MLVSS / MLSS ratio’s standard value obtained from different aeration tank samples of different capacity sewage treatment plant - A case study

Abstract

Waste water treatment system plays a vital role in controlling pollution of natural water bodies like lake, pond, river etc., by Municipal and Industrial effluents. Different industrial effluents play its own role in contaminating the water bodies which in turn creates huge impact for aquatic and terrestrial life. From past studies we understood that, all the sewage treatment systems have a secondary treatment step which are mainly driven by Bacterial oxidation or in other terms can be pronounced as Biological augmentation, Biological calcification etc., In environmental engineering term this bacterial growth will be pronounced as MLSS (Mixed Liquor Suspended Solids) and MLVSS (Mixed Liquor Volatile Suspended Solids). MLVSS will be an inclusive part of the MLSS and also can be sorted as live bacterial cells which can really does the oxidation process in the secondary treatment step of Sewage treatment plant. Hence, this study was performed to evaluate the percentage or concentration of MLVSS available in the total value of MLSS. For this study aeration tank water samples were collected from 6 different STP capacities from 6 different areas. All the samples were tested for MLSS and MLVSS concentration with the available standard method of drying. Drying with 105° C in oven gives the value of MLSS and drying with 550° C in furnace gives the value of MLVSS. With all the tested samples the concentration of MLVSS from the total MLSS was evaluated and standardized.

Full text

Indian Journal of Microbiology Research 2022;9(2):144–148
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Indian Journal of Microbiology Research
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Case Report
MLVSS / MLSS ratio’s standard value obtained from different aeration tank
samples of different capacity sewage treatment plant - A case study
Gayathri Parivallal1, Ranadive Ananth Govindaraju1,*, Arun Nagalingam1,
Sumitha Devarajan2
1Green Enviro Polestar, Puducherry, India
2St.Josephs College of Arts and Science, Cuddalore, Tamil Nadu, India
ARTICLE INFO
Article history:
Received 30-04-2022
Accepted 25-05-2022
Available online 08-07-2022
Keywords:
MLSS
MLVSS
TSS
STP Aeration design
Biological oxidation
Biological calcification
Sewage treatment plant
MLVSS standard percentage
ABSTRACT
Waste water treatment system plays a vital role in controlling pollution of natural water bodies like lake,
pond, river etc., by Municipal and Industrial effluents. Different industrial effluents play its own role in
contaminating the water bodies which in turn creates huge impact for aquatic and terrestrial life. From
past studies we understood that, all the sewage treatment systems have a secondary treatment step which
are mainly driven by Bacterial oxidation or in other terms can be pronounced as Biological augmentation,
Biological calcification etc., In environmental engineering term this bacterial growth will be pronounced as
MLSS (Mixed Liquor Suspended Solids) and MLVSS (Mixed Liquor Volatile Suspended Solids). MLVSS
will be an inclusive part of the MLSS and also can be sorted as live bacterial cells which can really does
the oxidation process in the secondary treatment step of Sewage treatment plant. Hence, this study was
performed to evaluate the percentage or concentration of MLVSS available in the total value of MLSS.
For this study aeration tank water samples were collected from 6 different STP capacities from 6 different
areas. All the samples were tested for MLSS and MLVSS concentration with the available standard method
of drying. Drying with 105◦C in oven gives the value of MLSS and drying with 550◦C in furnace gives
the value of MLVSS. With all the tested samples the concentration of MLVSS from the total MLSS was
evaluated and standardized.
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1. Introduction
MLSS (Mixed Liquor Suspended Solids) are usually
expressed in grams per litre (Water online, 2011). Mixed
liquor is a mixture of activated sludge, settled sludge, live
microbes and even dead cells contained in an aeration basin
in the activated sludge treatment. The term MLSS is a
general parameter used to design a wastewater treatment
plant in the suspended growth process.1Most of the Sewage
Treatment Plant designs were done with the consideration of
MLSS as a critical operational parameter.2Different sewage
treatment technologies such as Activated Sludge process
* Corresponding author.
E-mail address:anandpatriot@gmail.com (R. A. Govindaraju).
(ASP), Sequential batch reactor (SBR), Fluidized air
bed bioreactor (FBBR), Moving bed Bioreactor (MBBR),
Membrane Bioreactor (MBR) etc., consider MLSS as a
vital parameter for their design. MLSS concentrations have
a direct impact on viscosity of the waste water.3,4 Proper
concentration of MLSS in the aeration zone can create a
healthy environment for microbial survival and improves
the settling velocities of the solids.5,6 This study shows
the vitality of MLVSS (Mixed Liquor Volatile Suspended
Solids) which tend to be the live microbes facilitating a
healthy aeration zone in any sewage treatment plant. Sewage
treatment plant has BOD (Biochemical Oxygen Demand) as
food and MLVSS as Microbes. Hence, always a healthy F/M
https://doi.org/10.18231/j.ijmr.2022.026
2394-546X/© 2022 Innovative Publication, All rights reserved. 144

Parivallal et al. / Indian Journal of Microbiology Research 2022;9(2):144–148 145
(Food to the Microorganism ratio) to be maintained in any
sewage treatment plant to have a better oxidation potential.
1.1. Food-to-microorganism ratio (F/M Ratio)
The aeration zone of waste water treatment unit is carefully
controlled based on the food enters the system and
microorganism fed on the food. Here the BOD (Biochemical
Oxygen Demand) or COD (Chemical Oxygen Demand)
considered to be the food entering the system and Bacteria
oxidizes the same in the presence of oxygen. The microbes
will most efficiently break down the organic matter in water
if they are present in the right proportion.6,7 Hence, the food
to microorganism ratio (F/M ratio) should be maintained
properly in the aeration zone. Always a comfortable F/M
ratio will be considered for different technologies, since the
retention time plays a vital role. Proper retention time helps
the microorganisms to serve better in oxidizing the organic
matter.1
1.2. MLSS and MLVSS
The term mixed liquor suspended solids (MLSS) also can
be spelled as Total Suspended Solids (TSS) present in the
Aeration zone of a Waste water treatment plant. MLSS test
is made to find out the total grams of suspended solids
available in the aeration system. This can be determined
by using a filter disc which can filter the suspended solids
and dried it at 105◦C for 1 hour in hot air oven. MLVSS
in other hand will help in determining the concentration
of volatile suspended solids in the aeration basin. MLVSS
is critical in determining the operational behavior and
biological inventory of the system. The filter used for MLSS
testing is ignited at 550◦C for 30 minutes. The weight lost
on ignition of the solids represents the volatile solids in
the sample. On the whole MLSS is the suspended solids
present in the aeration tank which include both organics
and inorganic. MLVSS, on the other hand observed to be
the volatile portion only, which basically means, this is the
portion that are considered to be the microbes.8
Fig. 1: Stabilized aeration tank
Fig. 2: SSV (Settled sludge volume)
Fig. 3: Aeration zone front view
Fig. 4: Settled sludge
2. Materials and Methods
(Methods: APHA, 2012 Standard Methods for the
Examination of Water and Wastewater, 22th Edition. 2540
A, D & E).
Procedure:
Step 1: First weigh the filter paper to get baseline
weight. Make sure the filter paper is dry.
Step 2: Filter all 6 samples collected from the aeration
tank of different STPs in the weighed filter paper.

146 Parivallal et al. / Indian Journal of Microbiology Research 2022;9(2):144–148
Step 3: After filtration allow the filter paper to dry in an
oven at 105◦C for 1 hour.
Step 4: The dried filter paper is weighed in a weighing
balance to obtain the MLSS value in grams.
Step 5: The same filter paper is then dried to ash in 550◦
C in a Muffle furnace for 30 minutes.
Step 6: Flash off the volatile organic fraction leaving
inorganic portion of the MLSS.
Step 7: Now measure the volatile organic portion to
obtain the value of MLVSS in grams.
2.1. Sewage treatment plant existing
Aeration tank samples from 6 different sewage treatment
plants were collected for this study. All the sewage
samples were taken from the existing treatment plant in
and around the Bangalore location which was erected and
commissioned by M/S. Green Enviro Polestar, Pondicherry.
The treated water used for toilet flushing and gardening.
Sample 1 Project: Lakshmi Shree group Apartment,
Whitefield, Bangalore.
Capacity: 80 KLD (Kilo litres per day) STP.
Technology: Sequential Batch Reactor (SBR)
Sample 2 Project: KERC (Karnataka Electricity
Regulatory Commission Building, Bangalore).
Capacity: 100 KLD (Kilo litres per day) STP.
Technology: Sequential Batch Reactor (SBR)
Sample 3 Project: NCBS (National Centre for Biological
Science, GKVK Campus Bangalore).
Capacity: 200 KLD (Kilo litres per day) STP.
Technology: Moving Bed Bioreactor (MBBR)
Sample 4 Project: Pyramid Banksia Apartment, Jakkur,
Bangalore
Capacity: 280 KLD (Kilo litres per day) STP.
Technology: Moving Bed Bioreactor (MBBR)
Sample 5 Project: NPS (National Public School,
Devanahalli, Bangalore)
Capacity: 40 KLD (Kilo litres per day) STP.
Technology: Activated Sludge Process (ASP)
Sample 6 Project: Homely Homes Tranquil Apartment,
Hegde Nagar, Bangalore
Capacity: 25 KLD (Kilo litres per day) STP.
Technology: Activated Sludge Process (ASP)
3. Results and Discussion
The selected waste water samples from 6 different STPs
were tested for the content of MLSS and MLVSS as
elucidated in (METHODS: APHA, 2012 Standard Methods
for the Examination of Water and Wastewater, 22th Edition.
2540 A, D &E). The obtained values of all the samples
were tabulated separately. Triplicates of both the MLSS
(Mixed Liquor Suspended Solid) and MLVSS (Mixed
Liquor Volatile Suspended Solid) values were determined
to get a standard result. Mean values were taken and sorted
as the standard values for the future research. The results
show that 68.85% of MLVSS concentrations available in all
the selected STPs total MLSS Value.
Table 1: Sample 1: Lakshmi Shree group apartment, Whitefield,
Bangalore
Sample 1
STP Capacity : 80 KLD
Description Replicate
1 (mg/l)
Replicate
2 (mg/l)
Replicate
3 (mg/l)
Mean
Value(µ
=∑X/
n) (mg/l)
MLSS 3652 3451 3345 3482.66
MLVSS 2410 2456 2234 2366.66
MLVSS/
MLSS %
65.99 71.17 66.78 67.95
Table 2: Sample 2: Karnataka electricity regulatory commission
building, Bangalore)
Sample 2
STP Capacity : 100 KLD
Description Replicate
1 (mg/l)
Replicate
2 (mg/l)
Replicate
3 (mg/l)
Mean
Value(µ
=∑X/
n) (mg/l)
MLSS 2545 2322 2356 2407.66
MLVSS 1650 1453 1324 1475.66
MLVSS/
MLSS %
64.83 62.57 56.19 61.29
Table 3: Sample 3: National centre for biological science, GKVK
campus, Bangalore)
Sample 3
STP Capacity : 200 KLD
Description Replicate
1 (mg/l)
Replicate
2 (mg/l)
Replicate
3 (mg/l)
Mean
Value(µ
=∑X/
n) (mg/l)
MLSS 2844 2322 2541 2569
MLVSS 1866 1562 1654 1694
MLVSS/
MLSS %
65.61 67.26 65.09 65.94
Table 4: Sample 4: Pyramid banksia apartment, Jakkur, Bangalore
Sample 4
STP Capacity : 280 KLD
Description Replicate
1 (mg/l)
Replicate
2 (mg/l)
Replicate
3 (mg/l)
Mean
Value(µ
=∑X/
n) (mg/l)
MLSS 3241 3427 3355 3341
MLVSS 2657 2451 2224 2444
MLVSS/
MLSS %
81.98 71.52 66.28 73.15

Parivallal et al. / Indian Journal of Microbiology Research 2022;9(2):144–148 147
Table 5: Sample 5: National Public School, Devanahalli,
Bangalore
Sample 5
STP Capacity : 40 KLD
Description Replicate
1 (mg/l)
Replicate
2 (mg/l)
Replicate
3 (mg/l)
Mean
Value(µ
=∑X/
n) (mg/l)
MLSS 2882 2754 2840 2825.33
MLVSS 1524 1850 1922 1765.33
MLVSS/
MLSS %
52.87 67.17 67.67 62.48
Table 6: Sample 6: Homely homes tranquil apartment, Hegde
Nagar, Bangalore
Sample 6
STP Capacity : 25 KLD
Description Replicate
1 (mg/l)
Replicate
2 (mg/l)
Replicate
3 (mg/l)
Mean
Value(µ
=∑X/
n) (mg/l)
MLSS 3850 3744 3785 3793
MLVSS 3210 3114 3044 3122.66
MLVSS/
MLSS %
65.61 67.26 65.09 82.32
Table 7: Average MLVSS % obtained from all samples
Description Obtained Mean
Value of MLVSS %
Average MLVSS
%
Sample 1 67.95
68.85 %
Sample 2 61.29
Sample 3 65.94
Sample 4 73.15
Sample 5 62.48
Sample 6 82.32
Fig. 5: Concentration of MLVSS present in the total MLSS
4. Conclusions
Both MLSS (Mixed Liquor Suspended Solids) and MLVSS
(Mixed Liquor Volatile Suspended Solids) plays a critical
role in the aeration tank design of any waste water treatment
plants. MLVSS preference in aeration tank design can be
most effective than the MLSS preference. Although most
of the sewage treatment plant designs were made using
MLSS value as a base line parameter scale, MLVSS value
consideration will give high productivity and consistence.
Hence, this study concludes that MLVSS standard value can
be considered between 60% to 65% to get a high system
efficacy.
5. Source of Funding
None.
6. Conflict of Interest
The authors declare no conflict of interest.
Acknowledgements
I would like to thank all my co-authors for the technical
support.
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Author biography
Gayathri Parivallal, Chief Operations Officer
Ranadive Ananth Govindaraju, Chief Executive Officer
Arun Nagalingam, Research Associate
Sumitha Devarajan, Assistant Professor
Cite this article: Parivallal G, Govindaraju RA, Nagalingam A,
Devarajan S. MLVSS / MLSS ratio’s standard value obtained from
different aeration tank samples of different capacity sewage treatment
plant - A case study. Indian J Microbiol Res 2022;9(2):144-148.