Removing nitrate from drinking water

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Removing Nitrate from Drinking Water

Salah Abheiri

BSc: Environmental Science

This work is presented for the degree of

Research Master with Training, Murdoch University

School of Environmental Science

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I

I declare that this thesis is my own account of my research and

contains as its main content work which has not previously been

submitted for a degree of any tertiary educational institution.

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II

Abstract

Water resources in many parts around the world are becoming critical

because of human activity. This leads many countries around the

world to rely more on their groundwater as an essential source of

drinking water. The situation in Libya is critical because there is no

access to surface fresh water. The rainfall rate is very low, but there is

a huge quantity of ground water with good quality (average TDS

around 1030

mg/l) and this leads the country to rely on this water

source. The Great Man-Made River Authority (GMRA) was established

to produce and transfer water from the southern part of the country

(desert) where ground water is available to the northern coastal strip

where most of the population is concentrated. However, the water in

some wells in the East Japal Hassouna (EJH) well-field has a high

nitrate concentration, more than 50 mg/L as NO

3-

. To solve this

problem and reduce the nitrate content to less than the limits of WHO

Guidelines (50 mg/l as NO

3-

and10 mg/L NO

3-

-N), one of the available

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III

energy to remove nitrate from synthetic water similar to water in EJH

wellfield by operating a RO unit in a closed system and using a single

solar pump to deliver feed water to the RO unit and through the unit

as well. A range of nitrate concentrations treated by applying different

pressures for each nitrate concentration. Nitrate removal percentages

ranged between 78% to 90% depending on the initial nitrate

concentration of feed water and the applied pressure. An ion exchange

experiment was also conducted to remove nitrate from synthetic water

similar to water in the EJH wellfield and from a nitrate solution by

performing column and batch test experiments. Several nitrate

concentrations and contact times were applied. Nitrate removal for the

synthetic water were excellent (100% nitrate removal) but chloride

concentration in the produced water increased over the limits of WHO

guidelines. When the same nitrate concentration (20 mg/L NO

3-

-N) in

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IV

ACKNOWLEDGEMENTS

For his interest and valued guidance I wish to express my

appreciation and thanks to Prof. Goen Ho.

I would like to thank Dr. Stewart Dallas who co-supervised this work

for his valuable advice.

I am grateful to Woodside Company for their sponsorship and

Murdoch Link for their support during this work.

I would like to thank my employer (GMRA) for their support and

enabling me to finish this course.

I acknowledge Geoff and Karin from BW solar company for providing

the Lorentz PS 600 solar pump and the Dow Chemical Company for

providing me with NSR-1 Anion Exchange Resin.

I am thankful to Prof. Nick Costa for his help and support during my

study.

I would like to thank the ETC staff for their support in conducting the

RO experiment.

I would like to thank Mr. Ahmed Ammari for his support in computer

skills.

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V

2

LITERATURE REVIEW ... 9

2.1 BACKGROUND ... 9

2.2 ION EXCHANGE ... 10

2.3 REVERSE OSMOSIS... 13

2.3.1 Reverse Osmosis Membrane ... 14

2.4 RENEWABLE ENERGY SOURCES ... 15

2.5 ELECTRODIALYSIS ... 17

2.6 BIOLOGICAL DENITRIFICATION ... 18

2.7 TREATMENT ASSESSMENT ... 19

2.8 CONCLUSION ... 25

3 MATERIALS AND METHODS ... 26

3.1 NITRATE REMOVAL TECHNIQUES ... 26

3.2 CHEMICALS FOR EXPERIMENTS ... 26

3.3 REVERSE OSMOSIS TECHNIQUE ... 26

3.4 3.3.1REVERSE OSMOSIS EXPERIMENT ... 26

3.4.1 3.3.2 Typical RO experiment ... 27

3.4.2 3.3.3 Flow measurements ... 30

3.3.4 Sampling programme ... 30

3.3.5 Power regeneration by PV cells ... 30

3.3.6 Power consumption ... 31

3.5 ION EXCHANGE EXPERIMENT... 31

3.4.1 Regeneration of NSR1 Resin ... 32

3.4.2 Batch test ... 32

3.4.3 Column experiment ... 34

4 RESULTS ... 39

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4.1.1 First reverse osmosis experiment 8.3 mg/L NO3- -N concentration ... 39

4.1.2 Second reverse osmosis experiment 15.4 mg/L NO3- -N concentration ... 42

4.1.3 Third reverse osmosis experiment 27.6 mg/L NO3- -N concentration ... 44

4.1.4 Fourth reverse osmosis experiment 35.2 mg/L NO3- -N concentration ... 45

4.1.5 Fifth reverse osmosis experiment 9.6 mg/L NO3- -N concentration ... 46

4.1.6 Sixth reverse osmosis experiment 20.5 mg/L NO3- -N concentration ... 48

4.2 ION EXCHANGE EXPERIMENT ... 49

4.2.1 Column experiment ... 49

4.2.2 Batch tests ... 52

5 DISCUSSION ... 55

5.1 REVERSE OSMOSIS EXPERIMENTS ... 55

5.1.1 Recovery Ratio ... 55

5.1.2 Quality of results ... 55

5.1.3 Permeation constant ... 56

5.2 ION EXCHANGE EXPERIMENT ... 56

5.2.1 Batch tests ... 56

5.2.2 Column experiment ... 57

5.2.3 Comparision between batch test and column experimet (breakthrough point) ... 58

5.3 DISCUSSION OF BOTH TECHNIQUES ... 60

5.3.1 Nitrate removal capacity ... 60

5.3.2 Treated water quality ... 60

5.3.3 Power consumption ... 62

5.3.4 Brine disposal ... 62

5.3.5 Cost of treatment ... 62

5.3.6 Sustainable Environment ... 63

5.3.7 Conclusion ... 63

6 CONCLUSION AND RECOMMENDATIONS ... 64

6.1 CONCLUSION ... 64

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VII

List of Tables

TABLE 1:WATER SITUATION IN LIBYA IN 1998 ... 2

TABLE 2:CURRENT SOURCES MUNICIPAL WATER SUPPLY IN WATER SCARCE COUNTRIES ... 2

TABLE 3:IMPORTANT DETAILS ABOUT GMRA SYSTEMS (SAHLI,2004) ... 4

TABLE 4:COMPARISION BETWEEN CONVENTIONAL AND ADVANCED WATER TREATMENT METHODS TO REMOVE INORGANIC IONS... 9

TABLE 5:DESALINATION PRODUCTION AND PERCENTAGE OF VARIOUS PROCESSES IN 2000 (HISHAM,2002) ... 21

TABLE 6:ENERGY CONSUMPTION PER UNIT OF PRODUCT WATER FOR VARIOUS DESALINATION TECHNIQUES ... 22

TABLE 7:NITRATE CONCENTRATION AND NITRATE REJECTION RATIO AGAINST PRESSURE ... 39

TABLE 8:THE RELATIONSHIP OF PRESSURE AGAINST FLOW RATES AND RECOVERY RATIO... 40

TABLE 9: PERMEATION CONSTANTS ... 41

TABLE 10:THE RELATIONSHIP BETWEEN NITRATE CONCENTRATION AND PRESSURE ... 42

TABLE 11:THE RELATION BETWEEN PRESSURE AND FLOW RATE ... 43

TABLE 12: PERMEATION CONSTANT VALUES ... 44

TABLE 13:NITRATE CONCENTRATION AND NITRATE REJECTION RATIO AGAINST PRESSURE ... 45

TABLE 14:FLOW RATES AND RECOVERY RATIO AGAINST PRESSURE ... 45

TABLE 15:NITRATE CONCENTRATION AND REJECTION RATION AGAINST PRESSURE ... 46

TABLE 16:FLOWRATES AGAINST PRESSURE ... 46

TABLE 17:NITRATE CONCENTRATION AND NITRATE REJECTION RATIO AGIANST PRESSURE ... 47

TABLE 18:FLOW RATES AND PRESSURE RELATIONSHIPS... 47

TABLE 19:NITRATE CONCENTRATION AND NITRATE REJECTION RATIO AGIANST PRESSURE ... 48

TABLE 20:FLOW RATES AND PRESSURE RELATIONSHIPS... 48

TABLE 21:NITRATE REMOVAL (GR) AND FEED WATER TREATED VOLUMES (L) IN COLUMN EXPERIMENTS... 52

TABLE 22:BATCH TEST OF ION EXCHANGE ... 53

TABLE 23:BATCH TEST OF HIGH NITRATE CONCENTRATION ... 53

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VIII

List of Figures

FIGURE1: A MAP OF LIBYA SHOWING GMRA WELLFIELDS (ABDELGADER 2009)... 3

FIGURE 2: OSMOSIS AND REVERSE OSMOSIS (ELYANOW, 2005) ...13

FIGURE 3: RO EXPERIMENT ...27

FIGURE 4: ION EXCHANGE EXPERIMENT ...34

FIGURE 5 : RELATIONSHIP BETWEEN PRESSURE AND NITRATE REJECTION RATIO ...40

FIGURE 6: RELATION OF RECOVERY RATIO WITH PRESSURE ...41

FIGURE 7: RELATIONSHIP BETWEEN PRESSURE AND POWER ...41

FIGURE 8: RELATION BETWEEN PRESSURE WITH NITRATE REJECTION RATIO ...42

FIGURE 9: THE RELATIONSHIP BETWEEN PRESSURE AND RECOVERY RATIO ...43

FIGURE 10: THE RELATIONSHIP BETWEEN PRESSURE AND POWER ...44

FIGURE 11: THE RELATION BETWEEN NITRATE CONCENTRATION OF EFFLUENT AND TIME FOR EXPERIMENTS 1&2 ...49

FIGURE 12 : ION EXCHANGE EXPERIMENT 3 ...50

FIGURE 13 : ION EXCHANGE EXPERIMENT 4 ...51

FIGURE 14: ION EXCHANGE EXPERIMENT 5 ...51

FIGURE 15 : A REGRESSION LINEAR BETWEEN DESIRED (PREPARED) AND MEASURED NITRATE CONCENTRATION...53

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List of Equations

EQUATION 1: CATION EXCHANGE REACTION (1) ...10

EQUATION 2: ANION EXCHANGE REACTION (2) ...10

EQUATION 3: NSR1 EXCHANGE REACTION (3) ...11

EQUATION 4: REGENERATION REACTION (4) ...11

EQUATION 5:DENITRIFICATION REACTION (1) ...18

EQUATION 6: DENITRIFICATION REACTION (1) ...18

EQUATION 7: TO CALCULATE NITRATE REJECTION RATIO ...29

EQUATION 8: TO CALAULATE RECOVERY RATIO ...29

EQUATION 9 : TO CALCULATE NITRATE BALANCE ...29

EQUATION 10: TO CALCULATE PERMEATION CONSTANT...29

EQUATION 11 : TO CALCULATE FLOW RATE ...36

Removing nitrate from drinking water