THESIS ON SEQUENTIAL BATCH REACTOR
1.1 Introduction
Increasing
population of the world has increased the demand of water manifold but the
United Nation report on the world water developments has published that lots of
cities suffer from water scarcity and and the water available is also getting
polluted rapidly due to industrialization and many development processes. Out
of our total available water 97% is barkish and only 3% is fresh out of which
only 1% is available for consumption. But due industrialization or
agriculturalization even the fresh river water or ground water is getting
contaminated. River Ganga one of the purest and holiest river of all the time
has got polluted to such an extent that is now not fit even for bathing
purpose. Love canal in USA is also a classical example of ground water contamination.
So all these problems are becoming threat to man-kind and the need for
treatment of waste water before releasing in to the natural sources has became
indispensable.
Industrial
activities produce various hazardous pollutants in to sewage which have been
characterized by Environmental Protection Agency (EPA) in to three groups:
priority, conventional and non conventional. The purpose of sewage treatment is
to fulfill the significant discharge standards set down by the CPCB. Sewage
treatment could be done by many methods such as aerobic, anaerobic, or mixed
where the bacteria feed the organic matter and grow in size by multiplying and
thus settles down as sludge which could be removed by sedimentation. Aerobic
processes are preferred mostly because they don’t produce foul smell but
whenever high concentration of organic matter is present then anaerobic process
is followed.
Sewage
treatment plant (STP) is required to treat and make the effluents compatible
for their disposal in to the environmental sources such as rivers ponds or any
underground resource to eliminate or reduce the contamination factor and thus
reducing their hazardous after- effects. Various types of treatment plants are
available for the treatment of sewage out of which SBR is among most advanced
and efficient technology.
The
Sequential batch reactor is a fill and draw activated sludge system for the
treatment of waste water where the aeration and setting phase occurs
simultaneously in the the same tank which requires less space. The problem of
rising sludge encounterd in ASP is also eliminated in it and hence it may be
referred as modified activated sludge process (Mace and Mata-Alvarez 2002).
Moreover SBR is also widely acceptable for the treatment of winery waste water
due to their particular characteristic: high organic load associated to higher
biodegrabality (BOD5/COD ranges between 0.5 to 0.6 and 80% of the
COD is soluble).COD concentration is also ten to hundred times higher than
normal (Basset et al., 2014). Apart from
above SBR is able to remove very high BOD loading so it is very efficient in
treating Dairy waste, sugarcane industry waste, medical waste etc.
The
sequential batch reactor process periodic fill and draw system with complete
mixing taking place during during the batch reaction reaction step just after
filling the reactor and and subsequently aeration and clarification occurring
in the same tank. SBR process generally comprises of five steps following in
proper sequence as follow: 1 fill, 2 react or aerate, 3 settle or sedimentation
or clarification, 4draw or decant and last step is 5 idle which is the rest
time between two operational cycles. Several modifications in process handling
have been made in the times associated with each steps to improve the
efficiency, for better granule formation, for better nitrogen and phosphorus
removal. Studies have shown that almost all types of granules are formed in
SBR.
Sludge
wasting is regarded as important feature in the SBR operation that greatly
affects its performance. Wasting is not included as one the five basic steps as
no set time period within is dedicated to it within the periodic cycle. Sludge
wasting mostly occurs during the react
phase so that a uniform discharge of solids including larger flocs as
well as fine materials occurs. So proper knowledge of Bio Kinetics is very
useful in determination of proper size, control and operations. Studies of bio
kinetic parameters gives an idea abiut the yield and also the decay rate rate
at which the organisms decay so it provides basic information about required
size of the reactor. A unique feature of the SBR system is that there is no
need for a return activated sludge (RAS) system to be provided (Metcalf &
Eddy). Because both aeration and settling occurs in the same tank, therefore no
sludge is lost during the react phase and non has to be returned to maintain
the solids content in the aeration chamber.
The
process modification is very easy due to flexible nature of the SBR. The
cycles, hydraulic retention time (HRT), sludge retention time (SRT) can be
changed and hence it provides wide scope for treatment that is too in a single
reactor which is most advantageous factor. SBRs are also used as pre or post
treatment options along with other treatment facilities successfully. As per
the experimentation conducted by various
authors removal efficiency of SBR for Chemical Oxygen Demand (COD), Biochemical
Oxygen Demand(BOD), Total Nitrogen(TN), Total Phosphorus(TP), nutrients, total
suspended solids(TSS) etc. is more satisfactory compared to conventional
methods.
A
wide research work is going on SBR for different processes to be followed. Many
researchers use advanced methods like many algae to be used or using activated
carbon for better improvements.
Characteristics
of waste water
It
is indispensable to know about the quality and characteristics of waste water
which is to be treated and various types of pollutions which could be present
in that.
The characteristics of the wastewater can be characterized
under physical, chemical and biological heads. Physical characteristics
consists of color, temperature and weight. The recently produced wastewater is
of grey color but as the time passes, it changes to black color. Besides this,
the solids present in the wastewater enhance the weight of the wastewater which
has been calculated 1,000,000 gm in one cubic meter in the wastewater. The temperature of the wastewater is higher
than the normal water because of the
heating pipes in the structures and various other activities. The temperature
of the wastewater is estimated to be in between 20 and 30oC.
Industrial activities produce various hazardous pollutants
into sewage, which can be further observed through studying Environmental
Protection Agency (EPA) which categorized these pollutants into various
groups: priority, conventional and
nonconventional.
1.2 Objective
The
objective of the present investigation was aimed to assess the performance of
sequential batch reactor for COD removal in complete reaction cycle. The main
purpose of the designing SBR system is to design the biological kinetics
parameters such as yield coefficient (Y), life form decay rate coefficient (Kd),
COD removal rate (K), half velocity
constant (Ks), and maximum specific growth rate (Um),
which serves as the key factor in governing the treatment process of SBR and
their respective size handling and HRT of the system. Proper determination of
biological parameters gives good efficiency.
Chapter 2
2.1 Review of Background
Bibliography
In
the past, wastewater treatment was meant of releasing the pollutants into
rivers. The earlier wastewater treatment attempts were releasing the pollutants
into rivers, which were the sources of many water supplies. Sewage systems design came in to the
notice when the research made by Louis Pasteur and his colleagues shew that the
bacteria which is subsisted in sewers can cause fatal diseases. Sewer systems
started to grow from the early 1900s but with the development of cities, there
were less space available for disposal and
filtration furthermore, because of the increase in the population, the
amount of wastewater produced increased rapidly. All this lead to the large
dimension of treatment facilities today and thus former designs proved to be
unsatisfactory for present needs in society.
2.2
Sequencing Batch Reactor History
Activated Sludge process has become the most
broadly used secondary unit process for the treatment of sewage. Arden and
Lockett’s investigations during 1913 involved aerating sewage for several weeks
after which the treated liquor was allowed to settle and the supernatant liquid
was decanted. Thus, the activated sludge process was firstly operated as a
batch reactor and were identified as the fill & draw method. Sequential batch
reactor treatment process may be characterized by a repeated cycle which
consists of series of sequential process phases; filling, reaction, settling,
& decanting.(Kader, 2009)
2.2.1
Activated Sludge process
Enacted muck process is the most broadly utilized suspended development process for metropolitan wastewater treatment. The treatment of wastewater is finished by an organic procedure, which takes after high-impact process and happen in the air circulation tank where the wastewater is circulated air through with oxygen. By making reasonable conditions, microscopic organisms develops quickly which frames runs and gases and consequently rushes are then expelled by an auxiliary clarifier.Thus, in the initiated slop process, the scattered development reactor is an air circulation tank or a bowl which contains the suspension of the wastewater and microorganisms called the blended alcohol. The materials of the air circulation tank are blended completely by air circulation gadgets which supply oxygen to the organic suspension. Water powered maintenance time in the air circulation tank for the most part goes between 3 to 8 hours anyway can be higher with wastewater containing higher BOD. Air circulation of wastewater containing waste natural issue is done in an air circulation bowl where smaller scale life forms uses both dissolvable and suspended natural issues. At that point a piece of the natural issue is orchestrated into new cells and other part is oxidized to carbon dioxide and water to acquire vitality. In enacted slop process the new cells which are produced amid the response are expelled from the water as flocculated ooze in settling tanks. After the air circulation process, microorganisms get isolated from the fluid by sedimentation process and consequently the elucidated fluid is optional effluents. Reusing of a piece of optional gushing is an imperative normal for ASP with a specific end goal to keep up a high blended alcohol suspended strong (MLSS) level. The rest of the bit is expelled from the tank and sent to slime handling unit to keep up a generally consistent grouping of microorganisms in the framework. Distinctive varieties of the essential enacted muck process like oxidation jettison and expanded air circulation are in like manner utilize, anyway the key is comparative.
2.2.2
Sequential batch reactor cycles
Sequencing
Batch Reactor is another appreciative method for the treatment of wastewater.
SBR is called an unsteady activated sludge system in which the wastewater
undergoes various stages successively in a single reactor. Basically we can
interprete the SBR as a set of
containers that works on a fill and draw basis. Each tank in the SBR is filled during a discrete period of time and
then works as a batch reactor. After the desired aeration and mixing is done,
the mixed fluid is allowed to settle for some time and after that clear supertant
is drawn from the tank.
Each
cycle in the SBR system consists of five distinct time phases: Fill, React,
Settle Draw and Idle. Several types of Fill and React phases are available,
that differ in accordance of their aeration & mixing method. Sludge produced
may be wasted either after the end of react or during Settle, Draw or Idle
period. A properly designed SBR can be constructed by any usual continuous flow
activated sludge system by providing some SBR tanks in parallel. The primary
processes occurring in a sewage treatment method of Fill React, Settle and Draw
are carried out in a single batch reactor. The order of these operations
carried out for the effective treatment involves five phases - Fill, React,
Settle, Draw and Idle which are explained as below.
2.3 Process of SBR
Simple
working of SBR consists of following steps.
a)
Fill
The fill process comprises of filling the
reactor with wastewater between a low water level and a high water level. The
influent to the reactor could be either raw wastewater or primary effluent and
is distributed into the retained settled sludge. Fill process could occur under
mixed, unmixed, aerated or non aerated conditions. In practical, any aeration system (i.e.
floating mechanical, diffused, or jet) could be used. The feed amount to be
used is determined based on a number of parameters such as loading rate, HRT
(hydraulic retention time), F/M (food to microorganism ratio), and settling
characteristics of the organisms. The time of fill depends upon the capacity of
each reactor, the number of parallel reactors in operation, and the variations
in the wastewater flow rate. (Aziz et al., 2011)
b)
React
The
react phase begins once fill is completed which includes mixing and aeration
(dissolved oxygen (DO) > 2 mg /L). During this phase, no influent flow into
SBR aeration and sludge could not be wasted (Surampalli et al., 1997). Aeration process
serves to oxidize organic carbon, nitrify ammonia, and promote uptake of phosphorus in the sludge, while
anoxic conditions support denitrification of nitrite and nitrate into nitrogen
gas. Time donated to this phase could be as high as 50% or even more of the
whole cycle time (Al-Rekabi
et al., 2007).
c)
Settle
When the react phase ends, settle phase
starts. During this phase, neither influent flow to SBR nor wastage of sludge
is permitted. It means that the settle phase begins when all the mixing and
aeration processes are turned off and the mixed liquor suspended solids (MLSS)
is allowed to settle down and Clear supernatant appears in the upper part of
the reactor. The duration of settle can be adjusted for sludge settleability
depending upon the characteristic of sludge.
d)
Decant
Once settle process terminates, the treated
wastewater is withdrawn from the reactor and discharged during decant phase.
During this phase, no influent flows to SBR as well as no aeration is conducted.
The decant process takes place after an important depth of supernatant has
appeared and the supernatant is decanted from the upper part of the reactor via
automatic valves or other proper measures.
e)
Idle
The period included between draw phase and the
fill phase of the next cycle is termed as idle. The idle time may be employed
effectively to waste settled sludge. It is an optional phase and no influent is
fed to the reactor meanwhile in addition to the absence of aeration. This
process could be cancelled when an
influent, holding tank, balance tank, or some other techniques of handling
overload flow is obtainable. In addition, it could also be eliminated where two
or more tanks are used.
Figure
2.1: Schematic diagram of sequential batch reactor
2.4 Advantages of SBR
Lower effluent COD: The effluent obtaining
from the batch reactor will have lower COD. The batch nature of the process and
the feast period i.e., high organic concentrations during Fill promotes the
growth of organisms with high organic uptake rates. The famine period at the end
of React phase shows the utilization of recalcitrant organics. The combined
effect of these feast and famine periods is the optimal removal of BOD and COD
Better Settling Sludge: The feast and famine conditions that occur
in each cycle promotes the growth of floc-forming organisms and thus has the
tendency of having good settling of sludge.
Smaller Footprint: The elimination of the external clarifier
reduces the area to be used by sequential batch reactor i.e., the system
footprint. Existing conventional flow systems can be easily and economically
retrofitted into an SBR operation when additional capacity is desired, but no
additional land or tanks are available.
Greater Flexibility:
If it becomes necessary for nutrient removal in the future, cycles within the
system can be easily modified. This feature of the system provides greater
operational flexibility.
2.5 Disadvantages
·
It is a non- continuous flow system.
·
A higher level of experience of timing
units and controls is required (compared to conventional systems), especially
for larger systems.
Higher
level of maintenance (compared to conventional systems) is associated with more
sophisticated controls, automated switches, and automated valves.
2.6 Literature Review on Sequencing
Batch Reactor history
(Chan et al., 2011) done the review
in which the treatment of metropolitan wastewater is finished by performing
coagulation as a first procedure taken after by SBR treatment. An alternate
outline was endeavored for the SBR reactor in this review. This permits
ceaseless inflow of wastewater while the other bunch shrewd working strides of
the SBR procedure are held. The SBR cycle is 12 hrs. Two punctured puzzle
plates that contains a substantial number of 2-mm gaps which possessed an
aggregate surface region around 20% of the plate, isolated the SBR tank into
three equivalent compartments. This punctured astound plate served to limit the
impact of the persistently in-streaming wastewater on the "settle"
and "draw" periods of the SBR procedure. The changed SBR results were
contrasted and ordinary SBR comes about and presumed that adjusted SBR gives
similar outcomes with extra preferred standpoint of consistent stream. The COD
and BOD evacuation was 93.7% and 91.9 % individually.
(Li and Zhang, 2002) completed the
SBR procedure for treating dairy wastewater with different natural burdens and
HRTs. At one day HRT and 10000mg/l COD, the evacuation effectiveness of Total
solids, Volatile solids, COD, Total Kjheldal Nitrogen (TKN) and nitrogen was
accounted for to be 63.4, 66.3, 80.2, 75 and 38.3% individually.
(Mohseni-Bandpi and Bazari, 2004) played out the
seat scale oxygen consuming SBR procedure to treat the wastewater originating
from a mechanical drain production line. The variety of natural stacking, air
circulation period and cycle period were done in the SBR framework. The
outcomes acquired were especially tasteful since the COD expulsion was over 90%
in all conditions. The adaptability and treatability of the dairy waste was
shown in this review.
(Kayranli and Ugurlu, 2011) examined the
treatment of artificially arranged wastewater to watch the measure of organic
supplement evacuation and to discover controlling elements on them as broke
down oxygen (DO), oxidation lessening potential (ORP) and pH. The SBR framework
was tried for different SRT's i.e. 10, 15 and 25 days. The individual profiles
of pH, DO, nitrogen evacuation, phosphorus expulsion and ORP were plotted
verses process duration.
(Ben et al., 2009) examined the
achievability of all the while nitrogen and phosphorus expulsion from swine
compost in SBR. The 8 hr. per cycle SBR was performed with rotating
anaerobic–anoxic–aerobic conditions watched the diminishments of aggregate
nitrogen, add up to phosphorus, COD, BOD5 and turbidity by around 98, 95, 96,
100, and 95%, separately. The centralizations of smelling salts nitrogen and
solvent phosphorus (SP) were likewise diminished by around 100 and 97%.
(Scheumann and Kraume, 2009) completed the
examination to treat landfill leachate in SBR to appraise the BOD5 and COD
evacuation effectiveness and biomass yield coefficient. At different HRTs, SBRs
were worked with oxygen consuming anaerobic condition and high-impact condition
i.e. with and without anoxic stage. It was watched that because of progress in
HRT there is no adjustment in BOD expulsion proficiency yet COD evacuation
productivity was influenced of around 4 to 5 % in both conditions. Additionally
there is significant increment in biomass rot rate.
(Neczaj et al., 2007) explored the
investigation of SBR for co-treatment of dairy wastewater and leachate. Two
consecutive cluster reactor setups were utilized, among which one was treating
only dairy wastewater while other was dairy wastewater having 25% weakening of
landfill leachate. Creators performed explore by doing variety in air
circulation period. The most reasonable air circulation period for co-treatment
of dairy wastewater and landfill leachate was 19 hrs with anoxic period of 2
hrs. The COD, BOD and TKN evacuation efficiencies were 98.4%, 97.3% and 79.2%
separately which indicates attractive treatment capacity of SBR. Creators
likewise explored different avenues regarding variety in HRT alongside changed
natural stacking rate (OLR). The outcomes appeared there is huge impact on
expulsion proficiency i.e. proficiency was lessened because of not so much HRT
but rather more OLR. The best gushing quality was seen under OLR of 0.8 kg
BOD5/m3 d and HRT of 10 days for co-treatment procedure of landfill leachate.
(El-Gohary and Tawfik, 2009) gone for
expulsion of shading and COD of receptive colors wastewater. The utilization of
SBR in this review was for expanding proficiency of COD expulsion. The bolster
to the SBR was artificially pretreated wastewater with alum and Cytec. The COD
expulsion effectiveness of SBR was 68% and 76% for BOD evacuation. Creators
specified about the presentation of anaerobic process for color expulsion rather
than substance treatment before SBR treatment which is not been tested in this
review.
(Majumder and Gupta, 2009) checked the
execution of SBR under different groupings of colors in the influent. The
execution was checked in view of color expulsion, COD, Turbidity, Effluent TSS,
blended alcohol suspended solids (MLSS), blended alcohol unpredictable
suspended solids (MLVSS) and SVI. The color evacuation productivity was
observed to be 31 to 57 % and there was no critical impact on COD expulsion and
ooze properties with respect to variety in color focus. In the experimentation
it is watched that just a single HRT (1.83 days) kept for all conditions and
there is a degree for extra experimentation with respect to volumetric natural
stacking rate and particular natural stacking rate like COD variety and
furthermore conditions can be differed like oxygen consuming, anaerobic and so
forth.
(Timur and Özturk, 1999) utilized the
six seat scale ASBR's to concentrate the treatability of landfill leachate. It
was reasoned that crude leachate with high quality can be dealt with in ASBR.
The COD expulsions of 64±85% are conceivable at volumetric and particular
stacking rates shifting 0.4±9.4 g COD/lit/day and 0.17±1.85 g COD/g VSS/day
individually. Of all the COD evacuated 83% is changed over to methane. With the
suspicion that the rest is changed over to biomass, the computed biomass yield
is 0.12 g VSS/g/CODrem. The connection between microbial development and
substrate usage was defined and consequences of biomass yield coefficient and
particular biomass rot rate steady were ascertained and furthermore tentatively
decided, the distinction between the tentatively decided and computed esteems is
sensible; and presumed that contrasted with regular technique, this strategy
can be connected all the more effortlessly.
Discourse
As
the treatment of modern wastewater is a noteworthy and confused issue with
respect to the natural contamination, one can have the better arrangement as
SBR. The wide assortment of wastewaters can be dealt with utilizing SBR as can
be finished up from the writing survey. The procedure adjustment is simple
because of adaptable nature of the SBR. The cycles, HRTs, SRTs can be changed
and consequently it gives wide extension to treatment that is too in a solitary
reactor which is most worthwhile element. A few changes are attempted like
expansion of punctured confuse plates for making the states of constant stream
in a group reactor(Lim et al., 2010) which was less
to the regale from treatment perspective. Extra review identified with
different quality of wastewater with SBR is a piece of further degree. The
adjustment in ventures regarding oxygen consuming, anaerobic, anoxic
additionally were attempted (Scheumann and Kraume, 2009; Uygur and Kargi, 2004) which likewise
were on positive side as the treatment is concerned. The adjustment of cycle
length alongside variety in stages would be further extent of study.
SBRs
are additionally utilized as pre or post treatment choices alongside other
treatment offices effectively. The substance coagulation pretreatment taken
after by SBR for metropolitan wastewater (Lin and Cheng, 2001) and furthermore
wastewater containing colors (El-Gohary and Tawfik, 2009) gave tasteful
outcomes, though the ultrasound treatment for leachate (Neczaj et al., 2005) likewise
helpful for COD expulsion. It can be seen from writing survey that supplement
from wastewater can be evacuated viably with SBR(Li and Zhang, 2002; Neczaj et al., 2008)
CHAPTER
3
Materials and methods
3.1 Design of SBR
Reactor
was fabricated under 3 parts comprising of settled sludge, next part for
supernatant liquid and third comprising of free board.Feed sludge having MLSS
of 2500 mg/l and reactor volume was
taken as 7 L.
Assuming
S.V.I as 120 mass of settled sludge was calculated as below.
Mass
of settled sludge =
Applying
mass balance
,
Providing
20% excess for uncertainity we adopt Vs as 2.5
.
Figure
3.1 Design of SBR reactor
In
this study, we have collected sludge as well as sewage from the treatment plant
present in Saidpur, Patna. For performing various experiments and various
tests, various chemicals and various equipments are required which are
mentioned later.
In the present study
experiments were carried out to acclimatize seeds under laboratory condition
for combined process of carbon oxidation, nitrification and denitrification.
Acclimatization refers to the adaptation to the new climate. From this we mean
that for the growth of microbes in the new environment, we have to prepare some
seed solution. The preparation of this seed solution is termed as seed
acclimatization.
The
whole SBR treatment process involves three stages:
1. Development and acclimatization of seed
2. Reactor fabrication
3. Reactor performance
3.2
Materials
3.2.1 Synthetic wastewater
Synthetic
wastewater was prepared according to the table in one litre solution and was
stirred properly on magnetic stirrer. After that it was diluted to 6 litre
solution to make the composition of desired strength and COD of sample was
cross checked by close reflux method. Composition of synthetic wastewater is
summarized in table 2
3.2.2 Process of acclimatization
A five litre solution of the above composition
was prepared everyday and its initial COD was calculated and then the solution
was feed to the reactor wher the whole cycle was repeated for 3 hours of cycle
and was decanted. Afterwards the COD of the effluent was calculated. The
process was repeated continuously for a period of 25 days till the COD of the
effluent became constant.
Table 3.1: Synthetic wastewater composition
|
mg/L
|
COD mg/L
|
N mg/L
|
P mg/L
|
Chemical compounds
|
Urea
|
91.74
|
23.22
|
42.81
|
0
|
Na-acetate
|
79.37
|
79.37
|
0
|
0
|
KH2PO4
|
46.8
|
0
|
0
|
6.28
|
Food ingredients
|
Starch
|
122
|
122
|
0
|
0
|
Total
|
|
225
|
42.8
|
6.28
|
3.2.3 Chemicals : name of chemical (quantity
required)
Mangnese Sulphate (500gm), Sodium Hydroxide (500gm), Potassium Iodide
(250gm), Sodium Azide (250gm), Sodium Thiosulphate (500gm), Starch Powder
(500gm), Sulphuric acid (2 lit), Potassium dichromate (500gm), Silver sulphate
(25gm), Mercury sulphate (250gm), Ferroin indicator (200ml), Sulphanilamide acid (100gm), NED
dihydrochloride (50gm), Sodium Nitrate (500gm), Conc. Hcl (1 lit).
3.2.4
Glassware
·
Volumetric flasks: 50 mL, 100 mL, 250
mL, 500 mL, 1000 mL
·
Erlenmeyer flasks: 250 mL, 100 mL
·
Measuring cylinders: 10 mL, 25 mL, 100
mL
·
Pipettes of capacity: 1 mL, 10 mL, 25 mL
·
Evaporating dish
·
Desiccator
·
Glass bottles :100 mL, 250 mL, 500 mL,
1500mL
·
Plastic bottle: 5000 m L
·
Beakers
Figure 3.2: Experimental setup of SBR during
mixed phase
Fig 3.3: Experimental setup of SBR during settled
phase
3.2.5 Equipments: Instrument used for
calculation of required parameters is summarized in table
Table
3.2: Equipment used
S. No
|
Parameters
|
Instrument used
|
1
|
pH
|
pH meter
|
2
|
MLSS
|
Drying Oven
|
3
|
MLVSS
|
Muffle Furnance
|
4
|
COD
|
Spectrophotometric technique and close
reflux method
|
3.3 Reactor fabrication
The
experiment is carried out in a reactor of volume 7 L. A feed reservoir is
required for keeping the sample from which sample is allowed to fall in reactor
under gravity with the help of some inlet tube. Sludge is placed in the reactor
up to the height of 0.2h. Now the sample is filled in the reactor up to the
height of 0.8h – 0.9 h where h= height of reactor. Some freeboard of about
50-60 mm height is maintained in the reactor. An effluent pipe is provided
slightly above the sludge level. A stirrer is provided for mixing the contents.
An air compressor generally used in large aquarium is provided in the bottom.
3.3
Methods
Total Solids
Dried at 103-105°C
1.
Heat clean porcelain crucibles to 103-105°C for 1h. Weigh immediately before
use.
2.
Transfer a measured volume of well-mixed sample to preweighed dish and weigh
the filled crucible. Dry sample for at least 24 hours in an oven at 103-105°C.
Cool dish to room temperature in desiccator and weigh.
Calculation:
mg total solids/L: ((A-B)*1000)/sample volume [ml]
A=weight
of dried residue + dish [mg],
B=weight
of dish [mg]
Volatile Solids
Ignited at 550°C
1. Ignite clean
crucible at 550 +/- 50°C for 1h in a muffle furnace.
2. Ignite
residue produced by TS-method to constant weight in a muffle furnace at a
temperature of 550°C.Have furnace up to temperature before inserting sample.
Weigh after crucible has cooled down to room temperature in desiccator.
Calculation:
mg Volatile Solids/L= ((A-B)*1000)/sample volume [ml]
A= weight of residue + dish before
ignition [mg],
B=weight of residue + dish after
ignition [mg]
Chemical
Oxygen Demand (COD)
Closed
Reflux Method
Reagents: Standard potassium dichromate
digestion solution, 0.0167M: Add to about 500ml distilled water 4.913g K2Cr2O7,
primary standard grade, previously dried at 103°C for 2h, 167 conc H2SO4 and
33.3g HgSO4. Dissolve, cool to room temperature and dilute to 1000ml.
Sulfuric
acid reagent: Add Ag2SO4, reagent or technical grade, crystals or powder, to
conc H2SO4, at the rate of 5.5g Ag2SO4/kg H2SO4. Let stand 1 to 2d to dissolve
Ag2SO4.
Procedure
1. Add 1.5ml potassium dichromate digestion
solution into a 10ml tube.
2. Add 3.5ml sulphuric acid reagent into the
tube
3.
Add 2.5ml of sample into the tube; also add 2.5ml of deionized water to two
tubes which can be used as blank.
4. Close tube tightly and shake well
5.
Place tubes in preheated block digester reflux for 2h at 150°C.
6.
Cool down to room temperature
7.
Transfer the digested sample to 10ml tubes.
8.
Analyse photometrically, using the blank to zero the Spectrophotometer (Program
600).
3.4 Kinetics for Carbon Oxidation
Kinetic
constants are evaluated for any biological treatment process for getting
appropriate design system. For COD consumption the kinetic constants are estimated according
to the equation as described below:
The
biokinetic parameters used for kinetic study are:
=
maximum substrate utilization rate per unit mass of microorganism (day-1)
=
saturation constant or half velocity constant (mg L-1)
=
yield coefficient (mg of MLVSS produced/mg of SCOD)
=
endogenous decay coefficient
For determining kinetic coefficient, following
equations are used:
Dividing
the above equation by x yields
The
linearized form of this equation was obtained by taking its inverse:
=
Mass concentration of COD utilized (mg L-1)
=
COD concentration at half the maximum growth rate suspended solids (day-1)
Maximum rate of COD utilization per unit mass
of suspended solids (day-1)
Uc
= Specific organic carbon utilization rate
(mg of SCOD/day/mg of MLVSS)
For
determining
and Y
Where
X= concentration of MLVSS
t = time in days
S = substrate concentration (
)
Arranging
equation as below
It
can be re written on finite time and mass basis
Where
= amount of specific cell mass produced
over unit time,µ(
)
= specific
substrate utilization rate, U (
)
The
growth rate may be represented as
µ =
CHAPTER 4
Results and disussions
During the present study it was found
that the COD removal efficiency was not considerable during the early days but
as the characteristics of sludge got improved due to continuous acclimatization
of seed and COD removal efficiency increased as the time elapsed. After 20 days
it was found that the removal efficiency of COD efficiency became almost
perpetual and very near to 90%.
The COD removal efficiency is as below in Fig
4.1
Figure 4.1 COD removal efficiency during
acclimatization phase.
During the cycle it was found that
substrate was consumed almostly 90% during the period of 3 hours. It was
observed that most of the COD was consumed within first half an hour of cycle.
The COD removal profile is shown as
below in Fig 4.2
Figure 4.2 COD Removal profile at
stabilized condition.
During the reaction phase it was seen
that substrate growth increased sharply during the early period of cycle but
growth rate decreased as the hydraulic retention time increased. It was seen
that growth rate almost ceased at the end of cycle. The substrate growth is as below
in Fig 4.3.
Figure 4.3. MLSS and MLVSS growth
profile during stabilized condition.
Figure 4.4 Substrate utilization
kinetics for COD of waste water in SBR
Biological kinetic equation for above
graph is as below
The
value of
and for
COD is determined as
49.11
2.62
=
=
1.86
Fig 4.4: Microbial growth kinetics for
carbon oxidation of waste water in SBR
The above graph is plotted as per
linearlized Monod equation
where,
= amount of cell mass produced over unit time
µ(1/day)
=
specific substrate utilization rate,
(1/day)
Result
62 %
=
0.013/day
Table
4.1 Bio kinetics coefficients determined from study
Coefficient
|
Basis
|
Value
|
Reference (Metcalf)
|
|
per day
|
2.62
|
2-10
|
|
mg/L COD
|
49.11
|
15-70
|
|
mg VSS/ mg COD
|
.62
|
0.4-0.8
|
|
per day
|
0.013
|
0.010-0.075
|
|
per day
|
1.86
|
|
CHAPTER 5
Conclusions
During
the course of acclimatization the sludge quality improved with the progress of
time and the steady state reached and it was concluded after the COD removal
became almost constant and efficiency reached about 85%.
The
kinetic parameters, organism decay rate (
), COD removal rate (
), yield coefficient (
),
half-velocity constant i.e., substrate(COD) concentration at one half the
maximum growth rate (
) and maximum specific growth rate (
)
governing the treatment process were found
out to be 0.013 per day, 2.62 per day,
0.62 mg VSS/ mg COD, 49.11 mg/L COD and 1.86 per day respectively. These values
are found to be very near to the normal range of bio-kinetic values for sequential
batch reactor. The higher value of sludge yield coefficient(
) and lower value of organism decay
coefficient (
) shows that there is very high
production of excess sludge in the reactor. Thus Optimum sludge removal at
frequent intervals has to be designed and sludge disposal mechanism need to be
developed.
From
the study it is evident that the
and
are directly proportional to the effluent
substrate
concentration, on the other hand μm is inversely proportional to the effluent
substrate concentration.
It
was also evident that most of the COD was consumed within first few minutes
which accounts that bacteria within famine phase were of good quality.
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