Sewage Treatment Plant (STP)

70 Pages·2014·1.51 MB·English

WWEELLCCOOMMEE
Sewage Treatment
Method of Treatment-Aerobic, Anaerobic.
• Aerobic-Sewage treatment in the presence of Oxygen-
MMBBBBRR,, SSBBRR--wwhheerree aaeerraattoorrss//bblloowweerrss aarree iinnssttaalllleedd--
generally no smell during treatment.
• Anaerobic-Sewage treatment in the absence of
Oxygen-UASB-No aerators/blowers are required-foul
smell during treatment.
Aerobic Treatment
• Continuous pumping of Oxygen is required to maintain
treatment process. The aerators/blowers have to be
operated continuously.
• The plants required to run through DG Sets in case
Electric supply not available.
• Once supply of Oxygen stopped due to non functioning of
aerators, the stabilization process interrupted and require
re-stabilization which may take much more time.
• Hence independent feeders required to ensure assured
electric supply.
Necessity of Aeration
• For tanks up to depth of 0.50 m, the aeration takes place in a
natural way.
• If the depth of tank exceeds 0.50 m, aeration system is required
to supply oxygen to bacteria. If the aeration system is not
ooppeerraatteedd ffoorr ssuucchh ddeepptthhss,, iitt wwiillll iinnddiiccaattee tthhaatt tthhee sseewwaaggee
treatment is not done satisfactorily and desired parameters will
not be achieved in any case.
• Even during flow over the launders and weirs, the aeration of
sewage takes place.
VARIOUS SEWAGE TRAETMENT
TECHNOLOGIES
• Oxidation Pond
• Moving Bed Biofilm Reactor (MBBR)
• Sequential Batch Reactor (SBR)
• Upflow Anaerobic Sludge Blanket Reactor
(UASB)
Moving Bed Biofilm Reactor (MBBR)
The STP is said to be running successfully, if:-
• The bio film layer shall accumulate on the bio media.
• The flocs should generate in Clarifier.
• The smell of sludge should not be foul.
• When starting the plant initially, the air blowers should be
operated for passing the air through diffusers and run
continuously, otherwise the desired parameters will not be
achieved.
• Fill both aeration tanks to the normal operating sewage
depth, thus allowing the aeration equipment to operate at
maximum efficiency.
Moving Bed Biofilm Reactor (MBBR)
• Using all of the aeration tanks will provide the
longest possible aeration time.
• The effluent end of the aeration tank should
have a dissolved oxygen level of at least 1.0
mmgg//LL.. DDOO iinn tthhee aaeerraattiioonn ttaannkk sshhoouulldd bbee
checked every two hours. Generally the DO is
approx. above 4 in aerated sewage.
• The COD reduction in treated sewage Vs. raw
sewage cannot be less than BOD reduction.
Sequential Batch Reactor (SBR)
• The first is to make certain that all mechanical, electrical and control
equipment is operating properly.
• The purpose of Fill-React operation is to add substrate (raw
sewage) to the reactor. The addition of substrate or filling is
controlled by a timer to a set time period. The filling operation is
also controlled by level transmitter to limit filling volume upto
mmaaxxiimmuumm lleevveell.. UUssuuaallllyy,, SSBBRR ttaannkkss aarree ddeessiiggnneedd ttoo ttaakkee ffllooww aass
it comes into STP with all variations from peak flow to minimum
flow without necessiating any equalization tank.
• The Settling process is controlled by time and is usually fixed
between 30 minutes to an hour so that the sludge blanket
remains below the withdrawal mechanism during the next
phase.
• The purpose of Decantation is to remove the clarified, treated
water from the reactor.
Sequential Batch Reactor (SBR)
• When starting the plant initially, the diffuser should be
operated first and run continuously, otherwise the desired
parameters will not be achieved.
• The precaution needed is to make sure that power supply is
available continuously. If power supply fails, immediately
bring the genset on-line.
•• CCOODD ttoo BBOODD rraattiioo iinnddiiccaatteess tthhee bbiiooddeeggrraaddaabbiittiittyy ooff tthhee
sewage. Normally, sewage will have COD to BOD ratio
between 1.5 to 2. If the ratio is more than 2, entry of
industrial effluents into sewer network is a possibility.
• The daily tests shall be COD, TSS, pH, Dissolve oxygen,
Ammonia and dissolved phosphate. BOD can be a weekly
test.
IMPORTANT ASPECTS IN ACTIVATED SLUDGE PLANT
• Oxygen is required in aeration tanks;
- Low DO in influent sewage
- Influent sewage may become septic
• Operational variables in aeration tanks
-- RRaattee ooff ffllooww ooff sseewwaaggee
- Air supply
- MLSS
- Aeration period
- DO in aeration tank and settling tank
- Rate of sludge return and sludge condition