Performance Evaluation of Waste Water Treatment: …Senior Lecturer, Department of Civil...

Performance Evaluation of Waste Water

Treatment: A Case Study on

Sewage Treatment Plant (STP)

K.N. Rukmini Florence

Assistant Professor, School of Civil Engineering,

REVA University, Bangalore, Karnataka, India

Chiranjeevi Rahul Rollakanti

Senior Lecturer, Department of Civil Engineering,

Middle East College, Knowledge Oasis Muscat, Al Rusayl, Sultanate of Oman

Dr. C.Venkata Siva Rama Prasad

Associate Professor, Department of Civil Engineering,

Vignana Bharathi Institute of Technology (Autonomous),

Aushapur (V), Ghatkesar (M), Medchal (D), Telangana, India

C. Venkata Sai Nagendra

Assistant Professor, School of Civil Engineering,

REVA University, Bangalore, Karnataka, India

Abstract- India faces a number of water and wastewater issues and water related health hazards. Almost 80% of the

water supplied for domestic use, comes back as wastewater. In most of the cases untreated wastewater is let out which

either sinks into theground as a potential pollutant of ground water or is discharged into the natural drainagesystem

causing pollution in downstream areas.Sewage Treatment Plants (STPs) have been constructed in most places to reduce

the degradation of water quality of the receiving water bodies by reducing the total pollution load on the same and to

ensure a healthy environment both aesthetically along with preserving the ecosystem involved. Poorly treated wastewater

with high levels of pollutants caused by poor design, operation or maintenance of treatment systems creates major

environmental problems, when suchwaste water is discharged to surface water or on land. The present study has been

undertaken to evaluate performance efficiency of a waste water treatment plant-A sewage treatment plant is considered

for case study. Waste water samples were collected at different stages of treatment units and analysed for the major water

quality parameters, such as Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Suspended

Solids (TSS), Total Settleable Solids, Total Dissolved Solids (TDS), Nutrients (N&P) and Oil grease. The performance

efficiency of each unit in treating the pollutants was evaluated. Overall performance of the plant also has been estimated.

The obtained results were very much useful in identification and rectification of operational and maintenance problems

as well as the future expansion to be carried out in the plant to meet the increased hydraulic and organic loadings.

Keywords – STP, Waste Water, BOD, COD, TSS, TDS.

I. INTRODUCTION

The term wastewater typically encompasses liquids and waterborne solids from residential, agricultural or

commercial purposes as well as other waters that have been used in the activities of man, whose quality has been

compromised, and which are discharged into a sewer system. Since several years the word "sewage" has been used

and usually refers to waters which contain only sanitary waste. Technically, "sewage" means any drainage that goes

into a drain. Domestic wastewater is a stream that appears turbid or opaque and contains solids in suspension. It is

grey in colour when young, and has a musty, though not bad, scent. Domestic wastewater can contain all sorts of

liquid materials available in different quantities, such as fecal solids, bit of fruit, gasoline, trash, pulp, rags, wood,

plastics and other materials disposed of in a community's everyday life. In such conditions, the colour of the liquid

can slowly change from gray to black, due to biochemical changes caused by bacteria. If this occurs, foul and

unpleasant odors form and on the surface or in the liquid black solids surface. A drainage that has undergone a

Journal of Xi'an University of Architecture & Technology

Volume XII, Issue IV, 2020

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transition like this is considered septic. Wastewaters consist of liquids in which solids remain as settable particles,

scattered as colloids, which are materials that are not readily settled, or solids in dissolved form. The wastewater

mixture would contain vast amounts of microscopic species, mainly bacteria capable of eating the mixture's organic

portion (fats, proteins, and carbohydrates) and bringing about dramatic improvements in wastewater.

Since all wastewater sources and inputs are highly variable and an important microbial aspect is also present, the

composition of all wastewaters is continuously changing. A wastewater is also called raw wastewater, or raw

sewage, before reaching a wastewater treatment system. Wastewater treatment and proper disposal is required. This

would promote environmental conservation and restoration of the environment, as the wastewater obtained by cities

and towns will eventually be recycled to obtain water or land. If the minimum effluent content is defined for

acceptable allowable concentrations of solids (both suspended and dissolved), organic matter, nutrients, and

pathogens, the aim of the procedure is to meet the set requirements consistently. The design engineer's task is to

create a plan that will ensure the technological viability of the treatment procedure, taking into account certain

considerations such as cost of construction and repair, supply of building materials and machinery, as well as skilled

labour. Primary treatment alone won't yield an effluent with an appropriate concentration of residual organic

content. The treatment schemes use almost exclusively biological approaches to effect secondary treatment for the

elimination of organic waste. The biological substance is metabolized by bacteria in biologic treatment facilities.

Also, tertiary treatment methods and/or pathogen elimination can be used, depending on the criteria for the final

effluent consistency. Most wastewater treatment facilities currently use aerobic digestion for the elimination of

organic matter. The popularly used aerobic processes are the activated sludge process, oxidation ditch, trickling

filter, and aerated lagoons. Both aerobic and anaerobic processes are used by the stabilisation ponds. During recent

years, due to higher electricity rates and resulting rises during aerobic plant operational costs, increased focus has

paid to the use of anaerobic treatment systems for wastewater treatment and sewage treatment.

The degree of treatment needed can be calculated, in accordance with the legislation, by contrasting the important

characteristics of wastewater with the needed effluent properties. Number of different treatment alternatives for

achieving the quality of treated wastewater can be created.

The individual treatment methods are usually classified as:

a. Physical unit operations

b. Chemical unit processes

c. Biological unit processes.

First and foremost aim is to clean away solid surfaces of the water we use in our houses. This screening and

settling cycle is known as primary therapy. While this eliminates the larger pollution products, the wastewater is also

made of organic material, which doesn't smell fantastic and can contaminate them and absorb the available oxygen

because it decomposes if poured directly into our water sources. That is why nearly all treatment plants use an

aeration method to facilitate the growth of beneficial microorganisms in a cycle called secondary treatment that

break down the biological material in the waste. The goal of primary, secondary and tertiary effluent treatment in the

wastewater treatment process is to eliminate or remove organic matter, solids, contaminants, disease-causing

organisms and other toxins from the treated wastewater until it is released into a body of water. Many additives are

often applied during the manufacturing cycle in addition to disinfectants to help stabilize or strip off contaminants

like phosphorus or nitrogen. Several examples of fertilizer reduction methods include the addition of coagulant for

phosphorus reduction and ammonia removal air stripping. To protect the environment and the public health, we need

to eliminate the toxins from wastewater. When our culture consumes water the water is polluting with contaminants.

If left untreated, these pollutants would negatively affect our water environment. Organic matter can, for example,

induce loss of oxygen in lakes, rivers, and streams. This biological decomposition of organics could result in fish

kills and/or foul odors. Waterborne diseases are also eliminated through proper wastewater treatment. Additionally,

there are many pollutants that could exhibit toxic effects on aquatic life and the public. Treatment is required for

suspended solids and for dissolved organics. Physical processes are used to remove suspended solids, screens

remove debris and large solids and gravity or aerated grit chambers capture sandy matter. Gravity sedimentation

normally is used to remove finer (organic), suspended solids. For special applications, centrifugation, dissolved air

flotation, and filtration are used to remove suspended solids. In fact, dissolved organics are treated using biological

processes. The more popular structures are aerobic and involve aerobic or optional ponds, drain trickling, and

processes of activated sludge. Concentrated waste is considered for anaerobic treatment systems, such as primary

sludge or high pressure industrial wastewaters.

Waste water contains nutrients that may promote aquatic plant growth, and may contain poisonous

compounds or compounds that may be mutagenic or carcinogenic. A network of tanks, generators, and pump

stations store and transport wastewater to the treatment plant. The amount of time it takes for the waste to enter a

treatment facility is very critical and can impact performance of treatment plants. The collection system should



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sustain a velocity of at least two feet per second (2 fps) to avoid any settling of solids that appear to clog pipes and

cause odors. The sewage or drainage system is designed to flow to a single place for the treatment. The collection

system consists of smaller sewers, about four inches in diameter. The pipes get bigger in diameter as more

households and businesses are connected to the network. Pumping stations are also used where gravity systems are

not feasible to raise the wastewater. The wastewater begins to flow into the collecting system and finally enters the

treatment facility for waste water. The flow first receives provisional care after it enters the factory. Preliminary

treatment is followed by primary treatment, then secondary treatment, and perhaps advanced or tertiary treatment.

The solids or “sludge” removed from the wastewater stream also needs to be treated.

II. LITERATURE REVIEW

We have reviewed the literatures relevant to the objective of the project, i.e., Performance evaluation of a

wastewater treatment plant. A discussion on the purpose of performance evaluation of treatment plant i.e. Efficiency

test of each unit of the treatment plant is conducted.

Few of the literatures we have reviewed include “To evaluate the performance of Sewage Treatment Plant:

A case study” by Kavita N. Choksi, Margi A. Sheth and Darshan Mehta. In this paper, the treated and non-treated

samples are collected from Anjana Sewage Treatment plant located at Surat .The important parameters are analysed

using the collected samples and the efficiency of the plant is obtained.

Again a decent work is done by B.G. Mahendra and Prema in their paper entitled, “Performance Evaluation

of Existing Wastewater Treatment Plant”. Their work contained performance evaluation of wastewater Treatment

Plant of Dairy Industry i.e. KMF, Gulbarga.

Apart from it, two books entitled “Wastewater Engineering” by Dr. B.C. Punmia, Er. Ashok Kumar Jain and Dr.

Arun K. Jain and; “Water Supply and Sanitary Engineering” by G.S. Bridie and J.S. Bridie were referred. These

books has carried out complete design and detailing of each unit of the plant.

III. DETAILS OF THE STUDY AREA

The present study deals with the performance of sewage treatment plant A. SOURCE: Wastewater from VENGAMAMBA ANNAPRASADA KSHETRAM is the main source of waste to this plant. LOCATION: Treatment plant ‘A’ is situated at Annarao Cottage Area, near Srivarimettu footpath in Tirumala CAPACITY: 0.5MLD TYPE OF TREATMENT: Primary, Secondary and tertiary treatment.

Fig.1 Location Layout



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Fig. 2. Sewage treatment flow chart

Table 1. Technical details of plant –A

Sl.

No

Unit Sizes Instruments

1 Fine screen chamber Gates with guides

2 Grit Chamber 14.0 X 0.5 X 0.9m Gates with guides

3 Aeration Tank 22.0 X 22.0 X 3.5m Fixed type aerators

with gear box & 20HP

motor – 2Nos

4 Secondary Clarifier 8.00m dia X 3.5m Drive unit with 3.0 HP

motor and worm

reduction gear box

5 Flash mixer 0.9 X 0.9 X 3.0m

6 Flocculator Tank 1.8 X 1.8 X 3.5m

7 Tube settler 4.0 X 2.0 X 3.0m

8 Sludge recirculation pumps Sludge motors

with50HP-2Nos

9 Stabilization Tank 2.5m dia X 3.0m

10 Sludge drying beds 12.0 X 15.0m - 3Nos

11 Pressure sand filter 1.8m dia X 1.5m

12 Activated carbon filter 1.6m dia X 2.0m

13 Chlorination Tank 4.0 X 2.0 X 3.0m

14 De-chlorination Tank 2.5 X 2.0 X 2.3m

15 Treated Water Tank 5.9 X 4.9 X 3.5m Screening and Grit Chamber:

Screening is the first procedure at the disposal of wastewater facilities. This method effectively involves removing large non-biodegradable and floating solids, such as rags, papers, plastics, tins, containers and wood that often reach a



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wastewater function. Efficient disposal of these constituents will protect the downstream plant and machinery from any potential injury, excessive wear and tear, pipe blockages and the buildup of undesirable material that will interfere with the appropriate wastewater treatment processes. Most of the organic waste is screened off through screen.

Fig. 3. Screening and Grit Chamber

Aeration Tank:

Aeration tank constructed of reinforced concrete and left open to atmosphere.

Size of aeration tank: 22m X 22m X 3.5m

Total capacity: 0.5MLD

Fig. 4. Aeration Tank

Wastewater contains soap, detergents and other surfactants which, when the waste water is aerated, create foam. The

operation of foaming creates a froth that includes solids of sludge, grease and a significant amount of bacteria from

waste water. A filamentous bacterium acts as hydrophilic cells, and plays a vital function in stabilizing foam. The

shaped foam is typically sticky, viscous and brown in colour and can be managed by directly spraying a chlorine

solution into the foam sheet. Joint pipes of a 250 mm diameter HDPE (high density polyethylene) pipe are used as the

contact between aeration tank and clarifier.

Clarifier:

Clarifier operates on the settling theory of gravity. With the support of scraper blades, heavier suspended solids settle

in the clarifier and these settled solids are swept to the middle well supplied for sludge processing. Clarifier removes

from the degreeted liquid the larger dissolved solids and the floating material. Aeration tank outlet is connected to

clarifier. Clarifiers can efficiently extract 50 to 60 percent of the dissolved solids from wastewater and 25 to 40

percent of the BOD (Biochemical Oxygen Demand). Denser particles settle down to the bottom and fluid flow back

into the clarifier region.



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Components of clarifier:

a) Reinforced influent well

b) Skimmer arm

c) Inlet

d) Sludge scraper drive mechanism

e) Weir plates

Sludge deposited is then routed to the sludge chamber and then discharged onto the sludge drying beds.

Stabilization Tank:

Fig.5. Storage Tank

Dimensions: 5m in dia X 3.0m depth. The treated water from clarifier is allowed to the stabilization tank leaving the sludge in clarifier. Then water is pumped to storage tank.

Pressure Sand Filter:

Sand filtration is also used, and solids are removed from water using a very robust process. The filtration medium consists of a several sand sheet with a variation of size and gravity parameters. Sand filters can be provided whether hand operated or entirely mechanically in various size sand materials.

Activated Carbon Filter:

Activated carbon filters are typically used to absorb organic compounds and/or collect free chlorine from water, thereby making the water safe for discharge or use in manufacturing processes. The reduction of organics in potable water, such as humic and fulvic acid, avoids the chemical reaction of chlorine in water with the acids and the production of trihalomethanes, a class of known carcinogens.

Sludge Drying Bed:

The drying bed for the sludge is the partitioned region of sand. Sludge is spread layer-shaped on the drying beds. Based on the atmospheric conditions, sludge is dewatered by the evaporation of surplus water over a span of several weeks. For forestry, dried sludge is re-used as soil conditioner.

Storage Tank:

The treated water from the plant is stored in the storage tank before finally distributed to the consumers.

The treated water from the storage tank is distributed for gardening in the nearby garden. Total storage capacity in

the collection tank = 0.5 MLD



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Fig.6. Various Components of STP

IV. RESULTS AND DISCUSSION

Wastewater treatment and safe disposal is required. This will promote environmental protection and restoration of

the environment, because the wastewater gathered from cities and towns will eventually be recycled to obtain water

or land. If the minimum effluent content is defined for acceptable allowable concentrations of solids (both

suspended and dissolved), organic matter, nutrients, and pathogens, the aim of the procedure is to meet the set

requirements consistently.

In the present study, samples were collected and laboratory tests were carried out from inlet and outlet of each unit

of a sewage treatment plant A which is situated at Annarao Cottage Area, near Srivarimettu footpath in Tirumala.

The results are as follows:

PH:

The concentration of hydrogen ions defined as pH, is a important parameter in biological unit activity. The

fresh sewage's pH is marginally higher than the community's supplied water. Decomposition of organic matter,

however, can lower the pH while the presence of chemical wastewater can cause significant fluctuations. The pH of

the raw water usually is between 5.5 and 8.0

Table 2. Determination of pH

Sl. No. Samples pH

1 Screens inlet 6.73

2 Screens outlet 6.72

3 Aeration outlet 6.8

4 Clarifier outlet 6.8

5 Stabilisation tank 7.10

6 Treated water tank 7.22

The values observed from the above table are in decreasing order from screens inlet to the mixed storage. The

permissible limit of pH is 8.5. Treated effluent is within the limits and hence it can be disposed onto agricultural

lands.



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TOTAL SUSPENDED SOLIDS:

The overall volume of solids contains the solids which are suspended and dissolved. This can be detected

by evaporating the water sample and measuring the remaining residual residue. The suspended solids hold much of

the organic matter, and this further increases the degree of water contamination.

Table 3. Determination of TOTAL SUSPENDED SOLIDS

Sl. No. Sample TSS mg/l

1 Screens inlet 700

2 Screens outlet 600

3 Aeration outlet 560

4 Clarifier outlet 300

5 Stabilization tank 240

6 Collection Tank 150

The values observed from the above table are in decreasing order from screens inlet to the mixed storage.

The permissible limit of TSS ranges from100 to 150mg/l. Treated effluent is within the limits and hence it can be

disposed onto agricultural lands.

TOTAL DISSOLVED SOLIDS:

Table 4. Determination of TOTAL DISSOLVED SOLIDS

Sl. No Sample TDS(mg/l)

1 Screens inlet 2200


3 Aeration inlet 2000



6 Collection tank 1000


permissible limit of TDS ranges from 500 to 2000mg/l. Treated effluent is within the limits and hence it can be


CHEMICAL OXYGEN DEMAND (COD):

The COD provides calculation of the oxygen required for chemical oxidation. It does not differentiate between

oxidizable biological material and non oxidizable material. However, the COD-to-BOD ratio does not substantially

shift for specific waste and so this measure may be used easily to define treatment unit output efficiencies.

Table 5. Determination of COD

Sl. No Samples COD (mg/l)

1 Screens Inlet 340





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5 Storage 132

6 Collection tank 96


In general, the COD of raw sewage at various places is reported to be in the range of 200 to 700 mg/L. Treated

effluent is within the limits and hence it can be disposed onto agricultural lands

BIOCHEMICAL OXYGEN DEMAND (BOD):

The sewage BOD is the amount of oxygen needed under aerobic conditions for the biochemical

decomposition of biodegradable organic matter. The oxygen absorbed during the cycle is related to the amount of

organic matter which is decomposable.

Table 6. Determination of BOD

Sl. No. Sample BOD(mg/l)

1 Screens inlet 200





6 Collection Tank 30


The permissible limit of BOD is 50mg/l. Treated effluent is within the limits and hence it can be disposed onto

agricultural lands.

NITRATES:

Nitrates presence indicates fully oxidized and the most stable form of nitrogenous organic matter in

sewage there by indicating the well oxidized and treated sewage increase in proportion of nitrates during the process

of sewage treatment serves as guide for measuring the progress achieved in sewage treatment.

Table 7.Determination of Nitrates

Sl. No Samples % transmission Nitrates(mg/l)

1 Screens inlet 42 1.34

2 Screens outlet 43 1.32

3 Aeration outlet 44.3 1.30

4 Clarifier outlet 52.3 1.06

5 Stabilization tank 57.2 0.98

6 Collection tank 69.5 0.70

The values observed from the above table are in decreasing order from screens inlet to the mixed storage. The permissible limit of nitrates should be nil. Therefore tertiary treatment is necessary before using it for agriculture purpose.



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PHOSPHATES:

Phosphate joins the domestic water from animal waste, discharged from kitchen grinders and concentrated inorganic

phosphate compounds used in various household detergents, from human body waste.

Table 8. Determination of phosphates

Sl. No. Samples %Transmission Phosphates

1. Screens inlet 67.5 0.42

2. Screens outlet 73.9 0.36

3. Aeration outlet 74.0 0.34

4. Clarifier outlet 75.0 0.32

5. Stabilization tank 76.5 0.31

6. Collection tank 97.2 0.1


The permissible limits of phosphates 4 to 12mg/l. Treated effluent is safe to dispose off onto lands and for

agriculture purpose.

TOTAL SETTLEABLE SOLIDS:

Table 9.Determination of Total Settleable Solids

Sl. No Sample TSS (ml/l/hr)

1 Screens inlet 10

2 Screens outlet 8

3 Aeration outlet 5



6 Collection Tank 0

The values shown from the table above are in declining order from the inlet of the screens to the mixed volume. The

permissible TDS limit is 500 to 2000mg / l. Treated effluent remains beyond the boundaries and should thus be

disposed of on farm land.

OIL AND GREASE:

Bacteria also do not readily break down fatty organic materials from vegetables and petroleum, which can cause

contamination in receiving ecosystems. When vast amounts of oils and greases are discharged from municipal

structures to collect waters, they raise BOD, so they can rise to the surface so harden, creating undesirable

conditions for esthetics. They can also catch garbage, plants and other products, creating foul odors, attracting

mosquitoes and flies and other vectors of disease. Too much oil and graase in some situations triggers septic

conditions in wetlands and lakes by stopping oxygen from entering the surface from the atmosphere.



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Table 10.Determination of oil and grease.


permissible limit of oil and grease ranges from 8 to 10mg/l. Treated effluent is within the limits and hence it can be


V.CONCLUSIONS

The study indicates that there is efficient reduction in parameter from treatment units of sewage treatment plant.

From the present study the following conclusions are obtained.

1. pH values are in required range i.e.,6.5 to 8.5.

2. The observed values of TSS at screens inlet is 700mg/l and decreased to 150 mg/l at collection tank. The

permissible limit of TSS ranges from 100 to 150mg/l.

3. The observed values of TDS at screens inlet is 2200mg/l and decreased to 1000 mg/l at collection tank. The

permissible limit of TDS ranges from 500 to 2000mg/l.

4. The values of the BOD are within the permissible limits.

5. The observed values of BOD5 at screens inlet is 200mg/l and decreased by 85% to 30 mg/l at collection

tank. The permissible limit of BOD is 50mg/l.

6. The observed values of COD at screens inlet is 340mg/l and decreased by 71.76 % to 96mg/l at storage

tank. The permissible limit of COD ranges from 200 to 700mg/l.

7. The observed values of nitrates are in decreasing order from screens inlet 1.38mg/l to 0.7mg/l at the mixed

storage. The nitrates limit should be nil.

8. The observed values of phosphates are in decreasing order from screens inlet 0.42 mg/l to 0.1mg/l at the

mixed storage. The permissible limit of phosphorus ranges from 4 to 12mg/l.

9. The observed values of total settleable solids at screens inlet is 10mg/l /hr and decreased to 0 mg/l/hr at

collection tank.

10. The oil and grease are removed at desired level. The permissible limit of oil and grease ranges from 8 to

10mg/l.

11. Treated effluent is within the limits and hence it can be disposed onto agricultural lands.

12. All the parameters except nitrates are within the limits to utilize the treated water for gardening.

REFERENCES

1. American Public Health Association, (2005); Standard Methods for the Examination of Water and Wastewater, Twenty first edition

Washington D.C. 2. Peavy H.S., Rowe D.R. and Techobanoglous. G. (1987); Environmental Engineering, McGraw Hill, Singapore.

3. Metcalf and Eddy (2003); Wastewater Engineering Treatment and Reuse, Fourth Edition, Tata McGraw-Hill publishing Company

Ltd., New Delhi. 4. Lash, D. Leslie, and Kominek, Edward G., Primary-Waste-Treatment Method, In: Cavaseno, Vincent. Et al. (ed.), Industrial

Wastewater and Solid Engineering, McGraw-Hill, New York, 1980.

5. Metcalf & Eddy, Waste Water Engineering Treatment Disposal Reuse, 4th

edition, McGraw-Hill, New York, 2003.

6. Kemmer, Frank N. (ed.), Nulco Water Handbook, 2nd

edition, McGraw-Hill, New York, 1988.

7. C.V.S.R. Prasad, T.V. S. Vara Lakshmi, Experimental investigation on bacterial concrete strength with Bacillus subtilis and crushed

stone dust aggregate based on ultrasonic pulse velocity, Mater. Today:. Proc. (2020) 8. Nagendra, C. Venkata Sai, C. Venkata Siva Rama Prasad, and KN Rukmini Florence. "An Experimental Investigation On Properties

Of Concrete By Partial Replacement Of Cement With Dolomite And Sand With Crushed Sea Shell." International journal of scientific

& technology research volume 8, issue 10, october 2019, pp:1610-1614.

Sl. No. Sample Oil and grease(mg/l)

1. Screens inlet 7.8

2. Screens outlet 7.4

3. Aeration outlet 5.3

4. Clarifier outlet 1.2

5. Stabilization Tank 0.8

6. Collection Tank 0.2



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9. Abey Lulseged, K. Mehantharaja, C.V.S.R.Prasad. “A study on using plastic coated aggregate in bituminous mix for flexible

pavement” International Journal of Scientific Engineering and Technology Research. Vol.05.Issu.05, Feberuary 2016, Pages 0933-0936.

10. Standard Methods for The Examination of Water & Wastewater, 20th

edition, APHA-AWWA-WEF, 1998.



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