Q12.
A reservoir (etymology: from French rservoir a "storehouse" [1])
is a natural or artificial lake, storage pond or impoundment from a
dam which is used to store water. Reservoirs may be created in
river valleys by the construction of a dam or may be built by
excavation in the ground or by conventional construction techniques
such as brickwork or cast concrete.
The term reservoir may also be used to describe naturally
occurring underground reservoirs such as those beneath an oil or
water well.
TypesValley dammed reservoirA dam constructed in a valley relies
on the natural topography to provide most of the basin of the
reservoir. Dams are typically located at a narrow part of a valley
downstream of a natural basin. The valley sides act as natural
walls with the dam located at the narrowest practical point to
provide strength and the lowest practical cost of construction. In
many reservoir construction projects people have to be moved and
re-housed, historical artifacts moved or rare environments
relocated. Examples include the temples of Abu Simbel[2] ( which
were moved before the construction of the Aswan Dam to create Lake
Nasser from the Nile in Egypt ), the re-location of the village of
Capel Celyn during the construction of Llyn Celyn,[3] and the
relocation of Borgo San Pietro of Petrella Salto during the
construction of Lake Salto.
Construction of a reservoir in a valley will usually necessitate
the diversion of the river during part of the build often through a
temporary tunnel or by-pass channel.[4]In hilly regions reservoirs
are often constructed by enlarging existing lakes. Sometimes in
such reservoirs the new top water level exceeds the watershed
height on one or more of the feeder streams such as at Llyn
Clywedog in Mid Wales.[5] In such cases additional side dams are
required to contain the reservoir.
Where the topography is poorly suited to a single large
reservoir, a number of smaller reservoirs may be constructed in a
chain such as in the River Taff valley where the three reservoirs
Llwyn-on Reservoir, Cantref Reservoir and Beacons Reservoir form a
chain up the valley.[6]Bank-side reservoir
Where water is taken from a river of variable quality or
quantity, bank-side reservoirs may be constructed to store the
water pumped or siphoned from the river. Such reservoirs are
usually built partly by excavation and partly by the construction
of a complete encircling bund or embankment which may exceed 6km in
circumference.[7] Both the floor of the reservoir and the bund must
have an impermeable lining or core, initially these were often made
of puddled clay, but have generally been superseded by the modern
use of rolled clay. The water stored in such reservoirs may have a
residence time of several months during which time normal
biological processes are able to substantially reduce many
contaminants and almost eliminate any turbidity. The use of
bank-side reservoirs also allows a water abstraction to be closed
down for extended period at times when the river is unacceptably
polluted or when flow conditions are very low due to drought. The
London water supply system is one example of the use of bank-side
storage for all the water taken from the River Thames and River Lee
with many large reservoirs such as Queen Mary Reservoir visible
along the approach to London Heathrow Airport.[7]Service
reservoir
Service reservoirs[8] store fully treated potable water close to
the point of distribution. Many service reservoirs are constructed
as water towers, often as elevated structures on concrete pillars
where the landscape is relatively flat. Other service reservoirs
are entirely underground, especially in more hilly or mountainous
country. In the United Kingdom, Thames Water has many underground
reservoirs built in the 1800s, most of which are lined with brick.
A good example is the Honor Oak Reservoir, constructed between 1901
and 1909. When it was completed it was the largest brick built
underground reservoir in the world[9] and is still one of the
largest in Europe.[10] The reservoir now forms part of the Southern
extension of the Thames Water Ring Main. The top of the reservoir
has been grassed over and is now the Aquarias Golf Club.[11]Service
reservoirs perform several functions including ensuring sufficient
head of water in the water distribution system and providing
hydraulic capacitance in the system to even out peak demand from
consumers enabling the treatment plant to run at optimum
efficiency. Large service reservoirs can also be managed so that
energy costs in pumping are reduced by concentrating refilling
activity at times of day when power costs are low.
Q13.
Grit ChambersGrit chambers are basin to remove the inorganic
particles to prevent damage to the pumps, and to prevent their
accumulation in sludge digestors. Types of Grit ChambersGrit
chambers are of two types: mechanically cleaned and manually
cleaned. In mechanically cleaned grit chamber, scraper blades
collect the grit settled on the floor of the grit chamber. The grit
so collected is elevated to the ground level by several mechanisms
such as bucket elevators, jet pump and air lift. The grit washing
mechanisms are also of several designs most of which are agitation
devices using either water or air to produce washing action.
Manually cleaned grit chambers should be cleaned atleast once a
week. The simplest method of cleaning is by means of shovel.Aerated
Grit ChamberAn aerated grit chamber consists of a standard spiral
flow aeration tank provided with air diffusion tubes placed on one
side of the tank. The grit particles tend to settle down to the
bottom of the tank at rates dependant upon the particle size and
the bottom velocity of roll of the spiral flow, which in turn
depends on the rate of air diffusion through diffuser tubes and
shape of aeration tank. The heavier particles settle down whereas
the lighter organic particles are carried with roll of the spiral
motion. Principle of Working of Grit ChamberGrit chambers are
nothing but like sedimentation tanks, designed to separate the
intended heavier inorganic materials (specific gravity about 2.65)
and to pass forward the lighter organic materials. Hence, the flow
velocity should neither be too low as to cause the settling of
lighter organic matter, nor should it be too high as not to cause
the settlement of the silt and grit present in the sewage. This
velocity is called "differential sedimentation and differential
scouring velocity". The scouring velocity determines the optimum
flow through velocity. This may be explained by the fact that the
critical velocity of flow 'vc' beyond which particles of a certain
size and density once settled, may be again introduced into the
stream of flow. It should always be less than the scouring velocity
of grit particles. The critical velocity of scour is given by
Schield's formula:V = 3 to 4.5 (g(Ss - 1)d)1/2 A horizontal
velocity of flow of 15 to 30 cm/sec is used at peak flows. This
same velocity is to be maintained at all fluctuation of flow to
ensure that only organic solids and not the grit is scoured from
the bottom. Types of Velocity Control Devices 1. A sutro weir in a
channel of rectangular cross section, with free fall downstream of
the channel.2. A parabolic shaped channel with a rectangular
weir.3. A rectangular shaped channel with a parshall flume at the
end which would also help easy flow measurement. Design of Grit
ChambersSettling Velocity The settling velocity of discrete
particles can be determined using appropriate equation depending
upon Reynolds number.
Stoke's law: v= g(Ss-1)d2 18Stoke's law holds good for Reynolds
number,Rebelow 1.Re=vd
For grit particles of specific gravity 2.65 and liquid
temperature at 10C, =1.01 x 10-6m2/s. This corresponds to particles
of size less than 0.1 mm. Transition law: The design of grit
chamber is based on removal of grit particles with minimum size of
0.15 mm and therefore Stoke's law is not applicable to determine
the settling velocity of grit particles for design purposes.
v2 = 4g(p-)d 3 CDwhere, CD= drag coefficient Transition flow
conditions hold good for Reynolds number,Re between 1 and 1000. In
this range CD can be approximated by CD= 18.5 =
18.5Re0.6(vd/)0.6Substituting the value of CD in settling velocity
equation and simplifying, we getv = [0.707(Ss-1)d-0.6]0.714
Primary SedimentationPrimary sedimentation in a municipal
wastewater treatment plant is generally plain sedimentation without
the use of chemicals. In treating certain industrial wastes
chemically aided sedimentation may be involved. In either case, it
constitutes flocculent settling, and the particles do not remain
discrete as in the case of grit, but tend to agglomerate or
coagulate during settling. Thus, their diameter keeps increasing
and settlement proceeds at an over increasing velocity.
Consequently, they trace a curved profile.The settling tank design
in such cases depends on both surface loading and detention time.
Long tube settling tests can be performed in order to estimate
specific value of surface loading and detention time for desired
efficiency of clarification for a given industrial wastewater using
recommended methods of testing. Scale-up factors used in this case
range from 1.25 to 1.75 for the overflow rate, and from 1.5 to 2.0
for detention time when converting laboratory results to the
prototype design.For primary settling tanks treating municipal or
domestic sewage, laboratory tests are generally not necessary, and
recommended design values given in table may be used. Using an
appropriate value of surface loading from table, the required tank
area is computed. Knowing the average depth, the detention time is
then computed. Excessively high detention time (longer than 2.5 h)
must be avoided especially in warm climates where anaerobicity can
be quickly induced.Design parameters for settling tankTypes of
settling Overflow rate m3m2/day Solids loading kg/m2/day
DepthDetention time
AveragePeakAveragePeak
Primary settling only 25-3050-60--2.5-3.52.0-2.5
Primary settling followed by secondary
treatment35-5060-120--2.5-3.5
Primary settling with activated sludge return
25-3550-60--3.5-4.5-
Secondary settling for trickling filters
15-2540-5070-1201902.5-3.51.5-2.0
Secondary settling for activated sludge (excluding extended
aeration) 15-3540-5070-1402103.5-4.5-
Secondary settling for extended aeration
8-1525-3525-1201703.5-4.5-
Q2.
Biochemical oxygen demand or B.O.D is the amount of dissolved
oxygen needed by aerobic biological organisms in a body of water to
break down organic material present in a given water sample at
certain temperature over a specific time period. The term also
refers to a chemical procedure for determining this amount. This is
not a precise quantitative test, although it is widely used as an
indication of the organic quality of water.[1] The BOD value is
most commonly expressed in milligrams of oxygen consumed per litre
of sample during 5 days of incubation at 20 C and is often used as
a robust surrogate of the degree of organic pollution of water.
BOD can be used as a gauge of the effectiveness of wastewater
treatment plants. It is listed as a conventional pollutant in the
U.S. Clean Water Act.
BOD is similar in function to chemical oxygen demand (COD), in
that both measure the amount of organic compounds in water.
However, COD is less specific, since it measures everything that
can be chemically oxidized, rather than just levels of biologically
active organic matter.
A standard temperature at which BOD testing should be carried
out was first proposed by the Royal Commission on Sewage Disposal
in its eighth report in 1912:
" (c) An effluent in order to comply with the general standard
must not contain as discharged more than 3 parts per 100,000 of
suspended matter, and with its suspended matters included must not
take up at 65F (18-3C.) more than 2.0 parts per 100,000 of
dissolved oxygen in 5 days. This general standard should be
prescribed either by Statute or by order of the Central Authority,
and should be subject to modifications by that Authority after an
interval of not less than ten years.
This was later standardised at 68F and then 20C. This
temperature may be significantly different from the temperature of
the natural environment of the water being tested. Investigators
also decided to eliminate anaerobic conditions.
Q5.
Sanitary Work is the application of engineering methods to
improve sanitation of human communities, primarily by providing the
removal and disposal of human waste, and in addition to the supply
of safe potable water. Initially in the mid 19th century, the
discipline concentrated on the reduction of disease, then thought
to be caused by miasma. This was accomplished mainly by the
collection and segregation of sewerage flow in London specifically,
and Great Britain generally.[1] These and later regulatory
improvements were reported in the United States as early as
1865.[2]It is not concerned with environmental factors that do not
have an immediate and clearly understood effect on public health.
Areas outside the purview of sanitary engineering include traffic
management, concerns about noise pollution or light pollution,
aesthetic concerns such as landscaping, and environmental
conservation as it pertains to plants and animals.
Sanitary work plumbing is any work involved in fixing or
unfixing any pipe, plumbing fixture or appliance including; any
trap, waste or soil pipe, ventilation pipe, or overflow pipe and
any pipe that supplies or is intended to supply water.
All sanitary plumbing must comply with the Building Code and,
where a building consent is required; the work must be checked by
the building inspector from the building control authority in your
area (your local council). A code compliance certificate cannot be
issued until the work has been signed off by the building
inspector.
A certifying plumber is responsible for the testing,
verification and the supervision of licensed plumbers, limited
certificate (trainee plumbers) and exempted persons.
Sanitary plumbing does not include the installation of
appliances such as dishwashers and washing machines; the
replacement or repair of taps, ball valves and plugs
Q1.Population is one of the most important factors for design of
the water systems, so it should be estimated, so as to know the
increasing demand and ensure continuous supply to them.
Population data is obtained by previous records and the rate of
increase is found out and this used for further analysis, which may
be by using the methods described below
1. Arithmetic growth method2. Geometric growth method3.
Curvilinear method4. Logistic method5. Decline growth method
6. Ratio growth
Related Pages Arithmetic growth method:
It is based on the assumption that the rate of growth of
population is constant. It means that the each year population
increase by the same increment.
Mathematically;dp / dt = Ka
Where,dp / dt is the rate of change of population
Ka = the constant arithmetic increment
Ka can be determined by finding the slop of the graph of
population against time. The population in the future is thus
estimated.
Engineering Drawing Civil Surveying Environmental Engineering
Notes Water Supply & Treatment Water treatment Environmental
Dictionary Geometric Design of Highways Water Consumption
Geometric method:
It is based on the hypothesis that rate of change of population
is proportional to the population. According to this, method it is
assumed that the rate of increase of population growth in a
community is proportional to the present population.
Mathematically:dP /dt P => dp / dt = Kg where Kg = Geometric
Growth constant.
If P0 is the population at any time t0 and Pf is the population
at time tf then
Pf P0 dp/p = Kg tf t0 dt = Ln (Pf/P0 = Kg (tf/t0)
=> Ln (Pf/P0 = Kg t
=> (Pf/P0 = (e) Kg t and Pf = P0 (e) Kg t
This method gives somewhat larger value as compared to
arithmetic method and can be used for new cities with rapid growth.
In normal practice, arithmetic and geometric growth average is
taken.
Q 6 What is water carriage system?A water carriage system is a
system of disposing waste matter from buildings using water to
carry it hydraulically in a piping system. It is basically a system
of piping through which sewage and domestic liquid wastes are
carried by the flow of water to the point of disposal.Water
conservationWater conservation encompasses the policies, strategies
and activities to manage fresh water as a sustainable resource to
protect the water environment and to meet current and future human
demand. Population, household size and growth and affluence all
affect how much water is used. Factors such as climate change will
increase pressures on natural water resources especially in
manufacturing and agricultural irrigation.[1]GoalsThe goals of
water conservation efforts include as follows:
To ensure availability for future generations, the withdrawal of
fresh water from an ecosystem should not exceed its natural
replacement rate.
Energy conservation. Water pumping, delivery and waste water
treatment facilities consume a significant amount of energy. In
some regions of the world over 15% of total electricity consumption
is devoted to water management.
Habitat conservation. Minimizing human water use helps to
preserve fresh water habitats for local wildlife and migrating
waterfowl, as well as reducing the need to build new dams and other
water diversion infrastructures.
StrategiesIn implementing water conservation principles there
are a number of key activities that may be beneficial.
1. Any beneficial reduction in water loss, use and waste
2. Avoiding any damage to water quality.
3. Improving water management practices that reduce or enhance
the beneficial use of water.
Q. 3 Ways of laying the water supply pipes. 1 Pipe materials:
The preferred pipe material is blue MDPE, size 25mm for normal
ground conditions. For contaminated ground, other specialist
materials must be used.
- United Utilities pipe size is 25mm for
- MDPE.
- We will consider larger diameter pipes in exceptional
cicumstances.
2 Ducting: Where a water pipe enters a building or runs
underneath a building etc, it must be located inside a suitable
duct. The correct size ducting is 100mm (4) diameter pipe. (Usually
plastic but can be other materials if suitable.) There must not be
any markings for other utilities on the duct, such as gas,
electricity, telecom etc.
3 Sealing both ends of the duct: A readily removable seal or
sealant should be used at each end of a duct. Do not use oil-based
sealant or other sealant that can damage the new water supply pipe.
Some builders use a thin layer of sand/cement, but care is needed
to avoid contact with the new water pipe. You should contact the
supplier of the pipework and sealant before selecting a material
for the job. It may be better to use a blank cap end with a purpose
made hole with grommet to allow the water pipe to pass through, if
this is available.
Water fittings laid underground It is essential that pipes
entering buildings below ground level are sealed against the entry
of fluids, vermin and insects, as diagrams 1, 2 and 3.
Where the incoming pipe:
- has less than 750mm of ground cover or the pipe enters the
building at a distance of less than 750mm from the external face of
the wall; or
- passes through an airspace below an internal suspended lower
floor, the water pipe should be insulated with suitable insulation
before being passed through the duct (see Important information
items 1,2,4 and 5 and diagrams for details).
Where compliance with the minimum cover of 750mm is impractical,
and with the written approval of United Utilities, the water
fittings should be installed as deep as is practicable below the
finished ground level and be adequately protected against damage
from freezing and from any other cause.
Q. 8 Specification for laying and joining of pipes
MATERIALS
2.1 Pipe Types
The perforated pipes shall conform to the requirements for the
class, type of joints,
diameter and length shown on the drawings and as defined in the
job specification,
and prior to perforation shall be one of the following
types:
2.1.1 Ceramic pipes complying with NZS 1823:1967, "Ceramic
(Earthenware) Sewer
Pipes for Use with Flexible Joints".
2.1.2 Unreinforced concrete pipes complying with the
requirements specified for Class C
pipes in NZS 3107:1978, "Precast Concrete Drainage and Pressure
Pipes".
2.1.3 Reinforced concrete pipes complying with the requirements
specified for Class S
(standard reinforced) or stronger pipes in NZS 3107:1978,
"Precast Concrete
Drainage and Pressure Pipes".
2.1.4 Corrugated steel pipes complying with AS 1761-1979
"Helical Lock-Seam
Corrugated Steel Pipes".
2.1.5 Nestable corrugated steel pipes complying with AS
2041-1977, "Corrugated Steel
Pipes, Pipe-Arches and Arches".
2.1.6 Plain wall PVC pipes complying with AS/NZS 1260:1999 PVC
pipes and fittings
for drain, waste and vent applications,Class SN4 or SN6.
2.1.7 High density polyethylene pipes complying with the
requirements specified for drain
pipes in NZS 7604:1981, "High Density Polyethylene Drain and
Sewer Pipe and
Fittings"
The perforations shall be circular 6.5 mm (+ 1.5 mm) in
diameter, arranged as shown
in Appendix 1` of this specification.
2.1.8 High density Polyethylene smooth bore perforated
Corrugated Plastic pipe which
shall, when tested in accordance with Appendix H of AS:2439,
Part 1-1981
"Perforated Drainage Pipe and Associated Fittings", have a pipe
stiffness of not less
than 500 at 5% deflection, and 400 at 10% deflection.
F(kN)
Pipe stiffness = ____________________________________
_y(m) x Measured specimen length (m)
Joints
The manufacturers recommended jointing system shall be used.
When rubber rings are used in flexible joints they shall comply
with BS 2494:1986
"Materials for Elastomeric Joint Rings for Pipework and
Pipelines", and shall be of a
type approved for use with the particular joint
Filter Material
Unless otherwise specified the filter material shall be as
follows:
Filter material shall be clean, durable stone having a crushing
resistance of not less
than 100 kN when tested in accordance with NZS 3111:1986 Section
14 or a mixture
of such material with clean hard sand.
The filter material when tested in accordance with NZS 4402 Part
2:1986, shall
comply with the following gradings:
TEST SIEVE APERTURE PERCENTAGE PASSING
26.5 mm 100
13.2 mm 85- 100
9.5 mm 80 95
EXCAVATION
Trenches shall be cut in such a manner as will ensure that the
pipes will be laid true to the
depths, grades and lines shown on the drawings. The width of the
trench shall not exceed
the specified dimensions.
Unless otherwise specified trenches shall have:
(i) a gradient of not less than 1 in 100;
(ii) vertical sides from the trench bottom to a minimum of 300
mm above the top of the
pipe; and
(iii) a minimum depth that will ensure that, when the pipes are
laid, the invert level shall
be not less than 1 metre below finished subgrade level.
Each pipe shall be individually set true to line and level.
All types of joints must be assembled according to the
manufacture's instructions.
Solvent weld joints may be used for PVC pipes.
Couplers to connect corrugated plastic pipes shall have gripping
lugs to engage the external
corrugations.
Pipe jointing shall be carried out in such a manner that the
finished joints present a smooth
invert surface between pipes.
The spigot and the inside of the socket of pipes shall be clean
before jointing.
When rubber rings are used for flexible joints in concrete and
ceramic pipes they shall be
free of dust, grease or dirt. The rubber rings shall be mounted
evenly on the extreme end of
the spigot, and the pipe lined up truly concentric with the
pipes already laid.
Q9- what is sewer or sewage? Explain its common sections.
The Wastewater Treatment Process
Sewage Treatment refers to the process of removing contaminants,
micro-organisms and other types of pollutants from wastewater.
Wastewater, or raw sewage, is water that drains from toilets,
sinks, showers, baths, dishwashers, washing machines and liquid
industrial waste. It is treated in a multi-stage process by the
Water Companies that make it safe to return to the environment.
The wastewater undergoes several stages in its municipal
treatment process for Environmental Protection:
Pre-Treatment
This involves the screening and removal of large debris,
including sanitary towels, tampons, sticks, leaves, rags,
wet-wipes, etc. from the raw sewage as these are not readily
biodegradable by the process bacteria. They are then dried and sent
to landfill sites or incinerated.
It also involves the removal of sand and grit which is settled
out in tanks and also removed to landfill sites.
Primary Sewage Treatment
This is another settlement stage, during which mainly organic
solids sink to the bottom and form a sludge and fats rise to the
surface and form a scum or crust. This crust is colonised by
aerobic bacteria (they breathe oxygen) and partially digested. The
liquid between these two layers drains off for processing in the
Secondary treatment stage and the sludge and crust are removed
periodically for further treatment.
Secondary Sewage Treatment
This stage involves the introduction of oxygen to the sewage and
uses aerobic bacteria to break down the organic matter, coming
mainly from human body waste, in the liquid part of the sewage.
They also reduce the amounts of other contaminants, detergents,
etc. and the quality of the resulting effluent is usually regarded
as safe for discharge to a watercourse, unless the watercourse is
sensitive or already polluted. The dead bacteria and humus are
allowed to settle out in a clarifying chamber and this sludge is
alsoremoved periodically for further treatment. Allsewage treatment
plants must have an EN 12566-3 2005 certificate for acceptance by
the Environment Agency.
Tertiary Treatment
This stage is required for sensitive discharge points eg. trout
streams. Tertiary treatment involves a further aerobic stage,
floowed by an oxygen depleted stage, which reduces nitrogen and
phosphorous. It can also include a disinfection process using UV
light, chlorination or ozone treatment to remove bacteria and
viruses.
