chlorine, chloramine,

chlorine dioxide or permanganate. Occasionally membrane processes, either membrane

filtration or ultrafiltration, accompany conventional treatment.

In coagulation, a positively charged coagulant (usually an aluminum or iron salt) is added to

raw water and mixed in the rapid mix chamber. The coagulant alters or destabilizes

negatively charged particulate, dissolved, and colloidal contaminants. Coagulant aid

polymers and/or acid may also be added to enhance the coagulation process. Turbidity and

total organic carbon (TOC) are measures of particulates and dissolved organics impacting

coagulation.


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During flocculation, gentle mixing accelerates the rate of particle collision, and the

destabilized particles are further aggregated and enmeshed into larger precipitates.

Flocculation is affected by several parameters, including the mixing speed, mixing intensity

(G), and mixing time. The product of the mixing intensity and mixing time (Gt) is frequently

used to describe the flocculation process.

There are two primary destabilization mechanisms in drinking water treatment: charge

neutralization and sweep flocculation. The mechanism is dependent upon the coagulant

dose. Most drinking water treatment plants operate using sweep flocculation, which

requires a higher coagulant dose, rather than charge neutralization. In charge neutralization,

the positively charged metal coagulant is attracted to the negatively charged colloids via

electrostatic interaction. Flocs start to form during the neutralization step as particle

collisions occur. Adding excess coagulant beyond charge-neutralization results in the

formation of metal coagulant precipitates. These metal hydroxide compounds (e.g., Al(OH)3

or Fe(OH)3) are heavy, sticky and larger in particle size. Sweep flocculation occurs when

colloidal contaminants are entrained or swept down by the precipitates as they settle in the

suspension.

The optimal pH range for coagulation is 6 to 7 when using alum and 5.5 to 6.5 when using

iron. For high alkalinity water, excessive amounts of coagulant may be needed to lower the

pH to the optimal pH range. In these cases, it may be beneficial to use acid in addition to the

coagulant to reduce the amount of coagulant needed and effectively lower chemical costs.

Enhanced coagulation is now widely practiced for removing disinfection byproduct (DBP)

precursors, and it also removes inorganics, particulates, and color causing compounds.

Removing these contaminants using coagulation depends on the amount of coagulant

added. It is important to determine the optimal dose for coagulation; insufficient doses will

not effectively destabilize the particles and adding excessive doses can cause detrimental

effects such as re-stabilization, excessive sludge production, or corrosion.


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Water quality parameters such as pH, temperature, and alkalinity may dictate effectiveness

of the coagulation-filtration process. The pH during coagulation has a profound influence on

the effectiveness during the destabilization process. The pH controls both the speciation of

the coagulant as well as its solubility, and it also affects the speciation of the contaminants.

For high alkalinity water, an excessive amount of coagulant may be required to lower the pH

to the optimal pH ranges (alum pH 6 to 7, iron 5.5 to 6.5). Temperature also impacts the

coagulation process because it affects the viscosity of the water. Thus lower temperature

waters can decrease the hydrolysis and precipitation kinetics. For some treatment

objectives, other parameters like iron, manganese or sulfate impact coagulation. Some of

the alternative coagulants such as polyaluminum chloride (PACl) can be advantageous over

the traditional coagulants in low temperature conditions as these coagulants are already

hydrolyzed, and therefore temperature tends to have less effect on the coagulation process.

Following flocculation, agglomerated particles enter the clarification unit where they are

removed by sedimentation by gravity or are floated and skimmed from the surface of the

clarification unit. In the sedimentation processes, the majority of the solids are removed by

gravitational settling; particles that do not settle and are still suspended are removed during

the filtration process. Sedimentation is generally accomplished in rectangular or circular

basins and is often enhanced by the addition of inclined plates or tubes which increase


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effectiveness of the process by effectively increasing the surface area of the sedimentation

basin. Dissolved air flotation (DAF) is another clarification process in which air is diffused as

fine bubbles and suspended particles are floated to the surface and removed by skimming.

Generally, DAF is most effective for small, fine, low-density particles like algae and may not

be effective is all instances. Like conventional sedimentation, solids not removed by DAF are

removed during filtration.

Two parameters frequently used to describe the clarification process are the overflow rate

and the detention time. The overflow rate is the process loading rate and is usually

expressed in gpm/sf or gpd/sf. Overflow rates for conventional sedimentation generally

range from 0.3 to 1 gpm/sf (500 to 1500 gpd/sf). Overflow rates for other processes can

vary significantly. There are proprietary sand-ballasted clarification systems that have been

demonstrated to operate effectively at overflow rates as high as 20 gpm/sf. Typical

detention times range from 1 to 2 hours, although many states require up to 4 hours for

full-scale surface water treatment.

The most commonly used filter type in the conventional treatment process is a dual-media

filter comprised of anthracite and sand; however, mono-media (sand), multi-media (garnet,

anthracite, and sand), and other media configurations, including the use of granular

activated carbon, are also used in drinking water treatment. During filtration, the majority

of suspended particles are removed in the top portion of the filter media. Filters are

backwashed to dislodge and remove particles trapped within the filter bed, to reduce head

loss (pressure build up), and to keep the filter media clean.

The filter loading rate is a measure of the filter production per unit area and is typically

expressed in gpm/sf. Typical filter loading rates range from 2 to 4 gpm/sf; however, higher

filter loading rates, 4 to 6 gpm/sf, are becoming more common at full-scale. This can be a

critical parameter because it determines the water velocity through the filter bed and can

impact the depth to which particles pass through the media. The filter run time describes


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the length of time between filter backwashes during which a filter is in production mode.

The filter run time is not only an indicator of the effectiveness of prior treatment (i.e., the

ability of the coagulation and clarification steps to remove suspended solids), but also plays

a role in the effectiveness of the filter itself. Filter performance, particularly with regard to

particulate contaminants, is often poorest immediately following a backwash. As the filter

run time increases and the concentration of solids in the media increases, the filtration

process often performs better with regard to particulate contaminant removal.

Residuals generated by the conventional treatment process include coagulation solids

(sludge) and spent backwash. Spent backwash is often returned to the treatment process as

a means to minimize water loss. Sludge may also be recycled to minimize coagulant and

coagulant aid doses and improve process performance. Process solids (i.e., coagulation

sludge and filtered solids) will contain elevated concentrations of contaminants removed

during the treatment process. Depending on the source water concentration of a particular

contaminant and any disposal limitations, it may be necessary evaluate the disposal of

process solids with respect to state and local hazardous waste regulations.


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Membrane Filtration

Membranes have been used in water and wastewater applications since the 1960's.

However, initially membrane processes were felt to be too expensive for this field, and were

only applied in niche applications or special circumstances. This changed during the 1990's

due to the emergence of several drivers, including legislation to achieve improved

treatment standards, and resource scarcity, which created the need to use membranes on

saline or wastewater sources. The rapid uptake of membranes since 2000 has led to a

dramatic fall in costs, to the extent that membranes now often compete with conventional

processes, while achieving much better quality standards.

There are two classes of membrane process used in the water and wastewater field. The

first category includes reverse osmosis (RO) and nanofiltration (NF). These membranes have

a dense non porous separating layer cast onto a porous support, and are used for the

removal of dissolved substances. The second category is membrane filtration, in which a

micro-porous separating layer provides a barrier to the finest particles present in the feed

source but allows dissolved components to pass through. Membrane filtration is often used

as a treatment process in its own right, but may also be used as pre-treatment to an RO

stage.

An early application was in the use of RO and membrane filtration for industrial water

treatment, either for general process water use or for ultrapure water production. This has

now been surpassed in importance by the use of membrane filtration in drinking water

treatment to remove turbidity and provide a disinfection barrier, particularly to parasitic

microorganisms such as cryptosporidium and giardia.

One of the longest established uses for membranes in water treatment is in the use of RO

for desalinating seawater. Even in the Middle East where energy is cheap, RO has recently

taken over from distillation processes as the preferred technology for most duties. A recent

new application of membranes in desalination is in the use of membrane filtration as a pre-

treatment to RO, and this area has grown at a dramatic rate since 2005.


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Last but not least, membranes are now being used in the newly emerging application of

wastewater reuse, the fastest growing and potentially most promising membrane

application in the water industry. In fact, membranes have been an enabling technology for

this application, since without membranes, wastewater treatment to a standard

guaranteeing quality and security would be too difficult and costly.

RO is required to ensure that dissolved organics, and sometimes salts, are removed to a

sufficient extent. Membrane filtration is needed as a pre-treatment to the RO, and this

application will form the subject this paper. Without membrane pre-treatment, stable

operation of the RO has been found to be unachievable, so the advent of the membrane

filtration boom for drinking water in the late 1990's enabled the commercial realization of

this application.

Technology

There are two types of membrane filtration technology for water and wastewater

treatment, namely ultrafiltration (UF) and microfiltration (MF). UF has pores of 0.010.02

m, while MF for water treatment has pores of 0.04 0.10 m. In wastewater applications,

coarser MF pore sizes of 0.2 and 0.4 m can be used, but the finer MF membranes for water

duties are also suitable. The separation spectrum illustrated in Figure 1 shows the particle

size that the different filtration technologies are designed to address, with some examples

of common challenges.


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The figure shows that membrane filtration is two to three orders of magnitude coarser than

RO. MF removes common particles found in water including bacteria and other microbial

organisms, while UF removes viruses in addition, thereby providing a physical disinfection

barrier. For RO pre-treatment of wastewater, membrane filtration is normally used in

combination with coagulation to control fouling, ensure operational stability and improve

removals of dissolved organics.

Resources

Water resources are under pressure from increasing population, especially in arid regions,

and greater use of water per capita due to economic development. Some attempts have

been made to reduce water usage through conservation programmes, but so far this has

just had the effect of containing growth.

Not only is demand rising, but traditional resources will become less available in the future.

Water supply is currently obtained mainly from freshwater resources, as illustrated by Table


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1 below [1]. Surface water is the most important water resource, but groundwater is also a

significant contributor accounting for 36% of total. New resources such as desalination and

wastewater reuse accounted for just 0.5% of the total in 2005. However, the balance of

resource supply will undergo a fundamental change in the coming decades. Groundwater is

effectively a non-renewable resource. Millennia are required for groundwater resources to

accumulate, but these resources can be depleted in just a few years.

Combined with the inexorable reduction of groundwater availability, the quality of

groundwater is under threat due to a variety of factors, such as saline intrusion near the

coast as the water table declines due to over abstraction. Also groundwaters are becoming

contaminated by industrial and agricultural residuals caused by increasing fertiliser and

pesticide since the Second World War. The effect of this activity has taken some decades to

become established, but since the early 1990's, treatment processes have been required in

the developed world for groundwater sources to control contaminant levels.

In the long term, new sources such as desalination and wastewater reuse will have to

replace groundwater, and the beginning of this trend has already started to occur. Growth

of novel resources significantly above the underlying growth rate of water use is therefore

assured for the foreseeable future. On top of this, the growth rates for membrane filtration

processes will be even greater, as membranes become established as the dominant

technical solution. Thus currently desalination and wastewater reuse markets have annual

growth rates of 8% and 14% respectively, but the use of membrane filtration in these

applications is growing at 17% or more [1,2].


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Currently, 10% of water abstracted is collected as wastewater, and just under half of this is

treated prior to disposal [1]. However, only a small fraction of treatment is to a reuse

standard. Wastewater is therefore available as an abundant resource for treatment to a

reuse standard. Most reuse at the moment is destined for industry and agriculture, with just

11% for municipal use. However, municipal applications are undergoing dramatic growth,

which will be illustrated by the case study at the end of the paper.

Energy Use

Unfortunately, these novel water sources require much more energy for treatment than

traditional freshwater resources, and this will become a major consideration for the future.

In particular, desalination is very energy intensive, and this provides an important

motivation for developing wastewater reuse as the default option where resource

constraints occur, leaving desalination for situations where there is no other choice. Energy

efficiency in water supply is now recognised as a major driver for the selection of alternative

resources.


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Ion Exchange

The ion exchange technology is used for different water treatment applications:

Softening (removal of hardness)

De-alkalisation (removal of bicarbonate)

Decationisation (removal of all cations)

Demineralisation (removal of all ions)

Mixed bed polishing

Nitrate removal

Selective removal of various contaminants

Softening

Natural water contains calcium and magnesium ions (see water analysis) which form salts

that are not very soluble. These cations, together with the less common and even less

soluble strontium and barium cations, are called together hardness ions. When the water

evaporates even a little, these cations precipitate. This is what you see when you let water

evaporate in a boiling kettle on the kitchen stove.

Hard water also forms scale in water pipes and in boilers, both domestic and industrial. It

may create cloudiness in beer and soft drinks. Calcium salts deposit on the glasses in your

dishwasher if the city water is hard and you have forgotten to add salt.

Strongly acidic cation exchange resins (SAC, see resin types) used in the sodium form

remove these hardness cations from water. Softening units, when loaded with these

cations, are then regenerated with sodium chloride (NaCl, table salt).


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Reactions

Here the example of calcium:

2 R-Na + Ca++ ---> R2-Ca + 2 Na+

R represents the resin, which is initially in the sodium form. The reaction for magnesium is

identical.

The above reaction is an equilibrium. It can be reversed by increasing the sodium

concentration on the right side. This is done with NaCl, and the regeneration reaction is:

R2-Ca + 2 Na+ ---> 2 R-Na + Ca++

What happens to the water

Raw water softened water

The water salinity is unchanged, only the hardness has been replaced by sodium. A small

residual hardness is still there, its value depending on regeneration conditions.

Uses of softeners:

Treatment of water for low pressure boilers

In Europe, most dishwashers have a softening cartridge at the bottom of the

machine


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Breweries and soft drink factories treat the water for their products with food grade

resins

Softening the water does not reduce its salinity: it merely removes the hardness ions and

replaces them with sodium, the salts of which have a much higher solubility, so they don't

form scale or deposits.

De-alkalisation

This particular process uses a weakly acidic cation resin. This resin type is capable of

removing hardness from water when it also contains alkalinity. After treatment, the water

contains carbon dioxide, that can be eliminated with adegasifier tower.The cation resin is

very efficiently regenerated with an acid, usually hydrochloric acid.

Reactions

Here the example of calcium:

2 R-H + Ca++(HCO3)2 R2-Ca + 2 H++ 2 HCO3

and the hydrogen cations combine with the birarbonate anions to produce carbon dioxide

and water:

H++ HCO3

CO2+ H2O


Raw water

WAC (H)

Decarbonated water
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Recombination of hydrogen and bicarbonate and removal of carbon dioxide with the

degasifier:

Decarbonated water

DEG

Degassed water

The salinity has decreased. Temporary hardness is gone

De-alkalisation is used:

In breweries

In household drinking water filters

For low pressure boilers

As a first step before the SAC exchange in demineralisation

De-alkalisation reduces the salinity of water, by removing hardness cations and bicarbonate

anions.

Decationisation

The removal of all cations is seldom practiced, except as a first stage of the demineralisation

process, or sometimes in condensate polishing where the decationiser precedes a mixed

bed unit. A strongly acidic cation exchange resin (SAC) is used in the H+form.

Reactions

Here the example of sodium, but all cations react in the same way:

R-H + Na+

R-Na + H+


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The equilibrium reaction is reversed for regeneration by increasing the hydrogen

concentration on the right side. This is done with a strong acid, HCl or H2SO4:

R-Na + H+ R-H + Na

+


Raw water

SAC (H)

Decationised water

DEG

Decat + degassed

water

In the second step, adegasifieris used again to remove the carbon dioxide formed by

combining the bicarbonate anions and the released hydrogen cation. The water salinity isreduced, and the water is now acidic. A small sodium leakage is shown.

Demineralisation

For many applications, all ions in the water must be removed. In particular, when water is

heated to produce steam, any impurity can precipitate and cause damage. As there are

cations and anions in the water, we must use two different types of resins: a cation

exchanger and an anion exchanger. This combined arrangement produces pure water, as

presented in thegeneral introduction. Demineralisation is also called deionisation. The

cation resin is used in the hydrogen form (H+) and the anion resin in the hydroxyl form (OH

), so that the cation resin must be regenerated with an acid and the anion resin with an

alkali.
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Adegasifier is used to remove the carbon dioxide created after cation exchange when the

water contains a significant concentration of bicarbonate.

The cation resin is usually located before the anion resin: otherwise if the water contains

any hardness, it would precipitate in the alkaline environment created by the OH

form

anion resin as Ca(OH)2or CaCO3, which have low solubility.

Layout SAC(DEG)SBA

Let us first consider a simple demineralisation system comprising a strong acid cation

exchange resin in the H+form, a degasifier (optional) and a strong base anion exchange resin

in the OH

form. The first step is decationisation as shown above:

RSAC-H + Na+ RSAC-Na + H

+

With calcium insead of sodium (also valid for magnesium and other divalent cations):

2 RSAC-H + Ca++

(RSAC)2-Ca + 2 H+

In the second step, all anions are removed with the strong base resin:

RSBA-OH + Cl

RSBA-Cl + OH

The weak acids created after cation exchange, which are carbonic acid and silicic acid

(H2CO3and H2SiO3) are removed in the same way:

RSBA-OH + HCO3

RSBA-HCO3

+ OH

And finally, the H+ions created in the first step react with the OH

ions of the second step to

produce new molecules of water. This reaction is irreversible:

H++ OH

H2O

1 & 2: Cation exchange beginning with the removal of temporary hardness (WAC, as in

dealkalisation) followed by the removal of all remaining cations (SAC):
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Raw water

WAC (H)

Decarbonated water

SAC (H)

Decationised water

3 & 4: Anion exchange begining after degassing with the removal of strong acids (WBA)

followed by the removal of weak acids (SBA):

Decat + degassed

water

WBA (FB)

Partially

demineralised

SBA (OH)

Demineralised water

A full demineralisation line is shown below, with a cation exchange column (WAC/SAC),

adegasifier,an anion exchange column (WBA/SBA), and a polishing mixed bed unit. The use

of a weakly acidic resin and the degasifier column are conditioned by the presence of

hardness and alkalinity in the feed water, as explained in the previous sections.
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A demineralisation line (click to enlarge)

Regeneration

Regeneration is done inthoroughfare,which means that the regenerant first goes through

the strong resin, which requires an excessof regenerant, and the regenerant not consumed

by the strong resin is usually sufficient to regenerate the weak resin without additional

dosage.

The cation resins are regenerated with a strong acid, preferably HCl, because H2SO4can

precipitatecalcium.

The anion resins are regenerated with caustic soda.

Ads by surf and keep

Regeneration of the demineralisation line (click to enlarge)

The quality obtained is the same as in the simple SAC-SBA layout, but because the weak

resins are practicallly regenerated "free of charge", the regenerant consumption is

considerably lower. Additionally, the weak resins have a higher operating capacity than the

strong resins, so the total volume of ion exchange resins is reduced.

Uses

Examples of demineralisation:
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Practically nothing is left:

Demineralised water

SAC (H) + SBA

(OH)

Nothing is left

Mixed bed polishing produces a water with less than 0.1 S/cm conductivity. With

sophisticated design and appropriate resins, the conductivity of pure water (0.055 S/cm)

can be achieved. Residual silica values can be as low as 1 g/L.

The pH valueshould not be used as a process control, as pH meters are unable to operate at

1 S/cm conductivity or below.

Uses

Treatment of water pre-demineralised with ion exchange resins

Polishing of reverse osmosis permeate

Polishing of sea water distillate

Treatment ofturbine condensate in power stations

Treatment of process condensate in various industries

Production of ultra-pure water for the semiconductors industry

Service de-ionisation(with off-site regenerated columns)
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Nitrate removal

Nitrate can be removed selectively from drinking water using strong base anion resins in the

chloride cycle, i.e. regenerated with a NaCl brine. The reaction is:

RSBA-Cl + NO3

RSBA-NO3+ Cl


Raw water

SBA (Cl)

Denitrated water

Conventional SBA resins can be used, but they also remove sulphate from water. See

theselectivity table. Depending on the resin type, some (selective resins) or all (non-

selective) sulphate is removed. Bicarbonate is only removed partially at the beginning of the

service run.

Uses

Mainly municipal water treatment
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Selective removal of various other contaminants

Selective removal of metals and other contaminants is mainly used for drinking water and

for waste. Many of these applications require special resins: chelating resin making stable

metal complexes, for instance.

Examples

Removal of boron (boric acid) from drinking water

Removal of nitrate from drinking water (shownabove)

Removal of perchlorate from drinking water

Removal of heavy metals from waste: Cd, Cr, Fe, Hg, Ni, Pb, Zn

In many of these applications, a residual concentration in the g/L range is possible.

Some contaminants are difficult to remove with ion exchange, due to a poor selectivity of

the resins. Examples: As, F, Li. See theperiodic systemof the elements with some ion

exchange data.
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Air Stripping

Air stripping is a full-scale technology in which volatile organics are partitioned from ground water

by greatly increasing the surface area of the contaminated water exposed to air. Types of aeration

methods include packed towers, diffused aeration, tray aeration, and spray aeration.

Air stripping involves the mass transfer of volatile contaminants from water to air. For ground water

remediation, this process is typically conducted in a packed tower or an aeration tank. The typical

packed tower air stripper includes a spray nozzle at the top of the tower to distribute contaminated

water over the packing in the column, a fan to force air countercurrent to the water flow, and a

sump at the bottom of the tower to collect decontaminated water. Auxiliary equipment that can be

added to the basic air stripper includes an air heater to improve removal efficiencies; automated

control systems with sump level switches and safety features, such as differential pressure monitors,

high sump level switches, and explosion-proof components; and air emission control and treatment

systems, such as activated carbon units, catalytic oxidizers, or thermal oxidizers. Packed tower air

strippers are installed either as permanent installations on concrete pads or on a skid or a trailer.


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Aeration tanks strip volatile compounds by bubbling air into a tank through which contaminated

water flows. A forced air blower and a distribution manifold are designed to ensure air-water

contact without the need for any packing materials. The baffles and multiple units ensure adequate

residence time for stripping to occur. Aeration tanks are typically sold as continuously operated skid-

mounted units. The advantages offered by aeration tanks are considerably lower profiles (less than 2

meters or 6 feet high) than packed towers (5 to 12 meters or 15 to 40 feet high) where height may

be a problem, and the ability to modify performance or adapt to changing feed composition by

adding or removing trays or chambers. The discharge air from aeration tanks can be treated using

the same technology as for packed tower air discharge treatment.

Modifying packing configurations greatly increase removal efficiency. A recent innovation is the so-

called low-profile air stripper that is offered by several commercial vendors. This unit packs a

number of trays in a very small chamber to maximize air-water contact while minimizing space.

Because of the significant vertical and horizontal space savings, these units are increasingly being

used for ground water treatment.

Air strippers can be operated continuously or in a batch mode where the air stripper is intermittently

fed from a collection tank. The batch mode ensures consistent air stripper performance and greater

energy efficiency than continuously operated units because mixing in the storage tanks eliminates

any inconsistencies in feed water composition.

The eventual duration of cleanup using an air stripping system may be tens of years and depends on

the capture of the entire plume from the ground water


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With two treatment plants for drinking water and one treatment plant for recycled water, we can

process up to 61 million gallons per day. Our pipeline system pumping units can deliver up to 38,000

gallons per minute. Water may be piped directly to you or into a tank until needed. Because of

Marin's hilly terrain, about 90 percent of the water must be pumped at least once before it reaches

the tap. Some water is pumped up to six times.

Our pipes range in size from the 3/4-inch pipe that connects your water meter to our main to the 42-

inch transmission pipes that carry source water to the treatment plants. The pipes are made of

various materials, depending on when and where they were installed. Since the late 1970s, however,

we've installed only welded steel and polyvinyl chloride (plastic) mains due to their expected long

life spans


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Question 2: Explain the source of Non Returned Water (NRW)

a.Distribution pipe

After passing the treatment process, the water stored in the storage tank is distributed through the

distribution system. Water distribution can be done with the method:

A. Gravity

B. Pump to distribution pipe

C. The pump and reservoir

Common features that are in the water distribution system are:

i. Able to provide adequate clean water

ii. Distribution system to be effective.

iii. Piping system capable of supplying water continuously with minimal maintenance.

iv. Materials used for the distribution pipes shall be durable and long-term adverse impact to

customers


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Distribution system must be economic in terms of design, layout and construction

Meter under registration

Apparent losses are usually caused by water theft, billing errors, or revenue meter under-

registration. While the first two causes are directly related to water utility management and may be

reduced by improving company procedures, water meter inaccuracies are considered to be the most

significant and hardest to quantify. Water meter errors are amplified in networks subjected to water

scarcity, where users adopt private storage tanks to cope with the intermittent water supply. The

aim of this paper is to analyse the role of two variables influencing the apparent losses: water meter

age and the private storage tank effect on meter performance. The study was carried out in Palermo(Italy). The impact of water meter ageing was evaluated in laboratory by testing 180 revenue meters,

ranging from 0 to 45 years in age. The effects of the private water tanks were determined via field

monitoring of real users and a mathematical model. This study demonstrates that the impact on

apparent losses from the meter starting flow rapidly increases with meter age. Private water tanks,

usually fed by a float valve, overstate meter under-registration, producing additional apparent losses

between 15% and 40% for the users analysed in this study

Conventional System

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Transcript of Conventional System