2. 3 stages of water treatment
Primary
solids are separated
Secondary
dissolved biological matter is converted into a solid
mass by using water-borne bacteria
95% of the suspended molecules should be removed
Tertiary
biological solids are neutralized then disposed, and
treated water may be disinfected chemically or
physically
4. Treatment stages - Primary treatment
(physical & chemical processes)
SCREENING:-
Screening is the first operation at any wastewater treatment works. This process essentially
involves the removal of large non-biodegradable and floating solids that frequently enter a
wastewater works, such as rags, papers, plastics, tins, containers and wood.Efficient
removal of these constituents will protect the downstream plant and equipment from any
possible damage, unnecessary wear & tear, pipe blockages and the accumulation of
unwanted material that will interfere with the required wastewater treatment processes.
Wastewater screening is generally classified into either coarse screening or fine screening.
SEDIMENTATION:-
After screening the water and floc moves slowly through large basins known as
sedimentation or settling basins. The water moves very slowly through these basins due to
their large size. This allows the floc to settle to the bottom of the basin. The floc that falls
to the bottom of the basins is collected into a hopper by large rotating scrapers where it is
removed several times daily by the plant operators. Clear water above the floc layer
(referred to as treatment residuals) flows out of the sedimentation basin and to the filters.
Removal of particles in the sedimentation basin improves the operation of the filters that
comprises the next treatment process after sedimentation.
5. FLOATATION:-
Flotation is a process that involves producing small air bubbles in the water being treated.
The bubbles then attach to floc particles produced by coagulation and flocculation . The
resulting bubble-floc agglomerates are buoyant and so float to the surface of the water
where they accumulate as a floating layer of sludge, known as float, before being removed.
FILTRATION:-
Water flows through a filter designed to remove particles in the water. The filters are made
of layers of sand and gravel, and in some cases, crushed anthracite. Filtration collects the
suspended impurities in water and enhances the effectiveness of disinfection. The filters
are routinely cleaned by backwashing.
COAGULATION:-
During coagulation, liquid aluminum sulfate (alum) and/or polymer is added to untreated
(raw) water. When mixed with the water, this causes the tiny particles of dirt in the water to
stick together or coagulate. Next, groups of dirt particles stick together to form larger,
heavier particles called flocs which are easier to remove by settling or filtration.
PRECIPITATION:-
Precipitation is the most common method for removing dissolved metals from wastewater
solution containing toxic metals. To convert the dissolved metals into solid particle form, a
precipitation reagent is added to the mixture. A chemical reaction, triggered by the
reagent, causes the dissolved metals to form solid particles.
6. DISINFECTION:-
Water is disinfected before it enters the distribution system to ensure that any disease-
causing bacteria, viruses, and parasites are destroyed. Chlorine is used because it is a very
effective disinfectant, and residual concentrations can be maintained to guard against
possible biological contamination in the water distribution system.
1.SCREENING
2.SEDIMENTATION
3.COAGULATION
8. Treatment stages - Secondary treatment
(biological process)
Anaerobic wastewater treatment differs from conventional aerobic treatment. The absence
of oxygen leads to controlled conversion of complex organic pollutions, mainly to carbon
dioxide and methane. Anaerobic treatment has favorable effects like removal of higher
organic loading, low sludge production, high pathogen removal, biogas gas production and
low energy consumption. Psychrophilic anaerobic treatment can be an attractive option to
conventional anaerobic digestion for municipal sewage and industrial wastewaters that
are discharged at moderate to low temperature.
ANAEROBIC TREATMENT:-
Naturally occurring microorganisms are the workhorses of wastewater treatment.
Consisting of bacteria, fungi, protozoa, rotifers, and other microbes, these organisms
thrive on many of the complex compounds contained in domestic wastewater. Secondary-
treatment processes (found at municipal wastewater treatment plants) are highly
engineered bioreactors. These bioreactors are designed to provide the microbes with the
optimum conditions to assist in the renovation of domestic wastewater. With the
mechanical addition of dissolved oxygen, aerobic and facultative microbes can rapidly
oxidized soluble, bio-available organic and nitrogenous compounds.
AEROBIC TREATMENT:-
10. Treatment stages – Tertiary treatment
Remove disease-causing organisms from wastewater
3 different disinfection process
Chlorination
UV light radiation
Ozonation
11. Most common
Advantages: low cost &
long term effective
Disadvantages: chlorine
residue could be harmful
to environment
12. Damage the genetic
structure of bacteria,
viruses and other
pathogens.
Advantages: no
chemicals are used
water taste more natural
Disadvantages: high
maintenance of the UV-
lamp
13. Oxidized most pathogenic microorganisms
Advantages: safer than chlorination
fewer disinfection by-product
Disadvantage: high cost
15. Some modified industrial effluent
treatment methods-for removal of
Oil & grease :
Industry – from oil
refineries
petrochemicals, chemical
plants ,etc.
Method – oil-water
separator which results-
[oil-at the top, cleansed
waste water-in middle
layer, sludge-at the
bottom layer.
Acids & alkalis:
Chemical, iron & steel, food
and agricultural.
Method – neutralization
under controlled
conditions.
16. Organic materials in
waste water :
Materials – solvents,
paints, pesticides- which
are difficult to treat
Methods – distillation,
adsorption.
Biodegradable organics :
Industry – food and
agricultural industry.
Process – i] activated
sludge process
ii] biological trickling filter
[i] [ii]
