Brine Solution Recovery Using Nanofiltration

By Dr. Isaac Solomon Jebamani¹, V. Gopalakrishnan², and G. Senthilkumar³
July 2009

  1. Assistant Professor in Civil Engineering, Government College of Technology (GCT), Coimbatore, Tamil Nadu, India
  2. P.G. Student, Government College of Technology, Coimbatore, Tamil Nadu, India
  3. P.G. Student, M.E. Environmental Engineering, GCT, Coimbatore, Tamil Nadu, India
Abstract
In this study, the nanofiltration process was contacted and the practical applicability of the nanofiltration for the recovery of brine solution from reverse osmosis reject water (textile dyeing wastewater) was studied. The Na and Cl of the effluent was found in the range of 19000 mg/L and 21000 respectively. The effect of operating variables such as flow rate, feed pressure, and recovery rate on pilot scale NF were studied. The study was contacted at different operational condition as follow as feed pressure is 12.2, 10.2 and 7.6 kg/cm² and the recovery rate is 75%, 65% and 55% respectively. The recovery of brine solution 60-80% was achieved in pilot scale NF at 10.2 kg/cm² and at 65% of recovery rate and the efficiency increases with decrease of pressure and decrease with increase of flow rate and recovery rate. The “Recovery of Brine Solution using Nanofiltration” was successfully done and the brine solution recovered can be reused in the process.

Keywords: Nanofiltration, Reverse Osmosis reject water, Brine solution (NaCl) Recovery Rates, Sodium Chloride, and TDS.

Introduction

Textile industry plays an important role in the industrial development of India and is the second largest sector of Indian economy, next to agriculture. As per the recent data published by the ministry of textile, it contributes about 17 percent to industrial production, 7 percent to the GDP, and 25 percent to the country’s export earnings. The textile industry in India is a key sector in terms of employment as it is the second largest employment. It provides direct employment to over 35 million (Ministry of textile annual report 2008-09). Textile industry is one of the major polluting industries, which consumes large amount of water for its various operations and generate huge quantity of wastewater which is having high Total Dissolved Solids, Sodium and chloride and is strongly coloured due to utilization of various dye stuff. The dyeing industry is characterized by using a large quantity of chemicals and huge quantities of water. Detergents and caustic are used to remove dirt, grit, oils and waxes. Bleach is used to improve whiteness and brightness. Dyes, fixing agents and many inorganic salts are used to provide the brilliant array of colors the market demands. Dyeing using reactive dyes generates warm wastewater strongly colored, containing suspended solids, concentrated NaCl and widely varying acid amounts. Dyeing one kilogram of cotton with reactive dyes requires from 70 to 150 litres of water, 0.6 kg of NaCl and 40 g of reactive dye [1]. The treatment generally used consists of 4 steps: Pretreatment of anaerobic, aerobic (Biological), reverse osmosis and nanofiltration. At the end of this treatment recyclable brine is obtained which contains the total salt added in the initial dye bath, pure water which is reusable for further operations and a small volume of concentrated liquor containing hydrolyzed reactive dyes and dyeing auxiliaries. State authorities and local municipalities have begun to target the textile industry to clean up the wastewater that is being discharged from the textile mills.

2. Materials and Methods

2.1 Membrane Technology

Membrane can be used to fulfil the purpose of recovery and recycling of valuable components and energy in textile, dyeing process and to fulfil the purpose of lowering the specific cost for further treatment by reducing volume of waste. In study membrane separation technology on aqueous waste stream was investigated. Membrane filtration technology has been used to treat a variety of industrial wastewater applications including flexographic ink, metal finishing, chemical mechanical planarization (CMP) and alkaline cleaning. However, wastewater treatment systems in these industrial applications are typically small, generally not exceeding 100 gpm. More recently, spiral wound and hollow fibre membranes have been applied to large capacity applications for wastewater treatment and reuse. This paper will discuss the use of membrane technologies within a wastewater treatment or reuse facility for both municipal and industrial wastewater [6].

2.3 Types of Membrane Technology

The four commonly used membrane types are: microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO). These processes differ in the pore size.

Fig 3
Fig 3 · Various Separation Processes

2.4 Separation of Different Particles By Membrane Techniques

When a feed stream is introduced into the membrane element under pressure and passed over the membrane surface in a controlled flow path, Solutes, whose sizes are greater than the pore size of the membrane, are retained and concentrated forming a liquid stream called the concentrate or retentate. Water and solutes smaller than the pores pass through the membrane and are called permeate. Membrane operation is characterized by the flux, or flow rate per unit area of membrane, and by its retention or the percent of each solute species which does not pass through the membrane [2].

Fig 4
Fig 4 · Membrane Process Performance Characteristics

2.5 Nanofiltration

Nano-Filtration is used to separate sugars and divalent salts and monovalent salts from aqueous solutions. NF has found wide application for water softening. It is also demonstrating ability to decolorize the solutions. However, NF modules are extremely sensitive to fouling by colloidal material and polymers. For this reason extensive pretreatment is required. UF makes an excellent pretreatment substitute by eliminating the polymer addition, chlorine disinfectant and mixed media per-filtration. Virtually all NF and RO membranes are thin film composite membranes. Nanofiltration element is a high area, high productivity element designed to remove a high percentage of salts, nitrate, iron and organic compounds such as pesticides, herbicides and THM precursors.

Nanofiltation is a pressure-driven membrane process. Nano filtration (NF) refers to a membrane process which rejects particles in the approximate size range of 1 nanometer. Organic molecules with molecular weights greater than 200-400 are rejected. Retains divalent salts and organics, Passes monovalent salts, water, acid and alkaline compounds. It is relatively a new term, has been employed for application that fall within the boundaries of UF and RO. The Pore size of Nanofilter is 0.001 micron (10-6 to 10-9)

2.6 Specifications of Membrane

Fig 5
Fig. 5 Spiral Wound Membrane
  1. Length
  2. Outer Diameter
  3. Permeate tube diameter
  4. wound diameter of membrane
Table 4 · Specifications of Membrane
Product Size Product water flow rate m³/day Minimum Rejection at 20000 ppm
MgSo4 Na2So4 Nacl Sucrose
HPA 100 4040 4”Ø x 40”L 6.40 99% 99% 90% 99.9%

Fig 6
Fig 6 · Cross View

2.6.1 Properties

pH tolerance : 1- 13 during operation and cleaning. Low fouling due to high Hydrophilicity. Low salt rejection at low molecular wt cut offs, allow operating on high salt concentrations at low pressures. Available in MWCO ranging from 50 to 500 Daltons. High operating flux rates due to hydrophilicity. Available in tape wrap, FRP wrap and net outer wrap constructions Chlorine tolerance up to 0.5 ppm continuous exposure. Membranes can operate on high BOD and COD feed streams.

Table 5 · Design Consideration of Parameters
Membrane Type Hydrophilized Polyamide
1. Maximum operating pressure 600 psi (42kg/cm²)
2. Membrane filtration area 7.9 sq.mtrs
3. Molecular weight cut-off Min.100 daltons
4. Operating Temperature Max. 70°C
5. Operating pH range 2 - 11 pH
6. Cleaning pH range 1.5 - 12 pH
7. Free Chlorine tolerance <0.5 ppm continues
8. Maximum feed silt density index 5 NTU
9. Outer wrap FRP/Tape wrap/sanitary
10. Maximum feed flow rate 10 m³/day
11. Maximum Pressure drop per element 15 psi

2.7 Experimental Setup and procedure

Fig 7
Fig 7 · Experimental Setup
  1. NF Feed tank
  2. Bypass valve
  3. Outlet valve
  4. Pump
  5. Pressure gauge
  6. Micron filter 5µ
  7. Micron filter 1µ
  8. Flow meter
  9. Centrifugal pump
  10. Nanofilter
  11. Pressure gauge (NF)
  12. Reject Outlet valve (NF)
  13. Permeate outlet

NF membrane was installed in the membrane module and a series of experimental runs were carried out. R.O. rejects water used as feed in the feed tank. The operating variables were transmembrane pressure, feed concentration, pH, competing compound and membrane types. [8] Nanofiltration experiments were carried out in different steps: In first step, experiments were carried out in 3 different recovery rates such as 75%, 65%, and 55%. (TDS of NF Feed = 17600 mg/L). In second step, the nanofiltration experiments were carried out at different pressures 12.2, 10.2 and 7.6 bars. In third step, different TDS concentrations were investigated. In fourth step each recovery rates operated 4 hours continuously. Then one litre brine solution samples were collected for analysis for every hour. All experiments were carried out in 4 hour to get optimum concentration of brine solution. In all the steps, the temperature was kept constant, between 20-25 °C, TDS concentration was mg/L.

Table 6 · Field Operational Conditions
Operational Condition NF Permeate Recovery
55% 65% 75%
1. Feed Flow (m³/hr) (Constant) 10.0 10.0 10.0
2. Feed Pressure (kg/cm²) 7.6 10.2 12.2
3. Reject Pressure(kg/cm²) 6.3 8.6 10.9
4. Δp (kg/cm²) 1.3 1.6 1.3

2.8 Study Area

The study was carried out in a dyeing industry located in Tirupur, Tamil Nadu, India. In this industry woven fabric is dyed for the required shade using different colour of reactive dyes in different proportions by jigger machine. Textile dyeing process involves desizing, scouring, bleaching, washing, dyeing, fixing, washing, finishing and drying of fabric. The unit was carrying out knitted fabric dyeing activities. For this study, raw wastewater was taken from the reverse osmosis reject tank of the dyeing unit . The wastewater was treated in primary, secondary and RO, after RO the permeate was reused in the process and RO reject water taken to nanofilter. The unit has achieved Zero liquid discharge. The unit has recovered brine solution from the Nanofilter and reused the same in the unit. Wastewater samples from the Nanofilter Feed collection tank (RO reject) and Nanofilter permeate (Brine solution) from the brine solution tank were collected and analyzed using standard methods.

2.9 Sample Collection

All experiments were conducted for four hours to obtain the steady state flux. Due to the very small membrane area, the permeate flow was very low, thus the permeate samples were collected every half an hour interval. Because of the preservation problem, the salt concentration of all permeate samples were measured immediately after each experimental run. The results obtained with changing the operating variables (as stated above) can be discussed as follows.

The samples collected from the above experimental procedure were operated. Three samples of Nanofilter feed (RO reject) and permeate of nanofilter were collected for three month. When the concentration of brine solution increases, decreased with the recovery rate. The following parameters were analyzed in the laboratory using “Standard methods”. The results were presented in Table 7 and illustrated in Fig. 8. The figure shows that left hand side beaker is nanofilter feed and right hand side nanofilter permeate.

Fig 8
Fig 8 · Nanofilter Feed and Permeate

Table 7 · Nanofilteration at Various Recovery Rates
Parameter Recovery 55% Recovery 65% Recovery 75%
NF Feed NF Permeate NF Feed NF Permeate NF Feed NF Permeate
1. pH 6.82 7.14 6.81 7.13 6.77 7.16
2. TDS 21326.66 10760 21928.89 11221.11 21495.55 11100
3. Total Hardness 643.33 233.33 656 257.77 647.77 282.22
4. Chloride 6442.22 3668.88 6336.66 3760 6307.78 3735.55
5. Sulphate 1100 267.78 5135.55 268.89 1190 285.55
6. Sodium 2758.66 1954.44 2785.55 2024.44 2865.55 2018.88
7. COD 757.77 238.89 790 242.33 826.66 255.55

3. Results and Discussion

The salt concentration varies in a similar way in the retentate as in the permeate: it continuously decreases during the diafiltration step (recover of sodium chloride in the permeate) and increases during the concentration (sodium chloride still slightly present in the solution and ionic species coming from dyes). Our results were compared to those obtained by an external certified laboratory and are found very close. The rejection of NaCl according to the NaCl concentration in the retentate, decreases when NaCl concentration increases. For economic reasons, it is profitable to recover only 85-90% of salt. We also studied the effects of the transmembrane pressure, the flow velocity, the feed temperature and pH. [13] Separation by nanofiltration follows two mechanisms. First, neutral organic compounds with molecular weights above the membrane MWCO get rejected by sieving mechanism due to the very small pore size of the NF membrane. Second, anions get rejected due to electrostatic repulsion with the common negatively-charged surface of the NF membrane. [10]

The experiments were conducted in the Nanofiltration Plant available in a dyeing industry at Tirupur. The Nanofiltration Plant was operated at 3 different conditions. Initially the Nanofiltration plant was operated at 55 %, 65 % and at 75 % recovery samples were collected and analysed. Samples were collected from the influent to Nanofiltration Plant and the permeate regularly. The samples were analysed at the Environmental Engineering Laboratory, at Government College of Technology, Coimbatore. All the results of the experiments conducted an the Nanofiltration Plant at the dyeing industry are summarized in Table -7 & 8. The table shows variations in pH, TDS, Total hardness, Chloride, Sulphate, Sodium and COD for 55%, 65% and 75% recovery. The efficiency of the Nanofiltration Plant in treating the dyeing wastewater is also given in Table - 8.

Table 8 · Performance of Nanofilteration at Various Recovery Rates
Parameter Recovery 55% Recovery 65% Recovery 75%
NF Feed NF Permeate % Efficiency in NF NF Feed NF Permeate % Efficiency in NF NF Feed NF Permeate % Efficiency in NF
1. pH 6.82 7.14 - 6.81 7.13 - 6.77 7.16 -
2. TDS 21326.66 10760 49.54 21928.89 11221.11 48.83 21495.55 11100 48.36
3. Total Hardness 643.33 233.33 53.73 656 257.77 60.70 647.77 282.22 56.43
4. Chloride 6442.22 3668.88 43.05 6336.66 3760 40.66 6307.78 3735.55 40.77
5. Sulphate 1100 267.78 75.65 5135.55 268.89 84.76 1190 285.55 76.00
6. Sodium 2758.66 1954.44 29.15 2785.55 2024.44 27.32 2865.55 2018.88 26.40
7. COD 757.77 238.89 68.47 790 242.33 68.18 826.66 255.55 69.08
Note: All the parameters are in ppm except pH

Fig 9
Fig 9 · Performance of Nanofiltration

3.1 Theoretical Calculation of Brine Solution

Formula

Calculated values as follow as, 23.12, 24.14 and 23.37 at 55%, 65% and 75% recovery of sodium chloride respectively. The unit is gram per litre.(gpl)

Fig 10
Fig 10 · Percentage of Recovery

The brine recovery efficiency increases with constant flow rate of feed, optimum pressure maintainin the nanofilter system. The percentage of recovery is optimized at 65%.

4. Conclusion

The objective of this research was to investigate the quality of permeate from a Nanofilter for a Dyeing industry. This was achieved through an extensive literature review and field visits performed at a Dyeing industry. The study shows that the recycling of brine solution concept is found technically feasible and economically viable in a dyeing industry. The average percent recovery of sodium and chloride are 60 to 80%, The most attracting part of brine solution recovered from these membranes is its extremely high sodium chloride content. Which is always demanded in dyeing sector for an improved finish and better quality of dyeing. In the performance study of Nanofiltration System. It was found that the brine solution quality at 65% recovery is most desirable since the total hardness level is less than 300 mg/l which is most wanted in the dyeing units.

The feed pressure of a RO are 12.2 kg/cm², 10.2 kg/cm² and 7.6 kg/cm² at 55%, 65% and 75% recovery of brine solution respectively. It is a fact that the increased pressure in a Nanofilter system affects life of membranes. Total hardness level is less than 300 mg/l at the pressure of 10.2 kg/cm² which is desirable. The quality of brine solution is also good and suitable for the dyeing industry. In view of the above it is concluded that the Nanofilteration system can be operated at 65% recovery rate of brine solution for the better performance of the system and better quality of the brine solution. It is also recommended that further studies is essential to eliminate Total Hardness from the brine solution to increase a usage of brine solution in dyeing units and to increase the rate of recovery.

References

  1. Carine Allègre, Philippe Moulin, Michel Maisseu, François Charbit.”Savings and re-use of salts and water present in dye house effluents”, 162 (2004) 13-22.
  2. P. Shyam Sundar, N. Karthikeyan and K. H. Prabhu “Waste Water And Its Treatment In Textile Industry”, 1 (2005) 12 - 25.
  3. Arlindo Canico Gomes, Isolina Cabral Goncalves, Maria Norberta de Pinho, John Jefferson Porter. Integrated nanofiltration and upflow Anaerobic Sludge Blanket Treatment of Textile wastewater for in plant reuse”, 79 (2007).
  4. H. Hassani; R. Mirzayee; S. Nasseri; M. Borghei; M. Gholami; B. Torabifar “Nanofiltration process on dye removal from simulated textile wastewater”, 20 (2008)
  5. Ioannis C. Karagiannis, Petros G. Soldatos Received 21 December 2006; accepted 28 February 2007 “Water desalination cost literature: review and assessment” 223 (2008) 448-456.
  6. Nidal Hilal, Gerald Buscaa, Nick Hankinsa, Abdul Wahab Mohammad “The use of ultrafiltration and nanofiltration membranes in the treatment of metal-working fluids” 167 (2004) 227-238.
  7. Shahid Naveed, I. Bhatti , Kamran Ali “Membrane technology and its Suitability for treatment of textile waste water in Pakistan”, 17(3) (2006) 155-164.
  8. Pritish Kumar Roy “Nanofiltration as a tertiary treatment for phosphate Removal from wastewater” 31 (1995) 43-57.
  9. D.G. Rickerby, M. Morrison “Nanotechnology and the environment, A European perspective 8 (2007) 19-24.
  10. Anna Marie M. Hufemia “Caustic soda recovery in a bottle washing plant using Membrane technology” (1996).
  11. Purnima Chauhan and Dr. Rekha R. “Membrane Filtration Techniques – Part II Scope for minimizing effluent load” Membrane filtration technique is a practical and cost effective solution to the problems for handling textile wastewater pollution.
  12. Douglas L Woerner “Membrane Technology In Textile Operations”
  13. Carine Allègre, Philippe Moulin, Michel Maisseu, Françoise Charbit “Treatment and valorization of the textile wastewater”, 19 (2004).

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