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Definitions in Waste Water Treatment
By: Haseeb Jamal
It is the measure of the settleability and compatibility
of sludge and is made from a laboratory column setting test.
The sludge volume index is defined as ‘the volume in mm
occupied by 1 gm of sludge after it has settled for a specified period of time’
generally ranging from 20 min to 1 or 2 hr in a 1 – or 2-l cylinder.
One-half hour is most common setting time allowed to the
mixed liquor to settle for 30 min. (larger cylinder is desirable to minimize
bridging of sludge floe and war effects).
Take the reading let Vs is the settled volume of sludge
(ml/l) in 30 min.
* If SVI is 50 - 150 ml/mg, the
sludge settle ability is Good.
1.The activated sludge forms the underflow of the final setting
tanks should be returned to the inlet of the aeration tanks at a rate
sufficient to maintain the MLSS concentration at the design value.
2.The flow are needed for return-sludge is determined form the
incoming sewage flow rate and the concentration at which the sludge is withdrawn
form the final setting tanks.
Hence a simple measure of the underflow concentration forms
the setting tanks is required.
The parameter conventionally employed for this purpose the
sludge volume index, SVI which is defined as 4 the volume occupied by sludge
containing 1.0g of sludge soiled (dry weight) after 30 min setting and thus it
has ht units ml/g.
Sometimes represented as SDI i.e sludge density
index. Once the SVI and operating MLSS concentration (x) is known, the
required rate of activated sludge return can be determined
R = 100 / [ 106/ (x) (SVI) -1] where
r = return sludge flow rate as a % age of incoming sewage flow.
SEDIMENTATION:
It is the removal of solid particles form a suspension by
settling under gravity.
CLARIFICATION:
It is a similar term which refers specifically to the
function of a sedimentation removal.
THICKENING:
It means the separation of water from Suspended Solids
where R = return sludge flow rate (ML/D) for Q in ML/D)
VARIATION OF THE ACTIVATED SLUDGE
PROCESS:
1. Activated sludge was introduced in 1941 and has undergone
many variations and adaptations.
2. The main objective of many modifications has been to
increase the loading capacity of the basic plug flow activated sludge plant by
provision of optimum condition design parameters for different variations are
summarized in table.
It is worthy of note that 5 modifications tapered aeration
step aeration the CMAS process, the pure oxygen system and the deep shaft
process all aim at either the improvement of oxygen transfer efficiency t the
efficient distribution of available oxygen to match demand.
A flow sheet of most of the commonly used variations is
similar to that of CAS (Conventional Activated Sludge).
CONVENTIONAL ACTIVATED SLUDGE:
Volumetric loading = kg of BOD
m3-d
Aerial loading rate = gm of BOD
m3-d
Td = V/Q in days and greater than 5 days.
m3-d
Aerial loading rate = gm of BOD
m3-d
Td = V/Q in days and greater than 5 days.
ALGAL-BACTERIAL SYMBIOSIS:
The combined and mutually- been facial action of algae and
bacteria in this process is called algal-bacterial symbioses.
·
Shock loading
(CSTR)
·
BODu
Aerate lagoons are activated sludge units operated without
sludge return.
Historically they were developed from waste stabilization
ponds in temperate climate where mechanical aeration was used to supplement the
algal oxygen supply in winter.
It was found, however that soon after the aerations were
put into operation the algal disappeared and the microbial flora resembled that
of activated sludge.
Aerated lagoons were now usually design as completely
mixed not-return activated sludge units.
Floating aerates are most commonly used to supply the
necessary oxygen and mixing power.
Anaerobic sludge treatment cell Primary Sedimentation Tank
and Secondary Sedimentation Tank are basically organic these can be treated to
aerobic.
· Anaerobic ponds and
septic tank are for waste water treatment.
· Sludge treatment =
Anaerobic sludge treatment.
·
Two stage digestion
up
·
High rate digestion
up
·
Fixed film
processes. A swm zone
SLUDGE: the concentrated
impurities settled at the bottom of the flower bed of sedimentation tanks.
Digestion:
To decompose or breakdown by heat and moisture or chemical
action. (to invent food equable forms)
Sludge treatment:
Anaerobic digestion it is defined as ‘it is the use of
microbial organisms in the absence of oxygen for the stabilization of oxygen
materials by conversion to mean and inure produce including CO2.
Organic matter + H2O (amoebas) CH4+
CO2 + NH3+ H2S + heat
Benefices of anaerobic digestion. Types of anabolic
detectors. It’s of two types:
· Conventional
(stranded) or low-rate digester or cold digester.
· High rate digesters
/ two stage digester are characterized by continuous miring except at time of
sludge with draw.
Haseeb Jamal. I am a Civil Engineer, graduated from University of
Engineering and Technology, Peshawar, Pakistan in 2010. I also have a
PG-Diploma in Disaster Management and MS in Urban Infrastructure Engineering
(In Progress). My expertise include civil related softwares like AutoCAD,
SAP2000, MS Project, Primavera, MS Office and GIS. My technical skills include
project management, monitoring and evaluation, structural assessment, disaster
risk management, Quantity survey, land survey, material testing, site management
and technical writing. I am trained in writing project progress reports as well
as proposals and concept papers. I have also received advanced training on
surveying, proposal writing, Monitoring and Evaluation of projects as well as
organizations.I have worked as Project Engineer at National Research and
Development Foundation, Peshawar and CENCON Associates. I also worked with
Spectra Engineering Solutions as Senior Civil Engineer in monitoring of World
Bank and UNDP funded projects all over Khyber Pakhtunkhwa and FATA. Currently,
I am working as Deputy Manager Development at NayaTel, Peshawar.
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