Energy-Efficient Textile Dyeing Effluent Recycling

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1 Efficient Effluent Recycling Jai Swaminathan 1 Energy-Efficient Textile Dyeing Effluent Recycling Jaichander Swaminathan Prof. John H. Lienhard V Dept. of Mechanical Engineering

2 Problem: Cheap Zero Discharge Textile: 14% of India s industrial output dyeing units Water intensive: 200 L/kg-fabric. Effluent causes pollution: Heavy metals, organics, salts Zero-Liquid-Discharge mandated by courts in Tamil Nadu Many industries forced to shut down Larger units and exporters achieving ZLD with reduced plant utilization Challenges Cost of desalination plant operation ~ half of total operating costs Reverse Osmosis (RO) followed by inefficient thermal concentrator MITEI EAB 2016 Efficient Effluent Recycling Jai Swaminathan 2

3 Efficient Effluent Recycling Jai Swaminathan 3 Conventional Treatment Process COD, BOD removal s 7 g/kg COD 800 mg/kg BOD 500 mg/kg s 7 g/kg TS 500 g/kg s 40 g/kg s = g/kg

4 Efficient Effluent Recycling Jai Swaminathan 4 Design Effluent Chemistry for Cheaper Treatment Choose the chemicals added in the processing steps Raw Effluent Treatment Chemical, biological treatment steps Salty water (dissolved impurities) Brine Crystallizer/ solar evaporator Make-up water To Desalination reduce the energy consumption for water recycling Only and solid overall wastes cost No disposal into environment

5 Efficient Effluent Recycling Jai Swaminathan 5 Textile Dyeing Process Process: Multiple baths water and chemicals 1, 2, 3, D D+1, D+2, N Time/ Bath No. Preparation Dyebath Post-dyebath wetting, lubricating agents,.. Salts, dye chemicals fixing agents, detergents.. Water ~ 6 fabric weight Chemicals Fabric Heat to control T s ~0 g/kg Bath Effluent s = g/kg s ~0 g/kg Overall effluent: s ~7 g/kg

6 Dyebath Salt: NaCl vs. Na 2 SO 4 >90% of the TDS contribution from dye-bath salt used Both NaCl and Na 2 SO 4 used successfully in industry Purpose is to enable dye-cloth interaction Deeper shade requires higher concentration s *+, corresponds to the salinity requirement for the darkest shade Sodium Chloride Cheaper per kg With ZLD requirement, polished brine of NaCl solution using Nanofiltration s *+, > 70 g/kg More expensive s *+, < 110 g/kg Sodium Sulfate MITEI EAB 2016 Efficient Effluent Recycling Jai Swaminathan 6

7 High Salinity Desalination Energy Efficiency Committee Meeting 1 7 Thermodynamic Advantage Lower thermodynamic least work for separation of Na 2 SO 4 solution compared to NaCl solution Least Work [kwh/m 3 ] s conc = 70 g/kg NaCl s conc = 110 g/kg Na2SO Feed Salinity s [g/kg] Swaminathan et al., (2016, August). Nanofiltration for high permeability textile effluent desalination presented at Water Reuse and Recycling Conference, Nice, France. International Desalination Association

8 Efficient Effluent Recycling Jai Swaminathan 8 Practical: Higher Permeability Membranes By designing the effluent chemistry with sulfates as the smallest anions possible to replace RO with higher permeability NF Rejection > 96% Average Salt Rejection [-] NF270 NF90 SW30HR Feed Salinity [g/kg] Pressure [bar] Osmotic Pressure NF270 NF90 SW30HR Feed Salinity [g/kg]

9 High Salinity Desalination Energy Efficiency Committee Meeting 1 9 Conclusions Textile dyeing effluent zero discharge costs too high for profitable operation Choosing suitable chemicals in the processing steps reduces cost of desalination and thereby overall system costs Sodium sulfate instead of sodium chloride enables: 40% lower thermodynamic least work of separation due to lower osmotic pressure Enables use of more permeable membrane while still achieving > 95% salt rejection Additional 30% lower energy consumption Overall: Elimination of energy intensive thermal desalination steps. Membrane based concentration at < 70 bar pressure Next step: Pilot testing with effluent water

10 Pilot Testing Partner: SP Textile Processors, Erode Pilot plant: one membrane element, 3 m 3 /day 1% total plant size Test permeate water for recycling Goal: measure pressure and salt rejection at various salinity levels characterize full scale system performance. Reusability test of NF permeate for various steps in the dyeing process MITEI EAB 2016 High Salinity Desalination Energy Efficiency Committee Meeting 1 10