Field Study of Reverse Osmosis Process in Wastewater Treatment MRITUNJAY CHAUBEY Pentair Water India L/52-55, Verna Industrial Estate, Phase II, Verna, Salcette, Goa-403722 (India) Ph : 91-0832-2883300, 2883312

E-mail : [email protected]

Abstract A field study has been carried out to investigate the performance of reverse osmosis (RO) plant at tertiary stage of treatment of wastewater. Monthly samples of treated and untreated effluents during the year round cycles are analyzed for the characteristic parameters such as total suspended solids (TSS), biochemical oxygen demand (BOD), chemical oxygen demand (COD), total dissolved solids (TDS), temperature and pressure requirement of high pressure pump. It is established that the performance of RO is improved by using solardetoxification at tertiary stage between biological treatment and reverse osmosis plant. The effect of temperature variation on the performance of RO systems was also investigated and it was found that the TDS removal efficiency and high-pressure requirement of RO decreases with increase in temperature. Key words: wastewater treatment, reverse osmosis, solardetoxification 1. INTRODUCTION The flow of water through a semi-permeable membrane from the more concentrated solution into the diluted solution under influence of pressure greater than the osmotic pressure is called Reverse Osmosis. The application of reverse osmosis in the treatment sequence of most documented biological treatment of wastewater was initially limited due to high capital cost, stringent feed limiting conditions of RO and inadequate knowledge on membrane behavior in wastewater environment (Nazim,2002 ; Metcalf and Eddy,2003). However with the emergence of less expensive and more effective membranes and scarcity of water in industries due to depletion of ground water level the application of reverse osmosis in wastewater treatment has regained interest. However, biological fouling of membrane is one of the major problems in the implementation of RO at tertiary treatment of wastewater. BOD, COD and bacteria are responsible for the problem of biological fouling of membrane. Solar photocatalytic oxidation reactions have the potential of demineralization of organic compounds as well as killing of bacteria in the treatment of polluted water (Parent et al.1996). Several semiconductors such as TiO2, Fe2O3, ZnO, ZnS, CdS are now known to have photocatalytic properties (Domenech.1993 ; Anheden et al.1995). Among them TiO2 is the most widely used for its high photocatalytic activity, stability and nontoxicity (Nogueira and Jardim.1996). In this paper, we have therefore, investigated the problem whether solar detoxification or its equivalent photocatalytic detoxification may be used as an intermediate stage between the biological treatment and RO to prevent the fouling of membrane. This in turn may lead us to a clean and green water purification technology, which may be usable as a zero effluent discharge scheme in industries.

2. FIELD STUDY OF PERFORMANCE OF REVERSE OSMOSIS PLANT USED AT TERTIARY TREATMENT OF WASTEWATER WITHOUT USING SOLARDETOXIFICATION PROCESS : A field study has been carried out to investigate the performance of reverse osmosis plants at tertiary stage of treatment of wastewater without using solardetoxification process in the treatment sequence. The treatment sequence used for this investigation is shown in figure 1. Monthly samples of treated and untreated effluents during the year round cycles are analyzed for the characteristic parameters such as total suspended solids (TSS), total dissolve solids (TDS), biochemical oxygen demand (BOD-5days), chemical oxygen demand (COD), temperature and high pressure requirement. The results of field investigations tabulated in table 1. Raw Effluent

PRIMARY TREATMENT 1. Equalization 2. Flash Mixing 3. Flocculation 4. Sedimentation

SECONDARY TREATMENT 1. Biological treatment 2. Clarification

REVERSE OSMOSIS

Treated Effluent Reuse in Process Figure 1: Treatment Sequence of ETP without Solardetoxification Process Table 1. Test Results of Reverse Osmosis Plant Used at Tertiary Stage of Treatment of Wastewater without using Solardetoxification Process 1. Constant Parameters Feed Flow : 500 LPH

Permeate Flow : 100 LPH

Recirculation Flow : 400 LPH

Fouling Factor : 0.85

Feed pH : 7

Membrane Used: TW30-2540 X 2 Nos.

Chemical Cleaning at Every 20 Days

Life of Membrane : 1.5 Years

Recovery Rate : 20%

Average System Flux : 19.22 L/m2-h

2. Variable Parameters Months JULY 2002 AUG 2002 SEP 2002

Untreated

TSS (mg/l) 45

TDS (mg/l) 1500

BOD (mg/l) 20

COD (mg/l) 101

Treated Untreated

00 50

28 1500

00 15

05 68

Treated Untreated

00 40

26 1500

00 10

03 36

Treated

00

25.5

00

00

Temperature (0C)

Pressure (bar)

30.90

6.82

29.30

7.05

28.50

7.16

Months OCT 2002 NOV 2002 DEC 2002 JAN 2003 FEB 2003 MARCH

2003 APRIL 2003 MAY 2003 JUNE 2003

Untreated

TSS (mg/l) 45

TDS (mg/l) 1500

BOD (mg/l) 7

COD (mg/l) 36

Treated Untreated

00 48

24 1500

00 5

10 31

Treated Untreated

00 45

20 1500

00 10

05 40

Treated Untreated

00 55

17 1500

00 15

12 67

Treated Untreated

00 48

16 1500

00 15

05 74

Treated Untreated

00 50

18 1500

00 10

10 61

Treated Untreated

00 52

22 1500

00 15

05 68

Treated Untreated

00 45

26 1500

00 20

00 91

Treated Untreated

00 55

29 1500

00 28

05 111

Treated

00

30

00

05

Temperature (0C)

Pressure (bar)

25.77

7.59

19.80

8.84

14.50

10.27

13.68

10.52

17.60

9.39

22.70

8.18

29.00

7.09

32.75

6.58

34.20

6.4

2.1 Total Dissolve Solids (TDS) Removal Efficiency The TDS removal efficiency of reverse osmosis plant used at tertiary stage of treatment of wastewater is studied. The results of field investigation are summarized in table 2. Table 2. Average Monthly TDS Removal Efficiency of Reverse Osmosis Plants Used at Tertiary Stage of Treatment of Wastewater MONTHS

AVERAGE TEMPERATURE ( oC )

TDS REMOVAL EFFICIENCY (% )

January February March April May June July August September October November December

13.68 17.60 22.70 29.00 32.75 34.20 30.90 29.30 28.50 25.77 19.80 14.50

98.93 98.80 98.53 98.26 98.07 98.00 98.13 98.27 98.30 98.40 98.67 98.87

TDS REMOVAL EFFICIENCY (%)

The results of table 2 indicate that the TDS removal efficiency of reverse osmosis plant increases as temperature decreases and vice versa. During present investigation, from figure 2, it is also observed that the TDS removal efficiency is maximum in month of January at an average temperature of 13.68 degree Celsius. Possible explanations for this behavior are that, when temperature increases the high pressure requirement decreases as shown in figure 3. Temperature change, effects solubility of various ions, degree of hydration, density and viscosity of water. Increase in temperature results in an increase in solubility of ions and decrease in the viscosity (different behavior at critical temperature) of water thereby resulting in a decrease in efficiency and pressure requirement of R.O. system. 99 9 8.8 9 8.6 9 8.4 9 8.2 98 9 7.8 9 7.6 9 7.4 JA N

FEB

MA R

A PR

MA Y

JUN

JUL

A UG

SEP

OCT

NOV

DEC

M ONTHS

Figure 2 : Effect of Temperature on TDS Removal Efficiency of RO Plant

HIGH PRESSURE (BAR)

12 10 8 6 4 2 0 JAN

FEB

MAR

APR

MAY

JUN

JUL

AUG

SEP

OCT

NOV

DEC

MONTHS Figure 3 : Effect of Temperature on High Pressure Requirement of RO Plant

2.2 TSS, BOD & COD Removal Efficiency The TSS, BOD & COD removal efficiency of reverse osmosis plant used at tertiary stage of treatment of wastewater is studied. The results of field investigation are summarized in table 1. From the present investigation it may be concluded that TSS and BOD removal efficiency of reverse osmosis plant used at tertiary stage of treatment of wastewater is 100%. The COD removal efficiency is slightly less than 100%. 3. FIELD STUDY OF PERFORMANCE OF REVERSE OSMOSIS PLANT USED AT TERTIARY TREATMENT OF WASTEWATER ALONG WITH SOLARDETOXIFICATION PROCESS : A field study has been carried out to investigate the performance of reverse osmosis plants used at tertiary stage of treatment of wastewater along with solardetoxification process in the treatment sequence. The treatment sequence used for this investigation is shown in figure 4 . Raw Effluent

PRIMARY TREATMENT 1.Equalization 2.Flash Mixing 3.Flocculation 4.Sedimentation

SECONDARY TREATMENT 1. Biological treatment 2. Clarification

SOLAR DETOXIFICATION

Treated Effluent Reuse in Process REVERSE OSMOSIS

Figure 4 : Treatment Sequence of ETP along with Solardetoxification Process Monthly samples of treated and untreated effluents during the September, October & November are analyzed for the characteristic parameters such as total suspended solids (TSS), total dissolve solids (TDS), biochemical oxygen demand (BOD-5days), chemical oxygen demand (COD). The results of field investigations tabulated in table 3. Table 3. Test Results of Reverse Osmosis Plant Used at Tertiary Stage of Treatment of Wastewater along with Solardetoxification Process 1. Constant Parameters Feed Flow : 330 LPH

Permeate Flow : 100 LPH

Recirculation Flow : 200 LPH

Fouling Factor : 0.85

Feed pH : 7

Membrane Used : TW30-2540 X 1 No.

Chemical Cleaning at Every 90 Days

Life of Membrane : 3 Years

Recovery Rate : 30%

Average System Flux : 38.44 L/m2-h

2. Variable Parameters Months SEP 2003 OCT 2003 NOV 2003

Untreated

TSS (mg/l) 10

TDS (mg/l) 1500

BOD (mg/l) 00

COD (mg/l) 00

Treated Untreated

00 08

17 1500

00 00

00 05

Treated Untreated

00 05

16 1500

00 00

00 07

Treated

00

13

00

00

Temperature (0C)

Pressure (bar)

28.50

12.84

25.77

13.80

19.80

16.59

3.1 Total Dissolve Solids (TDS) Removal Efficiency The TDS removal efficiency of reverse osmosis plant used at tertiary stage of treatment of wastewater is studied. The results of field investigation are summarized in table 4. Table 4. Average Monthly TDS Removal Efficiency of Reverse Osmosis Plants Used at Tertiary Stage of Treatment of Wastewater MONTHS

AVERAGE TEMPERATURE ( oC )

TDS REMOVAL EFFICIENCY (% )

September October November

28.50 25.77 19.80

98.87 98.93 99.13

The results of table 4 indicate that the TDS removal efficiency of reverse osmosis plant increases as temperature decreases and vice versa. During present investigation, from figure 5, it is also observed that the TDS removal efficiency follows the similar trend of figure 2 and shall be maximum in month of January at an average temperature of 13.68 degree Celsius. Possible explanations for this behavior are that, when temperature increases the high pressure requirement decreases as shown in figure 6. 3.2 TSS, BOD & COD Removal Efficiency The TSS, BOD & COD removal efficiency of reverse osmosis plant used at tertiary stage of treatment of wastewater is studied. The results of field investigation are summarized in table 3. From the present investigation it may be concluded that TSS, BOD & COD removal efficiency of reverse osmosis plant used at tertiary stage of treatment of wastewater is 100%.

TDS REMOVAL EFFICIENCY (%)

99.15 99.1 99.05 99 98.95 98.9 98.85 98.8 98.75 98.7 SEP

OCT

NOV

MONTHS

HIGH PRESSURE (BAR)

Figure 5 : Effect of Temperature on TDS Removal Efficiency of RO Plant

18 16 14 12 10 8 6 4 2 0 SEP

OCT

NOV

MONTHS

Figure 6 : Effect of Temperature on High Pressure Requirement of RO Plant 4. COMPARATIVE STUDY OF PERFORMANCE OF REVERSE OSMOSIS PLANT USED AT TERTIARY TREATMENT OF WASTEWATER WITH & WITHOUT SOLARDETOXIFICATION PROCESS : A comparative study has been carried out to investigate the performance of reverse osmosis plant in both conditions: with solardetoxification process and without using solardetoxification process. The parameters such as recovery, quantity of membrane, life of membrane, frequency of chemical cleaning, average flux of system and product quality are investigated to compare the performance in both cases. The results of above investigations are tabulated in table 5.

Table 5 Comparative Study of Reverse Osmosis Plant for Wastewater Treatment S.N.

Parameters Recovery Rate

Results of RO without Solardetoxification Process 20%

Results of RO with Solardetoxification Process 30%

1. 2.

Number of Membrane

TW30-2540 X 2 Nos.

TW30-2540 X 1 No.

3.

Life of Membrane

1.5 years

3 years

4.

Frequency of

20 days

90 days

Chemical Cleaning 5.

Average System Flux

19.22 L/m2-h

38.44 L/m2-h

6.

TDS Removal Efficiency

98.43%

98.98%

From the results of above investigations, it is established that there are following advantages in using solardetoxification at the intermediate stage between biological treatment and reverse osmosis process :-1. The rate of recovery of reverse osmosis increased by 10%. 2. The number of membrane required has decreased by 50% 3. The life of membrane has increased two times. 4. Frequency of chemical cleaning has increased by 4.5 times. 5. Average system flux has increased by two times 6. TDS removal efficiency has also increased by 0.5%. 7. 4.5 times increase in the frequency of chemical cleaning indicates that the biological fouling has prevented by 4.5 times. 5. ACKNOWLEDGEMENT The author wish to thank Dr. N. D. Kaushika, Professor of IIT Delhi, for providing the valuable suggestions and useful discussions.

5. REFERENCES 1. Anheden, M. Goswami, D. Y. and Svedberg, G. 1995. Photocatalytic Treatment of Wastewater from 5-floureouracil Manufacturing. Solar Engineering 1995 Proceedings of the 1995 ASME International Solar Energy Conference. 2. Birdi, G.S. and Birdi, J.S. 1998. Water Supply and Sanitary Engineering. Dhanpat Rai Publishing Company (P) Limited, New Delhi. 3. Domenech ,X. 1993. Photocatalysis for Aqueous phase De-Contamination is TiO2 the better choice. Photocatalytic Purification and Treatment of Water and Air, Ollis D.F. and Al-Ekabi H. (Eds.) , Elsevier, Amsterdam.

4. Metcalf and Eddy . 2003. ‘Wastewater Engineering : Treatment and Reuse” , Tata Mc. Graw – Hill, New Delhi. 5. Nazim, Cicek. 2002. Membrane Bioreactors in the Treatment of Wastewater Generated from Agricultural Industries and Activities. AIC 2002 meeting CSAE / SCGR program Saskatoon, Saskatchewan, paper No. 02 – 404. 6. Nogueira, P. F. R. and Jardim W.F. 1996. TiO2 Fixed Bed Reactor for Water Decontamination Using Solar Light. Solar Energy 56, 471 – 475. 7. Parent Y., Blake, D., Magrini-Bair, K., Lyons,C. , Turchi, C., Watt, A., Wolfrum E., and Prairie M. 1996. Solar Photocatalytic Process for the Purification of water : State of Development and Barriers to Commercialization. Solar Energy 56, 429 – 437. 8. Zhang, L. , Kanki, T., Sano, N. and Toyoda, A. 2001. Photocatalytic Degradation of Organic Compounds in Aqueous Solution by a TiO2 Coated Rotating Drum Reactor Using Solar Light. Solar Energy, Vol. 70 No. 4, pp 331 - 337.