Wastewater Content Flashcards
Fresh water accounts for what percent of total water?
2.5%
The 5 uses of water
domestic
industrial
commercial
public
leakage & wastage
UK water usage (L/capita.day)
150 L/capita.day
What is the average daily demand?
The average of the total amount of water used each day during a 1 year designed period
What is the maximum daily demand?
the maximum total amount of water used during any
24-hour period (e.g. the highest demand during a 3 year period). Note: This
number should consider and exclude any unusual and excessive uses of water
that would affect the calculation i.e., a broken water main.
What is the maximum hourly demand?
the maximum amount of water used in any single
hour of any day in a 3-year period. It normally is expressed in litre (or gallons) per
day by multiplying the actual peak hour by 24.
Water (properties)
Universal solvent
suspends fine solids
Explain the hydrological cycle
The hydrological cycle, also known as the water cycle, describes the continuous movement of water on, above, and below the Earth’s surface. It begins with the evaporation of water from oceans, lakes, and rivers, forming water vapor in the atmosphere. This vapor then condenses into clouds, leading to precipitation in the form of rain, snow, or other forms of water, completing the cycle as it returns to the Earth’s surface.
Water quality characteristics (Physical)
*Total solids (remain after
evaporation)
*Suspended solids (clay, silt,
algae…)
*Dissolved solids (TS-SS;
salts)
*Turbidity (colloidal matter,
reduces clarity of water)
*Colour (suspended or
dissolved)
*Tastes/odours (organics
from algae, decomposed
organics, industry,
detergents, H2S in GW)
*Temperature
Water quality characteristics (Chemical)
*pH (natural waters: 5 to 8.5)
*Major cations (Ca2+, Mg2+, Na+, K+)
*Minor cations (Fe2+ and Mn2+)
*Major anions (HCO3
-, SO4
2-, Cl-.)
*Minor anions (F- and NO3
-.)
*If NH4
+ and NO3
- are high indicative
of possible waste contamination
*Alkalinity (CO3
2-, HCO3
-, and OHcontent)
it is important in
coagulation, in lime-soda softening,
buffering capacity of a water.
*Acidity due to CO2
*Hardness (polyvalent metallic ions,
principally Ca2+ and Mg2+ scale as
CaCO3, GW is harder than SW)
*Conductivity (TDS=A×EC)
*Dissolved gases (O2, CO2, H2S, NH3,
N2, and CH4. )
*Chemical pollution (pesticides, NO3
-,
BrO3
-, DBPs, PPCPs, EDCs).
Water quality characteristics (Biological)
*Microbes are common in SW but
absent in GW (bacteria, protozoa,
fungi, algae, and viruses).
*Most bacteria in water are
beneficial to humans, but some
bacteria present in polluted
waters are pathogenic and can
cause waterborne diseases
*The coliform bacteria
Escherichia coli and Aerobacter
aerogenes, are indicator
organisms of pollution and easy
to test in the lab.
*Actinomycetes, fungi, and algae
are microbes that produce end
products that may cause tastes
and odours in water supplies.
How should water sources used for drinking water be protected from chemical contamination?
through land-use control,
definition of protection zones and application of adequate wastewater
treatment.
What is WHO?
prescriptive water-quality standards covering a range of physical- and chemical-quality
parameters for drinking water, started in the 1950s and still continues.
USA standards
The current National Primary and Secondary Drinking Water Regulations.
Primary standards are legally enforceable and secondary relate to aesthetic parameters and
are non-enforceable.
Typical standards (BOD5, TSS, P, N)
BOD5: 150 to 40mg/L
TSS: 150 to 400 mg/L
P: 5 to 15 mg/L
N: 40 to 80 mg/L
UK standards
BOD5, TSS
UK standards
BOD5: 20 mg/L
TSS: 30 mg/L
Nutrient standards
P, N
Nutrient standards if discharging
to sensitive areas:
P: 1-2 mg/L
N: 10-15mg/L
What is surface/storm water
clean water collected from roofs and paved
surfaces.
What is DWF
DWF: “the average daily
flow to the treatment works
during seven consecutive
days without rain (excluding
a period which includes
public holidays) following
seven days during which the
rainfall did not exceed 0.25
millimetres on any one day”.
DWF equation
DWF = LP + I + E
L: per capita consumption; P: population;
I: infiltration, E: industrial and commercial
effluent contribution.
treat 3DWF+ holding tanks for a further 3DWF;
excess of 6DWF overflows untreated to the
receiving water.
If discharge is to sensitive areas (e.g. beach),
then use 6DWF(treatment) + 6DWF(holding tanks)
DWF can be approximated by an equivalent
to 225L/head.day
Four components that make up WW flow
- Domestic
-industrial - Infiltration/inflow
- Stormwater
What can infiltration be estimated on
based on the area served by the collection system, it
may range from 0.2 to 28 m3/ha.day.
These rates can be reduced if additional care during construction of sewer lines is
taken to adequately seal the joints.
Exfiltration can result in pollution of the water supply.
If discharge to sensitive areas (DWF)
If discharge is to sensitive areas (e.g. beach), then use 6DWF(treatment) + 6DWF(holding tanks)
The elementary rational method:
The elementary rational method can also be used in urban sewer design:
Qp = 0.278CIA
Qp: flow rate (m3/s)
C: a runoff coefficient varying from 0.05 to 0.95 (e.g. for streets it varies between 0.7-0.9)
I: uniform rainfall intensity (mm/h)
A: catchment area (km2).
Residential wastewater flow as a ratio to the average.
Maximum daily 2.25:1
Maximum hourly 3:1
Minimum daily 0.67:1
Minimum hourly 0.33:1
Minimum pipe velocity, for flushing
> 0.75 m/s.
Maximum pipe velocity to prevent scouring and separation of liquids from solids
< 3.5 m/s
Peaking factor for domestic wastewater flowrates
Peak hourly flowrate = Average flowrate
* Peaking factor
(Use Chart)
Peak hourly flow rates are used to size
the hydraulic conveyance system and other
facilities such as sedimentation tanks and chlorine contact tanks where little volume is
available for flow dampening.
Sewer definition
A sewer is an artificial conduit (or pipe) or system of conduits used to remove
sewage (human liquid waste) and to provide drainage.
Mogden formula
C = R + V + B * O_t/O_s + S S_t/S_s
C : Charge per unit of effluent
R : reception and conveyance charge
V : volumetric and primary treatment cost
B : biological oxidation costs for settled effluent
Ot : the effluent COD following one hour quiescent settling
and with pH adjusted to 7.0
Os : the COD of the sewage
S : treatment and disposal costs of primary sewage sludge
St : TSS (total suspended solids) of the effluent
Ss : TSS of the crude sewage
