performance evaluation of waste water treatment plant - IJEST

K. Sundara Kumar et al. / International Journal of Engineering Science and Technology Vol. 2(12), 2010, 7785-7796

PERFORMANCE EVALUATION OF WASTE WATER TREATMENT PLANT

* K. SUNDARA KUMAR1, P. SUNDARA KUMAR1, Dr. M. J. RATNAKANTH BABU2

1Associate Professor, Dept. of Civil Engineering, K L University, Guntur, Andhra Pradesh, India

2Assistant Professor, Dept. of Civil Engineering, K L University, Guntur, Andhra Pradesh, India

Abstract The present study has been undertaken to evaluate performance efficiency of a waste water treatment plant. A sewage treatment plant operating on biological treatment method (Activated Sludge Process) with an average wastewater inflow of 23MLD bas been 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) and total dissolved solids (TDS). The performance efficiency of each unit in treating the pollutants was calculated. 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: Waste water treatment plant, BOD, TSS, Biological treatment, Removal efficiency 1. INTRODUCTION

"There is no truer sign of civilization and culture than good sanitation. A good drain reflects the culture as much as a beautiful statue", [1]. Wastewater is essentially the water supply of the community after it has been fouled by a variety of uses. The water supplied to a community receives a range of chemical substances and microbial flora during its use such that the wastewater acquires a polluting potential and becomes a health and environmental hazard. Communicable diseases of the intestinal tract such as cholera, typhoid, dysenteries and water borne diseases like infectious hepatitis etc., can be spread from uncontrolled disposal of waste water, and therefore prevention of communicable diseases and protecting public health attracts the primary objective of sanitary waste water disposal.

The sites for disposal of wastewater have traditionally been natural watercourses, land and the coastal waters. One of the major sources of organic pollution is effluents from sewage treatment works. Prevention of pollution of natural resources such as land and water by the waste water and adequate preparation or renovation of the wastewater before reuse, are further important considerations in formulating and designing appropriate waste water disposal arrangements.

Given the characteristics of raw wastewater and the requirements of disposal or reuse, the waste water usually requires some type of preparation or treatment before it is rendered fit for disposal or reuse. Generally, in many situations involving domestic wastewater, the treatment consists of removal of suspended solids and 5-day, 20°C BOD, which are the two usual parameters of prime interest. The degree of treatment provided to the wastewater will largely be based on the effluent standards prescribed by the regulatory agencies when the treated effluent is to be discharged into a watercourse or land. If the effluent is to be reused, the quality of the effluent required to support such reuse will indicate the degree of treatment necessary. The complete treatment of wastewater is brought by a sequential combination of various physical unit operations, and chemical and biological unit processes. The general yardstick of evaluating the performance of sewage treatment plant is the degree of reduction of BOD, and suspended solids, which constitute organic pollution. The performance efficiency of treatment plant depends not only on proper design and construction but also on good operation and maintenance.

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Performance evaluation of existing treatment plant is required (1) to assess the existing effluent quality and/or to meet higher treatment requirements and, (2) to know about the treatment plant whether it is possible to handle higher hydraulic and organic loadings. Performance appraisal practice of existing treatment plant units is effective in generation of additional data which also can be used in the improvement in the design procedures to be followed for design of these units. Existing facilities can be made to handle higher hydraulic and organic loads by process modifications, where as meeting higher treatment requirements usually requires significant expansion and/or modification of existing facilities [2].

One of the primary considerations in evaluating an existing wastewater plant is in the area of plant operation and control. A major tool required for proper process control is frequent and accurate sampling and laboratory analysis [3]. Poor conditions of sewerage system, improper design of the plant and organizational problems are important factors that cause treatment plant not to meet the effluent standards [4]. Overloading due o increase in population and water use, discharge of trade effluents are other reasons of recent times for the poor performance of waste water treatment plants [5]. The treatment efficiency may be badly affected if the system is hydraulically under loaded [6].

2. CASE STUDY Nesapakkam Sewage Treatment Plant The Chennai city sewerage system has been divided into five zones. Each zone has been provided with individual collection areas, pumping stations, force mains etc. Nesapakkam Sewage Treatment Plant is located on the western part of city and receives the sewage collected from zone 4, covering the areas like Saidapet, West-mambalam, Ashoknagar, M.G.R Nagar, K.K.Nagar, Thirunagar etc,. The plant was commissioned in 1974 which is the first sewage treatment plant in Chennai. The plant is designed to cater for an average flow of 23 MLD (million liters per day) with a peak factor of 2.67. Fig 2.1 gives the layout of the above plant.

Dimensions and specifications of the treatment units

Inlet chamber: Inlet chamber is a rectangular tank with 2 m x 3 m sides and 6 m depth.

Screen Chamber: Screen chamber is provided with manually cleaned bar rack of medium size. Width of the screen chamber is 2.41m and depth is 1.37 m. The bars are rectangular sharp edged ones having 6 mm thickness at clear spacing of 25 mm.

Detritus Tank: Side of the square detritus tank is 10m and Side Water Depth is 1.0 m

Primary Clarifier: There are two identical circular primary clarifiers with 21.4 m diameter and 2.4 m side water depth in each.

Aeration Tanks: Three numbers of aeration tank (Fig 4.5) of 40 m length, 10 m width and 3.8 m depth each are provided. The system is provided with 12 numbers of fixed aerators having a capacity of 12.5 HP each. The flow in the aeration system is in completely mixed flow regime.

Secondary clarifiers: There are two identical secondary sedimentation tanks (SST), having 24.5 meter diameter and 3.1m side water depth, each.

Primary and secondary digesters: The primary as well as secondary digesters are having 21.4 m diameter and 6.1 m side water depth.

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Fig. 2.1 Schematic Diagram of Nesapakkam Sewage Treatment Plant, Chennai

Sludge drying beds: There are 26 numbers of sludge drying beds with 30.5 m x 11.6 m x 0.3 m size each, which are meant for dewatering the sludge.

Balancing tank : Balancing tank is a rectangular tank with dimensions of 60 m x 27 m x 3 m. Six numbers of floating aerators with 5 HP capacity are installed in the balancing tank to provide aeration and mixing to avoid the settlement of solids.

Pump details: Raw sludge pump house is having three vertical centrifugal pumps with 20 HP capacities each, to pump the raw sludge from the clarifier to the digesters. Return sludge pump house is having four horizontal, centrifugal pumps with 10 HP capacities each, to pump the secondary sludge to the aeration tank to maintain the desired F/M ratio in the aeration tank. Filtrate pump house is having two submersible pumps with 5 HP capacities each to pump the filtrate from the sludge drying beds to the inlet chamber. Balancing tank is provided with two submersible pumps having 15 HP capacities each.

The average wastewater inflow in to the system is nearly 23MLD. The characteristics of wastewater from a grab sample tested in the laboratory are given in Table: 2.l

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Table: 2.1 Characteristics of wastewater

SI, No Name of Parameter Unit Raw Sewage

1 Colour - Grayish black

2 Odour . - -nil-

3 Temperature °C 24 to 32

4 BOD(5-day,20°C) mg/1 320

5 Suspended Solids mg/1 450

6 COD mg/1 480

7 Total Dissolved Solids mg/1 1100

8 Total Solids mg/1 1550

9 PH - 7.2 to 7.6

10 Alkalinity mg/1 250

11 Chlorides mg/1 450

12 Ortho Phosphates as P mg/1 20

13 Total Phosphate as P mg/1 30

14 Ammonical Nitrogen mg/1 60

15 Organic Nitrogen as N mg/1 35

16 Total Kjeldhal Nitrogen as N mg/1 95

17 Sulphate mg/1 65

18 Settleable solids ml/l 10

19 Dissolved Oxygen mg/1 -nil-

20 Specific Conductance Mho/cm 1980

3. METHODOLOGY

Performance appraisal has been carried out by comparing the concentrations of pollutants at the inlet and outlet of the treatment unit. The grab samples were collected at the inlet and outlet of all the treatment units and analysed as outlined in the standard methods for the examination of water and wastewater [7]. The samples were analysed for various parameters like pH, BOD, COD, TSS and TDS and depending on the results, performance of each unit was evaluated. By regression analysis correlation between BOD and TSS were established.

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4. RESULTS AND DISCUSSION

The evaluation of performance efficiency of the plant was undertaken in terms of effluent quality. The evaluation was based on the plant operation data such as FLOW, BOD, Total Suspended Solids measurements for the period of 6 months from June '09 toNov"09. The typical data for the FLOW, BOD, and Total Suspended Solids for the month of June are given in Table 4.1. Daily variations of these parameters are shown graphically in Fig 4.1, Fig 4.2 and, Fig 4.3 for the month of June '09. It has been observed that the overall treatment efficiency for the BOD removal is 94.56% and that for Total Suspended Solids removal is 93.72%.

Table 4.1 Typical Characteristics of the waste water for June '09

Date Flow m3/s BOD mg/1 TSS mg/1

UTE TE UTE TE 1.6.99 0.2575 360 17 470 27

2.6.99 0.2691 330 18 410 29

3.6.99 0.2602 340 19 430 27

4.6.99 0.2566 300 15 380 25

7.6.99 0.2602 350 18 440 28

8.6.99 0.2629 380 19 470 28

9.6.99 0.2602 340 18 425 27

10.6.99 0.2566 320 15 390 26

11.6.99 0.2611 300 17 350 25

14.6.99 0.2664 310 16 420 25

15.6.99 0.2816 350 18 480 28

16.6.99 0.2744 280 16 340 27

17.6.99 0.2869 300 17 390 28

18.6.99 0.2762 350 19 420 28

21.6.99 0.2744 350 18 480 26

22.6.99 0.2664 320 19 440 28

23.6.99 0.2566 300 19 480 29

24.6.99 0.2637 340 19 480 29

25.6.99 0.2807 380 19 520 28

28.6.99 0.2691 360 19 490 28

29.6.99 0.2664 320 18 410 27

30.6.99 0.2727 350 19 480 29

Note: UTE - Untreated effluent, TE - Treated effluent TSS - Total Suspended Solids

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To characterize the quality of waste water averages, standard deviations as well as maximum and minimum values were calculated for the above parameters from the data .The characteristics of the waste water(monthly average values) during the period of data collection from June '99 to November '99 are given in Table 4.2. The removal efficiency for the above parameters during the period of data collection from June '99 to November '99 is given in Table 4.3.

Table 4.2 Characteristics of the Wastewater (monthly average values) during the period of data collection

MONTH

PARAMETER

MAXIMUM

mg/l

MINIMUM mg/1

MEAN mg/1

STNDARD

DEVIATION

NO. OF

OBSER

-VATIONS

UTE TE UTE TE UTE TE UTE TE

JUNE

BOD 380 19 280 15 333.1 17.8 27.3238 1.3322 23

TSS 520 29 340 25 436.1 27.3 47.0874 1.2926 23

JULY

BOD 390 19 240 16 330.0 18.1 36.8781 1.0779 21

TSS 520 29 340 25 445.2 27.8 54.8287 1.1233 21

AUGUST

BOD 410 19 290 15 344.5 17.9 34.3271 1.0455 22

TSS 520 29 340 25 454.5 27.3 45.6411 1.4324 22

SEPT

BOD 360 19 300 15 331.5 17.7 20.6722 1.4545 20

TSS 480 29 360 25 434.5 26.7 40.5845 1.3327 20

OCT

BOD 380 19 180 10 316.3 16.7 58.4247 3.0107 19

TSS 410 29 320 15 422.1 25.1 59.5892 4.1486 19

NOV

BOD 410 19 210 17 346.3 17.9 54.3836 1.2140 22

TSS 540 29 360 25 474.0 27.2 51.3307 1.1518 22

Note: UTE - Untreated effluent, TE - Treated effluent TSS - Total Suspended Solids

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Table 4.3 : Removal Efficiency of BOD and TSS during the period of data collection (June '09 To Nov '09)

MONTH

PARAMETER

CONCENTRATION

IN THE INFLUENT

CONCENTRATION

IN THE EFFLUENT

REMOVAL

EFFICIENCY

%

TOLERANCE

LIMITS

JUNE BOD 333.1 17.8 94.65 20

TSS 4361 27.3 93.72 30

JULY BOD 330.0 18.1 94.48 20

TSS 445.2 27.8 93.89 30

AUG BOD 344.5 17.9 94.78 20

TSS 454.5 27.3 93.98 30

SEPT BOD 331.5 17.7 94.66 20

TSS 434.5 26.7 93.84 30

OCT BOD 316.3 16.7 94.69 20

TSS 422.1 25.1 94.05 30

NOV BOD 346.3 17.9 94.81 20

TSS 474.0 27.2 94.25 30

Table 4.4 Characteristics of the waste water (average values) in the individual units of the wastewater treatment plant

Sl.

No.

Unit Operation/Process

Concentration, mg/l

BOD TSS

1 Untreated Waste water 316.12 445.67

2 After Primary Clarifier 219.41 220.12

3 After Aeration Tank 59.17 1320.72

4 After Secondary Clarifier 19.12 29.14

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Table 4.5 Removal efficiency of the individual units in the waste water treatment plant

Sl. No.

Unit Operation/Process

% Removal Efficiency for

BOD TSS

1 Primary Clarifier 30.59 50.61

2 Aeration Tank 73.03 --

3 Secondary Clarifier 67.67 97.79

4

Activated Sludge Plant

(Aeration Tank & Secondary Clarifier)

91.28

86.76

Typical Variation of FLOW, BOD, TSS during the period of data collection for the month of June '99 are given in Fig. 4.1, Fig. 4.2, Fig, 4.3.

Fig. 4.1 Daily variation of Flow during the month of June’09

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Fig. 4.2 Daily variation of TSS during the month of June’09

Fig. 4.3 Daily variation of BOD during the month of June’09

Typical Variation of FLOW, BOD, TSS during the period of data collection from June '99 to October '99 are given in Fig. 4.4, Fig. 4.5, Fig, 4.6.

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Fig. 4.4 Variation of flow during the period of data collection (June’09 to Nov’09)

Fig. 4.5 Variation of BOD during the period of data collection (June’09 to Nov’09)

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Fig. 4.6 Variation of TSS during the period of data collection (June’09 to Nov’09)

CORRELATIONS

Establishment of constant relationships among the various measures of organic content depends primarily on the nature of the wastewater and its source. By using regression analysis, variation of influent BOD with the influent TSS and variation of removal efficiency of BOD with removal efficiency of TSS was determined. Because of the rapidity with which TSS test can be conducted, these correlations can be very useful as BOD measurement will take 5 days. Once the correlation has been established, TSS measurement can be used to good advantage for treatment plant control and operation.

Table 4.6 Correlations developed between BOD and TSS

Correlation between Expression Correlation coefficient

Variation of influent BOD with TSS y = (232.694) + (0.248455) x

y: BOD, x: TSS

r = 0.361863

Variation of BOD removal efficiency with TSS removal efficiency y = (70.76152) + (0.256231) x

y: BOD removal , x: TSS removal

r= 0.338677

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5. CONCLUSION

A waste water treatment plant with Activated Sludge Process as biological treatment method has been considered

for performance evaluation. The overall performance of the existing was satisfactory. The removal efficiency of

BOD was found to be 94.56% and that of TSS was 93.72%. The individual units are also performing well and their

removal efficiencies are satisfactory. BOD and TSS removal efficiencies of the primary clarifier are 30.59% and

50.61% respectively. BOD and TSS removal efficiencies of the activated sludge plant(Aeration tank + Secondary

clarifier) are 91.27% and 86.76% respectively.

6. REFERENCES

[1] Sastry, C.A., Hashim, M. A. and Agamuthu, P., Waste Treatment Plants, Narosa Publishing House, New Delhi, 1995 [2] Environmental Protection Agency, US, (1974), Process design manual for upgrading existing waste water treatment plants, Technology Transfer,

13-17. [3] Kaul, S. N., Mukherjee, P. K., Sirowala, T. A Kulkarni, H. and Nandy, T. (1993) Performance evaluation of full scale waste water

treatment facility for finished leather industry, Journal of Environmental Science and Health, 28. 1277-1286. [4] Storhaug, R. (1990) Performance stability of small biological chemical treatment plants, Water Science and Technology, 22. 275-282. [5] Dakers, J. L., Cockburn, A.G.(1990), Rising the standard of operation of small sewage works , Water Science and Technology, 22.261-266. [6] Kapur, A., Kansal, A., Prasad, R. K. and Gupta, S (1999) Performance evaluation of Sewage Treatment Plant and Sludge bio- methanation,

Indian Journal of Environmental Protection, 19. 96 - 100. [7] APHA, AWWA, WPCF. Standard Methods for the Examination of Water and Wastewater. 20th edition, American Public Health

Association, Washington,DC, New York, USA, 1998.

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performance evaluation of waste water treatment plant - IJEST