What is a Sewage Treatment Plant?
Sewage treatment plants process and
treat wastewater/sewage, breaking it down into a cleaner ‘effluent’ that can be
returned back to nature in a safer, eco-friendly form. They help restore
groundwater balance, curb diseases and stop degradation and pollution of the
environment.
In housing societies, the treated
water can be used for non-potable purposes such as gardening, washing cars,
construction, irrigation and toilet flushing.
Cleaner water would minimize
fatalities due to water borne diseases, there’d be less negative environmental
impact from water pollution and from a much narrower point of view, no house
would have to pay for water tankers, because there’d be abundance of
groundwater on macro scales and reusable water at community levels.
STP Technologies:
◈ MBBR - Moving Bed Bio
Reactor
◈ SBR - Sequential Bio Reactor
MBBR: Moving bed biofilm reactor (MBBR) is a biological
technology used for wastewater treatment process suitable for municipal and
industrial application. Another common name is moving bed film reactor.
It was invented in the 1980s. MBBR offer an economical solution for wastewater
treatment.
How does MBBR work?
In the MBBR process, feed is
sent to an aeration tank, also called a reactor, filled with thousands of small
pieces of plastic called carriers or media. These media maximize the surface
area as they provide area for microbial growth and are similar in density to
water, so they mix well throughout the tank.
SBR: The sequencing batch reactor (SBR) is a
fill-and- draw activated sludge system for wastewater treatment. In this system, wastewater is added to a single “batch”
reactor, treated to remove undesirable components, and then discharged.
How does MBBR work?
In
the SBR process, the operator first fills the tank with influent. Ventilation
and microbes then begin to promote biological reactions. After completing this
step, purification will take place. That is, sludge will settle. This process
is usually done in a separate tank, but in SBR it is done in
the same tank that acted as the reactor for the biological process.
After
the treatment process is complete, the operator pumps the treated wastewater
out of the tank and pumps out the old sludge. This last step in the process is
called idling. After reaching this point, the SBR system can start over and
re-run a series of sub processes that introduce a new batch of feed into the
tank and convert the contaminated wastewater into purified wastewater.
Like
many other types of aeration processes, SBR is often part of a larger framework
for wastewater treatment. Other steps, such as removing sand grains, can be
done in advance, and some steps, such as disinfection, can be continued. In
some cases, depending on the quality of the inflow and the desired quality of
wastewater, the SBR itself may act as the only means of wastewater treatment.
How does a sewage
treatment plant work?
They work in four phases
– preliminary, primary, secondary and tertiary treatment.
Preliminary treatment
Removes the biggies like plastic bottles, tree branches, rags, wrappers, solid, coarse objects and materials.
Primary treatment
Occurs inside a sedimentation tank which settles to the bottom all the organic and inorganic solids while the grease, oil and lighter solids are moved to the surface using skimmers. This phase is expected to remove at least 60% of solids (mechanically scraped off and directed to sludge treatment) while the remaining water moves to the next stage.
Secondary treatment
Entails secondary clarifiers separating biological floc from the liquid with the use of aerobic biological processes (through managed indigenous microorganisms that consume biodegradable soluble contaminants). This stage is focused on intensive cleaning of water (up to 90%) after flotsam and solids are cleared in primary treatment.
Tertiary treatment
Is advanced treatment that reduces pathogens, nitrogen, phosphorus and other inorganic compounds by disinfecting the water chemically, through ultraviolet light, or micro filtration, before releasing for reuse. Sludge is treated in digesting tanks with anaerobic bacteria and later used as fertilizer.
Maintenance of STP
Low-budget STPs
need frequent emptying and monitoring but even a good one would have to be dislodged
and serviced at least once a year. After desludging, it should be immediately
refilled by water to balance the internal and external pressure.
Under no
circumstances should rainwater enter the STP. It could flush out bacteria
and cause flooding.
Emptying of
primary tanks and soakaways must be done regularly by the society, not the
manufacturer’s service staff.
Below components
should be checked during maintenance visits:
·
Unobstructed, strong and
efficient blower and ventilation
·
Mechanical components
replacement if needed
·
Inspection for air
filters and pipes inspection
·
Diffuser inspection for
bubbles
·
Biomass color and smell
check
·
Final effluent quality
·
Damage repair in all
chambers
·
Lid seal integrity
·
Replacement of
diaphragms and valve boxes
Refer to the
manufacturer’s maintenance guidelines booklet for a detailed understanding of
every protocol.
STPs require a
CFO (Consent for Operation) from the state pollution boards which have to be
renewed every five years. Consent is granted after submitting paperwork,
consent fees and a thorough inspection from regional officers of the Board.
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