CHAPTER 1

INTRODUCTION
CHAPTER 1
INTRODUCTION
1.1. Domestic wastewater and its treatment
Water is one of the most critical resources for ensuring sustainable development. Many
developing countries are facing a water crisis due to increasing urbanization. Most of the
sources used for drinking water are getting polluted due to the discharge of untreated or
partially treated effluent. This discharge of untreated/ partially treated wastewater
contributes to improper sanitation, which causes many diseases. Substantial savings can
be made in the basic healthcare cost by providing appropriate wastewater collection and
treatment systems. The wastewater treatment process is generally classified into primary,
secondary and tertiary. Primary wastewater treatment consists of a screen chamber, grit
chamber, oil and grease trap and primary sedimentation tank provided for removal of
coarse solids, large floating objects, and settleable organic and inorganic solids.
Secondary treatment consists of biological treatment with the objective to remove
residual dissolved and suspended organic matter measured as Biochemical Oxygen
Demand (BOD) or Chemical Oxygen Demand (COD) and Nitrogen. Tertiary treatment is
provided for the removal of specific constituents, which cannot be removed by secondary
treatment. Conventionally, most of the domestic wastewater treatment plants are provided
with a screen chamber, grit chamber, oil and grease trap, and primary sedimentation tank.
The selection of technology for secondary treatment depends on applicability, flow rate
and its variation, sizing of units, sludge treatment, energy requirements, operating and
maintenance requirements and reliability (Metcalf and Eddy, 2005)[1]. In October 2017,
the Government of India has amended standards for discharge of treated effluent from
Sewage Treatment Plant (STP). More stringent standards are specified for effluent
discharge into water bodies as well as for land disposal/applications. Parameters such as
pH, BOD, Total Suspended Solids (TSS) and Fecal Coliform are included in standards
whereas the standard for Nitrogen is not included. In such a scenario, domestic
wastewater collection and its treatment to disposable standards is essential. It is necessary
to provide wastewater treatment systems either centralized or decentralized owing to the
urgent need for improved sanitary infrastructures in developing countries.

1.2. Decentralized wastewater treatment

A centralized system consists of a sewerage network for the collection of domestic
wastewater from the entire service area and its treatment at a central facility. Wastewater

1
is typically treated in a conventional treatment plant consisting of primary and secondary
unit operations/processes. Additionally, tertiary treatment may also be included as per the
requirement of discharge standards. In most of the domestic wastewater treatment plants,
conventional biological treatment technologies such as Activated Sludge Process (ASP)
or Trickling Filter are used for a centralized process (Tchobanoglous and Angelakis,
1996) [2]. It is possible to develop a centralized plant in stages to cater the future increase
in flow. High-energy consumption, significant pumping requirement, less flexibility in
operation, large capital and operating costs are drawbacks of centralized systems.
Centralized domestic wastewater treatment facilities in urban areas are implemented
effectively by local self-governments in India. However, the total capacity of such
centralized treatment plants is not sufficient to treat wastewater from the entire
population. According to a report by Central Pollution Control Board, Ministry of
Environment, Forest and Climate Change, Government of India (2015), total sewage
generation in Indian urban areas is 61948 million liters per day (MLD) whereas installed
treatment capacity is 23277 MLD. Moreover, new developments within and at the
outskirts of the large cities need to be provided with appropriate wastewater treatment
systems. This has necessitated the augmentation of existing wastewater treatment systems
and wastewater treatment from centralized to the decentralized manner with onsite reuse.
Besides, geographic and economic limitations are forcing local authorities to divert from
the construction and management of centralized sewage treatment plants to the provision
of decentralized wastewater management facilities.

Decentralized Wastewater Treatment Systems (DWTS) consist of the collection,

treatment and disposal or reuse of wastewater from individual houses, apartments,
colonies etc. DWTS can be adapted to local conditions. The systems are faster to
implement and easier to pilot new technologies. It is more convenient to reuse treated
wastewater and sludge from a decentralized plant. There are three main advantages of
providing decentralized wastewater treatment. First, larger sewers, pumping stations and
storage facilities to handle sewage flow are not required which results in significant cost
savings. Second, numerous opportunities are available for reusing treated water as well as
groundwater recharge. Third, the breakdown of one unit does not fail the entire system.
“A new generation of highly efficient, compact, user friendly and low-cost treatment
system is to be developed in order to serve the needs of developing countries. A new
approach in designing, fabricating, and operating decentralized package plants is

2
necessary. Mass production using modern industrial methods provides best chances to
serve the public with reliable, effective, robust and reasonably priced treatment plants.
Close collaboration between university researchers and industrial designers,
manufacturers and marketing people is necessary to keep research and development of
novel wastewater treatment methods in line with the actual field requirements” (Wilderer
[3]
and Schreff, 2000) . Appropriate systems for secondary treatment in DWTS include
Membrane Bioreactor (MBR), Constructed wetland, treatment systems developed by
Bremen Overseas Research and Development Association (BORDA), package treatment
plants based on extended aeration or SBR process and Moving Bed Biofilm Reactor
(MBBR).

MBR is providing a very high quality of effluent, but cost of the membrane, high
maintenance, energy requirements and a gradual loss in filtration capacity due to fouling
of the membrane are limiting the use of the process (Capodaglio et al., 2017)[4].
Decentralized Wastewater Treatment Systems (DEWATS) developed by BORDA
includes a combination of units such as settler, septic tank, anaerobic baffled reactor,
anaerobic filter, horizontal planted gravel filter, and anaerobic or aerobic pond. Longer
start-up periods for the anaerobic process, larger footprint, odour, mosquito breeding, and
low treatment efficiency are some of the disadvantages of DEWATS. Natural treatment
system such as constructed wetland is a low cost, have no or few moving parts, needs no
or very less energy and requires less operation and maintenance. However, the
dependency of performance on environmental conditions and substantial land area
requirements make the use of such technologies unfeasible. Package treatment plants
based on extended aeration process produce stable and high quality effluent with low
sludge production. The process requires a larger space and consumes more energy due to
longer aeration time. “MBBR is continuously operating, non-clogging biofilm process
which provide high surface area for biofilm development” (Odegaard et al., 1993;
Odegaard et al., 1994)[5,6]. Higher biomass concentrations, reduced sensitivity to toxicity,
faster settling of sludge and smaller footprint compared to ASP are advantages of MBBR.
MBSBR is a combination of MBBR and SBR. In this process, biomass is present as
attached to a carrier as well as in suspended form. A most important advantage of this
process is its ability to control surface area loading rates within the bioreactor, by

3
changing carrier fill ratio, which allows a high rate of treatment occurs within a small
footprint making it a cost effective treatment solution (Aygun et al., 2013)[7].

1.3. MBBR and SBR as decentralized wastewater treatment

Systems
1.3.1. Moving Bed Biofilm Reactor (MBBR)
MBBR process was developed in the late 1980s by Norwegian company named Kaldnes
in association with a Water Treatment Research Group at NTNU/SINTEF ‘(NTNU–
Norwegian University of Science and Technology, SINTEF–The Foundation for
Scientific and Industrial Research)’. The system consists of an aeration (reactor) tank,
diffused aeration system, specially designed carrier media, screen at outlet to retain the
carriers and secondary settling tank. The density of the carrier is slightly less than the
density of water (Odegaard, 1999)[8]. The carriers provide high surface area for the
growth of microorganisms that increase their concentration and reduce the footprint of the
aeration tank, which is necessary for wastewater treatment. Various carriers of different
sizes and shapes are available but the Kaldnes K1 carrier is the one mostly used
(Odegaard et al., 2000)[9]. The bacteria attached to the carrier are an integral part of the
process. The biofilm growth on the media surface increases to a certain extent, and then
gets detached. This phenomenon called as sloughing creates a new surface for further
bacterial growth. After complete growth of the bacterial layer and subsequent dying off, it
gets sloughed off. A part of the organic matter is synthesized into new cells and a part is
oxidized into carbon dioxide and water. The sloughed biomass is settled in a settling tank
and treated effluent is taken for downstream treatment. The sloughed biomass is further
dewatered. MBBR does not require sludge recycle and filling ratio of carrier in the
reactor may be adjusted based on preferences (Odegaard, 2006)[10]. Self-regulating
biomass, lesser sludge production, no requirement of return sludge, enhanced settling
characteristics, greater process stability, no need for operational adjustment are certain
advantages of the process.

1.3.2. Sequencing Batch Reactor (SBR)

SBR is a fill and draw type activated sludge process used for the treatment of organic
wastewater (Keller et al., 2001)[11]. Five steps carried for SBR are: (1) fill (2) react
(aeration) (3) settle (4) decant and (5) idle (Metcalf and Eddy, 2005)[1]. At least two SBR
tanks are required for continuous flow applications. SBRs are being used successfully to
treat both municipal and industrial wastewaters. Implementation of stringent effluent

4
standards require more efficient wastewater treatment to meet the effluent quality, before
discharging into receiving water bodies. Specifically, in areas having low flow, SBR is a
feasible substitute to conventional continuous flow activated sludge treatment of
domestic wastewaters for BOD5 and SS removals, nitrification, denitrification, and
chemical precipitation of phosphorus (Irvine et al., 1983)[12]. As the same reactor is used
for biological degradation and sedimentation in SBR operations, capital and operating
costs are lower than conventional activated sludge processes. More automation,
uninterrupted power requirement, skilled personnel for operation, two or more basins for
the continuous process are some of the drawbacks of SBR.

1.4. Concept of Moving Bed Sequencing Batch Reactor

(MBSBR)
Conventional suspended biomass reactors have disadvantages such as low volumetric
conversion resulting in large reactor volumes; lesser sludge settling velocity leading to
large-sized sedimentation tanks; and high excess bio-sludge production (Aygun et al.,
2013)[7]. These problems can be solved by adding carriers into the aeration tank of
activated sludge process or SBR to increase the amount and quality of bio-sludge of the
system resulting in improvement of the effluent quality and system efficiency
(Sirianuntapiboon and Yommee, 2005)[13].

MBSBR is a better treatment option due to its ability to take the advantages of both a
biofilm reactor and SBR. In conventional biofilm reactors, the biomass grows only on
carriers, whereas in MBSBRs, both biofilm on carrier and freely suspended biomass are
in the same tank. Movement of carrier and Mixed Liquor Suspended Solids (MLSS) is
done by aeration itself. Higher COD removal efficiency can be achieved at higher
Organic Loading Rate (OLR). This could be explained as a result of enhancement of
microbial growth and augmentation of their attachment on carriers when the OLR is
increased. As organic carbon is the energy substrate for many microorganisms,
microorganisms cause the degradation of carbon source and nutrients when enough
oxygen is provided. As a result, increasing carbon source results in faster growth of
microorganisms and enhancement of removal efficiency. This condition is ideal for
increasing the performance of MBSBR.

The biofilm carriers are made of polyethylene (density 0.92–0.96 g/cm3). The typical
carriers are cylindrical shaped; provided with the cross inside and longitudinal projections
outside. Fill percent and the specific surface area of the carriers are the two important
parameters in the process design (Aygun et al., 2013) [7]. The filling ratio of carrier to tank

5
 [7]
volume can be provided from 30 to 70 % (Aygun et al., 2013) . Prendergast et al.
(2005)[14], Sombatsompop et al. (2011)[15], Aygun et al. (2013)[7] have conducted study by
modifying the typical SBR to provide high surface area for biofilm growth. The
advantages of MBSBR process are:

i. MBSBR shows better biomass concentration in reactors with relatively higher

removal efficiencies, greater volumetric loadings, and better process stability
towards shock loadings and needs small footprint areas.
ii. MBSBR gives better performance for onsite and decentralized application wherein
flow and composition fluctuates widely, operations are intermittent, and the
design life is undefined.
iii. Surface area loading rates can be adjusted by changing fill percent of carriers in
the reactor which provides high rate treatment within a small footprint making it a
cost-effective treatment solution.
iv. MBSBR can simultaneously remove nitrogen.
Investigations are necessary for parameters that significantly affect MBSBR design and
operation such as carrier fill percent, type of media, aeration time/cycle time, OLR and
other operating conditions.

1.5. Problem statement

Organic carbon removal by MBSBR is governed by operating parameters such as carrier
fill percent, aeration time and OLR. The potential of MBSBR for organic carbon removal
from domestic wastewater in comparison with MBBR and SBR is to be assessed. The
design criteria for MBSBR are to be evolved and application of expressions for modelling
of kinetic processes in MBSBR is to be assessed.

1.6. Literature survey

A comprehensive literature survey is conducted and is presented under the sections viz.,
MBBR, SBR, and MBSBR. Even though the present study is on MBSBR, literature on
MBBR and SBR will be useful to understand treatability potential of MBBR and SBR.
The literature on SBR is large; therefore, only relevant literature on SBR is cited.

1.6.1. Literature on MBBR

1.6.1.1. Literature on MBBR for domestic wastewater
[16]
Rusten et al. (1997) surveyed retrofitted and new MBBR plants. The reactors were
provided with a sieve at the outlet end to keep biofilm carriers in the reactor. For newly

6
designed plants at Steinsholt, influent COD concentration was in the range of 380 to 620
mg/L. Maximum COD and BOD7 influent concentration was 1600 mg/L and 800 mg/L
respectively. The observed COD and BOD7 removal efficiency was 94.0% and 96.2%
respectively. Observed effluent COD was below 50 mg/L for more than 90% of the time.
Very low effluent BOD7 concentrations (below 25 mg/L) were reported. At Edidfoss
plant operated much under design load, effluent BOD7 concentrations were below 10
mg/L at all times. It was reported that both the new plants required very little supervision
as it was not necessary to monitor return sludge ratio, sludge wasting requirement, Sludge
Volume Index (SVI), and sludge bulking problem. Further, it was reported that the
capacity of a reactor could be changed by just changing the percent fill of carriers.

Odegaard (1999)[8] presented a general description of the MBBR process, results of

various applications and design values for domestic wastewater treatment. The diffusion
of compounds in and out of biofilm is important in every biofilm process and hence the
thickness of biofilm is important. Adequate turbulence was required for the development
of thin biofilm on carriers. More biomass than required might get developed due to
inadequate shearing of the biofilm, in case of insufficient turbulence. Typical biomass
concentration on the basis of reactor volume was observed in the range of 3-4 kg SS /m3.
The loading rate of 30 g COD/m2d produced compact biofilm, with none or very less
protozoan population. The loading rate of 10-15 g COD/m2d produces fluffy biofilm with
a rich variety of ciliated protozoa whereas loading rate less than 5 g COD/m2d yields very
fluffy biofilm. It was stated that MBBR can be applied for BOD/COD removal,
nitrification, and nitrogen removal. The process for only removal of BOD/COD is
generally designed with volumetric loading of 4-5 kg BOD7/m3d at 67% carrier filling
and 15 °C temperature which corresponds to 15 g BOD7/m2d. Residence time of 30 to 90
min is sufficient for the removal of carbonaceous organic matter. The standard carrier
filling ratio was specified as 67% and suggested to provide carrier fill less than 70% for
free movement in the suspension. Typical design values for different process objectives
were prescribed. The recommended loading rates were 25, 15 and 7.5 g BOD7/m2d for the
efficiency of 75-80 %, 85-90 %, and 90-95% respectively.

Andrettola et al. (2000)[17] evaluated performance by upgrading existing Rotating

Biological Contactor domestic wastewater treatment plant to MBBR in the cold climate
region. MBBR was filled with 53% by carriers resulting in the available surface area of
85 m2/m3 for biofilm growth. Experimentations were conducted during summer and
winter where wastewater temperature was in the range of 10 –16 OC and 4.8 – 8.2 OC,
respectively. The influent flow rate was varied in the range of 294–504 m3/d. During
7
summer, MBBR was operated with an average Surface Organic Loading Rate (SOLR) of
9.9 g COD/m2d (range 3.7 – 15.9 g COD/m2d) and 2.6 g BOD5/m2d (range 0.7 – 5.1 g
BOD5/m2d). COD and BOD5 removal efficiency was 79% and 84% respectively. In
winter, MBBR was operated with SOLR of 7.9 g COD/m2d (range 1.9 – 22.0 g
COD/m2d) and 2.6 g BOD5/m2d (range 0.4 – 5.3 g BOD5/m2d). COD and BOD5 removal
efficiency was 73% and 83% respectively. Considering temperature variability, no
significant effect of low temperature was observed on the removal of BOD5in MBBR.
The effect of Hydraulic Retention Time (HRT) on COD removal in MBBR was reported.
The effluent COD concentration was more than 50 mg/L for HRT less than 5 h showing
that HRT affects COD removal efficiency in MBBR. MBBR showed steady performance
for variation in flow, organic matter concentration and wastewater temperature.

Odegaard et al. (2000)[9] analysed the effect of carrier size and shape on the performance
of MBBR provided for domestic wastewater treatment. This study was conducted in two
parts. In the first part of experimentation, three MBBRs of 20 L, 20 L, and 30 L capacity
were operated in parallel. The reactors were provided with HRT of 68 min. SOLR was
varied from 10 to 120 g COD/m2d. Two sets of investigations were conducted in the first
part. In the first set, reactors were filled with three different types of carriers by 60% and
given the same volumetric load. COD removal rate was higher for carriers smaller in size
having a greater specific surface area. In the second set, the reactors were filled with
KMT, AWT and ANOX carriers by 22%, 36%, and 60% respectively to provide the
same specific surface area (100 m2/m3) in the reactors. Observed COD removal
efficiency was similar for all three reactors showing performance dependency on specific
surface area. Effective surface area was an important parameter for the design of MBBR;
whereas the shape and size of the carrier were less important. For loading rate lower than
50 g soluble COD/m2d, the availability of biodegradable matter was limiting the
degradation. Further, there was no increase in COD removal for COD loading above 60
g soluble COD/m2d. In the second part, MBBRs were operated for different residence
times of 375, 52 and 27 min. Higher residence time has shown higher COD removal
which was related to hydrolyses of slowly biodegradable organic matter in the longer
residence time. The sludge settleability decreases with increasing organic loading.
Difficulties in the separation of biomass was observed due to the exponential growth of
fast growing microorganisms in suspended fraction owing to high OLR.

Orantes and Gonzalez-Martinez (2003)[18] evaluated the performance of MBBR using

low cost carriers (polyethylene corrugated tubing) for domestic wastewater treatment.
The study was conducted on a pilot scale using 900 L reactor filled with 27% by carriers
8
resulting in a total available surface area of 143 m2 for biofilm growth. MBBR was
operated with varied SOLR of 2, 6, 10, 13, 18 and 35 g COD/m2d by changing the
wastewater flow rate. The lowest and highest SOLRs were related to HRT in the reactor
between 7.6 h and 0.8 h respectively. The temperature varied from 18 to 20 °C. Total
COD removal of more than 70% and between 40 and 60% for SOLR less than 10 g/m 2d
and more than 10 g/m2d were reported, respectively. Maximum COD removal of 81 %
for SOLR of 5.7 g COD/m2d and HRT of 5.7 h was reported. The sludge production was
increased linearly with an increase in organic loading and inversely with HRT. Observed
yield from 0.12 to 0.40 kg Dry Mass/kg COD removed for lower and higher organic
load, respectively, were reported. Mean cell residence time values were observed from
2.0 to 23.1 d for the highest and lowest organic loading rates, respectively. Insignificant
change in mean cell residence time was observed by increasing organic load above 10 g
COD/m2d.

Daude and Stephenson (2003)[19] evaluated the design and operational suitability of
MBBR for the treatment of domestic wastewater for small scale plants. Two MBBRs in
series having a total volume of 6 m3 filled with 50% carriers were used during the study.
The plant was operated initially at 30% of design flow and at 70% of design flow at the
end of the study. The study was conducted for organic shock load, hydraulic shock load
and effect of power failure. To simulate the effects of excessive use of non-biodegradable
products, bleach and detergents were added. Final effluent was recycled to increase
hydraulic loading. Initially, recycling was done 3 times of design flow and then 10 times
of design flow for the second test. Electricity supply was intentionally cut for 8 d to study
the effect of power failure. Even with an increase in influent organic loading, average
effluent BOD5 and Suspended Solids (SS) values were 15.6 mg/L and 21.0 mg/L.
Nitrification was started after 40 d. The temperature of the bioreactor was 21 °C to 23 °C
and the pH was near neutral. Organic carbon was mainly treated in the first reactor;
whereas NH4-N was removed in the second reactor. Though the shock load of bleach and
detergents increased influent COD, there was insignificant effect on the quality of
effluent. An increase in hydraulic loading had doubled effluent turbidity and suspended
solids from 20 Nephelometric Turbidity Unit (NTU) to 40 NTU and 19 mg/L to 38 mg/L
respectively. After 8 d of power failure, efficiency for organic carbon removal was
resumed within a week whereas it took about 25 d to restore ammonia removal.

Odegaard (2006)[10] described MBBR and presented applications of the process. It was
reported that the thickness of biofilm on carriers is important for the diffusion of
compounds in the process. Turbulence in the reactor was important to obtain thin and
9
evenly distributed biofilm and transportation of the substrate to biofilm. It was prescribed
to provide mixer in an anoxic and anaerobic process tanks for movement of carriers
whereas it can be achieved by aeration in aerobic process. Less than 70% carrier fill was
suggested for free movement of carriers in suspension. The provision of primary
sedimentation was recommended to avoid clogging of the screen at the outlet of the
bioreactor. Residence time of 15 to 90 min was suggested for the removal of
carbonaceous organic matter in MBBR. COD, BOD7 and phosphorous removal was 94.4
%, 97.4 % and 95.8%, respectively at ‘Steinsholt’ plant. Also, efficiency for COD and
phosphorous removal at ‘Svarstad’ plant was 89%. MBBR was efficient for BOD
removal as well as nitrification and denitrification from domestic wastewater at a lower
temperature also.

Trapani et al. (2008)[20] studied the effect of carrier filling ratio on the performance of
Hybrid MBBR (HMBBR- MBBR with sludge recycle). Two reactors of 6.5 L each filled
with 66% and 35% carriers were used in pilot plants. The corresponding specific areas
were 330 and 190 m2/m3. The plant was provided with an organic load up to 1.2 kg
COD/m3d and operated with HRT of 6.5 h. Return sludge was recycled from the clarifier
to the anoxic tank at flow rate equal to the influent. Nitrate recycling was done from the
aeration tank outlet to the anoxic tank with a flow rate of 4 L/h. Average COD removal
efficiency of 90% was reported even with a variable organic loading rate. The average
efficiencies for COD removal were 90 and 89%, for the 35 and 66% carrier fill,
respectively. Comparing the results obtained for 66% and 35% carrier fill, it was
observed that 35% HMBBR had a higher COD removal efficiency than the 66%. System
with 35% carrier was observed more suspended biomass concentration which promoted
higher enzymatic hydrolysis and bioflocculation resulting in higher COD removal. There
was an optimum carrier concentration in the hybrid reactor, above which the performance
of the system was decreased.

Ahmadi et al. (2011)[21] conducted field investigation for the upgradation of STP
consisting of ASP to MBBR in full scale. Corrugated cylindrically shaped carriers made
up of HDPE having a specific surface area of 700 m2/m3 were used. Influent COD and
BOD5 during the study were varied between 280 – 438 mg/L and 130 - 173.5 mg/L
respectively. After upgradation, the inflow had increased from 1049±88 to 1944±275
m3/d, HRT had reduced from 20.6±1.6 to 5.8±1.2 h and Volumetric Organic Loading
Rate (VOLR) had increased from 0.32±0.04 to 1.8±0.36 kg COD/m3d. The average solids
retention time had increased from 5.28±0.64 d to 22.1±1.53 d, after upgradation. COD
removal efficiency of ASP was 77% whereas after upgradation to MBBR, COD removal
10
efficiency was 78%. Reduction in HRT by 75% and increase in VOLR by more than 5
times had given nearly the same efficiency for COD reduction in MBBR.

Lopez-Lopez et al. (2012)[22] studied effect of attached biofilm and carrier fill percent on
organic matter removal in a MBBR pre-treated with electro-coagulation. The experiment
was conducted in a pilot plant with 20 L of working volume using domestic wastewater.
Aeration and mechanical stirrer systems were used for the movement of carriers. Two
types of carriers Anox Kaldnes K1 and Aqwise ABC5 were used with varying fill of
20%, 35%, and 50%. Attached biomass was determined based on the solids in suspension
detached from carriers. Biofilm developed on carries was separated by centrifugation,
washed off and suspended solids were determined. Knowing the number of carriers per L
in the reactor, the amount of biomass in the reactor was determined. Biofilm was
developed in 11 days on the K1 carrier, whereas it required 19 days for achieving similar
biofilm density with the Aqwise carrier. The observed attached biofilm density on K1
carrier was 6.5 g/L with no variation for different carrier fill percent, whereas the Aqwise
ABC5 carrier achieved a density of 4 g/L at the end of sludge recycling. An increase in
carrier fill percent from 20 to 35 and 50 had increased COD removal. There was no
significant increase in COD removal from 35% carrier fill to 50% carrier fill. Minimum
carrier fill of 35% and minimum HRT of 7 h were recommended for the design of the
plant.

Martin-Pascual et al. (2012)[23] studied the influence of carrier types in MBBR for organic
matter removal from domestic wastewater. The study was conducted using a pilot plant of
3 L working volume, in 3 phases using HRT of 5 h, 10 h and 15 h and carrier filling of
20%, 35%, and 50%. Three types of carriers ABC5, K1 and BIOCONS having density of
0.92 – 0.96 g/cm3, 0.92 – 0.96 g/cm3 and 0.88 – 0.92 g/cm3 respectively, were used. The
reactors were provided with diffusers and stirrer for sufficient air diffusion and keeping
complete mix conditions. An arrangement for the removal of excess sludge was also
provided in each reactor. Aerobic conditions were maintained by controlling Dissolved
Oxygen (DO). Influent flow rate of 0.6 L/h, 0.4 L/h and 0.2 L/h corresponding to HRT of
5 h, 10 h, and 15 h respectively, were used during 3 phases of the study. Initial biofilm
density of 7.52 g/L, 7.669 g/L, and 4.89 g/L was reported for Aqwise ABC5, K1 and
BIOCONS carries, respectively, which was decreased and stabilized during the study
period to 2.149±0.338 mg/L for all the carriers. The maximum soluble COD removal
obtained for carrier K1, ABC5 and BIOCONS were 56.97%, 58.92%, and 46.13%,
respectively, with 50% carrier fill and 15 h of HRT. An increase in organic matter
removal was observed with increase in HRT and decrease in carrier filling percent.
11
Higher HRT was required for removal of organic matter with BIOCONS carrier due to
the tendency of carrier to move at the top because of low fluidization by these carriers.
The other carriers K1 and ABC5 had shown similar performance for 35% and 50% fill.
This was due to less movement of carriers for 50% fill resulting in less contact of influent
with biofilm. For lesser fill percent, a considerable decrease in organic matter removal
was reported.

Azizi et al. (2013)[24] evaluated the performance of ASP, MBBR and Packed-Bed Biofilm
Reactor (PBBR) for decentralized wastewater treatment. Laboratory scale study was
conducted in 3 reactors of 11 L capacity each. Cylindrically shaped polypropylene carrier
having a specific surface area of 350 m2/m3were used in MBBR. Carrier filling percent
used was 20, 30, 40, 50 and 60. The study was conducted using 6 h HRT. Optimum
carrier fill was 40% for effective treatment; whereas there was no increase in organic
matter removal for higher fill percent. The organic loading rate at 40% carrier was 0.024
kg/m2/m3 considering COD of 600 mg/L. It was reported that increasing the surface area
of media percentage does not make any change due to constant organic loading.
Reduction in carrier fill below 40% resulted in a significant decrease in COD removal
efficiency. The systems were operated for HRT between 12 h and 1 h for the
determination of optimum HRT. COD and BOD5 below 100 mg/L and 30 mg/L were
achieved within 6 h, 3 h and 2 h in ASP, MBBR, and PBBR respectively showing that
biofilm based process provided higher treatment efficiency.

Javid et al. (2013)[25] studied the feasibility of upgrading municipal wastewater treatment
plants using MBBR. The study was conducted in a pilot plant of 60 L volume having
equal length and width. The reactor was filled by 60% Kaldnes carriers having a specific
surface area of 500 m2/m3 and a filling ratio of 60%. The wastewater was fed after grit
removal and primary sedimentation. It took one month for the development of biofilm on
carriers. Treatment efficiency in removal of BOD5 and COD was examined at different
HRT of 1.0 h, 1.5 h, 2.0 h, 2.5 h, 3.0 h, and 4.0 h. The plant was operated with Food to
Microorganism (F/M) ratio from 0.5 to 1.88 g BOD5/ g MLVSS.d. The maximum and
minimum OLR applied was 3.48 kg BOD5/m3d and 0.73 kg BOD5/m3d respectively.
BOD5 removal efficiency of more than 80% for HRT more than 1.5 h was reported. The
average COD removal efficiency was recorded as 70.48%, 75.10%, 79.19%, 83.49%,
88.23% and 92.30 % for 1.0 h, 1.5 h, 2.0 h, 2.5 h, 3.0 h and 4.0 h HRT, respectively. An
increase in HRT had increased COD removal efficiency. The decrease in organic loading
had reduced MLSS concentration.
12
1.6.1.2. Literature on MBBR for industrial/ synthetic wastewater
Wang et al. (2005)[26] analysed the effect of carrier fill percent on the performance of a
suspended carrier biofilm reactor. Synthetic wastewater with an average COD of 200
mg/L was treated in a bench scale reactor of 6 L volume. Baffles were provided at
corners to avoid dead pockets and keep carriers in suspension specifically during high fill
percent. With this arrangement, carriers were completely fluidized for 75% fill. The
polyvinyl chloride particles having a specific surface area of about 30.7 m2/kg and
density of 1004.2 kg/m3 were used as carriers. The study was conducted in seven
reactors simultaneously using carrier filling of 10%, 20%, 30%, 50%, 60%, 70% and
75% and HRT of 1 h. The wastewater temperature was 18 to 23 °C during the study. DO
concentration in the aeration tank was maintained at 3.0 to 5.6 mg/L. COD removal rate
was increased with an increase in carrier fill from 10% to 50% from 58.4% to 68.4% and
then dropped to 63.3%. This was concluded with carrier fill of 50% as an optimum
concentration for COD removal by MBBR. Insignificant nitrification rate for carrier fill
less than 20% was observed whereas increasing carrier fill from 30% to 75% has
increased nitrification and decreased ammonia concentration in the effluent. Very high
air flux was required to maintain carriers in suspension for more than 50% fill, which led
to increase in shear stresses on biofilm resulting in enhancement of biofilm detachment.
The biofilm detachment was increased due to the collision of carriers at higher fill
percent. A significant reduction was observed in suspended and attached biomass
concentration for carrier fill above 50%. The morphology of biofilm was also studied.
The structure and composition of biofilm was altered with a change in carrier fill percent.
Rough and fluffy biofilm was observed for lower carrier fill (20%). Thin and dense
biofilm was observed for higher carrier fill.
[27]
Aygun et al. (2008) evaluated the effect of high organic loading on COD removal
efficiency and production of sludge in MBBR using a laboratory scale reactor of 2 L
volume. The reactor was filled by 50% with the Kaldnes K1 carriers having a specific
surface area of 500 m2/m3. HRTs in the reactor and in the settler were kept as 8 h and 4 h,
respectively. Synthetic wastewater with COD of 500, 1000, 2000, 4000 and 8000 mg/L
was used for the study. Variation in wastewater temperature and pH was 18.4 to 23.6 °C
and 6.72 to 7.88 respectively. The observed COD removal efficiency for SOLR of 6, 12,
24, 48, 96 g COD/m2d were 95.1%, 94.9%, 89.3%, 68.7% and 45.2% respectively. The
organic removal efficiency was decreased with an increase in SOLR. The SOLR of 6 to
96 g COD/m2d corresponded to VOLR of 1.5 to 6.0 kg COD/m3d. Sludge production for
lowest and highest OLR was 0.35 g TSS/d and 12.25 g TSS/d respectively. Average

13
observed yield was 0.12, 0.39, 0.37, 0.42 and 0.56 kg TSS/kg COD for influent COD of
500, 1000, 2000, 4000 and 8000 mg/L respectively. The detachment of biomass was
increased linearly with increase in organic loading.

Piculell et al. (2014)[28] studied COD removal in biofilm, sloughed biofilm and free
growing biomass fractions of MBBR. The study was conducted using different synthetic
wastewaters in a laboratory scale model filled with 50% by AnoxKaldnes K5 carriers
with a protected surface area of 800 m2/m3. It was reported that soluble COD removal by
suspended fraction of biomass varies with HRT due to changing suspended solids
concentration. COD removal was significantly dependent on biofilm at low HRT whereas
the contribution of free-growing bacteria and sloughed-off biofilm increased at higher
HRTs. Further study was conducted to understand the effect of oxygen concentration and
HRT on soluble COD removal using acetate as a substrate in a 0.55 L reactor. Soluble
COD removal was increased linearly with increase in DO only at an HRT of 0.05 d;
whereas no increase in soluble COD removal was observed for HRT of 0.1 and 0.14 d.
Soluble COD removal was dependent on DO only at lower HRT. This was due to
washout of suspended solids at lower HRT without much contribution in COD removal
whereas sloughed and suspended biomass contributed in COD removal at higher HRT.
Most of the suspended biomass in MBBR was due to sloughed biofilm in MBBR. The
activity in the biofilm was more important at low HRT whereas the contribution of free
growing bacteria and sloughed biomass was increased at higher HRTs.

Vyrides et al. (2018)[29] studied the performance of MBBR for the treatment of bilge
water having COD of 2900 –12800 mg/L. The study was conducted on a pilot plant with
a working volume of 180 L filled with 10%, 20%, and 40% by Mutag Biochip Carrier and
operated for HRT of 36 h. The bilge water was initially treated using dissolve air flotation
to remove oil and further treated physico-chemically. The constant air was supplied for all
experimental runs to maintain the same hydraulic conditions. DO was observed between
4 to 5 mg/L. Maximum COD removal efficiency of 60% was reported for carrier fill of
40% whereas 45% efficiency for 10% and 20% carrier fill. There was no increase in COD
removal efficiency for increase in carrier fill from 10% to 20%.

Bering et al. (2018)[30] evaluated the performance of MBBR for real laundry wastewater
treatment. The surfactants used in the laundry were biodegradable. Two MBBRs in series
were provided. The total volume of reactors used was 260 L filled with Kaldnes K5
carrier by 50%. Compared to domestic wastewater, low concentration of nitrogen, slightly
high concentration of phosphorous and high concentrations of anionic and non-ionic

14
surfactants were observed. Influent wastewater BOD5 and COD values were in the range
of 335 – 542 mg/L and 727 – 944 mg/L, respectively. The ratio of BOD to COD was
varied from 0.37 to 0.62. Urea was added to increase nitrogen concentration. MBBR was
started with HRT of 10.4 h and subsequently operated with HRT of 7.8 and 6.24 h. DO
concentration of 2 to 4 mg/L was maintained in MBBR. The observed BOD5 and COD
removal efficiency was 95–98% and 90–94% respectively. BOD5 removal efficiency of
95 to 98% was reported for SOLR of 2–5 g/m2d. Five days were required for stable
treatment and to achieve 90% COD removal efficiency when the flow was increased to
0.8 m3/d, whereas when the flow was increased to 1 m3/d, it took 6 days to achieve 90%
efficiency but the operation was unstable.

1.6.2. Literature on SBR

Irvine et al. (1983)[12] studied the municipal application of the sequencing batch process.
The study was conducted by converting conventional continuous flow activated sludge
treatment plant. The total cycle time was 6 h. Average BOD5 and TSS removal of more
than 90% were observed in full scale SBR for domestic wastewater treatment operated
with average MLSS of 2300 mg/L and aeration time of 0.4 h and 0.7 h.

Ketchum et al. (1987)[31] compared biological and chemical phosphorous removals in

continuous and sequencing batch reactors. Very low effluent BOD (average 3– 21 mg/L),
TSS (average 3– 32 mg/L) and phosphorous (average 0.3 – 1.30 mg/L) concentration was
achieved in domestic wastewater in SBR.

Norcross (1992)[32] presented an overview of SBR. It was reported that oxygen uptake
and F/M ratio are constantly changing during the cycle of SBR. The design of SBR on the
basis of F/M ratio was recommended. It was suggested to provide aeration proportional to
flow. An average BOD removal efficiency of 99% and 98% was achieved in SBR
installed at various industries and municipalities, respectively.

Chang and Hao (1996)[33] studied SBR for nutrient removal. The study was conducted
using 4 L bench scale reactor in two phases. In the first phase, cycle time, HRT, Solids
Retention Time (SRT) and F/M ratio of 8 h, 16 h, 15 d and 0.16 to 0.23 g COD/g MLSS.d
were used respectively. Whereas 6 h cycle time, 12 h HRT, 10 d SRT and 0.19-0.26 g
COD/g MLSS.d F/M ratio were used in second phase. The study was conducted in
temperature controlled room at 20±2 °C. In all SBR studies, 50% of reactor volume was
decanted. Average COD removal in phase I and II were 95% and 91% respectively. The
phosphate removal efficiency in phase I and phase II were 80 and 98% whereas total
nitrogen removal efficiency was 61 to 78% respectively. Observed effluent COD was the

15
same in both phases whereas total nitrogen and phosphorous removal efficiencies were
improved in the second phase.

Keller et al. (2001)[11] demonstrated higher nitrogen and phosphorous removal in full
scale SBR plant. The process was termed as UniFed process and was patented
internationally. Its main feature was the uniform introduction of influent into the bottom
of the tank during sludge settling / compacting phase. The system was operated with 47 h
HRT and 23 d SRT for the influent flow of 850 m3/d. Mean influent BOD5, COD, total
nitrogen and total phosphorous was 210 mg/L, 563 mg/L, 54.50 mg/L and 9.70 mg/L
respectively. More than 90% COD, nitrogen and phosphorous removal from domestic
wastewater in SBR was achieved. Entire HRT including settling and decanting phase was
used in the process.

Debik and Manav (2010)[34] worked on the optimization of sequence in SBR for
biological nutrient removal from domestic wastewater. The experiments were conducted
in a laboratory with a reactor volume of 4 L. The MLSS concentration was maintained at
5500±500 mg/L. Optimum SBR performance was evaluated with a changing sequence of
anaerobic and aerobic phase. It was reported that a sequence of 0.5 h fill, 2 h anaerobic, 2
h aerobic 1, 1 h anoxic, 0.75 h aerobic 2, 1 h settle and 0.5 h decant provided optimum
performance. COD, total Kjeldahl nitrogen, ammonical nitrogen, and total phosphorous
removal efficiencies were 91% ±3, 78% ±7, 85% ± 5, and 87% ± 2, respectively.

Ketchum (1997)[35] elaborated the significance of various stages of the SBR process. HRT
of 12 h was required for treatment objectives to meet organic matter and suspended solids
removal whereas 18 h to 24 h for highly fluctuating flow rates and for removal of
phosphorus and nitrogen. Settling time of 0.5 h for shallow tanks and 0.75 h for deep
tanks was suggested. Decanting time of 1.0 h was recommended. React time between 1.5
h to 3.0 h was recommended based on treatment objectives.

1.6.3. Literature on MBSBR

Prendergast et al. (2005)[14] studied the efficiency of SBR and Sequencing Batch Biofilm
Reactor (SBBR) for the removal of organic carbon and phosphorus. The study was
conducted on a laboratory scale reactor with a working volume of 27.6 L using domestic
strength synthetic wastewater having COD of 1000 mg/L. The reactor was placed in a
temperature controlled room at an average temperature of 10 °C. Cross-flow corrugated
plastic BIOdek media having a specific surface area of 240 m2/m3 was moved vertically
in and out of the wastewater using a pneumatic piston. The dipping cycle of media was
divided as 4 s in the air, 2 s traveling down, 4 s in the water, and 2 s traveling up

16
resulting overall motion of 5 cycles per min. Cycle time of 8 h (3 h aeration) was divided
as 59 min feeding, 1 min mixing, 3 h anoxic/anaerobic, 3 h aerobic and 1 h settling. The
draw and idle phases were not considered whereas anoxic/anaerobic period was provided
for nitrogen and phosphorous removal. The average VOLR of 1.2 kg COD/m3d and
SOLR of 8.8 g COD/m2 d were used in the study. Average COD removal of 94% in
SBBR was reported with an average COD concentration in the effluent was 65±14 mg/L.
The average COD removal rates in SBBR were 8.3 g/m2d and 1.1 kg/m3d, expressed in
terms of carrier surface area and reactor volume, respectively. The total orthophosphate
loading rates were 0.34 g/m2d and 0.083 kg/m3d and average removal rates were 0.2
g/m2d and 0.36 kg/m3d which showed efficiency of 44%.

Sirianuntapiboon and Yommee (2005)[13] studied MBSBR and SBR. The study was
conducted on a laboratory scale model of 7.5 L working volume. Synthetic wastewater
was used indicating poultry slaughterhouse characteristics having BOD5 of 400, 600 and
800 mg/L. The system was operated with a suspended biomass concentration of 1500
mg/L and HRT of 1.5 d, 3.0 d, and 5.0 d. The reactor was filled with carriers prepared
from tubes of used tyres having the density of 1.925±0.21 g/cm3 and a total surface area
of 0.39 m2 in the reactor. For influent BOD5 of 400 mg/L, observed BOD5 removal
efficiency was 96.5%, 97.2%, and 97.9% in MBSBR and 95.7%, 97.7% and 97.2% in
SBR for HRT of 1.5 d, 3.0 d and 5.0 d respectively whereas COD removal efficiency
was 95.3%, 96.6%, and 97.5% in MBSBR and 93.9%, 95.3% and 96.1% in SBR for
HRT of 1.5 d, 3.0 d and 5.0 d respectively. Effluent quality of MBSBR was more stable
compared to SBR for the same operating conditions. There was a nominal increase of 1 –
2% in BOD5 removal efficiency by the addition of carriers. The efficiency of MBSBR
decreased with increase of BOD5 or decrease in HRT. Effluent quality was enhanced
with increase in HRT. The total biofilm mass in MBSBR was about 5400-6700 mg. The
total biomass in MBSBR was 30% more than SBR under the same organic loading rate.
An excess sludge in MBSBR was lower than SBR. The amount of waste sludge also
decreased with the increase in HRT or decrease in organic loading. SVI of the suspended
biomass of MBSBR was about 20% lower than that of the SBR under the same organic
loading. For OLR of 264±29.8 g BOD5/m3d, observed SVI for MBSBR and SBR was
73±2.3 mL/g and 95±3.2 mL/g, respectively. Better SVI was observed at the lowest
OLR. The total biomass in MBSBR was about 30% higher than that of SBR, which
resulted in a decrease of F/M of the system by about 30%.

Sombatsompop et al. (2011)[15] conducted a comparative study of SBR and MBSBR for
piggery wastewater treatment. The study was conducted on a laboratory scale model with
17
a working volume of 6 L. The cycle consisted of 1 h filling, 8 h reacting, 2 h settling and
1 h drawing and idling. MLSS was kept as 3000 mg/L and the process was operated for 2
cycles per day. Both the systems were operated at HRT of 18 h and SRT of 10 d.
MBSBR was filled by 20% with PVC sponge having density and specific surface area of
0.0145 g/cm3 and 400 m2/m3 respectively. Piggery wastewater taken from an anaerobic
system of a pig farm, was settled for 1 h, filtered through a 1 mm mesh screen and then
fed to the reactors. Feed wastewater was prepared by mixing raw piggery wastewater
with tap water to provide COD concentrations of 500, 1000, 1500 and 2000 mg/L, and
organic loads of 0.59, 1.18, 1.77 and 2.36 kg COD/m3d, respectively. COD removal
efficiency of SBR and MBSBR was higher than 60% at an organic load of 0.59 kg
COD/m3d and higher than 80% at the organic loads of 1.18 –2.36 kg COD/m3d. SBR and
MBSBR had given the same efficiency for lower organic loading. As the organic load
was increased to 1.77 kg COD/m3d and 2.36 kg COD/m3d, efficiency for MBSBR
increased from 62% to 86% and that for SBR from 61% to 78% showing more efficiency
for MBSBR than that for SBR. An increase in organic load had increased the removal
efficiency of MBSBR or remain unchanged while that of SBR gradually decreased at
high organic loads. MBSBR was thus more effective at a high organic load than SBR.
The cited reason was enhanced distribution of liquid flow and better oxygen transfer due
to the movement of carriers in MBSBR. The dissolved oxygen concentrations at all
organic loads in MBSBR were greater than those in SBR. BOD removal efficiency was
similar to COD removal. BOD removal efficiency in MBSBR was more than 90% at a
high organic loading rate of 1.18 –2.36 kg COD/m3d. The effluent suspended solids from
the SBR and MBSBR were increased with increasing OLR. Effluent suspended solids
were higher in SBR than MBSBR at higher OLR. Ammonium oxidation by oxygen
occurred more efficiently in MBSBR. SVI for both reactors was in the range of 40 and
60 mL/g, indicating that the sludge had good settling capability.

Aygun et al. (2013)[7] evaluated the effect of power failure on the performance of SBBR.
The study was done on laboratory scale reactors with a working volume of 2 L using
domestic wastewater from the university area. The study was conducted using 1 SBR and
3 SBBRs with a fill volume of Kaldnes K1 carriers 40, 50 and 60 % having a specific
surface area of 500 m2/m3. Raw wastewater was fed to the reactors without primary
settling. DO was maintained above 3 mg/L in the SBR and SBBRs. The reactors were fed
with 24 h composite samples having average COD and BOD5 of 383±57 mg/L and
280±32 mg/L respectively. The reactors were operated for a cycle time of 6 h consisted of
0.5 h fill, 4 h aeration (HRT 7.5 h), 1 h settling and 0.5 h decanting. Attached biomass

18
was measured by detaching biomass from 10 carriers, diluting them in demineralized
water. The value was referred to the number of carriers used for detachment and
considering the number of carriers per L. Influent COD and TSS concentrations were
varied from 295 to 480 mg/L and 147 to 254 mg/L respectively. The average values of
COD and TSS were 383 ± 57 and 204 ± 41 mg/L respectively. The observed COD
removal rate for SBR was between 78.30% and 89.3%. Average COD removal rates were
86%, 88.5%, 90.6% and 94.2% for SBR and SBBR with carrier fill % of 40, 50 and 60,
respectively. COD removal rate was increased with an increase in carrier fill due to
increase in biomass concentration. The observed attached biomass in the MBSBRs was
3.78 g/L, 4.62 g/L and 5.32 g/L for 40, 50 and 60% carrier fill respectively. The study
was conducted using VOLR of 1.23±0.18 kg COD/m3d and SOLR varying from 6.13,
4.90 and 4.09 g/m2d for carrier fill of 40%, 50%, and 60 %, respectively. The observed
MLVSS to MLSS ratio was between 0.70 and 0.81. F/M ratio was between 0.38 and 0.58
kg COD/kg MLSS.d, 0.22 and 0.28 kg COD/kg MLSS.d, 0.18 and 0.24 kg COD/kg
MLSS.d, and 0.15 and 0.20 kg COD/kg MLSS d for SBR and MBSBR with carrier fill of
40%, 50% and 60%, respectively. SVI values for all reactors were reported below 150
mL/g. While comparing SBR and SBBRs, SVI was decreased with an increase in biomass
in the reactor. The cited reason was denser attached biomass in SBBR than the suspended
biomass. SBR and SBBRs were subjected to short term (6 h) and long term (24 h) power
failure. COD and TSS removal, and sludge settling properties were affected due to power
failure. Lowest COD removal was reported in SBR during both the cases. All reactors
were reached to steady state conditions after one day for short term power failure. As
interruption was increased due to power failure, more time was required to recover and
reach steady state conditions.

Jucherskia et al. (2019)[36] studied the operational reliability of a small sequencing batch
biofilm reactor. The study was conducted in a small MBSBR plant having a reactor
volume of 1000 L using domestic wastewater flow of 600 L/d. The reactor was operated
for 4 cycles per day. Wastewater flow of 225 L from 6:00 am to 8.30 am, 225 L from
3.00 pm to 5.30 pm and 150 L from 10.00 pm to 11.30 pm fed in equal dosage. Each
cycle was divided as filling the reactor, intermittent cyclic aeration with discontinuities of
1 or 2 min, 90 min settling and 18 min decanting. Average influent BOD5 and COD of
321 mg/L and 503 mg/L were observed with moderate variation. It was reported that
17.4% of the samples analysed for BOD5 and 3.7% samples analysed for COD in the
effluent were higher than the permissible standard of 40 mg/L and 150 mg/L respectively.
Effluent BOD5 and COD were exceeded annually by 9% and 2% respectively. High

19
reliability levels for TSS and COD whereas lower reliability for BOD and very low
reliability for total nitrogen and total phosphorous were reported.

1.7. Gaps in research on MBSBR and scope of present

research work
The analysis of the literature reviewed shows that MBBR and SBR are studied in depth.
However, studies on MBSBR are very limited. Studies by Prendergast et al. (2005)[14] and
Sirianuntapiboon and Yommee (2005)[13] used synthetic wastewater to assess MBSBR for
organic carbon removal. Aygun et al. (2013)[7] used domestic wastewater as a feed, 40%
to 60% carrier fill and 4 h aeration time to assess MBSBR performance. Based on these
reviews and analysis, the gaps in research on MBSBR are identified and are listed below.

1. Studies on MBSBR with domestic wastewater collected from a decentralized

system are required.
2. The effect of design and operational parameters viz. carrier fill percent, aeration
time, HRT, OLR (surface and volumetric) is not assessed for organic carbon
removal by MBSBR.
3. The contradictory findings reported on carrier fill percent while operating MBBR
need validation/confirmation for MBSBR.
4. Design criteria are not yet evolved as MBSBR is still an emerging concept for
domestic wastewater treatment.
5. Comparison of MBSBR with MBBR and SBR for organic carbon removal is
essential as no such studies are reported for domestic wastewater.
6. The development of sludge and its settleability and effect of aeration time on
sludge production need to be studied.
7. Applicability of kinetic models for organic carbon removal from domestic
wastewater removal in MBSBR is not yet studied.

1.8. Objectives of the present research work

The following objectives are defined based on the research gaps identified (for the present
research work on MBSBR):

1. To carry out characterization studies on domestic wastewater from an identified

decentralized system for designing a sampling plan.

2. i) To design and develop laboratory scale experimental setup for SBR and
MBSBR and

20
 ii) To conduct performance evaluation studies for organic carbon (measured in
terms of COD) removal by varying the following parameters:

 carrier fill percent

 cycle time/ aeration time

 OLR (surface and volumetric)

3. To analyze sludge developed in MBSBR qualitatively and quantitatively for

assessing settleability and effect of aeration time.

4. To apply the bio-chemical kinetic models for simulation of organic carbon (COD)
and estimation of kinetic parameters in MBSBR thereby identifying an applicable
model through statistical analysis.

5. To carry out a comparative study on performance evaluation of MBSBR with

SBR and MBBR in terms of organic carbon removal and cost.

1.9. Methodology
The decentralized system and drainage outlet to collect wastewater from this system were
identified. The wastewater characterization studies were carried out to know the
variability and strength of wastewater. The sampling plan was prepared and fresh
wastewater was used for all the batches of MBSBR and SBR. The laboratory-scale
experimental MBSBR and SBR systems were developed and biomass growth was
ensured in both the systems. MBSBR was operated by varying carrier fill percent,
aeration time and organic loading rate for COD removal. A minimum of five
batches/cycles were run for each combination of these operational parameters. SBR
system was also run for the same operational conditions. Kinetic modelling study using
various models reported in the literature was conducted using the operational results of
MBSBR. An applicable kinetic model was identified for simulating effluent COD. The
kinetic coefficients and bacterial growth parameters were estimated. A comparative study
of MBSBR with SBR and MBBR was carried out in order to know the potential of
MBSBR for COD removal with reference to SBR and MBSBR. The design criteria of
MBSBR to treat domestic wastewater was evolved based on exhaustive experimental
work and kinetic modelling study. Finally, the applicability of present research work was
demonstrated through the design of a decentralized wastewater treatment system for a
real-life case study (Rajarampuri, Kolhapur) using design criteria evolved in this study.

21
1.10. Organization of study
The organization of the study is given in Table 1.1.

Table 1.1 Organisation of study

Title Contents
Introduction Relevance of study, literature survey, gaps in
research, scope of work and objectives of the study
Experimental study on moving Characteristics of wastewater from selected source,
bed sequencing batch reactor development of laboratory setup, experimental
investigation, experimental results and discussions

Kinetic modelling of moving Applicability of different kinetic models for organic

bed sequencing batch reactor carbon removal in MBSBR from domestic
wastewater
Comparative study of moving Comparison of MBSBR with SBR and MBBR
bed sequencing batch reactor performance for domestic wastewater treatment
with sequencing batch reactor
and moving bed biofilm reactor
Design of moving bed Illustrative design of MBSBR for present case study
sequencing batch reactor for
decentralized wastewater
treatment
Conclusions and Conclusions from present study and
recommendations recommendations for further study

22