b.s. Asgmt 1 Report

8/6/2019 b.s. Asgmt 1 Report

http://slidepdf.com/reader/full/bs-asgmt-1-report 1/32

BUILDING SERVICES

251

_______________________

ASSIGNMENT 1



ABSTRACT

Water Cycle

Water cycle is a natural process which occurs continuously on Earth. The sun, which

drives the water cycle, heats later in the exposed surface of liquid, namely the oceans,

lakes, streams etc. There will never be any more fresh water on Earth than there is now.

No new water is being made and water can¶t escape from the Earth. Water we use now

has existed on earth since the beginning of time, as they are recycled over and over

again. The water cycle is essential for the survival of life on Earth. It has been happening

for billions of years. As the water moves from liquid to gas and back to liquid before

returning to earth, this natural process removes some of the impurities in the water.They

have been cleaned many times since then, as the Earth's fresh water supplies are

constantly refreshed through the natural process we call the water cycle which is our

planet's way of recycling water.

There are few stages that water go through in this cycle:

- Evaporation

- Condensation

- Sublimation

- Precipitation

- Infiltration

- Run-off

- Transpiration



Water particles evaporate as vapor into the air, whereas solids, ice and snow can

sublimate directly into water vapor. Rising air currents take the vapor up into the

atmosphere, along with water from evapotranspiration, where water given off through

the leaves of plants and evaporated from the soil. The vapor rises into the air where

cooler temperatures cause it to condense into clouds. Air currents move clouds around

the globe. Cloud particles collide, grow, and fall out of the sky as precipitation. Some

precipitation falls as snow and can accumulate as ice The hydrologic cycle begins with

the evaporation of water from the surface of the ocean. As moist air is lifted, it cools and

water vapor condenses to form clouds. Moisture is transported around the globe until it

returns to the surface as precipitation. Although, some of the water may evaporate back

into the atmosphere and some may penetrate the surface and become groundwater which

is called the infiltration stage. Groundwater either seeps its way to into the oceans,

rivers, and streams, or is released back into the atmosphere through transpiration. The balance of water that remains on the earth's surface is runoff, which empties into lakes,

rivers and streams and is carried back to the oceans, where the cycle begins again. Over

time, though, all of this water keeps moving, some to reenter the ocean, where the water

cycle starts all over again.



Water Treatment

Water Treatment Works to treat water so that it is safe to be used in our daily routine.

Normally it is only necessary to disinfect this water with chlorine to make it safe todrink. Water taken from rivers and reservoirs usually needs more treatment. This

involves a number of processes, both physical and chemical, and will vary depending on

the quality of the raw water to be treated. There are several methods of treatment of

water to kill living organisms. The application of chlorine compounds is the most

commonly used for disinfectant. Although, there are more other compounds that is used

as disinfectants depending on the water condition.Water is treated with lime and soda

ash precipitate the calcium and magnesium as carbonate and hydroxide, after which the

water is filtered. and then, the water is passed through a porous cation exchanger which

has the ability of substituting sodium ions in the exchange medium for calcium and

magnesium in the water . For high- pressure steam boilers or some other industrial

processes , almost complete deionization of water is needed , and treatment includes

both cation and anion exchangers. Aeration is a process of exposing water to air by

dividing the water into small drops ,by forcing air through the water ,or by a

combination of both . Aeration is used to add oxygen to water and to remove carbon

dioxide, hydrogen sulfide, and taste -producing gases or vapors .



WATER

Water is a colorless and tasteless liquid that covers about 75% of the earth¶s surface. It

is made up of hydrogen and oxygen. Ninety-seven percent of the water on earth is saltwater and the other 3% is freshwater. Most of the freshwater is frozen at the North and

South Poles. About a third of the freshwater is in rivers, streams, aquifers, and springs

that are part of our drinking water.

WATER CYCLE

The water cycle is also known as the hydrologic cycle. There are same amount of

water on the Earth now as there was when the Earth began. The water cycle is how the

earth's water recycles itself. It is the simplest natural cycle on Earth. It is the continuous

movement of water between the land, the ocean, rivers and creeks, and the atmosphere.

Water is always cycling around, through, and above the Earth. This cycle

happens because of the sun's heat and gravity. As it moves through the cycle, water

continually changes from liquid namely, rainwater, saltwater, to gas namely, water

vapour and back to liquid. The liquid can also get cold and become solid namely ice or

snow.

.





Water cycle works

When the sun shines on oceans, rivers, creeks and other water bodies, it causes

water (in liquid form) to evaporate. The heat from the sun provides enough energy for the hydrogen bonds between water molecules to break and the individual water

molecules to drift upwards to the atmosphere as water vapour (in gas form). When the

water in the ocean evaporates, salt, minerals and metals are left behind which means that

only fresh water makes its way up to the clouds.

Stages of the water cycle

Evaporation

Evaporation is the process by which water changes from a liquid to a gas or vapor. This

process occurs to exposed liquids. It is the primary pathway that water moves from the

liquid state back into the water cycle as atmospheric water vapor. Studies have shown

that the oceans, seas, lakes, and rivers provide nearly 90 percent of the moisture in our

atmosphere via evaporation, with the remaining 10 percent being contributed by plant

transpiration. Evaporation from the oceans is the primary mechanism supporting the

surface-to-atmosphere portion of the water cycle. After all, the large surface area of theoceans provides the opportunity for such large-scale evaporation to occur. On a global

scale, the amount of water evaporating is about the same as the amount of water

delivered to the Earth as precipitation. This does vary geographically, though.

Evaporation is more prevalent over the oceans than precipitation, while over the land,

precipitation routinely exceeds evaporation. Most of the water that evaporates from the

oceans falls back into the oceans as precipitation. Only about 10 percent of the water

evaporated from the oceans is transported over land and falls as precipitation. Once

evaporated, water molecule spends about 10 days in the air. The process of evaporation

is so great that without precipitation runoff, and discharge from aquifers, oceans would

become nearly empty.



Heat energy is necessary for evaporation to occur. The energy is used to break

the bonds that hold water molecules together, which is why water easily evaporates at

the boiling point (212° F, 100° C) but evaporates much more slowly at the freezing

point. Net evaporation occurs when the rate of evaporation exceeds the rate of

condensation. A state of saturation exists when these two process rates are equal, at

which point, the relative humidity of the air is 100 percent. Condensation, the opposite

of evaporation, occurs when saturated air is cooled below the dew point (the temperature

to which air must be cooled at a constant pressure for it to become fully saturated with

water), such as on the outside of a glass of ice water. In fact, the process of evaporation

removes heat from the environment, which is why water evaporating from your skin

cools you.

Condensation

Condensation is the phase change of water vapor into a liquid. When the conditions are

just right the water droplets fall back down to Earth as precipitation. Depending on the

air temperature, the water droplets can return to the Earth in either a liquid form (as rain)

or in a solid form namely snow, sleet or hail. Water vapour in the air gets cold and

changes back into tiny liquid droplets, forming clouds.\

During the condensation process, water molecules lose latent heat that were

added during the evaporation process. When latent heat is released it is convertedinto sensible heat which warms the surrounding air. Warming the air increases its

buoyancy and fuels of the development of storms. Condensation takes place in the

presence of the small particles that acts as condensation nuclei that are

usually hygroscopic which means they have a chemical affinity for water, and when the

air is nearly saturated.



Condensation nuclei act as a platform for condensation to take place, increasing

the size of a droplet and decreasing surface tension. They may absorb water well before

the humidity reaches saturation, sometimes at humidity as low as 80 percent. The air

must be at or near its saturation point for condensation to take place. Condensation

forms first on the larger nuclei and a haze develop which reduces visibility. As the

relative humidity increases, these particles take on more water and grow in size while

condensation also begins on smaller nuclei. Rapid cooling of the air called

supersaturation, such as in strong upward currents, can produce humidity of over 100

percent temporarily. Air can be cooled through contact with a cold surface or by uplift.

Contact cooling occurs when air comes in contact with a cooler surface and conduction

transfers heat out of the air. Under such conditions, droplets grow rapidly. Very small

nuclei become active and start to grow, and many thousands of droplets per cubic inch

will form. With this rapid cooling, even non-hygroscopic particles will serve ascondensation nuclei.

As condensation proceeds, droplets continue to grow until they reach a

maximum size of about 1/100 inch in diameter, the size of small drizzle drops. The

condensation process is unable to produce larger droplets for several reasons. As vapor

is used up in droplet formation, supersaturation decreases and the cloud approaches an

equilibrium state at saturation. Also, as droplets grow, the mass of water vapor changing

to liquid becomes large and the resultant latent heat released in the condensation

process warms the droplet and decreases the vapor pressure difference between it and

the surrounding vapor. Thus the vast majority of clouds do not produce rain.

Sublimation

Sublimation refers to the process of transition of a substance from the solid phase to

the gas phase without passing through an intermediate liquid phase. It is most oftenly

used to describe the process of snow and ice changing into water vapor without first

melting into water. Sublimation is a common way for snow to disappear in certain

climates.



Sublimation is an endothermic phase transition that occurs at temperatures and

pressures below a substance's triple point in its phase diagram. This process occurs more

readily when certain weather conditions are present, such as low relative humidity and

dry winds. It also occurs more at higher altitudes, where the air pressure is less than at

lower altitudes. Energy, such as strong sunlight, is also needed. Low temperatures,

strong winds, intense sunlight, very low air pressure very much is needed for

sublimation to occur.

In some conditions of below-freezing temperature, effective sublimation nuclei,

and supersaturation as noted before, sublimation starts by direct transfer of water vapor

to the solid phase on a sublimation nucleus. There is no haze phase as in the case of

condensation. Once sublimation starts, ice crystals will grow freely under conditions of

supersaturation. Since there are fewer sublimation than condensation nuclei available,

the ice crystals that form grow to a greater size than water droplets and can fall from the

base of the cloud.

Only very light snow, or rain if the crystals melt, can be produced by sublimation

alone. The loss of snow during sublimation is often caused by sunshine acting directly

on the upper layers of the snow. Moderate or heavy precipitation requires one of the

precipitation process in addition to sublimation.

Precipitation

Precipitation is is a process of which rain, snow, sleet or hail falling from the sky.When

the water returns to Earth, it either infiltrates the surface and collects underground in

aquifers or becomes run-off that flows into rivers and streams. When so much water has

condensed that the air cannot support its weight, the water falls from the clouds back to

Earth in the form of rain, hail, sleet or snow.

After condensation or sublimation processes have gone as far as they can, some

additional process is necessary for droplets or crystals to grow to a size large enough to

fall freely from the cloud and reach the ground as snow or rain. Because cloud dropletsare of small size and have consequent slight pull of gravity, negligible rate of fall, and

for all practical purposes are suspended in the air, even drizzle droplets seem to float in

the air. Raindrops range in size from about 1/50 inch to 1/5 inch in diameter. Drops

larger than 1/5 inch tend to break up when they fall. It takes about 30 million cloud

droplets of average size to make one raindrop about 1/8 inch in diameter.



There seem to be two processes which act together or separately to cause millions of

cloud droplets to grow into a raindrop:

1. The Ice-Crystal Process : We have seen that ice crystals and cloud droplets cancoexist in clouds with subfreezing temperatures. For the ice-crystal process of

precipitation to take place, clouds must be composed of both ice crystals and

supercooled liquid cloud droplets. The saturation vapor pressure with respect to

ice is somewhat less than that with respect to supercooled water at the same

temperature. If a cloud containing supercooled water droplets is saturated with

respect to water, then it is supersaturated with respect to ice, and the relative

humidity with respect to ice is greater than 100 percent. The force resulting from

the difference between vapor pressure over water and over ice causes vapor

molecules to be attracted to ice crystals, and the ice crystals will grow rapidly.

As the ice crystals gather up vapor molecules in the cloud, the relative humidity

with respect to water drops below 100 percent, and liquid cloud droplets begin to

evaporate. Vapor molecules move to the ice crystals and crystallize there. Thus,

the ice crystals grow at the expense of the water droplets and may attain a size

large enough to fall out of the cloud as snowflakes. If the snowflakes reach

warmer levels, they melt and become raindrops.

2 . Coalescence : Since rain also falls from clouds which are entirely above

freezing, there must be a second precipitation process. This is a simple process in

which cloud droplets collide and fuse together, or coalesce. Clouds which

produce precipitation are composed of cloud droplets of varying sizes. Because

of the different sizes, cloud droplets move about at different speeds. As they

collide, some of them stick together to form larger drops. The larger cloud

droplets grow at the expense of smaller ones, and actually become more effective

in the collecting process as they become larger. As it is larger, drops begin to fall

and they tend to sweep out the smaller drops ahead of them. The coalescence

process takes place in clouds of both above freezing and below freezing

temperatures. Snowflakes coalesce with other snowflakes as they fall to form the

large clumps which we sometimes observe. They may also coalesce with

supercooled water droplets to form snow pellets.



Precipitation products can be divided into three basic classes depending on their physical

characteristics when they strike the earth which are liquid, freezing, and frozen:

1. Rain and drizzle are the two kinds of liquid precipitation. The difference ismainly one of size and quantity of droplets. Drizzle droplets range in size from

about 1/500 to 1/50 inch. Drizzle is formed in, and falls from, stratus clouds, and

is frequently accompanied by fog and low visibility. Raindrops range in size

from about 1/100 to 1/4 inch. They are much more sparse than drizzle droplets.

Rain may come from liquid droplets formed by the coalescence process in warm

clouds, or from melted snowflakes originally formed in cold clouds by both the

ice crystal and coalescence processes. The snowflakes melt when they reach air

with above-freezing temperatures. Rainfall intensity may vary from a few drops

per hour to several inches in a matter of minutes. Heavier rainfall usually

consists of larger drops.

2. Freezing rain and freezing drizzle are formed and fall as liquid drops that freeze

on striking the ground. The drops may be above freezing, but usually they are

supercooled and freeze upon striking the ground or other cold objects. This

occurs usually with warm-front rain formed in the warm air above the frontal

surface, and then supercooled as it falls through the cold air beneath the front.

The temperature at the ground must be lower than 32° F.

3. Frozen precipitation consists of snow, snow pellets, sleet and hail:

Snow consists of crystals of ice formed in pure ice clouds or in mixed clouds.

The larger snowflakes are built up by the coalescence process. Air beneath the

cloud must be near or below freezing, or the snow will melt before reaching the

ground. The heaviest snowfalls occur when the temperature of the cloud portion

from which the snow is falling is not much below freezing.

Snow pellets are white opaque grains of ice, usually round. They form when ice

crystals coalesce with supercooled droplets, and usually occur in showers before

or with snow. They range in size from 1/16 to 1/4 inch.

Sleet consists of transparent hard pellets of ice, about the size of raindrops, that

bounce on striking the ground. They are formed by freezing of raindrops or by

refreezing of partly melted snowflakes falling through a below-freezing layer of

air. Sleet occurs most commonly with warm fronts.



Hail consists of balls of ice ranging in size from 1/5 inch to several inches in

diameter. They have layerlike structures indicating that they have grown by

successive steps. Hailstones apparently begin their growth when supercooled

water droplets impinge on ice pellets. The liquid water freezes on the ice pellet to

form a layer of ice. This process is repeated until the hailstone falls out of the

cloud. The repetition may be due to the hailstone being caught in strong updrafts

and carried upward into the region of supercooled droplets. It is also possible for

the process to begin at very high altitudes, in which case the hailstone grows as it

falls through successive concentrations of supercooled water. Hail is associated

with thunderstorms and very unstable air.

There are two other forms in which moisture from the atmosphere is deposited on the

ground. These are dew and frost. Dew and frost do not fall, but instead are deposited

when water vapor condenses or sublimes on the ground or on objects near the

ground. Dew forms when air next to the ground or to cold objects is chilled to the dew

point of the air, but remains above freezing. Frost forms by sublimation when the air is

chilled to its dew point and the dew point is below freezing. Dew and frost forming on

forest fuels at night can add considerably to the fuel moisture.

Infiltration

Infiltration occurs when water fall as rain, hail, sleet or snow and soaks into the ground,subsurface soil and rock. The process of water entering soil is where Infiltration

capacity is the maximum rate at which water can infiltrate the soil. The basic mechanism

is that the upper soil surface receives precipitation so that existing soil moisture is

displaced downwards by newly infiltrated water.

How much infiltrates depends greatly on a number of factors :

Precipitation : The greatest factor controlling infiltration is the amount and

characteristics as in intensity, duration etc. of precipitation that falls as rain or

snow. Precipitation that infiltrates into the ground often seeps into streambedsover an extended period of time, thus a stream will often continue to flow when

it hasn't rained for a long time and where there is no direct runoff from recent

precipitation.



Soil characteristics : Some soils, such as clays, absorb less water at a slower

rate than sandy soils. Soils absorbing less water result in more runoff overland

into streams.

Soil saturation : Like a wet sponge, soil already saturated from previous rainfall

can't absorb much more, thus more rainfall will become run-off.

Land cover: Some land covers have a great impact on infiltration and rainfall

runoff. Vegetation can slow the movement of run-off, allowing more time for it

to seep into the ground. Impervious surfaces, such as parking lots, roads, and

developments, act as a fast lane for rainfall, right into storm drains that drain

directly into streams. Agriculture and the tillage of land also changes the

infiltration patterns of a landscape. Water in natural conditions, infiltrated

directly into soil now runs off into streams.

Slope of the land : Water falling on steeply sloped land runs off more quickly

and infiltrates less than water falling on flat land.

Evapotranspiration : Some infiltration stays near the land surface, which is

where plants put down their roots. Plants need this shallow ground water to

grow, and, by the process of evapotranspiration, water is moved back into the

atmosphere.

Infiltration may also be controlled by factors including cracks, cultivation,freezing, the intensity and type of precipitation as mentioned, and the porosity of the

soil. Infiltration may not occur if the speed of the water is too great. The infiltration

rate is the speed of water entry into the soil, measured in mm/hour. Generally, the rate is

higher at the onset of a storm, because the soil is drier. The infiltration rate is a key

determinant of the volume of surface run-off. Some water that infiltrates will remain in

the shallow soil layer, where it will gradually move through the soil and subsurfac.

Eventually, it might enter a stream by seepage into the stream bank. Some of the water

may infiltrate deeper, recharging groundwater aquifers. Water may travel long distances

or remain in groundwater storage for long periods before returning to the surface or

seeping into other water bodies, such as streams and the oceans.



As precipitation infiltrates into the subsurface soil, it generally forms an

unsaturated zone and a saturated zone. In the unsaturated zone, the voids that is the

spaces between grains of gravel, sand, silt, clay, and cracks within rocks contain both air

and water. Although a lot of water can be present in the unsaturated zone, this water

cannot be pumped by wells because it is held too tightly by capillary forces. The upper

part of the unsaturated zone is the soil-water zone. The soil zone is crisscrossed by roots,

openings left by decayed roots, animal and worm burrows, which allow the precipitation

to infiltrate into the soil zone. Water in the soil is used by plants in life functions and

leaf transpiration, but it also can evaporate directly to the atmosphere. Below the

unsaturated zone is a saturated zone where water completely fills the voids between rock

and soil particles.

Natural refilling of deep aquifers is a slow process because ground water moves

slowly through the unsaturated zone and the aquifer. In places where the water table is

close to the land surface and where water can move through the aquifer at a high rate,

aquifers can be replenished artificially.

Run-off

Run-off is the water flow that occurs when soil is infiltrated to full capacity and

excess water from rain, meltwater, or other sources flows over the land. This is a major

component of the water cycle. When precipitation occurs, water only has a few locationswhere it can go. Water can infiltrate into the ground, evaporate, or become runoff. Water

that does not get absorbed into the soil, or rise back into the atmosphere as water vapor,

will run off surfaces collecting in varied locations as in low-lying areas, on floodplains,

flows into streams and rivers and more.

The environment in which water from precipitation lands will determine the

likelihood of surface runoff. For instance, paved areas prevent water from infiltrating

into the ground. The water will run off the surface if evaporation does not take place.

Most of the water which returns to land flows downhill as run-off. Some of it penetrates

and charges groundwater while the rest, as river flow, returns to the oceans where it

evaporates. As the amount of groundwater increases or decreases, the water table rises or

falls accordingly. When the entire area below the ground is saturated, flooding occurs

because all subsequent precipitation is forced to remain on the surface.



Different surfaces hold different amounts of water and absorb water at different

rates. As a surface becomes less permeable, an increasing amount of water remains on

the surface, creating a greater potential for flooding. Flooding can occur if the amount of

precipitation in an area exceeds the evaporation rate and infiltration capacity of the soil.

Significant floods can also occur as water hits paved areas and has no chance to infiltrate

into the ground. Hard ground surfaces and impermeable clay surfaces will also prevent

water from infiltrating and can cause flash floods.

Transpiration

Transpiration is the process by which water evaporates from plants, mainly from leaves.

This process helps evaporation to get the water vapour back up into the air. Transpiration is the process by which moisture is carried through plants from roots to

small pores on the underside of leaves, where it changes to vapor and is released to the

atmosphere. Transpiration is essentially evaporation of water from plant leaves.

Transpiration also includes a process called guttation, which is the loss of water in liquid

form from the uninjured leaf or stem of the plant, principally through water stomata.

There is a process called evapotranspiration where plants put down roots into the

soil to draw water and nutrients up into the stems and leaves and in addition combined

with evaporation. Transpiration rates vary widely depending on weather conditions, such

as temperature, humidity, sunlight availability and intensity, precipitation, soil type andsaturation, wind, land slope, and water use and diversion by people. During dry periods,

transpiration can contribute to the loss of moisture in the upper soil zone.

During a growing season of plants, the leaf will transpire many times more water

than its own weight. An acre of corn gives off about 3,000-4,000 gallons of water each

day, and a large oak tree can transpire 40,000 gallons per year.



The amount of water that plants transpire varies greatly on geographic conditions and

over time. There are a number of factors that determine transpiration rates:

Temperature : Transpiration rates go up as the temperature goes up, especiallyduring the growing season, when the air is warmer due to stronger sunlight and

warmer air masses. Higher temperatures cause the plant cells which control the

openings of stomata where water is released to the atmosphere to open, whereas

colder temperatures cause the openings to close.

Relative humidity : As the relative humidity of the air surrounding the plant rises

the transpiration rate falls. It is easier for water to evaporate into dryer air than into

more saturated air.

Wind and air movement : Increased movement of the air around a plant will resultin a higher transpiration rate. This is somewhat related to the relative humidity of the

air, in that as water transpires from a leaf, the water saturates the air surrounding the

leaf. If there is no wind, the air around the leaf may not move very much, raising the

humidity of the air around the leaf. Wind will move the air around, with the result

that the more saturated air close to the leaf is replaced by drier air.

Soil-moisture availability : When moisture is lacking, plants can begin to senesce

that is premature ageing which can result in leaf loss and transpire less water.

Type of plant : Plants transpire water at different rates. Some plants which grow inarid regions, such as cactus and succulents, conserve precious water by transpiring

less water than other plants.



WATER TREATMENT

Wastewater treatment, is the process of removing contaminants from wastewater,

both runoff (effluents) and domestic. It includes physical, chemical and biological processes to remove physical, chemical and biological contaminants. Wastewater

treatment is to produce a waste stream or treated effluent and a solid waste or sludge

suitable for discharge or reuse back into the environment. This material is often

inadvertently contaminated with many toxic organic and inorganic compounds. Sewage

can be treated in septic tanks, biofilters or aerobic treatment systems, or collected and

transported via a network of pipes and pump stations to a municipal treatment plant.

Industrial sources of wastewater often require specialized treatment processes. The

sewage treatment involves three stages, called primary, secondary and tertiary treatment.





In this process of wastewater treatment :

1. The solids are separated from the wastewater stream.

2. Then dissolved biological matter is progressively converted into a solid mass byusing indigenous, water-borne microorganisms.

3. Finally, the biological solids are neutralized then disposed of or re-used, and the

treated water may be disinfected chemically or physically.

The final effluent can be discharged into streams, river, bay, lagoon or wetland, or it

can be used for the irrigation green ways or park. If it is sufficiently clean, it can also be

used for groundwater recharge. Raw influent including household waste liquid from

toilets, baths, showers, kitchens, sinks and so forth is disposed via sewers. In manyareas, sewage also includes liquid waste from industry and commerce. Lots of sewage

also includes some surface water from roofs or hard-standing areas. Municipal

wastewater therefore includes residential, commercial, and industrial liquid waste

discharges, and may include storm water runoff.

Sewerage

This system includes of pipes used to collect and carry rain, waste water and tradewaste away for treatment and disposal.

Sewage systems that are capable of handling storm water are known as combined

systems or combined sewers. Such systems are usually avoided since they complicate

and thereby reduce the efficiency of sewage treatment plants owing to their seasonality.

The variability in flow also leads to often larger than necessary and subsequently more

expensive treatment facilities. In addition, heavy storms that contribute more flows than

the treatment plant can handle may overwhelm the sewage treatment system causing a

spill or overflow. As rainfall runs over the surface of roofs and the ground, it may pick

up various contaminants including soil particles and other sediment, heavymetals, organic compounds, animal waste, oil and grease.



Another sewage system is the foul sewers. It carry wastewater, that has been used for

cooking and washing, waste from toilets and from trade premises, etc. and flows to the

wastewater treatment.

Whereas for combined sewer, it is a single pipe system which carries both

wastewater and surface water to the wastewater treatment. These sewers are often found

in older town centre systems.

Mechanical treatment

y Influx (Influent)

y Removal of large objectsy Removal of sand and grit

y Pre-precipitation

Biological treatment

y Oxidation bed (oxidizing bed) /aeration system

y Post precipitation

Chemical treatment

Chemical treatment is usually combined with settling and other processes, such as

filtration to remove solids.

Primary treatment removes the materials that can be easily collected from the

raw wastewater and disposed of. The typical materials that are removed during primary

treatment include fats, oils, and greases, sand, gravels and rocks also referred to as grit,

larger settled solids and floating materials. This step is done entirely with machinery.



Many plants have sedimentation stage where the sewage is allowed to pass

slowly through large tanks, commonly called primary clarifiers or primary

sedimentation tanks. The tanks are large enough that sludge can settle and floating

material such as grease and oils can rise to the surface and be skimmed off. The main

purpose of the primary clarification stage is to produce both a generally homogeneous

liquid capable of being treated biologically and a sludge that can be separately treated or

processed. Primary settling tanks are usually equipped with mechanically driven

scrapers that continually drive the collected sludge towards a hopper in the base of the

tank from where it can be pumped to further sludge treatment stages.

Secondary treatment

Secondary treatment is designed to substantially degrade the biological content of the

sewage such as are derived from human waste, food waste, soaps and detergent. The

majority of municipal and industrial plants treat the settled sewage liquor using aerobic

biological processes. For this to be effective, the biota requires both oxygen and a

substrate on which to live. There are number of ways in which this is done. In all these

methods, the bacteria and protozoa consume biodegradable soluble organic

contaminants and bind much of the less soluble fractions into floc.

Secondary treatment systems are classified as fixed film or suspended growth.

Fixed-film treatment process including trickling filter and rotating biologicalcontactors where the biomass grows on media and the sewage passes over its surface.

In suspended growth systems such as activated sludge, the biomass is well mixed with

the sewage and can be operated in a smaller space than fixed-film systems that treat the

same amount of water. However, fixed-film systems are more able to cope with drastic

changes in the amount of biological material and can provide higher removal rates for

organic material and suspended solids than suspended growth systems.

Roughing filters are intended to treat particularly strong or variable organic

loads, typically industrial, to allow them to then be treated by conventional secondary

Treatment processes. Characteristics include typically tall, circular filters filled with

open synthetic filter media to which wastewater is applied at a relatively high rate. They

are designed to allow high hydraulic loading and a high flow-through of air. On larger

installations, air is forced through the media using blowers. The resultant wastewater is

usually within the normal range for conventional treatment processes.



Tertiary treatment

Tertiary treatment provides a final stage to raise the effluent quality before it is

discharged to the receiving environment. More than one tertiary treatment process may

be used at any treatment plant. If disinfection is practiced, it is always the final process.

It is also called effluent polishing.

Role of Bacteria in Wastewater Treatment

Treatment plants should be designed to take advantage of the decomposition

of organic materials by bacterial activity. This is something anyone can equate to lower

costs, increased capacity, and an improved quality of effluent; even freedom from bad

odors which may typically result when anaerobe bacteria become dominant and in their

decomposition process, produce hydrogen sulphide gas and similar by-products.

Considering the fact that the total organic load of wastewater or sewage is

composed of constantly changing constituent, it would be quite difficult to degrade all of

these organics by the addition of one enzyme, or even several enzymes. Enzymes are

specific catalysts and do not reproduce. What is needed is the addition of an enzyme

manufacturing system right in the sewage that can be pre-determined as to its activity

and performance and which has the initial or continuing capacity to reduce waste.



Wastewater Treatment Technologies

The principal biological processes used for wastewater treatment are divided into two

main categories :

1. Suspended growth processes : Microorganisms responsible for treatment are

maintained in liquid suspension by appropriate mixing methods. Many

suspended growth processes used in municipal and industrial wastewater

treatment are operated with a positive dissolved oxygen concentration (aerobic),

but applications exist where suspended growth anaerobic processes are used,

such as for high organic concentration industrial wastewater and organic sludges.

The most common suspended growth process used for municipal waste water

treatment is the Activated Sludge Process.

2. Attached Growth Process : Microorganisms responsible for the conversion of

organic material or nutrients are attached on inert packing material. The organic

material and nutrients are removed from the water flowing pass the attached

growth also known as the biofilm. Packing material in attached growth processes

include rock, gravel, sand, slag, redwood and range of plastics and other

synthetic materials. Attached growth processes are operated as aerobic or

anaerobic processes. The packing can be submerged completely in liquid or not

submerged, with air or gas space above the biofilm liquid layer. The most

common aerobic attached growth process used is the Trickling filter.



Classification of Wastewater Treatment Technologies

The wastewater treatment technologies can be broadly classified on the basis of mode of

operation as:

1. Aerobic (in presence of oxygen)

2. Anaerobic (in absence of oxygen)

Anaerobic Treatment

Advantages

y Less energy requirement since aeration is not required.

y Less biological sludge production

y Fewer nutrients required

y Methane production, a potential energy source

y Smaller reactor volume required

y Elimination of off-gas air pollution

y Rapid response to substrate addition after long periods without feeding.

Disadvantages

y Longer start-up time to develop necessary biomass inventory

y May require alkalinity addition

y May require further treatment with an aerobic treatment process to meet

discharge

Requirements

y Biological nitrogen and phosphorus removal is not possible

y Much more sensitive to the adverse effects of lower temperatures on reaction

rates.

y May be more susceptible to upsets due to toxic substances

y Potential for production of odors and corrosive gases.



Aerobic Treatment

The activated sludge process is a wastewater treatment method in which the

carbonaceous organic matter of wastewater provides an energy source for the productionof new cells for a mixed population of microorganisms in an aquatic aerobic

environment. The microbes convert carbon into cell tissue and oxidized end products

that include carbon dioxide and water. In addition, a limited number of microorganisms

may exist in activated sludge that obtain energy by oxidizing ammonia nitrogen to

nitrate nitrogen in the process known as nitrification.

Bacteria constitute the majority of microorganisms present in activated sludge.

Bacteria that require organic compounds for their supply of carbon and energy

predominate, whereas bacteria that use inorganic compounds for cell growth occur in

proportion to concentrations of carbon and nitrogen. Both aerobic and Anaerobic

bacteria may exist in the activated sludge, but the preponderance of species are cultative,

able to live in either the presence of or lack of dissolved oxygen. Fungi, rotifers, and

protozoan are also residents of activated sludge. The latter microorganisms are

represented largely by ciliated species, but flagellated protozoan and amoebae may also

be present. Protozoan serve as indicators of the activated sludge condition, and ciliated

species are instrumental in removing Escherichia coli from sewage. Additionally,

viruses of human origin may be found in raw sewage influent, but a large percentage

appears to be removed by the activated-sludge process.

The work of the activated-sludge process is dependent upon establishing a mixed

community of microorganisms that will remove and consume organic waste material,

that will aggregate and adhere in a process known as bio flocculation, and that will settle

in such a manner as to produce a concentrated sludge for recycling. Any of several types

of activated sludge solids separations problems indicate an imbalance in the biological

component of this process. In such a system, there is no interference with the

compaction and settling rates of the activated sludge prior to its recycling.



The activated-sludge process is a biological method of wastewater treatment that

is performed by a variable and mixed community of microorganisms in an aerobic

aquatic environment. These microorganisms derive energy from carbonaceous organic

matter in aerated wastewater for the production of new cells in a process known as

synthesis, while simultaneously releasing energy through the conversion of this organic

matter into compounds that contain lower energy, such as carbon dioxide and water, in a

process called respiration. As well, a variable number of microorganisms in the system

obtain energy by converting ammonia nitrogen to nitrate nitrogen in a process termed

nitrification. This consortium of microorganisms, the biological component of the

process, is known collectively as activated sludge.

The overall goal of the activated-sludge process is to remove substances that

have demand for oxygen from the system. This is accomplished by the metabolic

reactions of the microorganisms, the separation and settling of activated-sludge solids to

create an acceptable quality of secondary wastewater effluent, and the collection and

recycling of microorganisms back into the system or removal of excess microorganisms

from the system.



As for the process of water treatment, this process has to go through few stages , step-

by-step, in order for water to be cleanse for our daily use. These include :

1. Preliminary Treatment

Preliminary treatment or pretreatment is any physical, chemical or mechanical process

used on water before it undergoes the main treatment process. During preliminary

treatment, screens may be used to remove rocks, sticks, leaves and other debris.

Chemicals may be added to control the growth of algae and a pre-sedimentation stage

can settle out sand, grit and gravel from raw water.

Preliminary water treatment involves two components, the physical filtration of objectsfrom the water, and the addition of chemicals to stop algae growth. Water is passed

through screens, which remove objects such as sticks, paper and other debris from the

water before it enters the water treatment process. Chemicals, such as chlorine, are

added in order to stop algae from growing in the water, during some of the water

treatment steps to come.

2. Coagulation and Flocculation

After preliminary treatment, the next step is coagulation. Coagulation removes small

particles that are made up of microbes, silt and other suspended material in the water.

Treatment chemicals such as alum and similar substances which bond with salts and

other small particles suspended in the water are added to the water and mixed well

rapidly in a large basin. The chemicals cause small particles to clump together or

coagulate which allows bonds with salts and other particles to create larger particles.

Gentle mixing brings smaller clumps of particles together to form larger groups called

floc. Some of the floc begins to settle during this stage. The water is then, finally drained

through screens once again, with the finer mesh on the screens separating out the

majority of the floc particles.

During the flocculation stage, the heavy, dense floc settles to the bottom of the water in

large tanks. This can be a slow process. Once the floc settles, the water is ready for the

next stage of treatment.



3. Clarification

Clarification is also known as sedimentation. It occurs in a large basin where water is

allowed to flow very slowly. Sludge, a residue of solids and water, accumulates at the

basin's bottom and is pumped or scraped out for eventual disposal. Clarification allows

the recently-filtered water to sit in a large basin long enough for the removal of particles

which had been too small to be filtered out by flocculation filtering. As the water sits

undisturbed, these particles will slowly begin to settle to the bottom of the basin. The particles will settle into a sludge of sediment, allowing the water to be drained above the

sludge line, and the sediment to be scraped from the bottom of the basin.

4. Water Softening and Stabilization

In this stage, depending on the minerals that are left in the water after it's been clarified,

it may be considered to be hard or soft. Both types of water can lead to mineral buildup

and pipe damage. The addition of minerals to the clarified water can soften hard water

and harden soft water. Key minerals in this process include magnesium and calcium, the

levels of which are balanced carefully, so as to create relatively stable water with a

neutral pH.



5. Filtration

The filtration process removes suspended matter, which can consist of floc,

microorganisms including protozoan cysts such as Giardia and Cyrptosporidium, algae,silt, iron, and manganese precipitates from ground-water sources, as well as precipitants

which remain after the softening process. Turbidity is a physical characteristic that

makes water appear cloudy when suspended matter is present.These suspended materials

are filtered out when water passes through beds of granular material, usually composed

of layers of sand, gravel, coal, garnet, or related substances.

Once water stabilization has occurred and the magnesium, calcium and pH levels have

been balanced so as to make the water relatively neutral, a final filtration stage occurs in

order to remove any additional sediment that may still be in the water. A fine screen is

used when filtering, removing any material that might remain which is large enough to

be filtered out. The water will generally be much clearer after this step occurs, since

even clarified and stabilized water may appear slightly cloudy. After the final filtration,

the water can be stored in water tanks for use, and chemicals, such as fluoride, may be

added to the water in storage as the city or locale where it is being stored dictates.

6. Fluoridation and Disinfection

Fluoride, F-

is added to water to reduce tooth decay. Fluoridation is an effective,economical process endorsed by many public health groups worldwide. Fluoride is fed

into the water system as either a dry powder or in solution.

During disinfection, disease-causing organisms are destroyed or disabled. Chlorine, Cl2

is one of the most common disinfectants used because it is practical, effective and

economical.

Because chlorine dissipates rapidly, it is important to add the right amount of chlorine at

the water treatment plant to make sure disinfection continues while the water is flowing

through the distribution system.



CONCLUSION

Water Cycle

Water cycle has no starting point as the cycle moves on and on continuously and

repetitively every second. We can say that earth is the only planet in our solar

system which has water cycle which makes it a unique planet. The water first evaporates

from the surface of the earth due to sun's heat, then water bodies condenses at the higher

altitude due to low temperatures which causes precipitation in the form of rain, snow,

hail etc. It delivers the purest form of natural water namely, rain water as it is naturally

distilled. Then through precipitation the water again returns back to the surface. this

cycle goes on and on and in this way the water supply is regulated on earth which givesus major advantage to continue our daily life routine.

Water treatment

Water covers 75 percent of our planet's surface. We use water for so many different

things. Water picks up many impurities and contaminants, both natural and synthetic.

And since water is so widely used in so many different ways, treatment is often

necessary. Whether it is clean water for manufacturing, high purity water for medicalapplications or just safe drinking water, the treatment process is a vital part of our daily

lives. Out of all the Earth's resources, none is more precious than water. Water taken

from boreholes is already clean because it is filtered as it trickles through soil and rocks.

In conclusion the water must be cleaned before being distributed. The water has

to be passed through a filter and then made sure all of the useless and harmful chemicals

are out of the water so that the people do not get sick. Also, the physical and chemical

processes for making water for human consumption and other purposes that drinking

water must be bacteriologically safe, free from toxic or turbidity, color and taste -

producing substances.



REFERENCE

y http://www.ehow.com/about_4564001_the-water-cycle.html

y http://www.mnr.gov.on.ca/en/Business/Water/2ColumnSubPage/STEL02_16344

6.html

y http://www.sawater.com.au/SAWater/Education/OurWaterSystems/The+Water+

Cycle.htm

y http://education.melbournewater.com.au/content/water_cycle/natural_water_cycl

e/natural_water_cycle.asp

y http://www.answers.com/topic/infiltration

y http://www.freedrinkingwater.com/water-education2/1-water-treatment-

quality.htm

y http://www.exampleessays.com/viewpaper/7554.html

y http://www.essaypride.com/essays.php?free_essay=3425409&title=Water-

Treatment

y http://ga.water.usgs.gov/edu/watercyclesummary.html

b.s. Asgmt 1 Report

Documents